Relationships between light-treated cultures and lactose content in yogurt

The abilities of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus to decrease lactose content in milk after different light treatments have been compared in this study. Each one of cultures was treated by visible daily light, linear non-coherent polarized light or kept in dark. After fermentation lactose concentration was measured by ultrasound milk analyzer Lacto Scan. Experimental results show the decrease of lactose concentration in a range of 37,5% - 40,35%, dependant to the treatments and durations. There are significant differences in lactose concentration (p < 0,01) by cultures treated 40, 50 and 60 minutes, in relation to the kind of treatments. Each one of treatments in duration 30 show no statistical differences in lactose concentration (p = 0,05). Diagram of experimental results presents a percent of decrease in lactose concentration as a logarithmic function of the energy impute in the case of linear non-coherent polarized light.