Effects of heating method and conditions on the quality attributes of black mulberry (<i>Morus nigra</i>) juice concentrate

Abstract

Summary Black mulberry juice was concentrated by different heating methods including conventional heating and microwave heating at different operational pressures (7.3, 38.5 and 100 kPa). The effects of each method of heating on the quality attributes of the concentrated juice were investigated. The final juice concentration of 42°Brix was achieved in 140, 120 and 95 min at 100, 38.5, and 7.3 kPa, respectively, by using a rotary evaporator. Applying microwave energy decreased the required times to 115, 95, and 60 min. The changes in anthocyanin, antioxidant, phenolic content, turbidity, pH value, and acidity during concentration were investigated. Results showed that the degradation of anthocyanins was more pronounced in rotary evaporation comparing to microwave heating method. The higher phenolic concentrations resulted in a smaller EC 50 value, which corresponds to a higher antioxidant activity of the mulberry extract.