Whey Protein and Acetylated Monoglyceride Edible Coatings:  Effect on the Rancidity Process of Walnuts

Whey protein isolate (WPI)-based coatings and distilled acetylated monoglyceride (AMG)-based coatings were evaluated for their ability to delay the oxidative rancidity of walnut pieces. Tocopherol (Toco) and ascorbyl palmitate (AP) were added to improve the performance of the coatings. Results indicate that, despite the low oxygen permeability and good continuity of the WPI coatings, there was no significant delay in the oxidative rancidity of walnuts. Shrinking of the WPI coating during drying, resulting in the pressing of some oil out of the walnut tissue, is likely the cause of the lack of effect of the WPI coatings. All AMG coatings resulted in increased shelf life of walnut pieces. After 70 days, the delay in the rancidity was as long as in the case of walnuts treated with butylated hydroxytoluene. Addition of Toco and AP in the AMG coatings had a positive effect in delaying the rancidity.