Optimization of pasteurized milk with soymilk powder and mulberry leaf tea based on melatonin, bioactive compounds and antioxidant activity using response surface methodology

Melatonin is a natural hormone which regulates human circadian rhythms and is presented in milk at low concentrations. To improve melatonin concentration and amounts of bioactive compounds in pasteurized milk (PM), soymilk powder (SMP) and mulberry leaf tea (MLT) were added using mixture design response surface methodology (RSM) and levels of SMP, MLT and raw milk (RM) were optimized. PM containing 4.50% SMP, 4.50% MLT and 88.80% RM gave the highest chemical compositions, bioactive compounds and antioxidant activity. Mathematical models of chemical compositions, bioactive compounds and antioxidant activity showed significant differences, whereas sensory attributes were not significantly different in all modeled parameters. Optimum levels were 3.90% SMP, 4.50% MLT and 89.40% RM. Verification of optimum proportions showed that experimental values of chemical compositions, bioactive compounds and antioxidant activity agreed with model predictions. Optimum PM contained melatonin (1.49 ng/mL), free tryptophan (0.26 μg/mL), and total phenolic content (0.72 mg GAE/mL) with high antioxidant activity when assayed by DPPH, ABTS and FRAP. Results suggested that mixture design RSM has the potential to optimize SMP, MLT and RM levels to obtain PM with increased amounts of bioactive compounds and high melatonin content.