Oxidative rancidity of lipids pdf

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Pallavi Dave. Eunica Ramos. Mohammad Sultan. Alder Miranda. Frost Orchid. Causes of rancidity after seed oil extraction can be averted by incorporating strict measures in the packaging and handling of edible oils, but in the case of rice, the lipids are subjected to rancidity during the storage of milled bran.

This triggers rancidity [Fig. Typically, TAGs accumulate in the developing seeds and are degraded by endogenous lipases during germination. The composition of FAs included in the TAGs decides the fate of the oil stability from oxidative rancidity.

Tackling rice bran rancidity by pre and post-milling techniques Various methods have been applied to tackle the bran lipid rancidity.

These techniques are generally used before or after the milling of rice grains, including physical, chemical, and biological methods. However, these methods are cumbersome and require specialized skilled personnel to handle the oil mechanically. Also, the procedures can be limiting to the nutraceutical properties of the oil. List of clinical trial studies performed with rice bran products. Treatment -Rice bran extract in PSG capsules 2.

Group 3-HCD plus 0. Group 4 -HCD plus 0. Physical methods Various temperature treatments demonstrated that lipase activity ceases at low temperatures. Moreover, it cannot be used at large scale as it consumes high energy, and it is challenging to maintain low temperatures in industries. Biological methods The biological treatment of rice bran includes treating the grains with enzymes like alcalase, which inactivates the activity of lipases and LOXs.

The major drawback of this method is the high loss of vitamin B and E in the bran. Genetic engineering strategies can prove effective in this regard. Understanding the genetic factors involved in rice bran lipid rancidity Given the nutritional characteristics of RBO, it is essential to conceive strategies to reduce the bran lipid rancidity. A promising way of doing this is to understand the biological roles of genes involved in the rancidity route so that these genes can be manipulated by genome editing approach.

In this section, we have reviewed the genes, i. Despite being high in nutritional value, PUFAs are prone to oxidation due to the presence of unsaturation, thereby leading to shortened shelf-stability of the edible oils. These desaturases primarily occur as membrane-bound proteins located in chloroplasts as well as the ER.

This underlines the role of FAD as the candidate capable of altering the accumulation of to FA in rice. Hence, in comparison to other FAD2 genes, FAD has been regarded as the most suitable and primary target for downregulation. Several high oleic lines have been developed by targeting the FAD2 gene variants in rice. Thus, curtailing FAD2 expression in oilseed plants is indirectly correlated to reduced oxidative rancidity of rice bran lipids and can prove to be an effective strategy to enhance its shelf-life.

Oleosin: structural OB protein that stabilize OBs Plant seeds have dynamic and yet ubiquitous organelles in the form of TAG-containing OBs that act as indispensable energy sources during seed germination and post germinative growth.

Table 3. The three major characterized alkaline proteins that are associated explicitly with OBs are oleosin, caleosin, and sterol dehydrogenase steroleosin. Oleosin mRNA levels drastically decreased in the germinating seed grains when compared with the developing grains.

The degradation of the oleosin begins after the ubiquitination of the protein at lysine ubiquitination site amino acid via the ubiquitin-proteasome system. Since oleosin is essential in regulating the oil content, modifying the rice oleosin structure could be an alternative approach to delay the lipase attack over TAG molecules in rice bran.

Modification of oleosin cys- oleosin protein at N- and C-terminal amphipathic arms showed enhanced OB stability against lipases and proteases. However, there is still a scope of further exploration to understand how lipase uses oleosin as a docking site to mobilize the TAG reserve. More lipase-oleosin interaction studies in this direction will uncover the hidden aspects of such interactions. An in-depth molecular analysis in an oleosin-free background can potentially aim to prove the existence of a cross- talk between lipase and oleosin, and their capacity in reducing the TAG degradation.

Any attempt to regulate the function of the oleosin protein by protein engineering can aid in slowing the TAG deterioration pathway and thus promote lipid shelf-stability. Lipases: boon for grain germination but bane for bran lipid stability In oilseeds and cereal grains, TAG is the predominant storage reserve that serves to sustain the post- germinative as well as the pre-photosynthetic growth of the seedlings. Schematic diagram showing the proposed oleosin modification reaction by incorporation of cysteine amino acid in its amphipathic arms by the lipase action.

