Pulsed Light Treatment of Cut Apple: Dose Effect on Color, Structure, and Microbiological Stability

Abstract

This study investigated the effect of pulsed light (PL) dose on color, microstructure, and microbiological stability of cut apples during 7-day refrigerated storage. Apples were irradiated at two different distances from the lamp (5 or 10 cm) during 2 to 100 s (2.4 to 221.1 J/cm2). Cut-apple surface exposed to high PL fluencies turned darker (lower L* values) and less green (higher a* value) than the control, and this effect was more pronounced as PL dose and/or storage time increased. On the contrary, the application of few flashes (2.4 J/cm2) allowed maintaining the original color of apples slices along storage. Light microscopy images of treated samples showed degraded walls and broken plasmalemma and tonoplast, which may explain, at least partially, the increase in browning of irradiated apples at high doses. Inactivation patterns of inoculated microorganisms depended on PL dose and the type of microorganism. After 100 s PL treatment at 5 cm, no counts were observed for Saccharomyces cerevisiae KE162, while for Escherichia coli ATCC 11229 and Listeria innocua ATCC 33090, reduction levels were 2.25 and 1.7 logs, respectively. Native microflora population was in general higher in control samples than in 10 and 60 s PL irradiated apples along the whole storage. Although the application of high PL fluencies allowed obtaining greater microbial reductions, they also promoted browning of apple. Application of PL at a dose of 11.9 J/cm2 could extend the shelf life of cut apple with minimal modification in color.