Degree

Doctor of Philosophy (PhD)

Department

School of Renewable Natural Resources

Document Type

Dissertation

Abstract

The substantial economic losses caused by postharvest fruit loss due to their perishable nature and susceptibility to decay emphasize the urgency of developing packaging techniques. Sustainable and functionalized bio-based packaging materials would mitigate postharvest losses while aligning with prevailing environmental considerations. Bio-based edible coatings form a gas barrier on the fruit surfaces that alternate the internal atmosphere and mitigate the senescence and deterioration of postharvest fruits. Renewable natural resources such as cellulose, chitosan, sodium alginate, and essential oils have been widely used for coating applications due to their sustainability, biodegradability, and functionality. Various bio-based edible coatings have been developed for preserving the postharvest qualities of several fruits like strawberry, fig, peach, and blueberry. Sustainable nanomaterials such as cellulose nanocrystals (CNCs), cellulose nanofibers (CNFs), and chitosan nanofibers (ChNFs) were blended with sodium alginate (SA) as a stabilizer incorporating antimicrobial materials essential oils (EOs) to make coating suspensions with different formulations. The prepared suspensions were spray coated on the fruit surfaces. Strawberry treated with the SA/BCNCs/ChNFs/OEO coating, including bagasse CNC (BCNC), ChNF, SA, and oregano EO (OEO) had only 10.8% weight loss without microbial contamination after nine days of storage. In contrast, uncoated and bagasse CNCs coated strawberries had more than 37.0% and 28.6% weight loss and fungi infection detected. The SA/BCNCs/ChNFs and SA/BCNCs/ChNFs/OEO coated figs and peaches significantly kept their firmness (7.8 and 14.4 N). In comparison, uncoated fig and peach showed considerable firmness diminutions (2.3 and 9.8 N) after 9 and 14 storage days. Moreover, these coatings delayed the rising total soluble solids (TSS) and individual sugars (fructose and glucose) of figs, impeding the breakdown of starch to sugar by slowing down postharvest respiration behavior. Bioactive spraying coating suspensions consisting of ChNFs, cellulose nanofibers (CNFs), and lignocellulose nanofibers (LCNFs) attaching SA and tea tree EO (TTO) were coated on blueberries. The coating with LCNFs and SA (ChNFs/LCNFs/SA/TTO) was effective in retarding the moisture loss of blueberry. ChNFs/LCNFs/SA/TTO coated blueberries had a 16.2% TSS increase after 15 storage days, while uncoated and other coated blueberries had more than a 21.7% TSS increase. These results suggest that bio-based coatings with sustainable nanomaterials incorporating SA and EOs can effectively retain postharvest fruit quality due to their barrier properties against O2, CO2, and moisture resulting from the entangled matrix structure of the coating layer. The coating barrier led to substantial modifications on the surface atmosphere of fruits, contributing to delay moisture loss, oxidation, and senescence. Thus, bio-based coatings have a high potential for application as edible coatings for extending the shelf life of fruits.

Date

6-26-2023

Committee Chair

Wu, Qinglin

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Available for download on Monday, June 24, 2030

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