Metabolic and Biochemical Profiling of Phenolic Compound and their Biosynthesis in Oil Crops

Introduction

Background

The olive, known by the botanical name Olea europaea is the most imperative tree of the Mediterranean region, which accounts for 95% olive trees that are developed globally Loumou and Giourga [1]; Khan et al. [2]. Olive oil is the 6th abundant vegetable oil manufactured globally so we can say that prime objective behind olive plant production is oil extraction Conde et al. [3]; Peragon et al. [4]. Olea europaea is a specie that contains 46 chromosomes in each cell (diploid chromosome 2n=46). Seed development is an important process in olive and seeds are produced via out crossing. Khadari et al. [5]; Lee et al. [6]; Busconi et al. [7]. These seeds have the capacity to stay feasible for long term. It is a glycophytic specie and is more resistant towards stresses like salinity and dry season when contrasted with other fruit trees that are susceptible to these stresses. Oil which is solely taken out from fruits is generally called Olive oil. However, the term “virgin olive oil (VOO)” represents the oil that is separated from fruits by utilizing physical or mechanical approaches. Gila et al. [8] So, for the purpose of virgin olive oil production we can apply different techniques like cleaning with water, process of decantation, separation by the process of centrifugation and removing impurities by the process of filtration. However, such conditions should be necessarily provided, that supports adjustments (IOOC, 2014).

The importance of Virgin olive oil (VOO) inside the Mediterranean eating regimen is due to the fact, that it is surely an advantageous everyday nutrition for human wellbeing and is considered as an important part of daily diet Estruch et al. [9], Sahyoun et al. [10]. Europe is producing 78% of olive oil in the world production. While “Picual” and “Arbequina” are the two cultivars which isessential Spanish varieties regarding oil generation and Spain being the its biggest maker has produced average of 1.3 million tons’ oil in the course of recent years. Most of those cultivars are grown frequently, precise breeding methods are now undertaking to create new varieties. Bellini et al. [11]; Lavee et al. [12]. The phenolic components which were separated from the seeds of soyabean had effective anti-cancer activities which include gastric, breast, ovarian, prostate and colorectal cancers Belaj et al. [13]; Dong et al. [14]; Niedzwiecki et al. [15].

It is predicted that there is some kind of relationship between flavonoid contents, phenolic compound components in developed soybean. We can conclude that the goals of latest breeding projects are not just agronomic.

In this scenario, there is a need to fulfill two distinctive market methodologies

(i) Production of surplus virgin olive oil with good quality and its should be affordable for consumers as well,

(ii) Offering shoppers, a variety of extra VOO with fantastic norms and diverse tactile characterize or profiles.

These two approaches are associated with the Mediterranean daily nutrition. Shah et al. [16] The first perspective is normally identified with super-escalated development and exceedingly automated harvesting techniques. The second perspective indicates to ensure the protection of biodiversity of olive tree and conventional strategies as a component of the exceptional nutrition customs related with the eating routine of Mediterranean nations Ilarioni and Proietti [17].

The main goal of this review is to understand that phenolic profiling and its composition in oil seed crops. Also understand the different phenolic pathways in oil biosynthesis in oil seed crops. Study the what kind of enzyme involve in active the Virgin olive oil. Further perspective of the genetic factors involved in the advancement of olive fruit in regard to its phenolic composition.

Phenol Biochemical Composition Related to Nutrition:

Olive breeding programs have been negatively influenced because there essential agronomic and oil quality attributes which have not been given interest. Learning should be expanded to identify real variability of olive germplasm for a large number of useful traits. Few examinations on olive oil have revealed two fractions in its composition. The first one being the major fraction is saponifiable. This fraction constitutes 98 to 99% of the total weight of oil and called as the glyceride fraction. Kiritsakis et al. [18]; Romero et al. [19] Primary composition of major fraction consists of the lipid compound triacylglycerol (TAG). Further, there are some mono-glycerol and diglycerols found accumulated to this lipid compound. An investigation on virgin olive oil composition has revealed that oleic acid, linoleic acid, palmitic acid and some other acids are quintessential fatty-acid components of VOO (Table 1). Oleic acid is the most prevalent (68-81. 5%) of them and it also characterizes it amongst monounsaturated fatty acids oils (MUFA oils) Ramírez et al. [20].

Table 1: In this table describe techniques some are natural traits e.g. glycophytic which enhanced resistant, others are accomplished by artificially as shown in table.

