The Magical Chemistry and Nutritional Importance of Rice Seeds: A Review

Abstract

The most significant food on earth is rice. The nutrients included in rice include thiamine, riboflavin, niacin and tocopherol, as well as protein, fat, crude fiber, carbohydrates and minerals. It contributes significantly to human health by preventing diseases like high blood pressure, cancer, Alzheimer’s, heart disease, skin conditions and dysentery. As a result, rice is an excellent option for natural sources of antioxidants and other therapeutic characteristics, and it may have the capacity. The magical chemistry enlightens the insights of functional groups, which makes it a potent food. The review also discusses how the nutritional content of rice seed changes as it ages.

1. Introduction

Over 50% of people on earth eat rice as their primary meal. In 17 Asian and Pacific island nations, 9 North and South American nations, and 8 African nations, it is the main dietary energy source. In comparison to wheat’s 19% and maize’s (corn’s) 5% contributions to the world’s dietary energy supply, rice contributes 20% [1]. The amount of total free phenolics and total free flavonoids in the growing rice grains is rather high, which is connected well with their reduced capacity. The growing rice grains would be a rich source of phytochemicals because they have significant levels of free and soluble-ester ferulic acids. For billions of people worldwide, rice is a staple diet. It is a valuable source of fiber, carbs and numerous other nutrients. Humans have been eating rice since the Stone Age. Chinese archeologists discovered the earliest rice in 10,000 BC [2]. A cereal grass with nodes and internodes, rice develops as upright stems. It has ovate-acuminate, parallel-vented leaves that are oriented lengthwise and have short petioles. Two bracts that are connected at their roots form a “keel” around the spikelets, which are surrounded by two bracts [2]. Endosperm, bran and germ are the three components of a rice grain [2]. The grain itself is high in starch but low in fat or protein, but it still has all of the essential amino acids that humans require for nourishment; The World Factbook 2018 [3].

Rice seeds are tiny, oval-shaped grains that sprout on many long-grass species of the Poaceae (or Gramineae) family of grasses, including Oryza sativa, Oryza nivara, Oryza rufipogon, etc. Today, around 125 types of rice are cultivated throughout the world, each with unique properties and applications depending on their botanical categorization. Jasmine rice, which is sourced from Asia, is the most popular type of rice consumed worldwide. Basmati rice is sourced from India, and arborio rice is sourced from Italy. Indica, vannarica, paragrass (Vaccinium), and other varieties of rice are also produced all over the world. About 40% of cooked rice’s weight is made up of rice bran, which is highly nutritious. Starch, protein, fat and dietary fiber are the main ingredients of rice bran [4]. Rice bran contains a wide range of antioxidants including phenolic compounds such as flavonoids and tannins which have antioxidant properties [5]. Due to their ability to neutralize free radicals that harm cellular structures, phenolic compounds are regarded as potent antioxidants [6]. In addition to phenolics, rice bran also contains other types of antioxidants such as carotenoids which are responsible for providing yellow coloration in cooked rice products [7].

Rice seed is a very important part of the rice plant. It contains many essential nutrients for human consumption, and it also has many health benefits. Rice seed is composed of two major components: the endosperm and the bran. The bran consists mainly of pectin, cellulose, hemicellulose, lignin and some proteins, while the endosperm consists mainly of starch but also contains other compounds such as oil globules, amylopectin and others.

Rice seeds contain three different types of chemical substances: phytochemicals (substances generated by plants), secondary metabolites (substances created by microbes) and xenobiotics (compounds not produced by plants or microorganisms). Phytochemicals are seen as being more significant than secondary metabolites or xenobiotics since their positive effects on health outweigh their negative ones. Secondary metabolites can cause toxic effects if consumed in high amounts, but this is not true for phytochemicals since they have beneficial effects even when consumed in high amounts. Carotenoids have also been identified in rice seed (Oryza sativa). The primary carotenoid in rice is beta-carotene, which gives rice grains their orange hue. Beta-cryptoxanthin, gamma-carotene and alpha-carotene are other carotenoids that are present [8]. Beta-cryptoxanthin, which is abundant in carrots and is known for its capacity to absorb light energy, has been found to be a potent antioxidant [9]. Rice is a very nourishing food that is full of many vital nutrients like fiber, carbs, vitamins and minerals. More than half of the daily requirements of the most important nutrients for humans are provided by rice, which is also a fantastic source of energy [10]. It has been demonstrated that they possess antioxidant qualities, which may aid in shielding the body from harm brought on by free radicals. Highly reactive chemicals known as free radicals have the potential to harm biological tissues and cells. Antioxidants function as free radical scavengers, preventing cell damage and preserving the body’s health.

