Agriculture Reference
In-Depth Information
12
Extension of Shelf Life and Control of
Human Pathogens in Produce by
Antimicrobial Edible Films and
Coatings
Tara H. McHugh, Roberto J. Avena-Bustillos, and
Wen-Xian Du
Biopolymers Used for Edible Films and Coatings
Components of edible fi lms and coatings can be divided into three categories: hydro-
colloids, lipids, and composites. Hydrocolloids include proteins and polysaccharides,
such as starch, alginate, cellulose derivatives, chitosan, and agar. Lipids include
waxes, acylglycerols, and fatty acids (Min and Krochta 2005). Composites contain
combinations of both hydrocolloid components and lipids. The choice of formulation
for edible fi lm or coating is largely dependent on its desired function—such as bio-
degradability, edibility, aesthetic appearance, and good barrier properties against
oxygen—which varies based on the composition of the fi lm (Cha and Chinnan 2004).
In addition, edible fi lms and coatings can serve as supports containing antimicrobial,
nutritional, and antioxidant substances (Gennadios and others 1997).
Depending on their composition, the functionality of edible fi lm and coating mate-
rials may vary because each component confers different properties on the composite
matrix. Films made of hydrocolloids (polysaccharides or proteins) usually have strong
mechanical and gas barrier properties, but also have poor water vapor barrier proper-
ties and high permeability to moisture. In contrast, fi lms composed of lipids exhibit
good water vapor barrier properties, but they tend to show poor mechanical strength
and high oxygen permeability. Combining these components into one matrix allows
them to physically and/or chemically interact and may result in fi lms with improved
properties (Diab and others 2001). For example, fruit-based edible fi lms can be made
with excellent oxygen barrier properties, but not very good moisture barrier properties.
Combining fruit purées with various gelling agents (such as alginate) improves the
water barrier and tensile properties of the resultant fruit-based fi lms (Mancini and
McHugh 2000 ).
Polysaccharides are commonly used for edible fi lms because their fi lm - forming
properties are derived from cellulose, starch, alginate, and their mixtures. A plasticizer
is normally added to increase the fl exibility of the fi lm, and occasionally it is used
only to facilitate the polymer processing. The most commonly used plasticizers in
starch - based fi lms are polyols, such as sorbitol and glycerol. They are frequently added
into edible fi lms to relax the intermolecular forces and increase the mobility of the
polymeric chains to improve fl exibility (Durango and others 2006). Glycerol is a low-
molecular-weight nonvolatile substance that is often used to modify the mechanical
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