It was found that proportion among n-6 and n-3 unsaturated fats isn’t of most elevated, for example 16 (distributed extents for vegetable oils: 0-738) and subsequently its fundamental presumed medical advantages are normally connected with its minor division Dubois et al. [21]. Be that as it may, minor fraction comprises in excess of 230 distinct parts, which usually comprises 1-2% of total weight of oil. Moreover, A few classes can be incorporated into these compounds, e.g., non-glyceride esters (for example waxes, hydrocarbons (for example squalene),sterols (Figure 1) (for example campestral), few alcohols of aliphatic and triterpenic type, some polar stains(for example chlorophylls),tocopherols and volatiles (such as the aromatic aldehyde i.e. benzaldehyde) and a class of secondary metabolites called phenolic compounds (like hydro-xytyrosol), Ramírez-Tortosa et al. [20].However, it was found that not many of them were recognized as bioactive compounds Covas et al. [22] further explored the importance and advantages of those which were recognized as biologically active and significant. Olive-breeding projects with new dietetic targets have been driven to meet the increasing demands of the consumers with respect to olive oil quality Rugini et al. [23]; Velasco et al. [24]. It is generally accepted that the main health related characteristics of VOO are attributed by phenolic compound seven though VOO contains various minor compound fractions with fascinating organic exercises.

Hence, regarding both dietary and breeding aspects the phenolic compounds present in VOO are of great importance Bernardini and Visioli et al. [25]. Further, it is known that these phenolic compounds in VOO are the primary supporters of bitter and pungent sharp tangible descriptors which implies that these phenolic contents in VOO also have essential organoleptic connotations. In every single olive item, secoiridoid compounds are plentiful in which consist of phenolic alcohol tyrosol (p-HPEA) or its hydroxyl subordinate hydro xytyrosol (3,4-DHPEA) in their structure. Secoiridoids oleuropein, (Figure 1) ligstroside and dimethyl oleuropein are found to be the primary phenolic glucosides present in the olive. Their hydrolytic subsidiaries, the di aldehydic types of decarboxy-methyl oleuropein and decarboxy methyl ligstroside aglucones (3,4-DHPEA-EDA and p-HPEA-EDA, respectively) and the aldehydic types of oleuropein and ligstroside aglucones (3,4-DHPEA-EA and p-HPEA-EA, individually) are phenolic parts in olive oils which are known to be most essential components. It was reported by further examinations that levels of 3,4-DHPEA in plasma is connected to the capacity of VOO phenolics to the lessen chronic inflammation and oxidative harm Redondo et al. [26]; Bernardini et al. [13]. These results were helpful for the European Union to support a wellbeing guarantee on polyphenols of olive oil that contain less than 250 mg/kg of hydroxy tyrosol and its subordinates (European Commission, 2012).

Metabolic Profiling of Oil Seed Crops:

The complex phenomenon of phenol metabolism in the olive tree are regulated by different ecological Romero and Motilva [27] and genetic factors Talhaoui et al. [28] and these are the main determinants of the final composition phenolic contents in olive fruit. Likewise, the impact of other influential factors has been explained which include important farming practices, for example, restricted water system Gennai et al. [29], the advancement of pruning to expand light accessibility Famiani et al. [30] or determination of accurate harvest date Proietti et al. [31] etc. Further examinations revealed that during oil extraction process the activation of few oxidative enzymes and some endogenous hydrolytic is involved with the modification of phenolic glycosides which are present in the fruits of olive tree (Table 2). In such a way, it was found that there is a direct connection of phenolic profile of the olive fruit with phenolic characterization of VOO. It was also revealed that during milling and malaxation, action of hydrolytic and oxidative which is also related to profile of virgin olive oil. Purpose of improvement of VOO’s phenolic composition, a well-designed experimental structure should be considered for any program of breeding. There are many factors which affects the phenolic composition of VOO.

Table 2: In this table the classes of phenolic compounds and other compounds present in the oil seed crops, identification, role and for which it is used are described.

For this purpose, precise scientific tools are required to find the effect of each of these particular factors on the ultimate phenolic composition of VOO. It was revealed that there are ongoing projects of olive breeding which mainly focus on the quality of olive, but these programs have extra restrictions to those recently referenced Velasco et al. [24]. The reason of these limitations is a very little amount of oil production from a very vast number of genotypes in the beginning periods of the breeding. Thus, it is fundamental to carefully examine the fruit to predict total oil composition using solid logical analytical tools. Fatty acids, tocopherols, squalene, or sterols are important components of the composition of olive fruit and oil. For this reason, examinations were carried out which portrayed a huge connection between the profile of olive fruit and oil for above mentioned components Velasco et al. [32]; Rosa et al. [28]. Olive breeding programs till now do not provide any evidence about the utilization of phenolic fruit profiling as selection criteria in these programs.