Disulfide bridge S-S is shown as blue solid line and lipases are indicated in red arrows. However, this phenomenon does not mean that all classes of lipases are restricted to post-germinative growth.

The enzymatic reaction of lipase and Phospholipase D. The modelled structure suggested the presence of serine, histidine, and proline along with side- lining residues valine and aspartic acid in the substrate-binding pocket. A thorough understanding of the lipases during the onset of lipid mobilization is of utmost importance to understand their role in rice bran tissue.

In rice, a total of 74 putative lipases have been identified from publically available resources [Table 3]. The previous reports in oilseed plants indicate that down-regulation of lipase function may reduce the lipid degradation in seeds. This suggesting the process of TAG mobilization is important but not essential for seedling establishment. In order to achieve this goal, there is an urgent need to fill in the present research gaps associated with the characterization of undescribed lipases and their mechanism of activation before the commencement of lipid degradation.

These enzymes become activated during various developmental and physiological processes of plants. Among the various known phospholipases, PLD is highly active in rice bran and consists of a family of 17 members. However, to the best of our knowledge, studies correlating the involvement of PLDs with bran lipid rancidity are very limited, and there is a need to uncover the role of the enzyme during the onset of lipid degradation.

In addition, the identification and characterization of undescribed phospholipases presented in Table 3, can aid us in comprehending their mechanisms of action for future studies. Mechanism of action of lipoxygenase LOX. Schematic diagram showing the catalyzing action of LOX in the deoxygenation reaction of linoleic acid and resulting in the generation of 10 S Z hydroperoxy,octadecadienoic acid 9-HPOD or 9 Z ,11 E hydroperoxy-9,octadecadienoic acid HPOD derivatives.

In plants, LOX is believed to be associated with the seed germination as well as in mitigating biotic and abiotic stresses.

Moreover, the down-regulation led to an increase in the amount of acetic acid and hexanal by Overexpression of this gene led to decreased grain viability, which implied that LOX3 negatively affects grain longevity. However, recent studies have shown that there exists functional redundancy among LOX family genes[17,] and this information can be vital to exploit the LOX isozymes for achieving our goal of reduced bran lipid rancidity. This modulation could alleviate the resistance properties against pathogen attack without being growth lethal, and also improve the stability of bran lipids by minimizing the synthesis FA-hydroperoxides.

Conclusion and future perspectives The RBO demand is very high, and edible oil industries are interested in improving the shelf-life as well as the quality of the product. The issue addressed in this review is to overcome the problem of hydrolytic and oxidative rancidity of rice bran lipids that occurs when the milled bran is stored.

Several attempts were made to increase the quality and stability of bran lipids by using pre-milling or post- harvesting techniques. Unfortunately, very little attention has been paid so far to alter the genetics of rice plants to mitigate the cause of bran lipid rancidity.

Thus, it is necessary to adopt genetic and modern biotechnological solutions in the grain itself to enhance its inherent capacity to produce low rancid lipid without altering its nutritional qualities.

In this review, we have summarized the genes directly contributing to the lipid rancidity. Achieving mutation in different target genes through conventional mutagenesis or breeding approaches looks very difficult, and it is also more prone to unwanted linkage drag.

The technological advancement in the genome editing approach promises to provide an opportunity to attain the goal of oil stability, and has the potential to efficiently explore the valuable rice by-product for adding the economic value.

With the availability of well-annotated rice gene information, the gene discovery for biotechnological applications is now faster and plausible. Precise and efficient generation of multiple gRNAs using synthetic polycistronic genes via the endogenous tRNA processing system is achievable today.

This is beneficial for humanity at large and shall also cater to the current demands of edible vegetable oil with idealistic properties. Also, the information of the genes provided here can be utilized by the scientific community to explore future genome editing strategies in rice as well as in other oilseed crops.

Disclosure statement None. All authors read and approved the manuscript. D; Ohlrogge, J. Compartmentation of Triacylglycerol Accumulation in Plants. DOI: AOCS Press. Trends Food Sci. Carbohydrates Diet. Oleo Sci. Cereal Sci. Lipid Sci. Food Sci. Cogent Food Agric. Res dev mater sci. Pusa Basmati 1 Bran during Germination. Rice Lipids and Rice Bran Oil. European Journal of Lipid Science and Technology. Fut Rice Strategy India. Malaysian J. Acta Sci.

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