Open access peer-reviewed chapter

Rice Aroma: Biochemical, Genetics and Molecular Aspects and Its Extraction and Quantification Methods

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Nirubana Varatharajan, Deepika Chandra Sekaran, Karthikeyan Murugan and Vanniarajan Chockalingam

Submitted: May 25th, 2021 Reviewed: June 15th, 2021 Published: August 5th, 2021

DOI: 10.5772/intechopen.98913

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Abstract

Aroma in rice is unique and a superior grain quality trait, varieties especially Basmati and Jasmine-type are fetching a high export price in the International markets. Among the identified volatile aroma compounds, 2AP (2 acetyl-1-pyrroline) is believed to be the distinctive biochemical compound contributing the flavor in rice. Genetically, aroma in rice arises by the phenotypic expression of spontaneous recessive mutations of the OsBadh2 gene (also known as fgr/badh2 /osbadh2/os2AP gene) which was mapped on chromosome 8. An 8-bp deletion in the exon 7 of this gene was reported to result in truncation of betaine aldehyde dehydrogenease enzyme whose loss-of-function lead to the accumulation of a major aromatic compound (2AP) in fragrant rice. Among the different sampling methods and analytical techniques for the extraction and quantification of scentedness, simultaneous distillation extraction (SDE) is traditional and normalized, whereas solid-phase micro extraction (SPME) and supercritical fluid extraction (SFE) are new, very simple, rapid, efficient and most importantly solvent-free methods. These methods are coupled with Gas Chromatography–Mass Spectrometry (GC–MS), Gas Chromatography-Flame Ionization Detector (GC-FID) and/or Gas chromatography olfactometry (GC-O) and also with sensory evaluation for readily examining 2AP compound found in rice. The major factor affecting the aroma in rice was their genetic makeup. However, the aroma quality may be differed due to different planting, pre-harvest and postharvest handling and storage. For a more extensive elucidation of all effective and fundamental factors contributing to fragrance, it is essential to explore target quantitative trait loci (QTLs) and their inheritance and locations.

Keywords

  • aromatic rice
  • 2-acetyl-1-pyrroline
  • fgr
  • badh2
  • evaluation methods
  • affecting factors

1. Introduction

Rice (Oryza sativaL.) is a dietary staple food crop and the grain being consumed by atleast 50 per cent of the world’s population [1]. It had a decisive role in food, security and in improving the livelihood of people. With the continuous/marked improvement in standard of living of the people, the ethnic preference of rice is under conversion which increases the demand for superior fine quality rice. Most of the scented rice are inferior in agronomic performances and highly prone to environmental variations [2] yet it paves much attention for their first-rated aroma. The origin and evolution of the aroma gene betaine aldehyde dehydrogenase (BADH2) remains unclear but the haplotype analysis firmly establishes a distinct origin of the badh2.1allele within the Japonica varietal group [3] and the centre of origin is considered to be the Himalayan foothills in the Indian subcontinent from where it spreads to various parts of the world [4].

It was reported that rice aroma was controlled by single recessive nuclear gene in rice [5, 6]. The biochemical analysis of rice grain reveals the presence of numerous volatiles in fragrant rice revealing the major aromatic compound, 2-acetyl 1-pyrroline (2AP). Recent advances had also discovered the biochemical pathway for biosynthesis of 2-Acetyl-1-pyrroline (2AP) from different types of amino acids and polyamines [7]. Based on the rice genome sequence information [8], the OsBadh2gene (present on chromosome 8) is identified as a candidate gene for aroma, which is the most important aroma gene till now. However, several other genes and locus had been reported to be the contributor for aroma [9, 10].

Rice aroma quality evaluation is quite complex due to the complex interaction of numerous volatile compounds, and many affecting factors during planting and processing. With the rapid advancement in the instrumentation and sampling methods for the isolation and determination of 2AP concentration levels it is possible to analyze compounds even at very low concentrations (ppb levels) [11]. This chapter gives insights into the flavor chemistry, the progresses pertaining to the genetic and molecular understanding of fragrance, various extraction, quantification methods and their interaction with genetic and non-genetic factors in rice.

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2. Fragrant rice germplasm and varieties

Scented rices had been grouped into small, medium and long grained types based on grain length and could be categorized by their scentedness as mild and strong aromatic types. Broadly, the aromatic rice germplasm are grouped into three categories i.e. the Basmati, jasmine, and non-basmati/jasmine typed scented rice. The word ‘Basmati’ has its origin from two Sanskrit roots (vas = aroma) and (mayup = ingrained or present from the beginning) making the word vasmati and it has been pronounced as Basmati in course of time. Of the largest aromatic germplasm maintained at IRRI, about 86 had its root word as Basmati irrespective of grain dimensions and intensity of aroma [12].

A number of non-Basmati scented rices had been considered superior to Basmati in one or more characteristics like flavor, texture, linear elongation ratio on cooking, taste etc. Moreover, many of them can be cultivated under conditions and in areas where Basmati cannot be. Small-grain Bindli, for example, is superior to Basmati in aroma, grain elongation, taste and digestibility (as perceived by the farmers) and it performs well under water-logged conditions. A few such potential candidates could be Kalanamak, Tilakchandan, Sakar-chini and Dhania (U.P.), Ambemohar (Maharastra), Badshahbhog (Bihar and West Bengal), Bindli (waterlogged conditions of U.P.), Chakhao (Manipur), Madhumalti and Mushkan (H.P.), Kon-Joha - 1, Raja Joha and Krishna Joha (Assam), Randhuni Pagal (W.B.), Vishnubhog and Dhubraj (H.P.), Katarani and Sonachur (Bihar) [13]. The small and medium grain aromatic rices could be explored further and improved by selecting short stature, better yielding and early maturing plant types in order to develop varieties to be cultivated in non-traditional areas of basmati cultivation.

The scented rices are mainly cultivated and consumed in India, Pakistan, Thailand, Bangladesh, Afghanistan, Indonesia, Iran and United States. Of these, the major exporter of fine-grained fragrant rices includes India, Pakistan and Thailand Major aromatic rices of different states of India were presented in Table 1 [12].

StatesSmall grainMedium grainLong grain
Southern zone
Andhra PradeshJeeragasambha
KeralaJeerakasala, Gandhkasala
KarnatakaKagasali
North eastern zone
AssamBengoli Joha, Bhaboli Joha, Bhugui, Boga Joha, Bogamanikimadhuri, Boga Tulsi, Bogi Joha, Bokul Joha, Borjoha, Borsal, Cheniguti, Chufon, Goalporia Joha-1, Goalporia Joha-2, Govindbhog, Joha Bora, Kaljeera, Kamini Joha, Kataribhog, Khorika Joha, Kola Joha, Koli Joha, Kon Joha-1, Kon Joha-2, Krishna Joha, Kunkuni Joha, Manikimadhuri Joha, Ramphal Joha, Ranga Joha
ManipurChahao Amubi (black scented rice), Chahao Angangbi (pink/red scented rice)
Eastern zone
BiharBadshahbhog, Deobhog, Karia Kamod, Katami, Shyam Jeera, Kanak Jeera, Kanakjeeri, Badshapasand, Mircha, Brahmabhusi, Ramjain, Kamina, Dewta Bhog, Tulsi Pasand, Chenaur, Sona Lari, Sataria, Tulsi Manjari.Gopalbhog, Champaran Basmati (Lal), Champaran Basmati (Kali), Champaran Basmati (Bhuri), Bhilahi Basmati, Amod, Abdul, Bahami, Kalanamak, Kesar, SonachurBaikani
West BengalBadshabhog, Chinisakkar, Danaguri, Gandheshwari, Kalo Nunia, Kataribhog, Radhuni Pagal, Sitabhog, Tulai Panji, TulsibhogKanakchur, Katanbhog
Northern zone
HaryanaBasmati 370, Khalsa 7, Taraori Basmati, Pakistani Basmati
PunjabBasmati 370, Basmati 385, Pakistani Basmati
RajasthanBasmati (local), Basmati 370
Himachal PradeshAchhu, Begmi, Panarsa localBaldhar Basmati, Madhumalti, Chimbal Basmati, Mushkan, Seond Basmati
Central zone
Madhya PradeshChinore, Dubraj, Kalu Mooch, Vishnubhog, Tulsi Manjari, Badshabhog,Chatri, Madhuri, Vishnu ParagLaloo
Uttar PradeshAdamchini, Badshapasand, Bhanta Phool, Bindli, Chhoti Chinnawar, Dhania, Jeerabattis, Kanak Jeeri, Laungchoor, Moongphali, Rambhog, Ramjawain, Sakkarchini, Tinsukhia, Bengal Juhi, Thakurbhog, Yuvraj, BhantaphoolKarmuhi, Kesar, Parsam, Sonachur, Tilak Chandan, Kesar, Kalanamak, VishnuparagBasmati 370, Dehraduni Basmati, Type 3, Hansraj, Nagina 12, Safeda, Vishun Parag, Kala Sukhdas, Lal Mati, Tapovan Basmati, T-9, Dubraj, Duniapat (T9), Ramjinwain (T1)
Western zone
MaharastraAmbemohor, Chinore,Kagasali, Prabhavati, Sakoli-7

Table 1.

