PROTEOLITIC BACTERIA ISOLATED FROM RAW MILK

Milk is an important product in the country's economic scenario, in addition to its nutritional importance, it has a relevant role in generating income and jobs for society. In view of this, it must be in good conditions for consumption; free from microbiological, chemical or physical contamination. Because it has several nutrients in its composition, milk offers excellent conditions for development of desirable, pathogenic and deteriorating microorganisms. Among these, mesophilic and psychrotrophic bacteria are the most worrisome, because they can cause deterioration and loss in the quality of milk and dairy products. One of the main causes of milk spoilage is proteolysis, a protein degradation process carried out by proteolytic bacteria, causing alteration of taste and odor, loss of consistency and gelatinization in the product. Therefore, the present research aimed to isolate mesophilic bacteria from raw milk obtained from dairy farms in the microrregion of Caxias, MA, Brazil; and to test their capacity for proteolysis. Samples of raw milk were collected from 4 dairy farms in Caxias, MA (one property) and São João do Sóter, MA (three properties). The counting of viable aerobic mesophilic microorganisms in milk samples was carried out by pour-plate technique in Plate Count Agar (PCA), incubated at 36°C for 48 hours, according to Normative Instruction 62 – Brazil, and the results were expressed in Colony Forming Units/mL (UFC/mL). After the count, 223 colonies were selected for the proteolysis test, so they were transferred to milk agar and incubated at 32ºC for 48h, the strains were considered positive when they presented formation of translucent halos around the colonies. The mesophilic bacteria count of the present study (CFU/mL) ranged from 5,0x103 to 1,2x107, averaging 3,1x106, being above the total stipulated by Normative Instruction 62 for refrigerated milk. However, the analyzed samples are not included in this standard, since the raw milk collected was not refrigerated, because in all the properties it is destined directly to the consumer, without going through the refrigeration process. Regarding the proteolysis test, 115 (52%) of the 223 colonies tested showed proteolytic activity. In this way, the importance of milk refrigeration imposed by Normative Instruction 62 is observed, since it contributes to milk quality, retarding the growth and multiplication of deteriorating microorganisms, which directly affect the quality of this product.