Secondary Metabolites Distribution in Olive Fruit

Eocardiids is a class of fundamental secondary metabolites which are widely found in the Mesocarp tissue of olive fruit. These Secoiridods are actually gatherings of monoterpenoids with a cleave dimethyl cyclopentane skeleton and are common in few dicotyledonous families and few flowering plants of Oleaceae family. These secondary metabolites or Secoiridods are phenol-conjugated aggravates with a glycoside element and are bounteous in olive tree. Oleuropein (Figure 1), dimethyl oleuropein, oleuroside, ligstroside, nuzhenide are considered as most important Secoiridods in olive fruit are VOO. Also, their structure forms, such as the dialdehydic form of decarboxymethyl elenolic acid linked to either 3,4-DHPEA or p-HPEA (3,4-DHPEA-EDA and p-HPEA-EDA, respectively) the ligstroside aglycon (p-HPEA-EA) and an isomer of oleuropein aglycon (3,4-DHPEA-EA), are essentially important Obied et al. [33]. In extra-virgin olive oil, a secoiridoid compound called Oleocanthal (p-HPEA-EDA) was observed which was missing from the fruits Beauchamp et al. [34]. Flavonoids and lignans, phenolic acids and some phenolic alcohols like hydro xytyrosol (3,4-DHPEA) and tyrosol (p-HPEA) are some important phenolics of olive Oliveras et al. [35] which were seen in the fruits with the pulp being richest region of these phenolics Owen et al. [36].

In oil seed crops different pathways are involved MEP, MVA, Phenylpropanoid, secoridoid, sterol and terpenoid pathways.

Each pathway depends upon different enzyme that can work to active these phenolic compounds which is helpful for our health. In oilseed crops sucrose (Figure 1) is convert into PEP (Figure 1) by different process that is indeterminate until PEP is convert by different enzyme are involve shikimate (Figure 1) is a primary step to produce phenylpropanoid compound in oil seed crops. Shikimate are convert by different enzyme to produce the Phenylpropanoid pathway (Figure 1). PEP covert into Pyruvate (Figure 1) in the presence of glycolysis in plastid then covert into IPP (Figure 1) with the help of different enzyme. Pyruvate are converting Acetyl CoA (Figure 1) and acetyl CoA is convert in IPP (Figure 1) with the help of different enzymein cytosol (Figure 1). In oilseed crops Secoiridoid Biosynthesis (Figure 1) and Sterol and Terpenoid Biosynthesis (Figure 1) are start from IPP (Figure 1). If IPP (Figure 1) are active than both of these pathways is produced. In Secoiridoid Biosynthesis Geraniol (Figure 1) are convert into Deoxyloganic acid (Figure 1) by different enzyme work it. In Sterol and Terpenoid Biosynthesis GPP (Geranyl diphosphate) (Figure 1) are convert into FPP (Figure 1) produce Tetraterpene, Diterpene, Sesquiterpene and Squalene (Figure 1). Squalene is conert into Sterol and Triterpene (Figure 1). In all pathways different enzyme are involved to produce Phenolic compound (Figure 1).

At maturity there has been observed A high measure of glycoside Verbasco side Servili et al. [37] was observed in products of a few cultivars of olive. A small concentration of the compound comselogoside, vanillic acid Boskou et al. [38] and Jermanet al. [39], caffeic acid, p-coumaric acid, 3,4-dihydroxyphenylacetic acid (DHPAC) and homo vanillic alcohol are some other phenolics present in the fruit at maturity. Tocopherols Dabbou et al. [40], oleanolic acids and maslinic acid are few important triterpenic acids (Figure 1) found in olive fruit and are of great significance. Specific compounds which are present in various tissues of the fruit like stone, leaf, mesocarp and exocarp have been discovered by the investigation of phenolic profiles in these tissues. For example, flavonoids (Figure 1) quercetin, rutin and luteolin-7-glucoside were found to be present only in the fruit peel Servili et al. [41]. Similarly, only olive seeds contain phenolic compounds salidroside and nuzhenide Ryan et al. [42]; Mansour et al. [43]. A crucial gene, CHI (Figure 1) was observed for enhancing flavonol production. It is a protein which is involved in the primary stages of the flavonols biosynthesis pathway Muir et al. [44]. Petunia CHI (Figure 1) and CHS (Figure 1) (Chalcone synthase) genes in tomatoes which were overexpressed and increase insufficient amount of rutin and naringenin substance, separately. Be that as it may, RNAi hindrance of the tomato CHS1(Figure 1) genebrought about a solid decrease of both naringenin and quercetin levels Martens et al. [45].

