The impact of moisture sorption properties on the color and bioactives concentrations of black currant-yerba mate instant drinks

Abstract

BACKGROUND: Black currant (BC) and yerba mate (YM) have high contents of polyphenolic antioxidants beneficial for health. Obtaining freeze-dried BC/YM instant drinks can be a means for providing their advantages to consumers. However, their high sugar contents make them very hygroscopic causing undesirable changes in color and bioactives concentration. OBJECTIVE: To solve this problem it is necessary to determine the powder's sorption properties and the temperature/relative humidity's (RH) influence on their color and polyphenol, ascorbic acid and anthocyanins's concentrations. METHODS: We analyzed the sorption isotherms of freeze-dried BC/YM/maltodextrin/sugar powder at 10/20/40°C and compared them with those from YM/maltodextrin. RESULTS: Of all models tested (Caurie, GAB, Halsey, Oswin) GAB was the best. Monolayer moisture values (Wm) were ≤0.1kg H2O (kg d.m)-1 indicating good stability. Due to its higher sugar content, BC/YM powders were more hygroscopic and with higher exothermic isosteric sorption heat (Qst) than YM powders. Qst and differential entropy decreased exponentially with increasing moisture levels. Within the experimental conditions, isokinetic theory indicated that the whole sorption process was enthalpy controlled. Temperature and RH strongly modified BC/YM's color and ascorbic acid and monomeric anthocyanins concentrations. At all temperatures, optimum levels of these properties required RH ≤33. To achieve maximum physicochemical quality and stability the powder's moisture content must be ≤Wm, in this case, RH dropped to 9 (10°C) and 11.3 (20°C/40°C).