Zonal classification of scented Rices of different states of India [12].

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3. Biochemical basis of fragrance

Generally, the aromatic rice cultivars are enriched with large volatile and semi volatile compounds viz.,alcohols, aliphatic aldehydes, alkane, alkene, aromatic aldehydes, aromatic hydrocarbon, carboxylic acid, ester, furan, ketone, N-heterocyclic, phenol, and terpenes [14, 15, 16, 17].

3.1 Structure and chemistry of 2AP

Among the different volatile compounds, 2-acetyl-1-pyrroline (2AP) with popcorn-like aroma and lowest odor threshold is reported to be the potent biochemical compound to impart fragrance in rice [18]. The chemical structure of 2AP is an N-heterocyclic compound containing 1-pyrroline ring in which the hydrogen at position 2 is replaced by an acetyl group with a methyl ketone group. 2AP content in scented rice varieties include 0.04–0.09 ppm, whereas non-aromatic varieties have 10x less (<0.006–0.008 ppm) [19].

3.2 Biosynthetic pathway for 2AP

There are many contradictions and views regarding the biochemical pathway for 2AP synthesis and it is still being explored. It was reported that L-proline was the precursor for the production of 2AP [20]; and is involved in polyamine degradation pathway which is the main enzymatic pathway and there are some other non-enzymatic pathways reported having an influencing action on 2AP concentration. In the enzymatic polyamine pathway, arginine, ornithine, spermidine, putrescine, etc. are degraded into GAB-ald which spontaneously cyclises to Δ1-pyrroline, an immediate precursor of 2AP biosynthesis [21]. The non-functional badh2 enzyme (encoded by osbadh2gene) inhibits the conversion of the γ-aminobutyraldehyde (GAB-ald) to γ-aminobutyric acid (GABA) thereby allowing the formation of Δ1-pyrroline and ultimately the 2AP in scented rice whereas the reverse happens in non-scented rices (functional BADH2 enzyme coded by OsBadh2gene inhibits 2-AP formation) [22].

Some non-enzymatic direct pathways had also been described by many scientists and researchers. Glutamate produces proline and the proline accumulated during stress is converted to Δ1-Pyrroline-5-carboxylic acid (P5C) by the enzyme Δ1-Pyrroline-5- carboxylate synthase (P5CS). This P5C combines directly with methylglyoxal without involving any enzymes or might be converted to Δ1-pyrroline and thereby enhancing the 2AP concentration [23]. In normal plants the methylglyoxal produced from glycolysis is detoxified by glyoxalase enzymes and their concentration was kept low. It was speculated that 2AP is a generative volatile compound to detoxify methylglyoxal in rice plant [24] (Figure 1).

Figure 1.

2AP biosynthetic pathway in rice. (a) Enzymatic (BADH2-dependant) 2AP synthesis [21,22] (b) non enzymatic (BADH2-independant) 2AP synthesis [23].

2AP concentration differs in different plant parts of rice. The concentration is more in grains and flag leaf than in any parts of the plant [25, 26, 27]. Glutamate, ornithine and proline are important amino acids that serves as nitrogen (N2) source in the ring of Δ1-pyrroline [11]. The high aroma content in grains is mainly from the larger availability of N2 from the soil. So, the aroma concentration may vary depending upon the nitrogen availability to the plants [28]. Advanced researches are essential in correlating the genetic and biochemical aspects of scented rice varieties, particularly with regard to the nitrogen and acetyl group donor in 2AP in order to reveal the key enzymes that are involved in the biosynthetic pathway of aroma in rice.

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4. Genetic and molecular basis of fragrance

Inheritance of aroma is quite difficult to understand because it is controlled by number of unknown genes at different growth stages of rice and influenced by various concentrations of volatile and semi-volatile compounds. Although, plant breeders have reported the aroma inheritance by monogenic, digenic and polygenic pattern with recessive, dominant, complimentary and duplicate gene actions, indicating that complex genetic control of the trait. In majority of studies, the genetics of fragrance in rice is mainly due to single recessive gene [6, 9, 29, 30, 31, 32, 33] while other studies have also identified two, three or four genetic loci having influence on fragrance [9, 34, 35, 36, 37, 38]. Studies on the genetic control of aroma/fragrance/scent in rice have been presented in Table 2.

S.No.Gene actionReferences
1.Monogenic dominant[39, 40]
2.Monogenic recessive[29, 30, 31, 32, 38, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63]
3.Monogenic recessive with an inhibitor[41, 64]
4.Digenic or trigenic dominant[34]
5.Monogenic or digenic recessive[37]
6.Digenic recessive[38, 65, 66]
7.Three recessive genes[67]
8.Two dominant complimentary genes[68]
9.Three dominant complimentary genes[69, 70]
10.Four dominant complimentary genes[35]
11.Monogenic or digenic recessive or dominant, complimentary[71]
12.Monogenic or digenic dominant, duplicate[72]
13.Digenic dominant suppression epistasis interaction[73]
14.Polygenic[9, 10, 74]

Table 2.

Inheritance pattern of aroma in rice.

However, much of this conflicting information on the inheritance of aroma might have arisen due to (i) unreliable and cumbersome phenotyping methods used for fragrance determination [6], (ii) failure to consider the endosperm fragrance in rice seeds [29] and (iii) segregation distortion [9]. The nature of aroma inheritance appears to be cross/genotype specific due to the number of genes and the type of gene action varied with the genotype. However, the fragrance trait is a highly heritable as some of the lines derived from T142 (scented) x IR 20 (non-scented) cross, and some of the high yielding released aromatic rice varieties show strong scent.

The implementation of marker assisted selection is a significant supplement to traditional approaches, altering the selection process directly or indirectly from phenotype to genes [75]. A novel compound namely 2AP (2-acetyl-1-pyrroline) plays a major role in most of the aromatic rice cultivars for the presence and absence of unique popcorn like characteristic aroma. Several attempts have been made at molecular level for genetic mapping the fragrance gene governing the 2AP synthesis in different aromatic rice varieties such as Della [30], Azucena [9, 76], Suyunuo [77, 78] and Wuxianjing [77]. Quantitative trait locus (QTL) mapping was also performed in indica aromatic rice KDML105 (Jasmine) [52, 79], Kyeema [80] and Wuxiangxian [77] (Table 3).

Number of GenesType of markersChromosome locationReferences
1RFLP8[30]
1RFLP8[81]
1RAPD[52]
1 major gene and 2 QTLsRFLP, STS8, 4 and 12[9]
1SSR8[56]
1SSR8[32]
1SNP8[33]
1SSR8[80]
1EST, SSR8[82]
1SSR8[77]
1SSR[66]
1SSR8[83]
3 QTLsSSRQTLs on 3, 4 and 8[10]
1SSR, RFLP8[58]
1SSR8[60]
1SSR8[84]
1SSR8[85]
2[73]

Table 3.

Molecular mapping of fragrance gene in rice.

By using RFLP technique, a single recessive gene (fgr) that controls fragrance was mapped on chromosome 8 tightly linked with a single-copy marker RG28 and found that genetic distance between aroma gene and RG28 was 4.5 cM [30]. The close linkage between RG28 and fgr(5.8 cM) was confirmed by [9], also identified two quantitative trait loci for fragrance, one on chromosome 4 and the other on chromosome 12.

Further, a gene responsible for 2AP synthesis was mapped in a Jasmine rice variety KDML105 between the flanking regions of RG1 and RG28 [86]. The original region (1.13 Mb) flanking between RG1 and RG28 was narrowed down to 82.2 Kb in segregating population, within this region three KDML BACs were cloned and identified three new candidate genes. Among them, a single recessive gene (Os2AP) was identified which majorly contributing the 2AP synthesis in rice. The comparative analysis between aromatic KDML105 and Nipponbare for Os2AP gene sequences revealed two important mutational events within the exon 7 of Os2AP of KDML105, at positions 730 (A to T) and 732 (T to A), followed by the 8-bp deletion “GATTAGGC” starting at position 734 [87]. A similar mutational event was also reported by [79] within the flanking regions of RM515 and SSRJ07, a gene responsible for 2AP in Kyeema fragrant rice cultivar.

