Summary
The major sources of dietary lipids are edible oils, which include both vegetable and fish oils. Crude oil extracted from vegetable and fish sources contain mono‐, di‐, triacylglycerols along with impurities, which necessitates refining. The main objective of refining is to remove the contaminants that adversely affect the quality of oil, thereby reducing the shelf life and consumer acceptance. However, this refining process needs to be tailored as the composition of crude oil is highly variable, depending upon the plant/fish species, geographical location of the source and method of oil extraction. Recently, extensive efforts have been made to develop refining technology, using either conventional physical/chemical processes or several unconventional processes including biological and membrane processes. The first section of this review gives a brief description of general composition of some commonly used vegetable and fish oils, followed by the review of various refining methods and their effects on the oil constituents. Finally, an effort is made to understand the technological gaps in the existing methods and possible directions of research to overcome the said gaps.
Oil extracted from pelagic fishes, rich in n-3 polyunsaturated fatty acids (PUFA) like Eicosapentaenoic acid and Docosahexaenoic acid, have numerous health benefits. The oil also contains impurities like di- and mono glycerides, free fatty acids, phospholipids, unsaponifiable matter, metal ions and volatile compounds. Most of these impurities are removed by refining process without affecting valuable n-3 PUFA. However, due to the presence of residual impurities, environmental factors and higher degree of unsaturation, the oil exhibit hydrolytic and oxidative instability during storage. This study was aimed to identify the most detrimental factors causing hydrolytic and oxidative instability and deterioration of n-3 PUFA content in sardine oil during five-week storage. The effect of various extrinsic and intrinsic factors on the storage stability was investigated. The hydrolytic and oxidative instability was estimated by free fatty acid (FFA) content and totox value (TV) respectively. Moisture, sunlight, ferric ions and FFA were found to be most detrimental to oil quality and n-3 PUFA content. Although, addition of phosphotidylcholine and phospholipase-A showed high degree of hydrolytic and oxidative instability, n-3 PUFA destruction was minimal. Interestingly, even in the presence of ferric ions and FFA, phosphotidylcholine and phospholipase-A exhibited n-3 PUFA protection. The exact mechanism by which phosphotidylcholine and phospholipase-A offered protection to n-3 PUFA needs further investigation. From this study, it can be concluded that removing ferric ions, moisture and FFA from crude oil during refining is essential. Further, the refined oil must be stored under dark conditions in airtight containers to retard deterioration of oil quality.
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