Comparison of thermally pasteurized and ultrasonically pasteurized blueberry juice (Vaccinium corymbosum) and an investigation of blueberry juice effect on lipid oxidation during microencapsulation of poly-unsaturated fish oils

Abstract

Blueberries have received considerable attention due to their content of health promoting compounds such as polyphenols and anthocyanins. Thermal pasteurization (TP) is known to cause degradation of anthocyanins and juice color. Microencapsulation, particularly with incorporation of blueberry antioxidants, can improve the stability of menhaden (MO) and salmon (SO) fish oils rich in omega-3 fatty acids. The objectives of this research were to study the effect of TP and continuous ultrasonication processing on the microbiological, chemical and physical properties of blueberry juice (BJ) and to determine the effect of BJ on MO and SO lipid oxidation during microencapsulation. Fresh blueberries were blanched, blended and then centrifuged to obtain the juice. BJ samples were pasteurized at 80, 85 and at 90°C for 1, 2, 3, 4 and for 5 min. Unpasteurized BJ was pumped at 24 mL/min and at 93.5 mL/min to the continuous flow cell of an ultrasonic processor, where it was sonicated at three treatment levels (40, 80 and 100% amplitude). Sonicated (non-TP) and unsonicated (TP) juices were analyzed for coliforms, total aerobes, yeasts and molds. Total anthocyanin content, total phenol content, antioxidant activity, ◦Brix, titratable acidity, pH and color were also determined for both sonicated and unsonicated juices. Emulsions prepared with each type of fish oil having 0, 5 and 10% BJ were separately spray dried and microencapsulated powders were produced. All the powders were evaluated for microencapsulation efficiency (ME), color, peroxide value, anisidine value, and fatty acid methyl ester profile. Sonication at higher intensities reduced microbial counts equivalent to TP. Sonication did not affect BJ color or anthocyanins content while TP showed reduction of anthocyanins and change in juice color with increased temperature and time. Furthermore TP juices showed signs of Maillard browning with increased temperature and time. All microencapsulated MO and SO powders had high ME with low surface oil content. All powders containing 10% BJ showed less lipid oxidation during emulsification and spray drying than powders containing 5% BJ and 0% BJ. This study demonstrated that ultrasonication can be an alternative pasteurization treatment to TP and that BJ reduced lipid oxidation in fish oils during microencapsulation.