Using four BAC of Nipponbare spanning within a region of 386 bp from RM515 to SSRJ07, an in silico physical map was developed and suggested that one BAC clone (clone AP004463) as most likely to be having the gene. Further, resequencing of all 17 genes lying within the BACs helped in identification of a novel gene with 3 single nucleotide polymorphisms (SNPs) with the 8 bp deletion in the 7th exon of the gene, which resulted in a premature stop codon [10]. The newly identified gene was showing homolog with BAD1 (betaine aldehyde dehydrogenase 1) locus of chromosome 4 and hence named as BAD2 [79]. A comparative study between amino acids and sequences of Os2AP and BAD2 suggested them as one gene with two different names. Recent surveys of diverse fragrant germplasm support the association of badh2with fragrance [76, 78, 88], and transformation of a fragrant variety with the dominant non-fragrant allele has been proved to abolish aroma [21], confirming that badh2is the major and effective genetic determinant of aroma in rice (Figure 2).

Figure 2.

Structure of thefgrgene showing ATG, initiation codon, exons (15), introns (14) and the termination site (TAA).

The nucleotide sequences of 7 exon are shown for both the rice varieties. The fragrant variety shows a deletion of 8 bp with 3 SNPs that terminates prematurely, within this exon. Thus, fragrant varieties truncated protein might lack the conserved sequences which is encoded by 8, 9 and 10 exons and that are believed to be important for correct protein function [84].

Since the Badh2gene was isolated and cloned, more than a dozen mutation sites have been found in Badh2[3, 89, 90, 91] and a series of molecular markers were designed for these loci, which could be used for the identification of gene responsible for aroma, selection of different aromatic rice varieties and cultivation of new varieties of aromatic rice.

4.1 QTLs for aroma

A number of QTLs for aroma have been identified on chromosomes 4, 8 and 12, at least three QTLs have been located on chromosomes 3, 4 and 8 in Pusa 1121 [9, 10, 92]. Recently, three QTLs were detected for rice grain aroma on chromosome 5 (one QTL) and chromosome 8 (two QTLs) [93]. However, until now only a few QTLs and associated markers have been confirmed (Figure 3).

Figure 3.

QTLs for aroma with respective candidate genes in rice.

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5. Aroma extraction, identification and quantification methods

The extraction process is influenced by various criteria viz., type of matrix, volatility of the analyte, concentration of constituents in the sample and extraction conditions; therefore, efficient methods of extraction is needed [14]. However, so far there is no single method that will prove ideal for aroma extraction, identification, and quantification of rice. Although, several traditional and modern methods are available for extraction and isolation of rice aroma chemicals which are coupled with analytical methods (Figure 4).

Figure 4.

Extraction and isolation methods of rice aroma.

5.1 Isolation and extraction methods

Several extraction methods are available for extraction of VACs (volatile aromatic compounds) in rice. While considering the extraction efficiency, it differs dramatically for each method. Based on that, the selection of extraction technique can efficiently extract volatile compounds viz., alcohols, aldehydes, hydrocarbons, carboxylic acids, esters, furans, ketones, N2-containing, phenols and terpenes [94]. Most of the volatile compounds are insoluble in water so conventional extraction methods need non polar solvent as a medium.

The isolation techniques such as vacuum SDE apparatus; PTM, SDE, SEfbDI, SPME, SFE, HAS, and HSSE have their own distinguished characteristic feature. For extraction and isolation of 2-AP concentration from rice sample a desired efficient technique is a prerequisite. From the above methods, simultaneous distillation extraction (SDE), solid-phase microextraction (SFME) and supercritical fluid extraction (SFE) are the most widely used method for extraction of volatile compounds.

5.1.1 Simultaneous distillation extraction (SDE)

Simultaneous distillation extraction is a combination of vapor distillation and solvent extraction method for extraction of VACs [95]. SDE is also known as the Likens–Nickerson steam distillation, it is one of the most popular method for rice aroma chemical analysis. Solvent extract is the final product of these method. Many researchers have used this method for extraction of 2AP volatile compounds and it showed to be the most effective approach for a quantitative evaluation of 2AP. A laborious concentration step is still needed for traditional SDE procedure. Therefore, a modified version of so called micro-SDE device was proposed to overcome the problem [96].

The main advantage of this method is only a small amount of solvent is used for extraction and it also shortens the extraction time and improves the extraction efficiency. The solvents, such as: hexane, dichloromethane (DCM) and n-pentane, can be used and the amount of solvent required for SDE has been dramatically reduced compared to that of the conventional LLE. However, the major disadvantage of this method is the atmospheric pressure SDE was also obvious. Due to its high temperature, there is a possible occurrences of undesirable ester hydrolysis, Maillard reaction and sugar degradation [95].

5.1.2 Solid-phase microextraction (SPME)

This method was first introduced in early 1990s by Arthur and Pawliszyn [97]. Solid-phase microextraction is a newly emerging extraction technique for extraction of rice aroma compared with other method. It was applied in both laboratories as well as on-site [98]. Because of its persistence over other method of extraction, many results have been reported on 2AP aroma compound from rice grains [99].

Solid-phase microextraction has been used for the extraction of volatiles due to certain advantages, such as low-cost, simple, solvent-free, rapid and time-saving technique when compared with SDE method. This method can eliminate contamination, prolong the fiber lifetime and lead to reproducible results [98]. The chemistry of volatiles is decided with the help of desorption and adsorption behavior. If such extracted analytes are varied in their polarities that requires a different chemistry of SPME fiber [99].

5.1.3 Supercritical fluid extraction (SFE)

Supercritical fluid extraction is a separation and extraction process and it uses the supercritical fluids (SCFs) as the extraction solvent. It is a type of solvent which is clean and pure. The supercritical fluid is considered as ‘Green Chemistry’, because it is less toxic in compression compared to the organic solvents. The carbon dioxide (CO2) is an extensively used SCF; sometimes it is modified by ethanol or methanol as such co-solvents [100].

Nowadays, Supercritical fluid extraction (SFE) is widely used for extraction of volatile compounds from rice and also in other plant samples such as vegetables, fruits and so on [101].

It is a quick technique and it can recover the majority of the VACs [102]. Within 10–60 minutes the whole process would be completed and it produces the pure extract by releasing the pressure. One of the main disadvantage of SFE is less effective, than solvent extraction [101].

5.2 Identification and quantification methods

The identification and quantification of volatile aromatic compounds from various types of rice is a tedious process. The research on aroma in rice is conducted by the researchers, scientists and industry groups for more than four centuries but still now it is not possible to identify all aroma compounds presented in rice. To determine the sensory quality of foods, need more concentration/efforts towards the application of modern and recently developed technologies.

There are several analytical methods for identification and quantification of rice aroma viz.,GC–MS, GC–MS-FID, GC–MS-AFID, GC–MS-FTD, GC–MS-SIM, Capillary GC–MS, GC-O, GC-FID, GC-PFPD, GC-TOF-MS, GLC, GLC-Capillary or GLC-Packed column. From the above methods, Gas Chromatography–Mass Spectrometry (GC–MS), Gas chromatography-olfactometry (GC-O), Gas Chromatography-Flame Ionization Detector (GC-FID) these three methods are widely used for identification and quantification of aroma in rice sample.

5.2.1 Gas chromatography-mass spectrometry (GC-MS)

Gas Chromatography–Mass Spectrometry (GC–MS) method was the most common instrumental analysis method for rice aroma analysis and effective method for analyzing volatiles, and widely used for qualitative and quantitative analysis of volatiles in rice [103]. In this method, the volatile compounds present in rice are determined and separated by GC and then identified by GC–MS [12]. This method can separate VACs having a molecular weight of less than 1,000 Dalton [104]. To date, the identification and quantification of volatile components from rice depends on advanced technologies and improved GC with multidimensional use. The qualitative and quantitative analysis of VACs is proved to be very sensitive in this method. The performance of MS is based on generated charged particle (ions) from molecules of analyses.

5.2.2 Gas chromatography-olfactometry (GC-O)

Gas chromatography-olfactometry (GC-O) is considered as one of the most advanced analytical method for the identification and quantification of VACs in sample matrix of rice. In GC-olfactometry (GC-O) system, human nose was applied to detect the odor intensity of volatiles. Two detectors which perceived the odor-active compounds (hexanal, longifolene, 2-methoxyphenol and so on) eluted from the chromatographic column [105]. Although this method was very much useful for identification of aroma-active compounds from food samples. However, it is not suitable method for quantitative and qualitative analysis of VACs. As a result, the GC–O analytical method is not only an instrumental but also a sensorial analysis [106].

