Impact of Organic Fertilizers on Phenolic Profiles and Fatty Acids Composition: A Case Study for Cichorium intybus

Radicchio ( Cichorium intybus L.) is an increasingly appreciated leafy vegetable that exhibits great diversity in appearance, including different colored leaves, rosettes, or heads. Varieties of radicchio (‘Treviso’, ‘Verona’ ‘Anivip’, ‘Castelfranco’, and ‘Monivip’) commonly produced in Slovenia were investigated for their phenolic and fatty acid profiles. Plants were grown under organic and/or mineral fertilizer managements in greenhouse conditions. High-performance liquid chromatography analysis was used to study phenolic compounds in radicchio leaf samples. Thirty-three phenolic com‐ pounds were quantitatively evaluated. Significant differences were found between varieties and across different fertilizer managements. The total phenolic amount (TPA) was found in a wide range from 58 to 403 mg/100 g fresh weight (FW). Between varieties, the highest TPA was observed for var. ‘Treviso’ (300 mg/100 g FW) and the lowest TPA was observed for var. ‘Castelfranco’ (125 mg/100 g FW). The main phenolic compounds in radicchio leaves were represented by phenolic acids, chlorogenic acid and cichoric acid, respectively. The fatty acid levels of radicchio leaf samples were determined by the chromatographic analysis of fatty acid methyl esters using gas chromatography with flame ionization detector. The analysis revealed the amounts of C16:0, C18:0, C18:1n9, C18:2n6, C18:3n3, and C20:0 fatty acids. The total fatty acid levels varied from 170 to 500 mg/100 g FW. The highest fatty acid quantity was represented by C18:3n3 (≤63%) followed by C18:2n6 (≤45%) and C16:0 (≤24%). All radicchio samples had a ratio of n -6/ n -3 essential fatty acids below 1 and thus in accordance with the current dietary guidelines. Among different fertilizer managements, the highest total fatty acid levels were found for organic fertilizer (384 mg/100 g FW).


Introduction
Radicchio (Cichorium intybus L.; Asteraceae) is a popular salad vegetable in the Mediterranean region, and its usage is increasing in Europe. Other cultivated types of this species are Italian chicory, French endive, witloof, sugarloaf, and succory. It has been known since 1616, when it was first mentioned in Germany. Cultivation began in England in 1886 and later in 1926 also France. There is a discussion about whether radicchio should be classified as a root or a leafy vegetable crop. It can be produced for leaves, rosettes, or heads with a wide range of colors [1]. Radicchio is typically consumed as a raw vegetable in various fresh, mixed, or garnished salads [2,3]. Its popularity among consumers and its nutritional characteristics have great potential for growth in the local markets as well as in the international ones. Most radicchio varieties thrive best during cooler, moist weather and do not tolerate high temperature. Radicchio is a leafy vegetable that can withstand low temperatures, which gives it an advantage for consumption in the winter time of the year when the supply of fresh leafy vegetable in the market is limited [4]. In addition, radicchio represents a plant with several medicinal properties and effects [5].
Vegetable production in many countries depends on high-input systems to maximize yield and product quality, while they try to achieve low production costs, which keep local products competitive in international markets [6]. Conventional high-input farming system is often associated with problems, such as nitrate leaching and ground water pollution, degradation of soil structure, and pesticide contamination [7][8][9][10]. The answers to problems associated with conventional practices are alternative cropping systems. Over the past decade, criteria have been developed, which define organic crop production requirements [11]. Now, there exist several national systems of designated requirements to have vegetable products marketed as » organically produced«. In fresh vegetable market, organically grown products of reasonable quality are readily available, but their price is usually much higher compared to those grown by the other than organic manner [12,13].
The polyphenol compositions of vegetable depend on several factors. It is influenced by genetic as well as environmental factors, such as temperature, light, moisture, and the nutritional status of the soil in which the vegetable is grown [14,15]. It is also influenced by the growing manner, phase of maturity, postharvest managements, and storage conditions. Moreover, many vegetables are processed before they are used for consumption. Processing methods, such as cooking and canning, can also influence the polyphenol composition of the vegetable. Regular consumption of vegetables is proven to be associated with lower risks of various types of modern diseases, such as chronic or cardiovascular diseases [7,16].
