Milk Processed by Pulsed Electric Fields: Evaluation of Microbial Quality, Physicochemical Characteristics, and Selected Nutrients at Different Storage Conditions

摘要

Pulsed electric fields (PEF) technology was used to pasteurize raw milk under selected treatments. Processing conditions were: temperature 20, 30, and 40 ℃, electric field 30.76 to 53.84 kV/cm, and pulse numbers 12, 24, and 30 for skim milk (SM), and 12, 21, and 30 for whole milk (WM) (2 /i,s pulse width, monopolar). Physicochemical parameters (pH, electrical conductivity, density, color, solids nonfat [SNF]) and composition (protein and fat content) were measured after processing. Shelf life of SM and WM was assessed after processing at 46.15 kV/cm, combined with temperature (20 to 60 ℃) and 30 pulses. Mesophilic and psychrophilic loads and pH were evaluated during storage at 4 and 21 ℃. Results showed minor variations in physicochemical properties after processing. There was an interesting trend in SM in SNF, which decreased as treatment became stronger; similar behavior was observed for fat and protein, showing a 0.18% and 0.17% decrease, respectively, under the strongest conditions. Protein and fat content decreased in WM samples treated at 40℃, showing a decrease in protein (0.11%), and an even higher decrease in fat content. During storage, PEF-treated milk samples showed higher stability at 4 ℃ with minor variations in pH; after 33 d, pH was higher than 6. However samples at 21 ℃ showed faster spoilage and pH dropped to 4 after 5 d. Growth of mesophilic bacteria was delayed in both milks after PEF processing, showing a 6- and 7-log cycles for SM and WM, respectively, after day 25 (4 ℃); however, psychrophilic bacteria grew faster in both cases.