5.2.3 Gas chromatography-flame ionization detector (GC-FID)

Gas Chromatography-Flame Ionization Detector is the combination of FID with GC. This method is considered as very effective and crucial GC method because of its excellency [97]. It enables the separation, identification, and quantification of volatile compounds with their existing levels of concentrations from different food sample [98]. By comparing the retention time (RT) in GC-FID, the identification of volatile aromatic compounds of rice is completed and the retention times are converted into system-independent constant known as Kovatx retention index [99].

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6. Factors affecting rice aroma

6.1 Genetic factors

The genes controlling aroma was found to be a highly heritable and also relatively complex in nature. In chromosome 8 the main candidate gene was fgr/badh2/Os2APhomologous to betaine aldehyde dehydrogenase (BADH), whereas many other genes were also reported [103]. Deletion of 8 base pair in exon 7 or deletion of 7 base pair in exon 2 of BADH2 gene on chromosome 8 results in a loss of function of BADH2, which catalyzes the oxidation of 4-aminobutanal to 4-aminobutanoic acid. It was reported that 4-aminobutanal existed in solution equilibrium with its cyclic form 1-pyrroline which was a precursor for 2AP [107].

According to [88], the gene fgr/badh2/Os2APwas not the only aromatic gene in rice. The aromatic compound 2AP was identified in a number of rice varieties not carrying the 8-bp deletion. The aromatic landraces in Japan consists of six clades, none of which had the 8-bp deletion in exon 7 of BADH2 and also Japanese aromatic and non-aromatic landraces were found genetically different [108]. About 84 Subsp. indica rice landraces were investigated with respect to 8-bp deletion in BADH2 gene [109]. The results showed that aroma traits were genetically controlled by recessive monogenes, independent of cytoplasmic genes, however, aroma was also studied as a quantitative trait, and many genes were included in the expression [110].

6.2 Planting and harvesting factors

The maximum down regulation of BADH2 gene was reported in temperature of 25°C, highest 2AP content and excellent phenotypic aroma score, indicating the function of temperature on regulating phenotypic expression of aroma and final rice aroma quality. BADH2 gene expression is influenced by the temperature, phenotypic aroma score and 2AP content were investigated in three different temperatures (ambient or 28.29 ± 0.91°C, 25°C and 20°C) [2].

There is a significant positive effect on 2AP content in rice grains (Meixiangzhan and Nongxiang 18) by the application of manganese, which esults in probably improvement of enzyme activities involved in 2AP formation. Higher total soil nitrogen plays a major role in producing rice aroma. During flowering stage, it was found that Si contents in leaves were positively related with 2AP contents. Thus, indicating that Si application to some amount will improve 2AP contents in grains [111].

An increase of 2AP content in grains with salinity was observed for three improved aromatic rice varieties and salinity was thought to have a positive effect on rice aroma quality [112]. NaCl stress enhanced aroma production in Tulaipanji, Radhunipagal and Gobindobhog rice varieties while weaken that in Kalonunia [113]. Shading treatments during grain filling significantly increased 2AP content in both Yuxiangyouzhan and Nongxiang rice varieties, and had a selective effect on the metabolism of other volatiles [114].

6.2.1 Effect of planting density on 2-acetyl-1-pyrroline content

2AP content decreases with an increase in planting density. The content of 2-AP in rice grains obtained during the early season will be stored for 6 months. However, other seed quality attributes at the exception of head rice yield and grain vitreosity were not affected by planting density [115].

6.2.2 Effect of harvesting time on 2-acetyl-1-pyrroline content

Reduction in 2AP was observed with increasing harvest date during the early season. During the late season, however, the concentration of 2AP is gradually decreased from 10 DAH and seemed to stabilize at 40 DAH, a reduction rate of 60%. However, it is well compensated for by the high level of 2AP in both brown and white rices, which remains significant even after a storage period of 3 months at ambient temperature [116].

6.3 Processing factors

6.3.1 Cooking

Presoaking is a traditional pretreatment before cooking. It would result in uniform cooking and less cooking time. Presoaking for 30 min before cooking resulted in significant increase in sewer/animal flavor and summed negative flavor attributes, and significant decrease in sweet taste and summed positive flavor attributes, mainly as a result of an increase in sulfur-containing free amino acids and their breakdown products [19].

According to [117], divided the cooking process into four stages and identified the major compounds of Japanese rice cultivar Akitakomachi. In stage I (25 min, from the start of heating to start of steam coming out of rice cooker) were aldehydes such as n-nonanal, n-decanal, and (E)-4-nonenal. The dominating compounds identified at cooking stage II (13 min, from the start of steam coming out of rice cooker to the end of steam coming out of rice cooker) were hexadecanoic acid and tetradecanoic acid. The major compounds identified at cooking stage III (10 min, from the end of steam coming out of rice cooker to automatic stop of heating) and IV (keeping the rice warm for another 30 min) were aldehydes and fatty acids.

6.3.2 High hydrostatic pressure and superheated processing (HHP)

High hydrostatic pressure (HHP) had stabilized effects on low molecular weight volatiles [118], and it is one of the effective processing to improve products flavor. HHP was thought to be a good pretreatment option to enhance aroma quality of cooked rice. HHP process enhanced the formation of aldehydes, alcohols and ketones in germinated brown rice [119]. The volatile compounds in rice were cooked by superheated steam rice cooking machine were compared -with those of ordinary cooked rice [105].

6.3.3 Roasting and parboiling

While roasting there is a change in volatiles by the Maillard and caramelization reactions, and consequently form unique flavor, and usually increase the popularity of consumers. Increases the content of heterocycle compounds and decreases the content of hydrocarbons and benzene derivatives by roasting process [120]. Parboiling cause concomitant changes in the physical, chemical, and nutritional properties of grains, and consequently greatly affect organoleptic and other qualities. Hydrothermal treatment during parboiling would inactivate lipases, and inhibit the development of off flavors [121]. Hence, it was a good method to keep rice aroma during storage.

6.3.4 Milling

Un-milled black rice contained significantly larger amounts of total volatiles than milled black rice [122]. That is, the volatile compounds were mainly distributed in the bran layer of black rice (624 ± 17.7 ng g − 1), and significantly decreased by milling, especially the contents of acids, esters, and alcohols. When milling aromatic rice (Cheonjihyang-1-se), hexan-3-one, benzene, 2-pentylfuran, and pentanal decreased to 79%, 70%, 54%, 78% with milling time from 10s to 140 s, while (E)-non-2-enal, pentadecanal, (5E)-6,10-dimethylundeca5,9-dien- 2-one, and menthol increased 252%, 185%, 172% and 159% [123].

6.4 Storage factors

It was reported that, proteins, lipids and carbohydrates were decomposed into volatiles contributing rice odor during storage [124]. Enzyme catalyzed reactions were drastically inhibited at low temperature. This was one reason for slower deterioration of rice aroma. In general, lower storage temperature and better packaging materials would be more appropriate for aromatic rice to better maintain desirable rice aroma. OPP/Al/LLDPE package was superior to Nylon/LLDPE package, and storage at lower temperature (15°C) was better than ambient temperature, since they better retarded the formation of lipid oxidation products and other characteristic odorants in organic red aromatic rice [125]. Some paper assumed that lower temperature during storage would minimize volatilization of 2AP from rice [126, 127].

6.4.1 Effect of storage time and temperature on 2-acetyl-1-pyrroline content

Fragrant rice harvested in June and kept for 6 months at – 4°C contained up to four times 2-AP in all forms (brown and white), compared to those kept at 30°C. High losses of 2-AP occurred under a very warm condition of 30°C. There were also significant differences in the concentration of 2-AP between samples collected in November with losses of 25 to 35% occurring after storage of 3 months at 20°C compared to 8°C [115].

Therefore, insights into extraction and quantification methods and various factors affecting the quality of aroma are essential, and also modern biotechnological advances like Transcription Activator Like Effector Nuclease (TALENs), Zinc Finger Nuclease (ZFNs) and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) associated endonuclease Cas9 (CRISPR/Cas9) are being entrusted in improving the rice aroma content and quality. Researchers succeeded in editing Badh2gene and generating high yielding fragrance rice varieties by using TALENs [128] and CRISPR/CAS9 [129, 130, 131] technologies, which led to increased accumulation of 2AP.