2. Health benefits of Rice

Rice is a very healthy food that can provide many health benefits for those who consume it regularly. Some of the health advantages of eating rice include the following: lowering cholesterol fibre found in rice contributes to a reduction in blood cholesterol levels. Enhanced Digestion Increased consumption of fibre-rich foods, such as brown rice, will help digestion since they will keep you fuller longer, causing you to consume fewer calories than usual. This means that increasing your intake of whole grains will prevent your weight from rising as quickly because you will consume fewer calories than normal, which also lowers your risk of heart disease. The health benefits of rice and the avoidance of diseases including high blood pressure, cancer, skin care issues and dysentery are significant. Even tiny amounts of red rice can help you lose weight. It keeps us full. Figure 1 and Table 1 show the health benefits and nutrient content of rice per 100 g dry weight, respectively.

Figure 1.

Health benefits of different in rice seeds.

Nutrients	White rice	Brown rice	Red rice
Water Content %	12.7	37.6	12.4
Energy (KJ)	1736	1548	1426
Protein (g)	8.1	10.4	10.49
Fat (g)	0.8	0.9	0.81
Carbohydrate (g)	91	77.24	70.19
Fiber (g)	1.5	3.2	2.71
Sugar (g)	0.1	0.85	1.25
Calcium (mg)	32	23	18.71
Iron (mg)	0.91	1.47	13.45
Magnesium (mg)	28	143	192.27
Phosphorus (mg)	131	333	297
Potassium (mg)	131	223	128
Sodium (mg)	6	7	4
Zinc (mg)	1.24	2.02	1.91
Copper (mg)	0.25	1.2	0.8
Manganese (mg)	1.24	3.74	1.77
Selenium (μg)	17.2	23.4	18.19
Vitamin C (mg)	0.0	0.0	0.0
Thiamine (mg)	0.08	0.40	0.21
Riboflavin (mg)	0.06	0.09	0.05
Niacin (mg)	1.82	5.09	4.22
Pantothenic acid (mg)	1.15	1.49	1.72
Vitamin A (IU)	0	0.3	0.5
Vitamin E (mg)	0.13	0.9	1.2
Beta-carotene (μg)	0.1	1.2	1.5
Folate (μg)	9	20	23
Saturated fatty acids (g)	0.20	0.2	0.21
Polyunsaturated fatty acids (g)	0.24	0.21	0.31

Table 1.

Nutrient content of rice per 100 g dry weight [11, 12].

Here: KJ, Kilo Joule; g, gram; mg, milligram; μg, microgram; IU-International Unit.

3. Chemistry of rice seeds

Starch, protein and fiber are all present in the rice grain on their own. The starch level, which has roughly 70% of its calories from carbohydrates, is the primary factor that makes rice so nutritious. When combined with other nutrients like protein and fiber as part of a balanced diet, this carbohydrate content gives the body energy. Additionally, rice contains significant amounts of manganese, which supports bone health by preserving strong bones and teeth. According to research, rice contains phenolic, polyphenolic, flavonoid, anthocyanin, anthocyanidin, tannin, vitamin E, tocopherol, tocotrienol, oryzanol, ferulate, phytic acid, phytate and other compounds that are crucial to the bioactivity of rice seeds [13].

The phenolic chemicals are present in the grain’s cell wall in both a free form and an insoluble form. Phenolic chemicals can be divided into mono- and polyphenolics based on their structural similarities. It has been demonstrated that phenols contain antioxidant capabilities that assist shield cells from damage brought on by free radicals. Highly reactive chemicals known as free radicals have the potential to harm cells if they are not eliminated from the body. Antioxidants stop these dangerous chemicals from harming your body by removing them before they can cause any harm. Phenols have been demonstrated to lessen lipid peroxidation, which is what causes rancidity and is excellent for food preservation. The phenolic compounds gallic acid, protocatechuic acid (PCA) and vanillic acid are abundant in rice seed [13].

