Mass transfer properties of whey protein films and their effect on the rancidity process of dry nuts

Properties of Whey Protein Films and their Effect on the Rancidity Process of Dry Nuts Abstract Properties and applications of whey protein isolate (WPI)-based films were investigated. The permeability properties of WPI films and films containing only the major protein fraction of whey, {dollar}beta{dollar}-lactoglobulin ({dollar}beta{dollar}-Lg), were compared. As a first step, a procedure to obtain kilogram quantities of edible {dollar}beta{dollar}-Lg at {dollar}>{dollar}95% purity was developed. {dollar}beta{dollar}-Lg was separated from the rest of the whey proteins in a solution of 15% (w:w) whey protein isolate (WPI) in distilled water adjusted to pH 2 and 7% NaCl. {dollar}beta{dollar}-Lg was then separated from NaCl using diafiltration. Water vapor permeability (WVP) and oxygen permeability (OP) of WPI films were not statistically different from those of {dollar}beta{dollar}-Lg films with the same amount of glycerol, used as a plasticizer. Thus, the presence of the other whey proteins does not appear to affect WVP and OP properties of WPI edible films. Temperature had a exponential effect on the OP of WPI and {dollar}beta{dollar}-Lg films. Results followed the Arrhenius model, with activation energies in the 10.5-13.5 Kcal/mol range.; An application of WPI films formed as coatings on dry nuts to delay the rancidity process was studied. As a first step, accelerated tests for rancidity (peroxide value and static headspace analysis) of blanched peanuts, blanched roasted peanuts, and shelled walnuts were performed at high and low oxygen content. Results showed there is potential to extend shelf-life of roasted peanuts and walnuts by either an edible coating with a low oxygen permeability or nitrogen-flushing combined with oxygen-barrier packaging. A method to coat peanuts with whey protein aqueous solutions based on increasing coating solution viscosity was developed. Oxygen uptake and rancidity tests of coated and uncoated dry roasted peanuts were performed. WPI coatings were shown to be effective in delaying oxygen uptake and the rancidity process of dry roasted peanuts at an intermediate and a low storage relative humidity (53% and 21%). Greater thickness and lower relative humidity resulted in more effective coatings, which indicated that the mechanism of protection relies on the coatings' oxygen barrier properties.