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7. Conclusion and future prospects

Aroma in rice is a key quality trait determining its acceptability and marketability. 2AP has gained major importance among other volatiles as the primary compound for aroma. Aroma compound is encoded by betaine aldehyde dehydrogenase 2 (badh2) gene also called fragrance (fgr) gene which is located on chromosome 8 and the level of aroma depends on this gene caused by mutation in badh2of 8 bp deletion and 3 SNPs. Apart from Basmati genotypes possessing long slender grains, only few other medium/short slender grain rice varieties possessing aroma are in the market. Those short/medium slender aromatic genotypes are not high yielding and possess several other disadvantages. Development of aromatic rice varieties possessing superior grain qualities through conventional or molecular breeding approaches takes considerable number of years and in some cases retaining the superior grain qualities of elite genotypes still remains a challenge. In recent years, genome editing technologies like TALENs, ZFNs and CRISPR/Cas9 has been employed in developing superior quality rice grains and it has opened new avenues for accelerated improvement of rice varieties thereby gaining competitive advantage in improving economy on national and global scale. These new technologies seems to be an attractive strategy to overcome the number of years required for developing desired genotypes and also to overcome the problems due to linkage drag. It will accelerate the cultivation of new aromatic rice varieties with high quality, yield and multiple resistance.

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Conflict of interest

The authors declare no conflict of interest towards this chapter.