Polyphenols are organic compounds widely distributed in vegetables. All phenolic compounds have an aromatic ring that contains various attached substituent groups, such as hydroxyl, carboxyl, and methyl groups, and often other nonaromatic ring structures. Phenolics differ from lipids in higher solubility in water and lower solubility in nonpolar organic solvents. These properties greatly aid in the separation of phenolics from one another and from other compounds. Many phenolics arise from the shikimic acid pathway and its subsequent reactions. Among these are cinnamic, p-coumaric, caffeic, ferulic, chlorogenic, protocatechuic, and gallic phenolic acids. They are important not because they are abundant in uncombined (free) form but because they are converted into several derivatives besides proteins. These derivatives include phytoalexins, coumarins, lignin, and various flavonoids, such as the anthocyanins [17]. Chlorogenic acid is widely distributed in various parts of many plants and usually occurs in easily detectable quantities. Both chlorogenic and protocatechuic acids have special functions in disease resistance of plants. Gallic acid is important because of its conversion to gallotannins, which are heterogeneous polymers containing numerous gallic acid molecules connected in various ways to one another, to glucose, and to other sugars [18].
Of the various classes of naturally occurring compounds based on the flavonoid skeleton, flavone and flavonols are collectively the most abundant group. The distinction between flavones and flavonols, which are 15 carbon compounds, is an arbitrary one, as flavonols are simply a class of flavone in which the 3-position is substituted by a hydroxyl group [19]. Anthocyanins are present as glycosides, usually containing one or two glucose or galactose units attached to the hydroxyl group in the central ring or to that hydroxyl group at the 5position of the A ring. When the sugars are removed, the remaining parts of the molecules, which are still colored, are called anthocyanidins. Anthocyanins are soluble and reasonably stable, whereas anthocyanidins produced on acid hydrolysis are insoluble in water, unstable to light, and rapidly destroyed by alkali [20]. Flavones and flavonols are easier to identify than anthocyanins because they are more stable [21]. Several polyphenols, such as derivatives of hydroxycinnamic acids (HCA), flavonoids, and anthocyanins [4,6,[22][23][24][25][26][27], previously determined in radicchio leaves are presented in Table 1 Lipids are derived from long-chain fatty acids and alcohols or closely related derivatives. They are water-insoluble components of cells that can be extracted by nonpolar solvents. In various parts of the plants, mostly in the cell membranes, are small amounts of lipids (~2%). In higher plants, the predominant fatty acid residues consist of palmitic, oleic, linoleic, and stearic acid.
Fatty acids with <12 and >20 carbon atoms are less common in nature [28]. The most common fatty acids in plants are those containing 16 or 18 carbon atoms. These include saturated palmitic (C16:0) and stearic (C18:0) acids, monounsaturated oleic acid (C18:1n9), polyunsaturated linoleic acid with two double bonds (C18:2n6), and linolenic acid with three double bonds (C18:3n3) [29]. When the carbon atoms in the hydrocarbon chain of a fatty acid hold their full complement of hydrogen, they are described as saturated. Where two adjoining carbon atoms in the hydrocarbon chain of a fatty acid each lack a hydrogen atom, a double bond forms between them. The fatty acid is then said to be unsaturated. The term polyunsaturated fatty acid (PUFA) is accepted as referring to those fatty acids that contain two or more carbon-carbon double bonds within the hydrocarbon chain [30]. Particular PUFAs, which the human system can employ as building blocks while being unable to synthesize them, have been classed as essential fatty acids. The n-3 (ω-3, omega-3) PUFAs found in plants refer to a number of health benefits [31]. The most common and most important PUFA is linolenic acid, which is known as a precursor of the long-chain fatty acids (eicosapentaenoic and docosahexaenoic) [32]. Modern agriculture and food industrialization are associated with large changes in the structure of contemporary Western diets. The intake of n-6 fatty acids has enlarged during evolution, and the intake of n-3 fatty acids has been reduced. Consequently, the n-6/n-3 ratio increased from 1 to 10 or, in some places, even up to 20 or even 25. These differences in food consumption led to increased risk of numerous modern diseases [33].
