ABSTRACT
Starch is a polymeric carbohydrate composed of anhydroglucose units. This is not a uniform material, and most starches contain two types of glucose polymers: a linear chain molecule termed “amylase” and a branched polymer of glucose termed “amylopectin” (Rodriguez et al., 2006). Starches are often used in industrial foods as Šllers or structurizing agents. During recent years, starch has been used to produce biodegradable Šlms to partially or entirely replace plastic polymers. This is mainly due to its low cost as a raw material, its renewability in terms of the wheat crop, and its good mechanical properties (Xu et al., 2005). High-amylose starch such as cornstarch is a good source for Šlm formation; for instance, free-standing Šlms can be produced from aqueous solution
CONTENTS
11.1 Introduction .......................................................................................................................... 239 11.2 History of Edible Films and Coatings ..................................................................................240 11.3 ClassiŠcation of Edible Films and Coatings ......................................................................... 241 11.4 Edible Film Materials and Their Previous Applications ...................................................... 241
11.4.1 Plasticizers ................................................................................................................242 11.4.2 Antimicrobial, Antioxidant, and Other Functional Agents ......................................242 11.4.3 Antimicrobial Agents ...............................................................................................242 11.4.4 Antioxidant Agents ................................................................................................... 243
11.5 Starch Film-Forming Mechanisms: Gelatinization and Recrystallization .......................... 243 11.6 Appearance and Physical Properties of Starch Films ..........................................................246 11.7 Mechanical Properties of Starch Films ................................................................................ 247 11.8 Barrier Properties of Starch Films .......................................................................................248 11.9 Gas Barrier............................................................................................................................248 11.10 Water Vapor Permeability ....................................................................................................250 11.11 Aroma Barrier .......................................................................................................................250 11.12 Oil Barrier .............................................................................................................................250 11.13 Optical Properties: Gloss, Transparency, and Color ............................................................. 251 11.14 Summary .............................................................................................................................. 251 References ...................................................................................................................................... 252
of gelatinized amylose and then drying of the material in a controlled manner. Normal cornstarch consists of approximately 25% amylose and 75% amylopectin. Mutant varieties of corn are produced which contain starch with up to 85% amylose (Whistler and Daniel, 1985). Mark et al. (1966) reported that Šlms produced from high-amylose cornstarch (71% amylose) had no detectable oxygen permeability at RH levels less than 100%. This was true for both unplasticized and plasticized (16% glycerol) Šlms. This result is surprising in light of the fact that addition of plasticizers and absorption of water molecules by hydrophilic polymers generally lead to increased polymer chain mobility and subsequent to increased gas permeability (Banker et al., 2000). Partial etheriŠcation of high-amylose starch with propylene oxide, to yield the hydroxypropylated derivative, improves water solubility.
