Studies on the production of n-3 polyunsaturated fatty acid glyceride concentrate from Indian sardine oil

Abstract

Indian oil sardine (Sardinella longiceps) is a chief pelagic fishery resource of India and one of the richest and cheapest sources of n-3 polyunsaturated fatty acids (n-3 PUFA) such as Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA). The beneficial effects of n-3 PUFA in the prevention and treatment of coronary, neuromuscular, immunological disorders and allergic conditions are well documented. The crude oil extracted from Sardines contains mainly glycerides in addition to several undesirable components viz., free fatty acids, primary oxidation products, metal ions, pigments, moisture, phospholipids, phospholipases and insoluble impurities. Due to this, oil is highly susceptible to spoilage during storage and transhipment. Through a comprehensive study, a tailor made strategy was developed consisting of degumming, deacidification by solvent extraction, bleaching with granular activated carbon to eliminate all the aforesaid undesirable components, while retaining n-3 PUFA glycerides. This strategy was able to produce sardine oil of superior quality with minimal oil loss, without any loss of n-3 PUFA content. The effect of various extrinsic factors (light, temperature and moisture content) and intrinsic factors (metal ions, phosphotidylcholine, phospholipase-A and oleic acid) on storage stability of refined oil was undertaken to identifying the most detrimental factor during five-week storage. Moisture, ferric ions, oleic acid and sunlight were found to cause highest oxidative and hydrolytic instability and highest reduction in n- 3 PUFA content. Interestingly, even in the presence of ferric ions and oleic acid, phosphotidylcholine and phospholipase-A exhibited n-3 PUFA protection in spite of high oxidative and hydrolytic instability. In order to enhance n-3 PUFA content in the refined sardine oil, lipase mediated hydrolytic removal of unwanted fatty acids was attempted using Candida rugosa lipase (CRL) and Pseudomonas cepacia lipase. In order to facilitate reuse of CRL and to achieve higher efficiency and thermal stability, CRL was bioimprinted and immobilized. The preparation of immobilized enzyme and the hydrolysis of oil were optimized. The n-3 PUFA content in the deacidified oil was enriched up to 2.83-fold using bioimprinted immobilized lipase. The resultant oil had negligible di- and triglycerides content with the increase in the monoglyceride content. This proves higher efficiency in the hydrolysis of ester bonds of fatty acids,other than n-3 PUFA. The LC-MS data analysis of oil hydrolyzed by CRL-CLEA revealed the presence of increased quantities of monoglycerides of EPA and Palmitic acid (PA). Reusability studies showed the bioimprinted – immobilized lipase could be reused up to 5 runs without a substantial reduction in its performance.