References

  1. 1. Wakte K, Zanan R, Hinge V, Khandagale K, Nadaf A, Henry R. Thirty-three years of 2-acetyl-1-pyrroline, a principal basmati aroma compound in scented rice (Oryza sativaL.): A status review. Journal of the Science of Food and Agriculture. 2017;97(2):384-395. DOI: 10.1002/jsfa.7875
  2. 2. Prodhan ZH, Faruq G, Rashid KA, Taha RM. Effects of temperature on volatile profile and aroma quality in rice. International Journal of Agriculture and Biology. 2017;19(5):1065-1072. DOI: 10.17957/IJAB/15.0385
  3. 3. Kovach MJ, Calingacion MN, Fitzgerald MA, McCouch SR. The origin and evolution of fragrance in rice (Oryza sativaL.). Proceedings of the National Academy of Sciences of the United States of America. 2009;106(34):14444-14449. DOI: 10.1073/pnas.0904077106
  4. 4. Pachauri V, Singh MK, Singh AK, Singh S, Shakeel NA, Singh VP, Singh NK. Origin and genetic diversity of aromatic rice varieties, molecular breeding and chemical and genetic basis of rice aroma. Journal of Plant Biochemistry and Biotechnology. 2010;19(2):127-143. DOI: 10.1007/BF03263333
  5. 5. Huang N, McCouch SR, Mew T, Parco A, Guiderdoni E. A rapid technique for scent determination in rice. Rice Genetics Newsletter. 1994;11:134-137
  6. 6. Sood BG, Siddiq EAA rapid technique for scent determination in rice. Indian Journal of Genetics and Plant Breeding. 1978;38:268-271
  7. 7. Hinge VR, Patil HB, Nadaf AB. Aroma volatile analyses and 2AP characterization at various developmental stages in Basmati and non-Basmati scented rice (Oryza sativaL.) cultivars. Rice. 2016;9(1):38. DOI: 10.1186/s12284-016-0113-6
  8. 8. IRGSP (International Rice Genome Sequencing Project), Sasaki T. The map-based sequence of the rice genome. Nature. 2005;436:793– 800
  9. 9. Lorieux M, Petrov M, Huang N, Guiderdoni E, Ghesquière A. Aroma in rice: Genetic analysis of a quantitative trait. Theoretical and Applied Genetics. 1996;93(7):1145-1151. DOI: 10.1007/BF00230138
  10. 10. Amarawathi Y, Singh R, Singh AK, Singh VP, Mohapatra T, Sharma TR, Singh NK. Mapping of quantitative trait loci for Basmati quality traits in rice (Oryza sativaL.). Molecular Breeding. 2008;21(1):49-65. DOI: 10.1007/s11032-007-9108-8
  11. 11. Verma DK, Srivastav PP. Extraction, Identification and Quantification Methods of Rice Aroma Compounds with Emphasis on 2-Acetyl-1-Pyrroline (2-AP) and Its Relationship with Rice Quality: A Comprehensive Review. Food Reviews International. 2020;1-52. DOI: 10.1080/87559129.2020.1720231
  12. 12. Weber DJ, Rochelle R, Singh US. Chemistry and Biochemistry of Aroma in Scented Rice. In: Singh RK, Singh US, Khush GS. editors. Aromatic Rices. Oxford and IBH Publishing Co. Pvt. Ltd. New Delhi, India; 2000. p. 135-151
  13. 13. Singh RK, Singh US. Indigenous scented rices of India-farmers’ perception and commitment. In: Proceedings of the International Conference on “Creativity, innovation, and networking at grass root level”; 11-14 January 1997; Hyderabad. p. 11-14
  14. 14. Verma DK, Srivastav PP. Extraction Technology for Rice Volatile Aroma Compounds. In: Meghwal M, Goyal MR, editors. Food Engineering: Emerging Issues, Modeling, and Applications. Innovations in Agricultural and Biological Engineering. 2nd Volume. Apple Academic Press, USA; 2016. p. 246-284
  15. 15. Verma DK, Srivastav PP. Introduction to Rice Aroma, Flavor, and Fragrance. In: Science and technology of Aroma, Flavour and Fragrance in Rice. In: Verma DK, Srivastav PP, editors. Apple Academic Press, USA; 2018. p. 3-34
  16. 16. Verma DK, Mahato DK, Srivastav PP. Simultaneous Distillation Extraction (SDE): A Traditional Method for Extraction of Aroma Chemicals in Rice. In: Verma DK, Srivastav PP, editors. Science and technology of Aroma, Flavour and Fragrance in Rice. Apple Academic Press, USA; 2018a. p. 81-90
  17. 17. Verma DK, Mahato DK, Billoria S, Srivastav PP. Solid Phase Micro Extraction (SPME): A Modern Extraction Method for Rice Aroma Chemicals. In: Verma DK, Srivastav PP, editors. Science and technology of Aroma, Flavour and Fragrance in Rice. Apple Academic Press, USA; 2018b. p. 93-140
  18. 18. Buttery RG, Ling LC, Juliano BO. 2-Acetyl-1-pyrroline: an important aroma component of cooked rice. Chem Ind (Lond). 1982;12:958-9
  19. 19. Champagne ET. Rice aroma and flavor: A literature review. Cereal Chemistry. 2008;85:445-454. DOI: 10.1094/cchem-85-4-0445
  20. 20. Yoshihashi TN, Huong TT, Inatomi H. Precursors of 2-acetyl-1-pyrroline, a potent flavor compound of an aromatic rice variety. Journal of the Science of Food and Agriculture. 2002;50:2001-2004. DOI: 10.1021/jf011268s
  21. 21. Chen S H, Yang Y, Shi W W, Ji Q, He F, Zhang Z D, Cheng Z K, Liu X N, Xu M L.Badh2, encoding betaine aldehyde dehydrogenase, inhibits the biosynthesis of 2-acetyl-1-pyrroline, a major component in rice fragrance. Plant Cell. 2008;20(7):1850-1861. DOI: 10.1105/tpc.108.058917
  22. 22. Bradbury L M T, Gillies S A, Brushett D J, Waters D L E, Henry R J. Inactivation of an aminoaldehyde dehydrogenase is responsible for fragrance in rice. Plant Molecular Biology. 2008;68(4-5):439-449. DOI: 10.1007/s11103-008-9381-x
  23. 23. Huang T C, Teng C S, Chang J L, Chuang H S, Ho C T, Wu M L. Biosynthetic mechanism of 2-acetyl-1-pyrroline and its relationship with Δ1-pyrroline-5-carboxylic acid and methylglyoxal in aromatic rice (Oryza sativaL.) callus. Journal of Agricultural and Food Chemistry. 2008; 56(16):7399-7404. DOI: 10.1021/jf8011739
  24. 24. Prodhan Z H and Shu Q. Rice Aroma: A Natural Gift Comes with Price and the Way Forward. Rice Science. 2020;27(2):86-10. DOI: 10.1016/j.rsci.2020.01.001
  25. 25. Wijerathna YMAM, Kottearachchi NS, Gimhani DR, Sirisena DN. Exploration of relationship between fragrant gene and growth performances of fragrant rice (Oryza sativaL.) seedlings under salinity stress. Journal of Experimental Biology and Agriculture Sciences. 2014; 2(1): 7-12
  26. 26. Huang ZL, Tang XR, Wang YL, Chen MJ, Zhao ZK, Duan MY, Pan SG. Effects of increasing aroma cultivation on aroma and grain yield of aromatic rice and their mechanism. Scientia Agricultura Sinica. 2012; 45(6): 1054-1065
  27. 27. Mo Z, Ashraf U, Tang Y, Li W, Pan S, Duan M, Tian H, Tang X. Nitrogen application at the booting stage affects 2-acetyl-1-pyrroline, proline, and total nitrogen contents in aromatic rice. Chilean Journal of Agricultural Research. 2018; 78(2): 165-172
  28. 28. Yang S, Zou Y, Liang Y, Xia B, Liu S, Md I, Li D, Li Y, Chen L, Zeng Y, Liu L, Chen Y, Li P, Zhu J. Role of soil total nitrogen in aroma synthesis of traditional regional aromatic rice in China. Field Crops Research. 2012;125:151-160. DOI: 10.1016/j.fcr.2011.09.002
  29. 29. Berner DK, Hoff BJ. Inheritance of scent in American long grain rice. Crop Science.1986;26(5):876-878. DOI: 10.2135/cropsci1986.0011183X002600050008x
  30. 30. Ahn SN, Bollich CN, Tanksley SD. RFLP Tagging of a Gene for Aroma in Rice. Theoretical and Applied Genetics. 1992;84(7):825-828
  31. 31. Bollich CN, Rutger JN, Webb BD. Developments in rice research in the United States. International Rice Commission Newsletter. 1992;41:32-34
  32. 32. Cordeiro GM, Christopher MJ, Henry RJ, Reinke RF. Identification of microsatellite markers for fragrance in rice by analysis of the rice genome sequence. Molecular Breeding. 2002;9(4):245-250. DOI: 10.1023/A:1020350725667
  33. 33. Jin QS, Waters D, Cordeiro GM, Henry RJ, Reinke RF. A single nucleotide polymorphism (SNP) marker linked to the fragrance gene in rice (Oryza sativaL.). Plant Science. 2003;165(2):359-364. DOI: 10.1016/S0168-9452(03)00195-X
  34. 34. Kadam BS, Patankar VK. Inheritance of Aroma in Rice. Chronica Botanica. 1938;4:496-497
  35. 35. Dhulappanavar CV. Inheritance of scent in rice. Euphytica. 1976;25(1):659-662. DOI: 10.1007/BF00041603
  36. 36. Geetha S, Nadu T. Inheritance of aroma in two rice crosses. International Rice Genetic analysis of a quantitative trait. Theoretical and Applied Genetics. 1994;93:1145-1151
  37. 37. Pinson SRM. Inheritance of Aroma in 6 Rice Cultivars. Crop Science. 1994;34(5):1151-1157. DOI: 10.2135/cropsci1994.0011183X003400050002x
  38. 38. Vivekanandan P, Giridharan S. Inheritance of aroma and breadthwise grain expansion in Basmati and non-Basmati rices. International Rice Research Notes. 1994;19(2): 4-5
  39. 39. Jodon NE. The inheritance of flower fragrance and other character in rice. Journal of American Society of Agronomy. 1944;36:844-848
  40. 40. Kuo SM, Chou SY, Wang AZ, Tseng TH, Chueh FS, Yen He, Wang CS. The betaine aldehyde dehydrogenase (BAD2) gene is not responsible for the aroma trait of SA0420 rice mutant derived by sodium azide mutagenesis. In: 5th International Rice Genetics Symposium and 3rd International Rice Functional Genomics Symposium. International Rice Research Institute Press, Manila, Philippines. 2005.Vol.166
  41. 41. Ghose RLM, Butany WT. Studies on the inheritance of some characters in rice (Oryza sativaL.)’. Indian Journal of Genetics and Plant Breeding. 1952;12:26-30
  42. 42. Scod BC, Siddiq EA. Studies on component quality attributes of basmati rice,Oryza sativaL. Zeitschrift fuer Pflanzenzuechtung. 1980;84:299-301
