 Gloss and Durability of Whey Protein Isolate Coatings for Confectionery Products
By
K. L. DANGARAN and J.
M. Krochta
Department of Food
Science and Technology
University of
California, Davis, CA 95616
Whey protein isolate (WPI) coatings are being developed to
provide a glossy and durable finish to confectionery products. In steps to produce an alternative to
alcohol-based shellac glazes currently used by candy makers, water-based WPI
coatings plasticized with sucrose have been shown to provide the best gloss to
chocolates. We hypothesized that because of its high refractive index,
increasing the sucrose level in WPI films and coatings would increase
gloss. Our objective was to compare
different WPI/sucrose systems to determine which provided the most gloss and
which was most durable. The systems studied included WPI: sucrose ratios of
2:1, 1:1, 1:3, 1:6, and 1:10.
The specular reflection (gloss) of films made from the WPI
solutions was measured using a Micro-Tri-Gloss meter (ASTM D523-89). The tensile properties of films were
determined as a measure of film durability using ASTM method D882-97. To test gloss and durability of WPI/sucrose
coatings, a single layer of each formulation was applied to chocolate-covered
almonds. Gloss measurements were taken with a Tricor Gloss Analysis System
model 801. Durability of coatings was
tested using a drop test following a modified version of ASTM method
D441-86.
The level of gloss provided to both stand-alone films and to
coatings on the surfaces of chocolate-covered almonds was increased by
increasing the level of sucrose plasticizer in the coating formulation to a
level of WPI to sucrose equal to 1 to 3.
This ratio of protein to plasticizer was also found to give the toughest
films. It also provided the most durable
coating, able to survive physical stresses (repeated dropping) without visual
cracking and with the least amount of gloss fade. WPI:sucrose ratios of 1:6 and 1:10 resulted
in sucrose crystallization.
Increasing gloss provided by WPI coatings makes such
coatings a viable alternative to ethanol-based shellac coatings. Furthermore, increasing durability of sugar
coatings would decrease product and profit loss for the confectionery industry.
For more information on Dr. Krochta’s work and the Food Science and Technology Department at UC Davis, please visit Dr. Krochta's Web site - http://foodscience.ucdavis.edu/fst/faculty/KrochtaWeb/index.htm.
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