Over the past decade, radicchio has become popular for cultivation and consumption in different regions of the world. Scientific literature has revealed that radicchio plants contain important compounds with biological activity and several vitamins and minerals [4,18,[34][35][36]. The effects of fertilizer managements (organic, mineral) on the phenolic and fatty acid profiles in different radicchio varieties (red, red-spotted, green) are poorly discussed in scientific data. This chapter discusses the effect of fertilizers (organic, mineral, and combination) on the total phenolics, the main phenolic classes, and the fatty acids levels of five C. intybus varieties. Highperformance liquid chromatography (HPLC) was used for the analysis of phenolic compounds and their classes and gas chromatography (GC) was used for the determination of fatty acid levels.

Selection of plant material and fertilization experiment
The    The growing experiment in controlled conditions included two mineral fertilizers, two organic fertilizers, a combination of one organic and one mineral fertilizer, and the control (no added fertilizer). In each of the five radicchio varieties, the same six fertilizer managements were applied as presented in Table 2 in the following design: unfertilized control (CONT), two organic fertilizers (ORG1 and ORG2), two mineral fertilizers (MIN1 and MIN2), and combination of organic and mineral fertilizer (ORG1+MIN1). The experiment consisted of 30 plastic pots filled up with 7 L of soil with application of the selected fertilizers. Sowing was performed on 30 January 2012. Then, the pots were placed in the greenhouse and irrigated appropriately. Water-soluble mineral fertilizer (MIN1) was applied through the irrigation solution containing water and MIN1. The sampling of developed leaves was performed on 10 June 2012. A few leaves from each pot were lyophilized and powdered using a ball mill before analysis. The dry matter content of radicchio leaves varied from 6.8% to 14.8%.

Extraction and identification of phenolic compounds
Radicchio powder was mixed with the solvent 5% formic acid in methanol, which contained flavone as an internal standard. For extraction, an ultrasonic bath at 4°C for 30 min was used. After centrifugation, a 10 μL aliquot of supernatant was injected into the HPLC system. For analysis, reverse-phase HPLC coupled with a diode array detector (DAD) was used. The phenolic compounds were separated on Nucleosil C18 analytical column (250 cm × 4 mm; 3 μm) and eluted using 5% formic acid and HPLC-grade methanol at a constant flow rate. The gradient profile has been flowing to the protocol previously published for the analysis of complex polyphenol mixtures [37].
The DAD was scanning from 250 to 600 nm with four discrete channels. Phenolics were gathered into five classes and monitored at related wavelengths: unknown phenolic compounds (UPCs; 280 nm), HCAs and flavones (320 nm), flavonols (350 nm), and anthocyanins (540 nm). The quantification of each phenolic compound was carried out using the internal standard manner. The phenolic compounds in the radicchio leaves separated by HPLC are presented in Table 3. They were classified based on the absorbance spectra [38] and the comparison to representatives [39]. Chlorogenic and caftaric acids were confirmed by previously identified standards [40].

Determination of fatty acid levels
Fatty acid levels were analyzed using GC with prior prepared fatty acid methyl esters. In the protocol [41], NaOH and BF 3 in methanol were used for transesterification and heptadecanoic acid (C17:0) was used as an internal standard for the quantification of fatty acids. The solution of fatty acid methyl esters was quantified on the GC (Agilent 6890N, USA) with flame ionization detector (FID). At the constant flow rate, the separation was performed on a column for analyses of PUFAs as fatty acid methyl esters. The identification and quantification of fatty acids were carried out using a reference standard mixture of methyl esters of greater fatty acids regularly before the samples. The following fatty acids were detected in the radicchio plants: C16:0, C18:0, C18:1n9, C18:2n6, C18:3n3, and C20:0 ( Table 4).

