Counteracting Recontamination of Pasteurized Milk by Methylated Soybean Protein

Methylated soy protein (MSP) was evaluated as an antimicrobial agent that can counteract the potential post-pasteurization contamination of milk during a 30-day cold storage (4 A degrees C) or 24-h room temperature storage (25 A degrees C) as compared to its native form (SP). SP and MSP were added to buffalo milk at 0.5\% (w/v) after pasteurization and before storage. Milk microbiological and chemical analyses were carried out either directly to follow the spontaneous microbial contamination or after artificial contamination with three pathogens (Escherichia coli O157:H7, Listeria monocytogenes Scott A, and Salmonella enterica subsp. enterica serovar Enteritidis PT4). Supplementation of milk samples with MSP (0.5\%) significantly (p < 0.05) and considerably inhibited the levels of the spontaneously proliferating bacterial counts, i.e., total viable and Enterobacteriaceae counts were inhibited by about 2.5 log CFU mL(-1), while psychrotrophic and pseudomonads counts were inhibited by 1.8 and 1.6 log CFU mL(-1), respectively, after 16 days of preservation at 4 A degrees C. Similar trend of effects were also produced after 12-18 h of milk storage at 25 A degrees C. MSP (0.5\%) nearly hindered the proliferation of the three inoculated pathogens in pasteurized milk during 16 days of storage at 4 A degrees C or 12-18-h storage at 25 A degrees C. Based on milk acidity, SDS-PAGE pattern, and microbiological analysis, it is concluded that supplementation with MSP (0.5\%) can prolong the shelf life of pasteurized milk from 6 to 16 days when stored under cold conditions and from 8 to 18 h under room temperature conditions.