Impact of temperature assisted ultrasonication on the quality attributes of beetroot (Beta vulgaris L.) juice

Abstract

AbstractThe present study assessed the impact of ultrasonication in combination with moderate temperature on the physicochemical (pH; total soluble solids, TSS; total color difference ΔE*), biochemical (total phenols, TPC; antioxidant activity, AOX; betalain and enzyme activity) and microbiological (aerobic mesophiles, AM; yeast and mold, YM) attributes of beetroot juice. The experimental design involved different levels of process parameters, viz., frequency (28 and 40 kHz), temperature (30–50°C) and treatment time (10–30 min). The increase in TPC, AOX capacity and betalain contents 38%, 14% and 26%, respectively, was observed during US processing at 40 kHz. The betacyanin and betaxanthin were also well retained under the treatment domain. At the intense treatment condition of 40 kHz/50°C/30 min, the PPO and POD were inactivated by 78 and 85%, respectively. The microbial load (yeast and mold; aerobic mesophiles) was reduced to below detectable (<1 log CFU/mL) levels under the corresponding treatment condition. The ultrasonication of beetroot juice was optimized at 40 kHz/50°C/19 min with a desirability level of 0.656. This study establishes the efficacy of ultrasonication in combination with moderate temperature in rendering microbial safety and superior nutrient profile of beetroot juice, targeting an extended shelf life.Practical ApplicationsBeetroot juice is consumed in fresh form or used as an ingredient for product development. The juice is an ideal substrate for the extraction of natural colorants such as betalain and rich source of total phenolics. The juice is susceptible to enzymatic spoilage and microbial fermentation resulting in a loss of quality. Thermal processing retarded the enzyme activity and microbial proliferation but resulted in compromised juice quality. The nonthermal processing technologies such as ultrasonication impart a less intense effect on the juice matrix minimizing the effect of spoilage enzyme and microflora. The outcomes from this study emphasize the suitability of ultrasound processing in combination with moderate temperature in enhancing the shelf stability of beetroot juice with the retention of beneficial compounds.