Phenolic profiles
Thirty-three main phenolic compounds obtained using HPLC detection were selected in all five studied radicchio varieties from six fertilizer managements. Those were grouped according to their absorbance spectra and retention times to UPCs, HCAs, flavonols, flavones, and anthocyanins ( Table 4). All chromatograms of radicchio samples were similar, but the areas of individual peaks varied considerably. An example of chromatogram for var. 'Castelfranco' is presented in Figure 4. Anthocyanins, which are quite unstable, were found in minor quantities in only few radicchio samples. The phenolic profile data were comparable to former reports, which also found that chlorogenic and cichoric acids are the main phenolic compounds in radicchio leaves [4,6,26,42]. The total phenolic amount (TPA) in the analyzed radicchio leaves under different fertilizer managements varied from 58 to 403 mg/100 fresh weight (FW; Figure 5)  Across different managements, the highest TPA was seen for unfertilized (CONT) treatment (254 mg/100 g FW) followed by MIN1 (213 mg/100 g FW), combination of ORG1+MIN1 (183 mg/100 g FW), ORG2 (160 mg/100 g FW), ORG1 (129 mg/100 g FW), and MIN2 (126 mg/100 g FW). Significantly greater TPAs were seen for the radicchio varieties grown under unfertilized management and those with mineral fertilizer (MIN1). Crecente-Campo et al. [43] have reported that the organic or conventional cultivation system did not affect the TPA but only the antioxidant compounds. Vinha et al. [10] found greater TPA for organically grown vegetables, whereas Mitchell et al. [8] obtained only greater amounts for quercetin and kaempferol. According to Oliveira et al. [9], organic manner resulted in greater TPA and vitamin C. Some other studies [44,45] reported that the enzyme phenylalanine ammonia-lyase is involved in the biosynthesis of phenolics and is regulated by nitrogen. In general, the availability of soil nitrogen strongly impacts the synthesis of several phenolic compounds [46].
In relation to nitrogen fertilization, the response of radicchio varieties differs, as high and low nitrogen demanding varieties were previously reported [47]. The average values (n=3) with different lowercase letters in a row are significantly different (P<0.001; differences between the fertilizers), and those with different uppercase letters in a column are significantly different (P<0.001; differences between the varieties). The main classes of phenolic compounds (as mg/100 g FW) among radicchio varieties from different fertilizer managements are presented in Table 4. Statistical analysis showed significant differences between both fertilizer managements and the varieties for all of these main classes. HCAs were the greatest represented group of phenolic compounds in radicchios with a range of 60% to 95% followed by unknown phenolics, flavonols, and flavones (Figure 6).
Phenolic acids (specifically HCAs) were further on grouped according to their retention times as monomeric (<100 min) and oligomeric (>100 min). HCAs are mostly represented by chlorogenic and cichoric acid in all radicchio samples ( Table 5). The levels of HCAs varied in a wide range from 47 to 362 mg/100 g FW ( Table 4). The higher levels of total HCAs were found in var. 'Treviso,' up to two times more than the mean value, whereas var. 'Castelfranco' had the lowest amounts of HCAs. The analysis showed that radicchios contribute a smaller amount of monomeric (27%) in comparison to oligomeric HCAs (56%). Data showed that, across radicchio varieties, var. 'Treviso' had greater total HCA amount compared to other varieties ( Table 4). The main identified monomeric HCAs were caftaric and chlorogenic acids, whereas the most represented oligomeric was cichoric acid. Cichoric acid was best represented and accounted for 43% of total HCAs, whereas chlorogenic acid with 28% and caftaric acid with 3% were present in lesser quantities ( Table 5). All three phenolic acids together represent up to 74% of the total HCAs in radicchio samples (Figure 6). The HCA quantities were as follow: cichoric acid   The average values (n=3) with different lowercase letters in a row are significantly different (P<0.001; differences between the fertilizers), and those with different uppercase letters in a column are significantly different (P<0.001; differences between the varieties). Both flavonols and flavones are chemosystematic markers found in tribe Cichorieae of the Asteraceae family [27]. Total flavonol amounts of studied radicchio varieties were found in the range of 1.7 to 20 mg/100 g FW ( Table 4). The flavonols represented below 10% of TPA for most of the radicchio samples, except for var. 'Verona' ORG1 (13%) and var. 'Monivip' MIN1 (14%). Flavones represented only small concentrations ranging up to 2 mg/100 g FW ( Table  4). Arabbi et al. [48] found similar amounts of flavonoids ranging from 18 to 38 mg/100 g FW.  Table 3.
