Combined Effect of UV-C Light and Mild Heat on Microbial Quality and Antioxidant Capacity of Grapefruit Juice by Flow Continuous Reactor

Abstract

The efficacy of combined UV-C radiation (39.6 J/L) and mild heat (65.0 ± 3.0 °C) on the inactivation of aerobic mesophilic and yeast/molds in grapefruit juice (GFJ) (pH 3.12, °Brix 9.6, 2500 NTU, absorption coefficient 42.9 cm−1) using a flow continuous reactor was investigated. Changes in microbial load, ascorbic acid, and total phenols content, antioxidant capacity, pH, acidity, °Brix, and color were evaluated during 28 days at 4.0 ± 1.0 °C. The spoilage microorganisms were inactivated due to the synergistic effect of both technologies, but the ascorbic acid (74%) and phenol (14%) contents were considerably reduced, with losses of antioxidant capacity (DPPH• = 19% and ABTS•+ = 16%). During storage, the ascorbic acid level and antioxidant capacity gradually decreased. On the other hand, the treated GFJ did not show microbial growth while the untreated GFJ reached more than 4 logs CFU/mL. Conversely, no changes (P < 0.05) in the physicochemical parameters were observed. Principal component analysis is discriminated among the antioxidant compounds and physicochemical properties of the untreated and treated GFJ during storage. Application of UV-C in a Teflon-coil reactor combined with mild heat resulted in longer microbial shelf stability in the GFJ and was able to maintain the physicochemical properties of the juice unchanged during 28 days of storage. Hence, this process can be effectively applied as a combined method to ensure microbial quality.