Effects of heat treatment and ultraviolet radiation on physicochemical, microbiological, and bioactive properties of shalgam juice

Abstract

Herein, we aimed to investigate the physicochemical, bioactive, microbial, and sensory properties of 5 different ultraviolet (UV) treatment conditions, varying in flow rate (1.5–2.5–3.5 L/min), temperature (5–25°C), and UV-intensities (5.1–10.1 mW/cm²), along with heat treatment (HT, 72°C for 20 s), and untreated samples (C) over a storage period of 150 days. At the beginning of storage, the samples exhibited a dry matter content ranging from 2.15% to 2.38%, pH levels ranging from 3.46 to 3.53, and total acidity between 6.35 and 6.51 mg/L. L* values were recorded between 33.09 and 33.50, while ΔC values ranged from 9.13 to 9.24. However, by the end of storage, these values had changed to 2.28–2.43% for dry matter, 3.47–3.49 for pH, 6.22–6.35 mg/L for acidity, 34.94–35.57 for L* values, and 6.95–7.01 for ΔC values. Throughout storage, total mesophilic aerobic bacteria (TMAB), lactic acid bacteria (LAB), and yeast and molds were measured at the highest levels in the C samples when compared to HT and UV-treated samples. At the end of storage, compared to the initial values, TMAB levels in UV-treated samples decreased from 3.29–4.80 log cfu/mL to 3.13–3.92 log cfu/mL. On the other hand, compared to the initial values (3.29–4.01 log cfu/mL), LAB levels decreased by 1.93–2.42 log cfu/mL by the end of storage. Initially, in UV-treated samples, the TPC (total phenolic content) ranged from 398.15 to 403.86 mg GAE/g, DPPH antioxidant activity ranged from 811.52 to 834.89 mg TE/L, and TAC (total anthocyanin content) ranged from 5.58 to 5.74 mg/L. By the end of storage, an increase was observed in all bioactive properties analyzed. Furthermore, UV treatment positively impacted the bioaccessibility of bioactive compounds compared to the HT-treated sample. Overall, this study confirms that UV-C technology can be used as an alternative method for extending the shelf life of shalgam juice while preserving its sensory and bioactive attributes.