Assessing the impact of ultra‐sonication and thermo‐ultrasound on antioxidant indices and polyphenolic profile of apple‐grape juice blend

Abstract

Apple-grape juice blend (50:50) were subjected to blanching (thermal), high temperature-short time (72°C: 15 s), ultra-sonication (5 & 10 min), thermo-ultrasound (5 min, 40°C; 10 min, 40°C), and thermo-ultrasound (5 min, 50°C; 10 min, 50°C) and were compared to control treatment for the antioxidant indices. Furthermore, one best treatment each from ultra-sonication (10 min), thermo-ultrasound at 40°C (5 min), and thermo-ultrasound at 50°C (5 min) was analyzed through high performance liquid chromatography diode array detector (HPLC-DAD) for the quantification of individual phenolic acids, flavanols, stilbenes, and anthocyanins. Polyphenolic profile (HPLC-DAD) of apple-grape juice blends treated with ultra-sonicated (10 min), thermo-ultrasound (5 min; 40°C), and thermo-ultrasound (5 min: 50°C), resulted in identification of 23 polyphenols (9 phenolic acids; 6 flavanols; 1 stilbene; 7 anthocyanins). Results of HPLC characterization revealed a significant (p < .05) effect of tested treatments on all the polyphenols. Among phenolic acids, chlorogenic acid was observed to be highest (422.12 mg/L) in ultra-sonicated juice blend (TU-10:10 min) followed by caftaric, gallic, syringic, vanillic, caffeic, ferulic, and cinnamic acids. While, content of resveratrol (stilbene), epigallocatechin gallate (flavanol), and Malvidin 3, 5-diglucoside (anthocyanin) were also found to be maximum (33.08, 386.32, and 70.25 mg/L, respectively) in ultra-sonicated (10 min) apple-grape juice blend samples. Keeping in view the polyphenolic profile and consumer preferences, ultra-sonication could be employed industrially as an alternative substitute of thermal processing techniques to enhance the quality of apple-grape juice blend. Practical application For years, several nonthermal techniques are used for the preservation and quality improvement of fresh juices mainly by preventing the microorganisms and enzymes. Among these technique, single nonthermal treatment has a capacity to reduce the amount of microorganism and enzymes while a combined technique such as thermo-ultrasound has a better effect than single treatment, which have been investigated in this study. Therefore, this article would encourage the juice industrialists by applying these techniques for commercialization of juice and juice products in a more effectual manner.