Abstract
Abstract: The objective of this work was to evaluate the effects of whole milk microfiltration at low temperatures on bacterial counts and on its shelf life. The microfiltration process was evaluated at two temperatures (30 and 50ºC) and compared with the slow pasteurization process. Both slow pasteurization and microfiltration reduced the initial counts of aerobic mesophilic and psychrotrophic bacteria, as well as total coliforms in whole milk. Microfiltration at 50ºC was as effective as the pasteurization process, since it reduced the initial count of aerobic mesophilic bacteria in 4.4 log cycles; increased the product's shelf life, which reached 30 days without exceeding 1,000 CFU mL-1; and eliminated coliform counts at the temperatures of 35 and 45ºC, established by the Brazilian legislation. Microfiltration at 30°C reduced the aerobic mesophilic bacteria counts by 2.2 log cycles; however, Escherichia coli was found in the product, which exhibited a shelf life of less than five days. Therefore, microfiltration at 30ºC can be associated with thermal treatments, but, when applied alone, it shows unsatisfactory results.
Highlights
Membrane processes have been major tools in food processing for more than 25 years, making the food industry responsible for a significant part of the turnover of the membrane manufacturing industry worldwide (Fernández García et al, 2013)
Microfiltration at 30°C reduced the aerobic mesophilic count by 2.2 log cycles, being less effective than pasteurization, which decreased the mesophilic bacteria count by 3.78 log cycles
Schaffner et al (2003) reported that reducing the average initial microbial contamination level by 0.5 log can significantly reduce the fraction of milk samples that spoil after 14 days of refrigerated shelf life, when either mesophilic or psychotropic microbes are present
Summary
Membrane processes have been major tools in food processing for more than 25 years, making the food industry responsible for a significant part of the turnover of the membrane manufacturing industry worldwide (Fernández García et al, 2013). Membrane filtration is a pressure‐driven separation process that uses semipermeable polymeric or ceramic materials, in which part of the feedstock is rejected or retained, according to the pore size distribution of the membrane. Microfiltration uses pore size diameters of 0.2–2.0 μm and operation pressures of 0.05–0.2 MPa, allowing the retention of milk particles, such as somatic cells, fat globules, bacteria, and casein micelles (Walstra et al, 2005; Coimbra & Teixeira, 2010). The Southern Cone countries of Latin America have very particular characteristics regarding milk production and processing, but, overall, the microbiological quality of milk must still be improved. Due to large geographic extensions, for example, the microbiological count in this region is very irregular, oscillating between 1,400,000 and 1,000 cells per mL (Battaglini et al, 2013; Bolaños et al, 2014; Fagnani et al, 2014)
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