  43. 43. Shekhar BP, Reddy GM. Genetic basis of aroma and flavour component studies in certain scented cultivars of rice. In IV International SABRO Congress. 1981.May 4
  44. 44. Reddy VD, Reddy GM. Genetic and biochemical basis of scent in rice (Oryza sativaL.). Theoretical and Applied Genetics. 1987;73(5):699-700. DOI: 10.1007/BF00260778
  45. 45. Song W, Chen Z, Zhang Y. Inheritance of aroma in autotetraploid and diploid rices. Report of the National Rice Research Institute. 1989. p. 277
  46. 46. Huang QH, Zou XY. Inheritance of aroma in two aromatic rice varieties. International Rice Research Newsletter. 1992;17:5-6
  47. 47. Ali SS, Jafri SJ, Khan MJ, Butt MA. Inheritance studies for aroma in two aromatic varieties of Pakistan. International Rice Research Newsletter. 1993.18:2-6
  48. 48. Wu AH, Gao LK, Cai XZ, Zhao Z, Chen DX. The genetic analysis of fragrance in Shangnong scented glutinous rice’. Journal of Shanghai Agricultural College. 1994;12(1):31-34
  49. 49. Katare NB, Jambhale ND. Inheritance of scent in rice.Oryza. 1995;32:193-194
  50. 50. Li X, Gu M, Cheng Z, Yu H. Chromosome location of a gene for aroma in rice. Chinese Journal of Rice Research. 1995;4(2): 5-6
  51. 51. Kato T, Itani T. Effects of the gene for scented grain in a rice cultivar BG1 on agronomic performance’. SABRO Journal (Japan). 1996;28(1):1-9
  52. 52. Tragoonrung S, Sheng JQ, Vanavichit A. Tagging an aromatic gene in lowland rice using bulk segregant analysis. Rice Genetics III. IRRI; 1996. p. 613-8. DOI: 10.1142/9789812814289_0073
  53. 53. Li J, Ku D, Li L. Analysis of fragrance inheritance in scented rice variety, Shenxiangjing 4. Acta Agriculturae Shanghai. 1996;12(3):78-81
  54. 54. Li J, Gu D. 1997. Analysis of inheritance of scented rice variety Shenxiangjing 4 China Rice Research Newsletter. Rice Science. 1997;5(1):4-5
  55. 55. Sadhukhan RN, Roy K, Chattopadhyay P. Inheritance of aroma in two local aromatic rice cultivars. Environment and Ecology. 1997;15(2):315-317
  56. 56. Garland S, Lewin L, Blakeney A, Reinke R, Henry R. PCR-based molecular markers for the fragrance gene in rice (Oryza sativaL.). Theoretical and Applied Genetics. 2000;101(3):364-71
  57. 57. Dartey PK, Asante MD, Akromah R. Inheritance of aroma in two rice cultivars. Agricultural and Food Science Journal of Ghana. 2006;5:375-379
  58. 58. Lang NT, Buu BC. Development of PCR-based markers for aroma (fgr) gene in rice (Oryza sativaL.). Omonrice. 2008;16:16-23
  59. 59. Niu X, Tang W, Huang W, Ren G, Wang Q, Luo D, Xiao Y, Yang S, Wang F, Lu BR, Gao F. RNAi-directed downregulation of OsBADH2 results in aroma (2-acetyl-1-pyrroline) production in rice (Oryza sativaL.). BMC plant biology. 2008;8(1):1-0. DOI: 10.1186/1471-2229-8-100
  60. 60. Sun SX, Gao FY, Lu XJ, Wu XJ, Wang XD, Ren GJ, Luo H. Genetic analysis and gene fine mapping of aroma in rice (Oryza sativaL. Cyperales, Poaceae). Genetics and Molecular Biology. 2008;31(2):532-8. DOI: 10.1590/S1415-47572008000300021
  61. 61. Sarhadi WA, Hien NL, Zanjani M, Yosofzai W, Yoshihashi T, Hirata Y. Comparative analyses for aroma and agronomic traits of native rice cultivars from Central Asia. Journal of Crop Science and Biotechnology. 2008;11(1):17-22
  62. 62. Asante MD, Kovach MJ, Huang L, Harrington S, Dartey PK, Akromah R, Semon M, McCouch S. The genetic origin of fragrance in NERICA1. Molecular Breeding. 2010;26(3):419-24. DOI: 10.1007/s11032-009-9382-8
  63. 63. Vazirzanjani M, Sarhadi WA, NWE JJ AM, Siranet R, Trung NQ. Characterization of aromatic rice cultivars from Iran and surrounding regions for aroma and agronomic traits. SABRAO Journal of Breeding and Genetics. 2011;43:15-26
  64. 64. Tsuzuki E, Shimokawa E. Inheritance of aroma in rice. Euphytica. 1990;46:157-159
  65. 65. Geetha S. Inheritance of aroma in two rice crosses. International Rice Research Notes. 1994;19(2):5
  66. 66. Hien N, Yoshihashi T, Sarhadi WA, Thanh V, Oikawa Y, Hirata Y. Evaluation of Aroma in Rice (Oryza sativaL.) using KOH Method, Molecular Markers and Measurement of 2-Acetyl-1-Pyrroline Concentration. Japanese Journal of Tropical Agriculture. 2006;50:190-198
  67. 67. Siddiq EA. Breeding for quality improvement in rice-Present state and strategy for future. In: Rice in West Bengal IV. Directorate of Agriculture, West Bengal. 1983. p. 73-95
  68. 68. Tripathi RS, Rao MJBK. Inheritance and linkage relationship of scent in rice’. Euphytica. 1979;28:319-323
  69. 69. Nagaraju M, Chowdhary D, Rao MJBK. A simple technique to identify scent in rice and inheritance pattern of scent. Current Science. 1975;44(16):599
  70. 70. Reddy PR, Sathyanarayanaiah K. Inheritance of aroma in rice. Indian Journal of Genetics and Plant Breeding. 1980;40(2):327-9
  71. 71. Nayak AR, Acharya US. Inheritance of scent in rice (Oryza sativaL.). Indian Journal of Genetics and Plant Breeding. 2004;64:59-60
  72. 72. Sarawagi AK, Bisne R. Inheritance of aroma in indigenous short grain aromatic rice cultivars. Journal of Rice Research. 2006;1:180-1
  73. 73. Chaut AT, Yutaka H, Vo CT. 2010. Genetic analysis for the Fragrance of Aromatic Rice Variete. In: 3rd International Rice Congress, November 8-12, Hanoi, Vietnam. p. 3898
  74. 74. Richharia RH, Mishra B, Kulkarni VA. Studies in the world genetic stock of rice. IV. Distribution of scented rice. Oryza. 1965;2:57-9
  75. 75. Kiani G. Marker aided selection for aroma in F2 populations of rice. African Journal of Biotechnology. 2011;10(71):15845-8
  76. 76. Bourgis F, Guyot R, Gherbi H, Tailliez E, Amabile I, Salse J, Lorieux M, Delseny M, Ghesquière A. Characterization of the major fragance gene from an aromatic japonica rice and analysis of its diversity in Asian cultivated rice. Theoretical and Applied Genetics. 2008;117(3):353-68
  77. 77. Chen S, Wu J, Yang Y, Shi W, Xu M. The fgr gene responsible for rice fragrance was restricted within 69 kb. Plant Science. 2006;171(4):505-14. DOI: 10.1016/j.plantsci.2006.05.013
  78. 78. Shi W, Yang Y, Chen S, Xu M. Discovery of a new fragrance allele and the development of functional markers for the breeding of fragrant rice varieties. Molecular Breeding. 2008;22(2):185-92. DOI: 10.1007/s11032-008-9165-7
  79. 79. Lanceras JC, Huang ZL, Naivikul O, Vanavichit A, Ruanjaichon V, Tragoonrung S. Mapping of genes for cooking and eating qualities in Thai jasmine rice (KDML105). DNA Research. 2000;7(2):93-101. DOI: 10.1093/dnares/7.2.93
  80. 80. Bradbury LM, Fitzgerald TL, Henry RJ, Jin Q, Waters DL. The gene for fragrance in rice. Plant Biotechnology Journal. 2005;3(3):363-70. DOI: 10.1111/j.1467-7652.2005.00131.x
  81. 81. Yano M, Shimosaka E, Saito A, Nakagahra M. Linkage analysis of a gene for scent in indica rice variety, Surjamkhi, using restriction fragment length polymorphism markers. Japanese Journal of Breeding. 1992;41:338-339
  82. 82. Wanchana S, Kamolsukyunyong W, Ruengphayak S, Toojinda T, Tragoonrung S, Vanavichit A. A rapid construction of a physical contig across a 4.5 cM region for rice grain aroma facilitates marker enrichment for positional cloning. Science Asia. 2005;31:299-306
  83. 83. Li JH, Wang F, Liu WG, Jin SJ, Liu YB. Genetic analysis and mapping by SSR marker for fragrance gene in rice Yuefeng B. Molecular Plant Breeding. 2006;4:54-58
  84. 84. Bradbury LMT. Identification of the gene responsible for fragrance in rice and characterisation of the enzyme transcribed from this gene and its homologs. Southern Cross University ePublications@SCU Theses (2009)
  85. 85. Yi M, Nwe KT, Vanavichit A, Chai-arree W, Toojinda T. Marker assisted backcross breeding to improve cooking quality traits in Myanmar rice cultivar Manawthukha. Field Crops Research. 2009;113:178-186
  86. 86. Vanavichit A, et al. in Proceedings of the 1st International Conference on Rice for the Future (Bangkok, Thailand) (2004)
  87. 87. Vanavichit A, Yoshihashi T, Wanchana S, Areekit S, Saengsraku D, Kamolsukyunyong W, Lanceras J, Toojinda T, Tragoonrung S. Positional cloning of Os2AP, the aromatic gene controlling the biosynthetic switch of 2-acetyl-1-pyrroline and gamma aminobutyric acid (GABA) in rice. In 5th International Rice Genetics Symposium. Manila, Philippines, IRRI. 2005;44:19-23
  88. 88. Fitzgerald MA, Sackville Hamilton NR, Calingacion MN, Verhoeven HA, Butardo VM. Is there a second fragrance gene in rice?. Plant Biotechnology Journal. 2008;6(4):416-423. DOI:10.1111/j.1467-7652.2008.00327.x
  89. 89. Shao G, Tang S, Chen M, Wei X, He J, Luo J, Jiao G, Hu Y, Xie L, Hu P. Haplotype variation atBadh2, the gene determining fragrance in rice. Genomics. 2013;101(2):157-62. DOI: 10.1016/j.ygeno.2012.11.010
  90. 90. He Q, Park YJ. Discovery of a novel fragrant allele and development of functional markers for fragrance in rice. Molecular breeding. 2015;35(11):1-10. DOI: 10.1007/s11032-015-0412-4
  91. 91. He Q, Yu J, Kim TS, Cho YH, Lee YS, Park YJ. Resequencing reveals different domestication rate for BADH1 and BADH2 in rice (Oryza sativa). PLoS one. 2015;10(8):e0134801. DOI: 10.1371/journal.pone.0134801
  92. 92. Pachauri V, Mishra V, Mishra P, Singh A K, Singh S, Singh R, Singh N K. 2014. Identification of candidate genes for rice grain aroma by combining QTL mapping and transcriptome profiling approaches. Cereal Research Communications. 42(3):376-388. DOI: 10.1556/crc.42.2014.3.2
