Preparation of encapsulated konjac glucomannan-based fish oil and its use in high pressure processed goat milk

Abstract

This study was divided into 3 parts. The objective of first part aims to investigate the effect of konjac glucomannan (KGM) solution (0.02-0.5%, w/w) at different pH (3, 5 and 9) on the stability between 5% fish oil- skim milk with and without casein emulsion. The second part aims to study the effects of konjac glucomannan (KGM) solution (0.02-0.5%, w/w) at different pH (3-10) on the stability of 5%fish oil-milk emulsion. And the last part aims to study the effect of high-pressure (400, 500 and 600 MPa) on the improvement of the stability of 5%fish oil-milk emulsion. The results of first part show that, particle size of 5% fish oil- skim milk with casein emulsion was larger than % 5 fish oil- skim milk without casein emulsion at the same concentration and pH of KGM. Zeta potential of the emulsion from skim milk with casein was lower than emulsion from skim milk without casein at the same concentration and pH of KGM. Comparing the stability of emulsions, it was found that 5% fish oil- skim milk with casein were more stable than % 5 fish oil- skim milk without casein emulsion. The results from second part show that, particle size in emulsion was decreased with the increase in pH values of the KGM solution at all concentrations of KGM. Zeta potential of the emulsion was decreased when the pH of KGM solution was increased as well at all concentration of KGM. However, polydispersity index (PDI) was not changed when increase KGM concentration and pH. The increase in pH values of the KGM solution from 7-10 at the same concentration of KGM could increase the stability of the emulsion. Confocal laser scanning microscopy images confirmed an assumption that microstructures of KGM stabilized emulsions were controlled by pH. The images revealed that lowering the pH resulted in the expanded appearance of the aggregates. Moreover, the appearance of aggregates changed from isolated cluster to cluster networks as shown in emulsions at pH 7 vs emulsions at pH 10. Fish oil emulsions containing KGM in milk at different pH and concentration of KGM solution exhibited difference in stability. The mixture stability was enhanced when decreasing the KGM concentration in solution and increasing pH. The highest stability of the mixture was obtained with 0.04% KGM at pH 9 and 10. The emulsion at appropriate conditions was stable without separation for 10 days. After that, the emulsion at appropriate conditions was subjected to HPP. The results show that, particle size was decreased when increase pressure. Moreover, it was also found that the viscosity of the emulsion increased with increasing pressure. The stability of the HPP-treated emulsion increased from 10 days to 14 days without separation. The impact of HPP on the oxidative stability of lipids was increased when pressure was increased as the hydroperoxides values (PV) and thiobarbituric acid values (TBARS) were markedly enhanced by high pressure. However, no oxidative stability differences were observed between HPP and pasteurization. Moreover, HPP also significantly reduced the total plate count (TPC), coliform bacteria and S. aureus in emulsion. But as with oxidative stability, no differences result in reduce microbial between HPP and pasteurization.