It was found that F3H (Figure 1) (flavanone 3-hydroxylase) and FLS (Flavonol synthase)over expression had no consequences for flavonoid levels when contrasted with non-transgenic controls, however F3H (Figure 1) RNAi tomatoes brought about a 20% decline in wild-type rutin intensities Muir et al. [44] and Bovy et al. [46]. Further, the oil which is extracts from seed overexpression with multigene (CHS, CHI, and (DFR)(Figure 1) dihydroflavonol 4-reductase) from petunia into flax displayed larger amounts of quercetin (46– 90%), kaempferol (70– 83%), and anthocyanin (198%) than the control Zuk et al. [47]. The precursor compound of some triterpenic diols (for example, uvaol and erythrodiol) and amyrins (for example, α-and β-amyrins) is known as squalene (Figure 1) which is also an intermediate product of the pathways of sterol synthesis (Figure 1). Only olive and some other vegetable oils contain squalene (Figure 1) in a steady sum. Due to its perceived consequences for human wellbeing this compound is considered very significant phenolic compound Waterman et al. [48]; Bajoub et al. [49].

It was revealed that when the final size of olive fruit is achieved and process of ripening starts, progressive accumulation of 24-methylenecycloartanol, cycloartenol and β-sitosterol Sterolsbegins in olive fruit Stiti et al. [50]. Secoiridoids (Figure 1) usually represents the most perilous microconstituents present in virgin olive oils important for their sensory properties and wellbeing because Secondary metabolites are not soluble in oil. However, only a little amount of Secoiridoid compounds is recouped in the oil after the practice of mechanical extraction is done Montedoro et al. [51]; Martins et al. [52]. The secoiridoids compunds of olive are important agents against diseases like atherosclerosis and these are also involved in restraining peroxidation of lipoprotein conjugates of low-density Waterman et al. [48]. Further, their cancer prevention exercises have also been demonstrated Omar et al. [53]. Additionally, diseases like osteoporosis are prevented by the activities of these Secoiridoid compounds. Regarding well-being of human oleocanthal Beauchamp et al. [34]., hydro xytyrosol Omar et al. [53]. and Oleuropein are known to specifically affect human health in great ways. Furthermore, secoiridoids (Figure 1) are known to be engaged with oil oxidative security by acting as primary antioxidants. Secoiridoids (Figure 1) also impact oil taste Andar accountable for pungency and bitterness sensory notes hence it is adding to the quality of olive oil in different ways Servili et al. [37].

Role of Phenol Toward Ecological Aspects

The study of Phenolics is of great importance because they assume a critical job in the plant reaction to ecological signs and they are most essential resistance components against defoliating bugs Mumm et al. [54]. They likewise influence shoot spreading Umehara et al. [55] and have been guessed to be involved in the cell security and counteract fungal infiltration into the cambial region Beckman and Franceschi et al. [56]. Lately, A few information bolsters the possibility that the protection from explicit pathogens may likewise be identified with specific sorts of phenolics which acts as cell guards [57,58]. It was demonstrated that Oleuropein (Figure 1) displays the most grounded movement noted for a plant metabolite and it is thought to be in charge of the release of phytoalexins which an anti-parasitic substance Kubo et al. [59]; Abdellaoui et al. [60]. It behaves as a multifunctional alkylator that acts as aperfect protein cross linker. The strongest activities shown by this plant metabolite diminishes nutritive estimation of proteins which are involved in daily nutrition. Thus, it badly affects herbivores Konno et al. [61]. Till now, only some pathways of secoiridoid (Figure 1) metabolism in Oleaceae species have been suggested Butthe complete process of secoiridoid (Figure 1) metabolism is still not clarified Damtoft et al. [62]; Alagna et al. [63].

The composition and expression of secoiridoids varies considerably among varieties, formative stages and, tissues. Various ecological factors also influence the expression and composition of secoiridoids (Figure 1) Malik et al. [64]. Only few genes have been described which are engaged with biosynthetic processes of triterpene while there are some crucial genes, which regulate and degrade various secondary compounds in olive fruits, are still not defined Shibuya et al. [65] and Saimaru et al. [66]. The reason behind this failure is the absence of data for the olive genome sequencing. Till now, only few goals like transcriptome data of olive fruit, are achieved regarding olive sequencing Galla and Alagna et al. [67]. As the process of fruit metabolism is yet to be demonstrated and the genes related to the process are still to be identified so this transcriptome data of olive fruit could be a useful asset for the scientists to identify genes related with the process. Perennial woody species are long lasting and practical genetic investigations are hard to perform with them because productive protocols for transformation, invitro reculture and mutagenesis are absent. Therefore, it would be a valuable tool to understand regular variations for genes of great importance. The latest work done is to investigate various complex metabolic pathways by the combination of gene expression and metabolic informational indexes Saito et al. [68].

