Effect of pH and total fluence on microbial and enzyme inactivation in sweet lime (Citrus limetta) juice during pulsed light treatment

The study explores the effect of pH on microbial and enzyme inactivation in pulsed light (PL) treated sweet lime (Citrus limetta) juice. The matrix-pH was varied at 3.5, 4.0, and 4.5, whereas the intensity (total fluence) ranged between 1.2 and 3.0 kJ/cm(2). More than 5-log cycle reduction in Listeria monocytogenes and Escherichia coli was achieved at 1.8 kJ/cm(2) while Saccharomyces cerevisiae got inactivated at 2.1 kJ/cm(2). Complete inactivation of all the enzymes (polyphenol oxidase, peroxidase, and pectin methyl esterase) was achieved at 3.0 kJ/cm(2). A total color change (Delta E*) of 7.82 was noticed at 3.0 kJ/cm(2) with pH 3.5. Eventually, pH showed no significant result in ascorbic acid and bioactive degradation. PL treatment at 3.0 kJ/cm(2) produced microbially safe and enzymatically stable juice (at pH 3.5) with better retention of vitamin C. In this PL treated juice, 94.9% total phenolics and 79.5% vitamin C were retained, along with 97.7% antioxidant activity. Novelty impact statement At pH 3.5, the extent of microbial and enzymatic inactivation was highest. S. cerevisiae was the most resistant to PL compared to E. coli and L. monocytogenes. The matrix pH did not influence PL-induced degradation of vitamin C and bioactive compounds.