Potential of UV-C Light for Preservation of Cut Apples Fortified with Calcium: Assessment of Optical and Rheological Properties and Native Flora Dynamics

Abstract

The use of UV-C light (fluence 11.2 kJ/m2) to preserve calcium fortified cut apples was investigated. Impregnation treatments with calcium salts at atmospheric pressure (AI) (with and without previous blanching (B)) were performed to incorporate calcium into the apple matrix. An antibrowning dipping (AD) (ascorbic acid/calcium chloride solution) was also applied to non-blanched fortified apples. The impact of treatments on surface color, viscoelastic properties, microstructure, and native flora during refrigerated storage was analyzed. UV-C light was useful not only reducing microbial load of calcium-enriched apples (between 1.3 log cycles to non-detectable levels) but decreasing microorganisms’ growth (between 0.7 to 2.6 log cycles as compared with apples without UV-C exposure) during 7-day storage at 5 °C. AI caused marked browning, and not significant additional color changes due to UV-C exposure were observed. Blanching not only facilitated calcium incorporation (four times higher than in non-blanched tissues) inside the fruit but also helped in reducing browning. AD was also effective to minimize color changes but diminished the UV-C germicidal effect. AD + AI and B + AI treatments negatively affected viscoelastic properties, being the changes more pronounced in heated tissues. Both storage and loss moduli were reduced due to processing and during storage of samples, indicating that fortified apple tissues became less elastic and less viscous. However, exposure of AD + AI and B + AI apples to UV-C did not modify creep response neither at 0 day nor at day 7 and also had a negligible effect on dynamic spectra. Modifications in rheological properties and color were partially ascribed to microstructure features (breakage of cellular membranes with loss of functional cell compartmentalization and loss of turgor; modifications in cell walls). These findings suggest that UV-C irradiation could be used for prolonging shelf life of calcium fortified cut apples with minimal or negligible impact on color and viscoelastic properties.