Enzymatic modification of stearidonic acid soybean oil and improvement of oxidative stability
Ifeduba, Ebenezer Arinze
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The aim of this study was to design enzymatic processes for producing ‘heart-healthy’ stearidonic acid (SDA)-enriched triacylglycerol (TAG) concentrates from SDA soybean oil (SDASO) and to develop microencapsulation systems for improving the oxidative stability of SDASO. SDA concentrates were prepared from chemical and enzymatic hydrolysis products of SDASO. A 62% SDA free fatty acid fraction (SDA-FFA) was obtained by low temperature crystallization of the chemical hydrolysis product. Partial hydrolysis of SDASO by Candida rugosa lipase yielded a 51% SDA acylglycerol fraction (SDA-GLY). Using response surface methodology (RSM), reaction conditions for enzymatic acidolysis between SDA-FFA and SDA-GLY fractions were optimized to produce ~60% SDA TAG concentrates. Structured lipids (SL) were produced by Celite-immobilized, Rhizomucor miehei lipase-catalyzed incorporation of caprylic acid (C8:0) into SDASO Substrate molar ratio, reaction time, and enzyme load were optimized. The acidolysis of SDASO or an SDA-enriched TAG concentrate resulted in SLs with 17-33% C8:0 and 20-42% SDA. The microencapsulation of SDASO in gelatin (GE)-gum arabic (GA) coacervates crosslinked by transglutaminase (TG) or the Maillard reaction (MR) was investigated. The total oxidation (TOTOX) value of microencapsulated SDASO was determined after 28-30 days of storage. TOTOX values were highest in the TG-modified microcapsules (25.9-56.6), but lower in the control (19.9-47.6) and MR-modified microcapsules (10.2-18.4). When microcapsules were used to formulate SDA-fortified yogurt, oil release during heat treatment was lowest for the MR-modified microcapsules (1.1-8.6%), but higher for TG-modified (1.8-12.3%) and control (2.0-26.4%) microcapsules. MR-modified microcapsules displayed best oxidative and thermal stability. The antioxidant capacity of the MR-modified encapsulant was then optimized by varying the biopolymer composition and dry-heating time. GE and GA were crosslinked, with or without maltodextrin (MD), to produce anti-oxidative Maillard reaction products (MRP) which were subsequently used as encapsulants. The optimal Trolox equivalent antioxidant capacity (TEAC) for MRPs derived from the [GE-GA] and [GE-GA-MD] blend was ~ 26 and 29 mg Trolox eq/10 g, respectively. TOTOX values ranged from 24.5-33.1for the optimized [GE-GA] blend and from 7.1-14.3 for the optimized [GE-GA-MD] blend. Microencapsulation of SDASO using the optimal MR-modified [GE-GA-MD] blend may be suitable for making microcapsules with high oxidative stability and formulating SDA-fortified food products.