A longer shelf life for food

They imbue fruits and vegetables with distinct flavours, make breads fluffy and enhance bioavailability of certain micronutrients in food. Yet, they are also responsible for the rancidity and foul smell in grains and oils left for too long on the shelf. Lipoxygenases (LOX) are a set of enzymes which catalyse lipid peroxidation in cells, converting free fatty acids into hydroperoxides, which are then converted into other compounds by enzymes downstream – some beneficial, others not.

Could turning off the genes responsible for coding of the LOXs that lead to the production of rancidity be a cost-effective method of improving the shelf life of grains? A group of scientists at the ICAR-Indian Agricultural Research Institute (IARI), New Delhi, argue in a review paper (bit.ly/LOX-off) that the genetic method of controlling the rancidity-induced post-harvest loss might show the best results.

Lead author Parameshwaran Mathavaraj, a Research Scholar at IARI's Division of Genetics, says there are several existing ways to enhance shelf life, but each has its drawbacks. For instance, tailoring the fatty-acid profile of grains reduces rancidity but also reduces the content of beneficial fats. Enhancing the level of antioxidants in seeds endogenously is another method, but its effectiveness is reduced by improper processing and storing; more antioxidants can also impact the bioavailability of nutrients. Post-production physical and chemical methods, like controlling the temperature and humidity of storage area or mixing additives, are cost-intensive and ineffective, if done improperly.

"Our division is working on biofortification of maize with Vitamins A and E, and enhancing oil content from 3-4% to 6% with beneficial linoleic and linolenic acids, which LOX targets," says Mathavaraj. After analysing all the methods, the study concludes that tailoring the activity of LOX is the most effective approach. This will involve identifying naturally occurring "null LOX" genotypes and breeding them with high-yielding ones. However, since LOX is involved in numerous processes, the key is in identifying those genes responsible for the expression of the "truly objectionable" isoforms (proteins).

Sujata Vasudev, a geneticist formerly with IARI who studied mustard, switched off genes to improve the quality of oil and prevent formation of products that are harmful to the heart. However, she says, as LOX is involved in many processes benefitting the plant, it cannot be blindly shut down. "All [its] isoforms…need to be studied first. Only those genes should be silenced that are expressed in the grain that is to be stored. The expression of the other genes should not be altered, so that the plant metabolism is not disturbed. This is achievable through conventional breeding," says Vasudev.

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