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

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 degrees C), and UV-intensities (5.1-10.1 mW/cm2), along with heat treatment (HT, 72 degrees 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 Delta C 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 Delta C 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. In this study, the effect of UV-C as an alternative to heat treatment was applied to shalgam juice processing. UV application provided better bioactive properties than heat treatment. The microbiological properties of shalgam were held within the limits of Turkish standards.image