  93. 93. Talukdar PR, Rathi S, Pathak K, Chetia SK, Sarma RN. Population structure and marker-trait association in indigenous aromatic rice. Rice Science. 2017;24(3):145-54. DOI: 10.1016/j.rsci.2016.08.009
  94. 94. Grimm CC, Champagne ET, Lloyd SW, Easson M, Condon B, McClung A. Analysis of 2-Acetyl-l-Pyrroline in Rice by HSSE/GCIMS. Cereal Chemistry. 2011;88(3):271-277. DOI: 10.1094/CCHEM-09-10-0136
  95. 95. Chaintreau A. Simultaneous distillation-extraction: from birth to maturity-review. Flavour and Fragrance Journal. 2001;16(2):136-148
  96. 96. Schwambach SL, Peterson DG. Reduction of stale flavor development in low-heat skim milk powder via epicatechin addition. Journal of Agricultural and Food Chemistry. 2006;54:502-508
  97. 97. Zhang Z, Yang MJ, Pawliszyn J. Solid-phase Microextraction. Analytical Chemistry. 1994;66:844A–853A. DOI: 10.1021/ac00089a001
  98. 98. Grimm C, Bergman CJ, Delgado JT, Bryant R. Screening for 2-acetyl-l-pyrroline in the Headspace of Rice Using SPME/GC/MS. Journal of Agricultural and Food Chemistry. 2001;49:245-249. DOI: 10.1021/jf0008902
  99. 99. Cho S, Kays SJ. Aroma-active Compounds of Wild Rice (Zizania palustrisL.). Food Research International. 2013;54:1463-1470. DOI: 10.1016/j.foodres.2013.09.042
  100. 100. Yahya, FB. Extraction of aroma compound from pandan leaf and use of the compound to enhance rice flavour. PhD thesis submitted to School of Chemical Engineering, The University of Birmingham, Birmingham, UK. 2011
  101. 101. Duarte C, Moldao-Martins M, Gouveia AF, Costa SB, Leitao AE, Bernardo-Gil MG. Supercritical Fluid Extraction of Red Pepper (Capsicum frutescensL.). The Journal of Supercritical Fluids. 2004;30:155-161. DOI: 10.1016/j.supflu.2003.07.001
  102. 102. Yahya F, Lu T, Santos RCD, Fryer PJ, Bakalis S. Supercritical carbondioxide and solvent extraction of 2-acetyl-1-pyrroline from pandan leaf: The effect of pretreatment. Journal of Supercritical Fluids. 2010;55(1):200-207
  103. 103. Routray W, Rayaguru K. 2-Acetyl-1-pyrroline: A key aroma component of aromatic rice and other food products. Food Reviews International. 2017;34(6):539-565. DOI: 10.1080/87559129.2017.1347672
  104. 104. Lin, Pei-Ching. Comparison of Simultaneous Distillation and Extraction (SDE) and Headspace Solid Phase Microextraction (SPME) for Determination of Volatiles of Muscadine Grapes (Vitis rotundifolia). 2014
  105. 105. Takemitsu H, Amako M, Sako Y, Shibakusa K, Kita K, Kitamura S, Inui H. Analysis of Volatile Odor Components of Superheated Steam-cooked Rice with a Less Stale Flavor. Food Science and Technology Research. 2016;22(6):771-778. DOI:10.3136/fstr.22.771
  106. 106. Delahunty CM, Eyres G, Dufour JP. Gas Chromatography–olfactometry. Journal of Separation Science. 2006;29(14):2107−2125. DOI: 10.1002/jssc.200500509
  107. 107. Struve C, Christophersen C. Structural equilibrium and ring- chain tautomerism of aqueous solutions of 4-aminobutyraldehyde. Heterocycles. 2003;60(8):1907-1914
  108. 108. Ootsuka K, Takahashi I, Tanaka K, Itani T, Tabuchi H, Yoshihashi T, Ishikawa R. Genetic polymorphisms in Japanese fragrant landraces and novel fragrant allele domesticated in northern Japan. Breeding Science. 2014;64(2):115-124. DOI: 10.1270/jsbbs.64.115
  109. 109. Chakraborty D, Deb D, Ray A. An analysis of variation of the aroma gene in rice (Oryza sativa L. subsp. indica Kato) landraces. Genetic Resources and Crop Evolution. 2016;63:953-959. DOI: 10.1007/s10722-016-0414-z
  110. 110. Hashemi FSG, Rafii MY, Ismail MR, Mahmud TMM, Rahim HA, Asfaliza R, Latif MA. Biochemical, Genetic and Molecular Advances of Fragrance Characteristics in Rice. Critical Reviews in Plant Sciences. 2013;32(6):445-457. DOI: 10.1080/07352689.2013.807716
  111. 111. Mo Z, Lei S, Ashraf U, Khan I, Li Y, Pan S, Tang X. Silicon fertilization modulates 2-acetyl-1-pyrroline content, yield formation and grain quality of aromatic rice. Journal of Cereal Science. 2017;75:17-24. DOI: 10.1016/j.jcs.2017.03.014
  112. 112. Gay F, Maraval I, Roques S, Gunata Z, Boulanger R, Audebert A, Mestres C. Effect of salinity on yield and 2-acetyl-1-pyrroline content in the grains of three fragrant rice cultivars (Oryza sativaL.) in Camargue (France). Field Crops Research. 2010;117(1):154-160. DOI: 10.1016/j.fcr.2010.02.008
  113. 113. Banerjee A, Ghosh P, Roychoudhury A. Salt acclimation differentially regulates the metabolites commonly involved in stress tolerance and aroma synthesis in indica rice cultivars. Plant Growth Regulation. 2019;88:87-97. DOI: 10.1007/s10725-019-00490-6
  114. 114. Mo Z, Li W, Pan S, Fitzgerald TL, Xiao F, Tang Y. Shading during the grain filling period increases 2-acetyl-1-pyrroline content in fragrant rice. Rice. 2015;8: 9
  115. 115. Goufo P, Duan M, Wongpornchai S, Tang X. Some factors affecting the concentration of the aroma compound 2-acetyl-1-pyrroline in two fragrant rice cultivars grown in South China. Frontiers of Agriculture in China. 2010; 4(1): 1-9
  116. 116. Sriseadka T, Wongpornchai S, Kitsawatpaiboon P. Rapid method for quantitative analysis of the aroma impact compound, 2-acetyl-1- pyrroline, in fragrant rice using automated headspace gas chromatography. Journal of Agricultural and Food Chemistry. 2006;54: 8183-818
  117. 117. Zeng Z, Zhang H, Chen JY, Zhang T, Matsunaga R. Direct extraction of volatiles of rice during cooking using solid-phase microextraction. Cereal Chemistry. 2007;84:423-427
  118. 118. Xia Q, Li Y. Ultra-high pressure effects on color, volatile organic compounds and antioxidants of wholegrain brown rice (Oryza sativaL.) during storage: A comparative study with high-intensity ultrasound and germination pretreatments. Innovative Food Science & Emerging Technologies. 2018;45:390-400. DOI: 10.1016/j.ifset.2017.12.003
  119. 119. Xia Q, Mei J, Yu W, Li Y. High hydrostatic pressure treatments enhance volatile components of pre-germinated brown rice revealed by aromatic fingerprinting based on HS-SPME/GC–MS and chemometric methods. Food Research International. 2017;91:103-114. DOI: 10.1016/j.foodres.2016.12.001
  120. 120. Shi Y, Wang L, Fang Y, Wang H, Tao H, Pei F, Hu Q. A comprehensive analysis of aroma compounds and microstructure changes in brown rice during roasting process. LWT. 2018. DOI: 10.1016/j.lwt.2018.09.018
  121. 121. Rocha-Villarreal V, Serna-Saldivar SO, García-Lara S. Effects of parboiling and other hydrothermal treatments on the physical, functional, and nutritional properties of rice and other cereals. Cereal Chemistry. 2018; 95(1):79-91. DOI: 10.1002/cche.10010
  122. 122. Choi S, Seo HS, Lee KR, Lee SJ, Lee J. Effect of milling and long-term storage on volatiles of black rice (Oryza sativaL.) determined by headspace solid phase microextraction with gas chromatography-mass spectrometry. Food chemistry. 2019;276:572-582
  123. 123. Mahmud MMC, Oh Y, Kim TH, Cho YH, Lee YS. Effects of milling on aromatics, lipophilic phytonutrients, and fatty acids in unprocessed white rice of scented rice cheonjihyang-1-se. food science and biotechnology. 2018;27(2):383-392
  124. 124. Guan B, Zhao J, Jin H. Determination of Rice Storage Time with Colorimetric Sensor Array. Food Analytical Methods. 2017;10:1054-1062. DOI: 10.1007/s12161-016-0664-6
  125. 125. Tananuwong K, Lertsiri S. Changes in volatile aroma compounds of organic fragrant rice during storage under different conditions. Journal of the Science of Food and Agriculture, 2010;90(10):1590 – 1596
  126. 126. Yoshihashi T. Quantitative Analysis on 2-Acetyl-1-pyrroline of an Aromatic Rice by Stable Isotope Dilution Method and Model Studies on its Formation during Cooking. Journal of Food Science. 2002;67(2):619-622
  127. 127. Udomkun P, Innawong B, Niruntasuk K. The feasibility of using an electronic nose to identify adulteration of Pathumthani 1 in Khaw Dok Mali 105 rice during storage. Food Measure. 2018;12:515-2523. DOI: 10.1007/s11694-018-9868-3
  128. 128. Shan Q, Zhang Y, Chen K, Zhang K, Gao C. Creation of fragrant rice by targeted knockout of the OsBADH 2 gene using TALEN technology. Plant biotechnology journal. 2015;13(6):791-800. DOI: 10.1111/pbi.12312
  129. 129. Shao G, Xie L, Jiao G, Wei X, Sheng Z, Tang S, Hu P. CRISPR/CAS9-mediated editing of the fragrant gene Badh2 in rice. Chinese Journal of Rice Science. 2017;31(2):216-22. DOI: 10.16819/j.1001-7216.2017.6098
  130. 130. Ashokkumar S, Jaganathan D, Ramanathan V, Rahman H, Palaniswamy R, Kambale R, Muthurajan R. Creation of novel alleles of fragrance gene OsBADH2 in rice through CRISPR/Cas9 mediated gene editing. PloS one. 2020;12:15(8):e0237018. DOI: 10.1371/journal.pone.0237018
  131. 131. Usman B, Nawaz G, Zhao N, Liu Y, Li R. Generation of high yielding and fragrant rice (Oryza sativaL.) Lines by CRISPR/Cas9 targeted mutagenesis of three homoeologs of cytochrome P450 gene family and OsBADH2 and transcriptome and proteome profiling of revealed changes triggered by mutations. Plants. 2020;9(6):788. DOI: 10.3390/plants9060788

Written By

Nirubana Varatharajan, Deepika Chandra Sekaran, Karthikeyan Murugan and Vanniarajan Chockalingam

Submitted: May 25th, 2021 Reviewed: June 15th, 2021 Published: August 5th, 2021