Response surface optimization of the enzymatic clarification process for apple ber juice and pasteurization by thermal and pulsed light treatments

Apple ber (Zizyphus mauritiana) is an underutilized fruit, rich in vitamin C and polyphenols. The raw juice after mechanical pressing of this fruit is very turbid and needs to be clarified using the pectinase enzyme. The study deals with the optimization of the enzymatic clarification process of apple ber juice using the incubation time (0.5–2.5 h), temperature (30–50 °C), and pectinase concentration (0.2–0.6%) as independent variables with the enhancement in juice clarity and yield as dependent parameters. The experiments were conducted according to a three-level full factorial design (3³ runs), and the polynomial models were developed using response surface methodology (RSM). The RSM models were further optimized using numerical optimization. The optimized clarification condition was to incubate the mixture at 41 °C for 2.5 h with 0.50% enzyme. Clarity and yield were greatly enhanced by 44.7% and 43.4%, respectively. The thermal pasteurization (90 °C for 3 min) of the clarified apple ber juice led to a 53.4% loss in vitamin C and a 59.3% loss in antioxidant capacity compared to clarified juice. The clarified juice pasteurized by pulsed light treatment (treated at a total fluence of 2400 J/cm²) preserved 90% of vitamin C from the clarified juice. A team of 30 semi-trained sensory panelists scored its overall acceptability (O_A on a 9-point scale) as 6.6, whereas the fresh juice had an O_A of 7.3.