Pilot-Scale Enzymatic Conversion of Low Stability, High Free Fatty, Squid Oil to an Oxidatively Stable Astaxanthin-Rich Acylglyceride Oil Suitable for Nutritional Applications.

Abstract

Squid viscera, a byproduct of squid processing, contains oil rich in omega-3 fatty acids (up to 10% by mass) and the antioxidant astaxanthin. However, its high free fatty acid (FFA) content compromises stability. To address this, pilot-scale (200 L) enzymatic re-esterification of squid oil using immobilized lipase (Lipozyme RMIM) was demonstrated, resulting in high acylglyceride yields. The processed oil was analyzed for oxidation kinetics and thermodynamics using Rancimat, fatty acid composition using GC, omega-3 fatty acid positional distribution in the acylglyceride product using ¹³C NMR, and astaxanthin content. Lipase treatment reduced FFA levels from 44% to 4% and increased acylglycerides to 93% in squid oil. This reduction in FFA was accompanied by significantly increased stability (0.06 to 18.9 h by Rancimat). The treated oil showed no loss in astaxanthin (194.1 µg/g) or omega-3 fatty acids, including docosahexaenoic acid (DHA). DHA remaining predominantly at sn-2 indicated that the naturally occurring positional distribution of this omega-3 FFA was retained in the product. Lipase treatment significantly enhanced oxidative stability, evidenced by improved thermodynamic parameters (E_a 94.15 kJ/mol, ΔH 91.09 kJ/mol, ΔS -12.6 J/mol K) and extended shelf life (IP₂₅ 74.42 days) compared to starting squid oil and commercial fish/squid oils lacking astaxanthin. Thus, lipase treatment offers an effective strategy for reducing FFA levels and producing oxidatively stable, astaxanthin-rich acylglyceride squid oil with DHA retained at the nutritionally favored sn-2 position.