A Comparative Study on the Effect of Fermentation on Anti-Oxidative Properties of Thermal Processed Milk and Soy Milk

It has been shown that lactic fermentation of both milk and soy milk could boost their ant oxidative properties، in our previous study، using a native strain of lactobacillus planetarium for ultra-high-temperature (UHT) processed milk and soy milk fermentation، resulted in an increase in anti-oxidative properties of UHT milk، where the output was opposite for UHT soy milk. Since the obtained results were not expectable، here، in this study the effect of fermentation of the given samples were studied using three different lactobacillus strains as well as using less heated commercial milk and soy milk. The objective of the present study was to compare the lactic fermentation effects on anti-oxidative properties of sterilized and pasteurized milk and soy milk using three different lactobacillus strains. Commercial UHT milk and soy milk and their pasteurized type of products were used; Lactobacillus acidophilus، Lactobacillus Plantarum and Lactobacillus Rhamnosus were used as the lactic cultures and DPPH radical scavenging effect was applied as anti-oxidative index. The DPPH radical scavenging effects of unfermented UHT and pasteurized soy milk were obtained as 31. 8 ± 6. 7 and 35. 9 ± 1. 0، respectively; such data، for milk were shown to be 15. 0 ± 2. 3 and 15. 2 ± 2. 4. For both UHT and pasteurized milk، by individual usage of all three strains، fermentation increased the anti-oxidative index. Accordingly، despite different types of fermenting microorganism، the average of the observed data were 24. 4 ± 4. 0and 25. 1 ± 5. 2; however، in sterilized soy milk، DPPH (1، 1-diphenyl-2-picrylhydrazy) radical scavenging activity decreased to 24. 4 ± 12. 1، whereas the pasteurized one showed a considerable increase in this property up to the value of 45. 0 ± 3. 5 after fermentation. Difference in fermenting microbial stains did not make significant difference on the change in antioxidant properties of soy and soymilk. The results of this study confirmed our previous results that lactic fermentation would reduce the anti-oxidative characteristic of UHT soy milk. The type of thermal processing must be considered as the main reason; the fact that after fermentation، the pasteurized soy milk just showed as increase in anti-oxidative property as the milk samples.