Abstract
In this study a new nanocomposite film and coating based on chitosan-carboxymethyl cellulose-oleic acid (CMC-CH-OL) incorporated with different concentrations (0.5, 1 and 2%) of zinc oxide nano particles (ZnO NPs) have been suggested as a packaging material to increase the shelf life (microbial and staling) of sliced wheat bread. Water vapor permeability (WVP) of the CMC-CH film was significantly (P < 0.05) decreased after incorporation of oleic acid as well as ZnO NPs (2%) from 8.27 × 10−7 to 5.28 × 10−7 and 1.96 × 10−7 g/m.h.pa, respectively. Results of moisture content and water activity (aw) showed better maintenance of moisture content for breads stored by active coatings compared to the control one (bread without coating). Differential scanning calorimetry (DSC) thermograms of control bread showed an endothermic peak corresponding to amylopectin retrogradation. Control exhibited the highest firmness over 15 days of storage in all other samples. The results of microbial tests revealed an increase in microbial shelf life of sliced wheat bread from 3 to 35 days for CMC-CH-OL-ZnO NPs 2% in compared to the control. All active coatings lessened the number of yeasts and molds in sliced bread during 15 days, and further improvement in antimicrobial properties obtained for coatings contains 1 and 2% ZnO NPs with no fungal growth during 15 days.
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