Encapsulation of fish oil and astaxanthin using whey protein isolate and polysaccharide wall matrix

Abstract

Fish oil and astaxanthin are two functional ingredients with health benefits to humans, however both are susceptible to oxidation during processing. This study aimed to investigate the microencapsulation of fish oil and astaxanthin by spray drying them with whey protein isolate (WPI) and either maltodextrin (MD) or soluble corn fiber (SCF) to act as wall materials. The emulsions consisted of different wall/core ratios (4:1 and 2:1) and protein/polysaccharide ratios (2:1, 1:1, and 1:2) were prepared using a high-speed homogenizer first and then a high-pressure homogenizer. The average droplet size, particle size distribution and zeta-potential were evaluated, as well as the changes in antioxidant capacity and the oxidation extent of the core material, during 15-day storage trials. The emulsions that gave the best stability were then spray dried into microcapsules at inlet temperatures of both 160 °C and 180 °C. The characteristics of the microcapsules, including water activity, surface oil, encapsulation efficiency and reconstitution properties, were investigated. In addition, the storage stability of each microcapsule was compared with that of the original emulsion. Finally, an in vitro digestion assay was conducted to study the digestibility of the microcapsules. All the formulated emulsions showed narrow droplet size and particle size distribution, with the emulsions with a wall/core ratio of 4:1 and a protein/polysaccharide ratio of 2:1 having the best stability. The results indicated that the blending of astaxanthin and fish oil could effectively inhibit the oil phase oxidation, resulting in better stability. The inlet temperature of 160 °C showed better microcapsule physical characteristics, including good water activity, lower surface oil content, and higher encapsulation efficiency. Scanning electron microscopy revealed that the microcapsules had surface dents but no cracks, which could support core preservation capacity. The microcapsules were also found to have higher stability than that of the original emulsions. The in vitro digestion assay confirmed the bioaccessibility of EPA, DHA, and astaxanthin at the intestinal phase. It also illustrated that fish oil and astaxanthin spray dried with a combination of WPI and MD resulted in better digestibility than those spray-dried with a combination of WPI and SCF. Overall, this research demonstrates that spray drying for microencapsulation is a potential means of enhancing the stability of fish oil and astaxanthin, and that the co-encapsulation of astaxanthin with fish oil could further enhance the stability of fish oil in microcapsules.