Investigation of applicability ultrasound pasteurization and membrane concentration techniques for production of black mulberry (Morus nigra L.) juice concentrates

In this study, applicability of the ultrasound pasteurization and osmotic distillation methods were investigated as alternative method to classic thermal pasteurization and concentration for juice processes. The inactivation data of E. coli ATCC 25922 was evaluated at First order, Weibull, log-logistic, biphasic linear and modified Gompertz models with the aim of determining pasteurization standards in black mulberry juice. According to the thermal pasteurization data, Modified Gompertz model were found to provide the best fit, when the best fitting model for ultrasound pasteurization data was determined as Weibull. Through this evalution; thermal pasteurization was applied at 59 °C for 40 sec and at 80°C for 1 min (Representative commercial conditions), ultrasound pasteurization was applied at 30 °C, at 1,63 acoustic energy density for 14,5 min on continuous-mode. After the treatments, no differences were observed in analyzed parameters except for volatile components, color and turbidity values. When the thermal concentration method was compared with the osmotic distillation, no significantly differences were observed in pH, titratable acidity, antioxidant activity and color value of the black mulberry juice concentrates. However, turbidity and polymeric color ratio values were determined to be higher in the thermally concentrated samples. Additionally, these values also increased by increasing concentration. The number and concentration of volatile components of the samples (15 components, total amount 1,49 µg/mL) which were concentrated to 65Bx by osmotic distillation was found to be higher than the samples (7 components, total amount 0,50 µg/mL) which were concentrated by thermal method. Total monomeric anthocyanin content of samples, which were concentrated by osmotic distillation, was found to be higher than the samples which were concentrated by thermal method. Moreover anthocyanin degradation ratio of the samples, which were concentrated to 65 Bx by thermal method, was found to be 16,2% whereas anthocyanin degradation ratio of the samples, which were concentrated by osmotic distillation was 6,5%. Furthermore, anthocyanin content of the samples decrased by incraesing concentration level on both methods. In general when anthocyanin content changes were evaluated during heat treatment and storage, anthocyanin degradation followed a first-order reaction model. Generally antioxidant activity decreased whereas polymeric color ratio and turbidity values increased depending on the storage at 4, 25 and 35 °C. HMF formation was determined in the samples storaged at 25 and 35 ºC, furthermore, amount of HMF also increased by increasing storage time and temperature. Furfural which is accepted as an off-flavor indicator in juice was determined as 0,050-0,660 µg/mL in concentrates storaged at 25 ºC (concentrates produced by thermal concentration) and 35 ºC (both concentrates). No remarkable changes were observed in pH, titratable acidity and color value during storage.