A novel approach using UV-C light assisted by mild heat and natamycin as a hurdle strategy to preserve juice from non-commercial-grade apples

Abstract

The goal of this study was to investigate the effectiveness of using single UV-C light (1271 mJ/cm²) or assisted by mild heat (50 °C, UV-C/H) and the addition of 30 or 45 ppm of natamycin (Na) as emerging alternatives to preserve non-commercial-grade apple juice. Challenge tests using cocktails of E.coli (ECC), Salmonella (SC), and yeasts (YC) were performed, and Weibull and biphasic models were used to characterise microbial inactivation. Furthermore, juice sensory and non-sensory attributes and microbial and physicochemical stability during storage (23 days, 7 °C) were assessed. UV-C/H induced more significant inactivation in the bacterial cocktails These models distinctively explained microbial inactivation. During storage, UV-C/H prevented ECC and SC recovery, while both concentrations of Na increased YC inactivation and effectively prevented its recovery in the apple juice during the whole storage. A combined treatment of UV-C/H+30Na was proposed for subsequent analyses. Several physicochemical parameters, including pH, turbidity, soluble solids, 5-HMF content, D-fructose, total antioxidant activity (TAA) determined by DPPH (2,2-diphenyl-1-picrylhydrazyl), and total polyphenols remained unchanged in UV-C/H+30Na-treated juice However, it increased the total antioxidant activity by ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) Principal component analysis (PCA) showed that, during storage, the apple juice sample without any treatment (C) was positively associated with increases in native microbiota, turbidity and opacity In contrast, the UV-C/H+30Na-treated juice showed complete microbiota inactivation and increased values of TAA_ABTS and flavonoids. The addition of natamycin to the apple juice preserved by UV-C light assisted by mild heat resulted in no significant differences in sensory and non-sensory attributes as judged by a wide group of consumers, who appreciated the samples.