Plasticizer crystallization in whey protein films and coatings: Effect on appearance, barrier and tensile properties

Edible films and coatings made from whey protein have desirable barrier and appearance properties. Sucrose plasticized whey protein isolate (WPI) films and coatings are transparent, glossy and are excellent oxygen barriers. However, these properties negatively change over time. The research in this dissertation investigated the (1) effect of sucrose concentration on the gloss and durability of whey protein films and coatings, (2) kinetics of sucrose crystallization in WPI films and methods of controlling crystallization, (3) effect of sucrose crystallization inhibitors on gloss fade of WPI coatings, and (4) changes in WPI films properties due to sucrose crystallization.; The gloss and durability of WPI films and coating increased with increasing sucrose content up to a mass ratio of 1:3 (protein:plasticizer). Beyond this concentration, sucrose crystallized in the films and coatings initially giving them a white appearance and weak mechanical properties.; To develop control parameters and hinder sucrose crystallization in WPI films and coatings, the kinetics of sucrose crystallization in WPI films was studied. The effects of protein matrix, crystallization inhibitors and storage environment (23%, 33%, 44%, or 53% relative humidity) on the rate constants of sucrose crystallization were determined using the Avrami model of crystallization. It was found that a cross-linked, denatured whey protein (WP) matrix hindered sucrose crystallization better than a protein matrix of native WP. The crystallization inhibitors tested were lactose, raffinose, modified starch (Purity 69) and polyvinylpyrrolidone (Plasdone C15). Based on rate constants, raffinose was determined to be the most effective inhibitor of sucrose crystallization in WPI films.; These crystallization control parameters were studied in WPI-sucrose coatings to limit gloss fade and cracking. When applied to the surface of chocolate-covered peanuts and stored for 119 days in 23%, 33% or 44% relative humidity, the WPI-sucrose coating containing raffinose had significantly slower gloss fade than all other WPI-sucrose coatings investigate. Raffinose also hindered the loss of flexibility, the increase in oxygen permeability and the loss of gloss in WPI-sucrose films store in 53% RH for 60 days.; High-gloss, water-based WPI-sucrose coatings can be used as environmentally friendly replacements for shellac. This research improved the viability of this application.