Abstract: Whey protein isolate (WPI) is one of commonly used film-forming materials and has been considered as a good barrier to oxygen but a poor one to water vapor. In the present study, film-forming properties of Maillard reaction products (MRPs) formed from WPI and xylose such as physical and mechanical properties and water vapor permeability were investigated at different amounts of xylose and glycerol with the aim of optimizing film-forming conditions and a comparison with those of WPI was carried out. In addition, the effects of coating with WPI or WPI/xylose MRPs on lipid peroxidation in walnut kernel were probed. The results indicated that the optimal film-forming conditions of WPI/xylose MRPs were determined to be heating a reaction system containing 10 g of WPI, 5 g of xylose and 5 mL of glycerol per 100 mL at 80 ℃ for 45 min or at 90 ℃ for 30 min. Compared with WPI film, WPI/xylose MRPs film revealed a two-fold increase in penetration strength, an around 2.5-fold elongation strength and a decrease in water vapor permeability by about 24%. Coating with WPI/xylose MRPs film could delay the increase in acid value of walnut kernel, whereas coating with WPI film had no obvious inhibitory effect.

Key words: whey protein isolate, xylose, Maillard reaction products, edible film, walnut