Short- and Long-Term Effects of UV-B Irradiation on Microbial Populations in Fresh-Cut Spinach During Cold Storage

Ultraviolet B (UV-B) irradiation has been investigated as a non-thermal treatment for fresh produce, but its antimicrobial effectiveness may vary during storage. This study evaluated the effects of UV-B irradiation on microbial populations and quality attributes of fresh-cut spinach during cold storage. Prior to packaging, spinach leaves were treated with 0, 0.3, 0.6, or 0.9 kJ m−2 UV-B and stored at 5 °C for 12 days. Total mesophilic aerobic bacteria (TMAB), total psychrophilic aerobic bacteria (TPAB), Enterobacteriaceae, and yeast and mold counts, together with total soluble solids (TSS), visual quality, and color characteristics, including lightness (L*), hue angle (h°), and yellowness index (YI), were evaluated during storage. UV-B exerted only a temporary suppressive effect on microbial growth, particularly on days 5–7, whereas some microbial populations increased during later storage, demonstrating the absence of sustained microbial control. In contrast, the highest UV-B dose (0.9 kJ m−2) maintained the highest overall visual quality and a favorable color profile, characterized by relatively low L* and high h° values. TSS showed treatment- and time-dependent response without a consistent dose-dependent pattern. Integrated hierarchical clustering and heatmap analyses revealed pronounced temporal organization and demonstrated that microbial and quality responses did not necessarily progress in parallel. Overall, UV-B treatment contributed to the preservation of selected quality attributes but did not provide sustained suppression of microbial populations during refrigerated storage, indicating that complementary preservation technologies may be necessary for effective microbial management.