UBC Theses and Dissertations

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UBC Theses and Dissertations

Radiant energy vacuum microwave microencapsulation of natural antimicrobials for a controlled release application in fresh-cut Ambrosia apples Sáenz Garza, Natalia Edith


Microencapsulation of active compounds provides protection, ease of handling and dosing, as well as a controlled release. Fresh-cut fruit has a limited shelf-life which could be improved using natural antimicrobials in a microencapsulated form to achieve a controlled release. Vanillin and hexanal are two antimicrobials that are compatible with the food model chosen in this study, namely fresh-cut apple slices. Both vanillin and hexanal were microencapsulated in β-cyclodextrin-pectin blends by radiant energy vacuum (REV) drying and freeze-drying (FD). Although the encapsulation efficiency of vanillin in the REV-processed β-cyclodextrin-pectin blends was high (66%), a fast release into aqueous media and the textural effect of the encapsulant debris on the apple slices limited its practical application. Hexanal’s microencapsulation yield was not as high as that of vanillin, however, it was improved from 20% to 47%, for the most microbially efficient formulation, using a pilot scale 3.6 kW REV dehydrator. Hexanal containing microcapsules were tested for inhibition of Penicillium expansum in potato dextrose agar and on fresh-cut apple slices. Inhibition of P. expansum was examined by measurement of radial growth on the surface of potato dextrose agar (PDA) plates incubated for 5 days at 25°C and 10 days at 12°C. Apple slices inoculated with P. expansum spores were stored in sealed glass jars for 15 days and 12 days at 5°C and 12°C respectively. Shelf-life of fresh-cut apple slices was evaluated as inhibition of mould and secondary browning relative to control samples. Hexanal release profiles were quantified using solid phase microextraction-gas chromatography (SPME-GC) sampling of the headspace. Spore germination on PDA was inhibited for 5 days and radial growth for 10 days with 5.4-6.2 μg hexanal/mL air. Although FD gave a higher encapsulation yield, REV encapsulation produced the greatest inhibition of mould in PDA. Un-encapsulated hexanal inhibited mould on apple but caused rapid browning and softening of apple due to phytotoxicity. Encapsulated hexanal delayed quality loss without apparent phytotoxicity. REV and FD hexanal microcapsules produced similar shelf-life for up to 15 days at 5°C. Hexanal microencapsulation for a headspace application could present a viable strategy to extend the short-term shelf-life of fresh-cut fruit.

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Attribution-NonCommercial-NoDerivatives 4.0 International