Rice seed growth is significantly influenced by flavonoids. There are a lot of phenolic substances in rice seeds, including tannins, phenolic acids, flavonoids and stilbenes [13]. Both antioxidant and anti-inflammatory properties are present in flavonoids. Because quercetin is one of the most prevalent phenolic chemicals in rice seed, we will concentrate on it in this study. It has been suggested that quercetin plays a role in the germination, maturation and production of endosperm in the development of rice seeds [14]. The relative orientation of different moieties in a molecule’s chemical structure determines the metabolic actions of flavonoids and their metabolites. Following absorption, flavonoids are converted to smaller phenolic compounds in the liver by a process of glucuronidation, sulfation and methylation [14]. Figures 2 and 3 enlighten the chemical structure of nutritional components and their health importance, respectively. The relative orientation of different moieties in a molecule’s chemical structure determines the metabolic actions of flavonoids and their metabolites. Following absorption, flavonoids are converted to smaller phenolic compounds in the liver by a process of glucuronidation, sulfation and methylation [15]. In addition, free radicals including super-oxide anion (NO) and peroxynitrite play important roles in the inflammatory process [16].

Figure 2.

Chemical structures of phenolic and flavonoids present different in rice seeds.

Figure 3.

Health importance of nutrients present in different rice seeds.

4. Changes in chemical properties of rice seeds during aging

Rice qualities like hydration, swelling, solubility, viscosity and pasting alter as it ages. The aging process has an impact on the physical and chemical characteristics of rice, primarily the physicochemical characteristics that affect cooking and pasting. Due to changes in the components and interactions between the components like protein, lipid and starch, aging also has an impact on the quality and usefulness of rice. Although there is no change in the protein content during storage, the solubility of rice in water decreases as a result of the intrinsic albumin’s decreased solubility [17]. Contrarily, free amino acids in rice rise with storage [18]. Thus, the higher molecular weight peptides are increasing while the lower molecular weight peptides are decreasing [19].

The research stated that even after 13 weeks of storage, rice’s amylose and amylopectin quantities do not appreciably change [20]. Some literature has been found that an increased water-insolubility of starch and protein in rice with aging, resulting in a slower rate of cooking as α-amylase and β-amylase in rough rice decrease significantly during storage [17]. Due to the hydrolysis of lipids to form free fatty acids and the oxidation of lipids that may result in hydroperoxides, changes in the lipid profile of rice occurred during storage [17]. Free phenolic acids from the rice grain are released during storage, resulting in the creation of free fatty acids (FFAs), which deplete important antioxidants. It has been discovered that hydroperoxides, carbonyl compounds and amylase all interact with FFAs. These processes hasten the oxidation and condensation of proteins, which results in the accumulation of volatile carbonyl chemicals in the grain [17]. As a result of aging, the texture of rice becomes harder and less sticky compared with fresh rice as it is a complicated process and involves physical, chemical and biological changes in rice. It is difficult to address the combined consequences, and it is difficult to determine the paddy grains’ nutritional value and food safety. The hydrolysis and oxidation of lipids to free fatty acids or peroxides, which cause the increase in acidity and have a substantial impact on the flavor of rice, are also linked to the corrosion of rice flavor [17]. Research has also shown that rice seeds stored at ambient temperature show a significant change in textural properties over those stored at cold temperature [21], and remarkably, Tananuwong and Malila; 2011 [22] observed that after 12 months of storage at ambient conditions, hardness of hulled rice, when cooked, increases.

5. Conclusion

Rice is a powerhouse of antioxidants, vitamins and minerals like zinc, calcium, magnesium, zinc and sodium, which contribute greatly to overall well-being. Rice is also low on glycaemic index, which means that it can control blood sugar. The coronavirus pandemic has made us realize the importance of lung health like never before. With the contagious infection still lurking around, people with a history of lung diseases like asthma and respiratory problems are at high risk. Including rice in the daily diet improves lung capacity, with its copious amounts of magnesium and selenium. Rice not only improves and regulates breathing patterns but also improves oxygen consumption and circulation to each cell in the body. The aging impacts on rice seed quality enlighten future research and may further the investigation of techniques and alternatives to achieve high-quality rice seeds with minimal processing and for preservation of essential quality traits.