Milk Orange-Juice Processed by Microwave Technology: Physicochemical Properties, Bioactive Compounds, Enzyme Activity and Browning Index

This study aimed to evaluate the effect of microwave heating on antioxidant activity, ascorbic acid, total phenolic compounds, carotenoids, angiotensin I-converting enzyme (ACE) inhibitory activity, carbohydrate-hydrolyzing enzymes inhibitory activities (α-glucosidase and α-amylase) and browning index of milk orange juice milk. Nontreated (T1) and conventionally-treated (T2, 75°C/15s) samples were compared to different microwave treatments T3 (65°C/15s), T4 (65°C/30s), T5 (65°C/60s), T6 (75°C/15s), T7 (75°C/30s) and T8 (75°C/60s). Differences were observed for all parameters evaluated (p<0.05), being conventional heating samples (T2) presenting the worst performance (62.09, 64.98, 27.15, 12,64, 44,0, 141.98, 0.048, 51.83) for α-glucosidase , α-amylase, dpph, acid ascorbic value, phenolics, carotenoids, browning and ace values while for the microwave-treated samples these parameters ranged from 66.56 to 75.33 %, 75.58 to 94.96%, 14.32 to 15.99 mg/100mL, 53.53 to 56.73 EAG mg.100 mL-1, 148.13 to 181.54% µg.100 mL-1, 0.030 to 0.033 and 61.06 to 76.07%, respectively. Principal component analysis (PCA) bidimensional map with confidence elipses presented 82.99% the total data variability at the first two main dimensions (72.90 and 10.08%, respectively) with the an overlapping confidence ellipses for al microwave heating samples while T1 and T2 confidence elipses presented separated, being associated all the microwave treated samples with the parameters evaluated, excepted browning index as it was related to T2 sample. The dendrogram generated by the application of agglomerative hierarchical cluster analysis (HCA) presented adequate quality (Cophenetic correlation 0.742) and showed the existence of 3 different groups: group I (T2), group II (T4, T5, T6, and T8) and group III (T1, T3, and T7). Microwave-treated samples T3 and T7 (65°C/15s and 75°C/30s, respectively) achieved similar results with the sample without treatment (T1) and seem the most interesting conditions to processing the milk-orange juice drink. Overall, microwave technology has proven to be an interesting alternative for pasteurizing milk-orange juice drink.