QTLs Regulating the Different Phenolic Compound in Oil Crops

In order to understand intricate nature of these pathways we can utilize modern genetic techniques. Additionally, advanced genetic tools like Marker Assisted Selection (MAS) and other genomic apparatuses could be introduced in olive breeding projects to produce useful olive cultivars with attractive phenotypes in brief time. Moreover, research is progressing on its sequencing because genomic investigations could be accelerated if sequence information of olive is generated Torchia et al. [69]; Rosa et al. [70]. Different crop has different size of genome the size of olive genome is expected to be around 1,800 Mb and high amount of intra-specific genetic variations are found within Loureiro et al. [71]. Further advancements in olive like genome mapping, and identifying the sequence is still ongoing. These are cooperating in expanding further information about olive genome and it could be a one big step towards great achievements Collins et al. [72]. Work is still ongoing on sequencing of olive, though whole plastome sequencing of an Italian cultivar “Frantoio” was reported by Marriotti et al. [23]. An attempt on olive genome sequencing was endeavored recently by project entitled OLEA in Italy. There is a need to understand different essential biochemical and physiological elements of olive plant.

To understand these essential dynamics of the olive tree, latestgenomics studies should be employed which include omics studies like transcriptomic, proteomics and metabolic. Also, by understanding the role of proteins and their respective genes in Arabidopsis different pathways of lipid arrangement and oxidation have been identified for olive plant. Alkaloids, terpenoids (Figure 1) and phenolics are the three noteworthy groups of plant secondary metabolites This categorization is done on the basis of their biosynthetic origin Wink et al. [73]. Flavonoids (Figure 1) and non-flavonoids are two major types of phenolic metabolites which are originated from aromatic amino acids via phenylpropanoid (Figure 1) pathway. Flavonoids (Figure 1) and Iso-flavonoids are compounds with backbone of 2-phenylchromen4-one and 3-phenylchromen-4-one respectively. The purpose of this investigation is to include iso flavonoids to the term flavonoids. These iso flavonoids are found abundantly in soyabean seeds which are also contain other phenolic compounds in abundant Malencic et al. [74]. It was depicted that the phenolic components which were separated from the seeds of soyabean had effective anticancer activities which include gastric, breast, ovarian, prostate and colorectal cancers Xu and Chang [75,76]; Dong et al. [14]. It is predicted that there is some kind of relationship between flavonoid contents, phenolic compound components in developed soya bean. Endeavors have likewise been made to investigate this relationship and to understand the phenolic aggregation of the soybean seed.

Soybean with black seed coat is the plant under examination to identify these however, there was no specific relationship found between seed coat color and antioxidant activities of soybean seed (Qi et al. [77]). Some investigations on crop improvement have revealed that some oil crop like wild soybeans are important genetic assets for improvement after provided with a strong proof from Next-generation sequencing-based studies. So wild soybean can be introduced into crop improvement programs to modify other cultivars to achieve desired products Kim et al. [78]; Zhou et al. [79]. Few investigations have declared that QTL that regulates antioxidant contents lies on chromosome 19. This QTL was identified in a recombinant population that was developed by a cross between cultivated and wild soybean parents Qi et al. [77]. It was then confirmed that this QTL does not coincide with the QTL that controls anthocyanin contains a seed coat color Qi et al. [77], that provide a fact that high anthocyanin substance in seed coats has no direct relationship with high seed antioxidant exercises in oil crops like wild soybeans [80-90]. Besides, the identified QTL was found recognizably different from the other of QTLs genistein and total isoflavone which is present on chromosome 19. phenylalanine-ammonia lyase (PAL) (Figure 1)-encoding gene is found in this region Gutierrez et al. [80]. The committing step in the phenolic and flavonoid synthesizing via phenylpropanoid pathway is catalyzed by PAL (Figure 1) [91-95].

Figure 1: A proposed diagram showing the biosynthetic pathways of different phenolic compounds in oil seed crops.

Conclusion

Different studies are aiming to understand the composition, profiling and biosynthesis of phenolic compounds or secondary metabolites in oil seeds [96-101]. Although, addition of genomic data in databases has accelerated genomic studies but still there is a lot of scope available to researchers for mining the genes related to the breakdown of secondary metabolite in oil seeds. To understand these essential dynamics of the oil seeds, latest integrated genomics studies should be employed which include omics studies like transcriptomic, proteomics and metabolic. That will explore the functional characterization of proteins and genes involved in biosynthesis.

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