Multivariate data analysis by principal component analysis (PCA) and linear discriminant analysis (LDA) was used for plotting the radicchio samples based on their phenolic compounds. All 60 peaks were included in the analysis. Using PCA, 21 phenolic compounds were selected as the most discriminating variables: 10 HCAs, 3 UPCs, 3 gallic acid derivatives, 3 flavonols, 2 flavones, and a protocatechuic acid ( Table 3). The LDA scores of the data (30 samples, 21 variables) for first two functions are plotted in Figure 7. It should be emphasized that ORG1 and MIN2 fertilizer managements are characterized by slow nitrogen release [49].

Composition of fatty acids
The levels of the individual and total fatty acids (mg/100 g FW) of radicchio leaf samples are shown in Table 6. Data show significant differences for different varieties and fertilizer managements. Using GC analysis, the following fatty acids were identified and quantified: saturated fatty acids (SFAs) C16:0, C18:0, and C20:0; monounsaturated fatty acid (MUFA); and PUFAs C18:1n9, C18:2n6, and C18:3n3. Linolenic acid (C18:3n3) was represented the most and accounted for 48% to 63% of total fatty acids amount, whereas linoleic acid (C18:2n6) accounted for 16% to 30% and palmitic acid (C16:0) for 14% to 24% ( Table 6). Stearic (C18:0) and oleic (C18:1n9) fatty acids were less abundant (<5%), and the smallest levels were found for arachidonic acid (C20:0; i.e., <1%). The total fatty acid levels ranged from 173 to 503 mg/100 g FW ( Table 6). In comparison to other varieties, var. 'Castelfranco' showed greater levels of total fatty acid levels. Between fertilizer managements, there were significantly better total fatty acid levels when the organic fertilizers were used (ORG1 and ORG2). Obtained data are well in accordance to those for forage radicchios [50]. Blanckaert   The nutritional information of radicchio varieties for most optimal fertilizer management (ORG2), which signified the uppermost total fatty acid levels, is presented in Table 7. PUFAs represent the range from 79% to 81% of total fatty acid levels, SFAs the range from 16% to 19%, and MUFAs the range <3.6%. The ratio of n-6/n-3 fatty acids was below 0.48 for all radicchio varieties. Simopoulos [52] reported that past human diets had a ratio of n-6/n-3 fatty acids near 1, whereas modern Western diets have that ratio much higher (up to 20). The optimal ratio of n-6/n-3 fatty acids is believed to be from 1 to 4 [33,52]. Schreck et al. [53] found a higher ratio of n-6/n-3 fatty acids for the lettuce seedlings, whereas some prior readings on wild Cichorium leaves showed much lower values [54,55]. All analyzed radicchio varieties had the ratio at values are considered as optimal and fully in agreement with current nutritional recommendations [56].  Table 7. Nutritional information of different radicchio varieties derived from organic fertilizer (ORG2) management.

Conclusions
The phenolic profiles and distribution of classes of the five analyzed radicchio varieties (three red, one red-spotted, and one green) produced by different fertilizer managements under greenhouse conditions are extensively diverse. The analysis of phenolic profiles using HPLC allowed the identification and quantification of prevalent compounds. In the radicchio leaves, the predominant phenolic compounds are cichoric and chlorogenic acids. The phenolic distribution in radicchio leaves is very predisposed by both variety and fertilizer use. The highest TPAs were found for the unfertilized samples followed by the management with the water-soluble mineral fertilizer and the combination of organic and mineral fertilizers. The analysis of fatty acid profiles in radicchio leaves using GC determined six fatty acids. The main fatty acids consist of polyunsaturated linolenic acid (C18:3n3) and linoleic acid (C18:2n6). The main SFA was palmitic (C16:0). Significantly higher fatty acid levels among the fertilizer managements were seen for organic fertilizers. Radicchio seems to have an excellent nutritious balance of essential fatty acids. In summary, the phenolic and fatty acid profiles of radicchio are highly influenced by growing conditions and indicate considerable dietary and nutritional value due to its bioactive phytochemicals.