PRESERVATION OF RAW BUFFALO'S MILK BY THE ACTIVATION OF LACTOPEROXIDASE SYSTEM AND ITS EFFECT ON YOGURT PREPARATION

ABSTRACT The perishable nature of milk is the main problem for collection of raw milk in developing countries, especially during summer season. In this study, naturally occurring lactoperoxidase system of raw buffalo's milk was stabilized by equal proportions of 10, 20 and 30 ppm of hydrogen peroxide (H2O2) and sodium thiocyanate (NaSCN) immediately after collection. The results of the quality control tests (i.e., total viable counts, titratable acidity, pH and milk stability) indicated that milk stabilized with 10, 20 and 30 ppm of H2O2 and NaSCN, stored at 40C, significantly (P < 0.05) increased the shelf life of raw milk up to 8 and 16 h as compared with control, which curdled within 6 h of milking. Later on, these stabilized milk samples were assessed for the preparation of yogurt by using a mixed culture of Streptococcus thermophilus and Lactobacillus bulgaricus. A significant (P < 0.05) reduction of lactic acid production was observed and the proportions of H2O2/NaSCN increased compared with control. This effectiveness was more pronounced with 20 and 30 ppm as compared with 10 ppm. The results of organoleptic evaluation showed that yogurt prepared from 10 ppm stabilized milk got the highest score. PRACTICAL APPLICATIONS This study reveals a significant effect of lactoperoxidase system on preserving raw buffalo's milk for more than 16 h at 40C as compared with control. Therefore, this system provides an opportunity for the collection of raw milk from wildly scattered remote areas where no proper transportation and chilling units are available. This system also seems to be useful for the collection of evening milk. However, both higher concentrations of hydrogen peroxide (H2O2) and sodium thiocyanate (NaSCN) showed deteriorative effects on yogurt starter culture activity for yogurt making. Only 10 ppm concentration proved to be suitable for yogurt preparation. Thus, it was concluded that minimum level of H2O2/NaSCN concentration is required for cultural activity in product development procedures.