Aggregability and digestibility study of fruit juice fortified camel milk powder proteins

Abstract

In this work, we observed the effect of grape juice (% concentrated juice/% concentrated camel milk: GJ20/80, GJ50/50) and pomegranate juice (PJ20/80, PJ40/60) fortification on camel milk (CM) protein solubility and digestibility. Proteins were dissolved in sodium phosphate buffer to 50 mg/ml and defatted prior Bradford assay of protein concentration, then analyzed by Size Exclusion-Ultra High-Performance Liquid chromatography (SE-UHPLC). The CM protein aggregation and their stability were further monitored at different pH 2.0, 4.0, and 7.5 via sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Freeze dried CM (FDCM) was the reference sample and our results showed that GJ50/50 and PJ40/60 with the highest fruit juice ratio had the lowest protein content in the supernatant, hence the decreased solubility. SE-UHPLC of supernatants showed a slight decrease in retention times of 11 kDa and 62 kDa proteins for GJ50/50 and PJ40/60 suggesting a possibility of adduct formation due to fortification leading to higher molecular weight. The simulated static in vitro gastrointestinal digestion of samples revealed that most soluble proteins were readily digested by pepsin, trypsin and chymotrypsin enzymes leading to small peptides. However, the SDS PAGE of pellets showed the partial resistance of casein and α-lactalbumin against peptic digestion.