Multiple-pass high-pressure homogenization of milk for the development of pasteurization-like processing conditions
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Multiple-pass ultrahigh pressure homogenization (UHPH) was used for reducing microbial population of both indigenous spoilage microflora in whole raw milk and a baroresistant pathogen (Staphylococcus aureus) inoculated in whole sterile milk to define pasteurization-like processing conditions. Response surface methodology was followed and multiple response optimization of UHPH operating pressure (OP) (100, 175, 250 MPa) and number of passes (N) (1-5) was conducted through overlaid contour plot analysis. Increasing OP and N had a significant effect (P < 0·05) on microbial reduction of both spoilage microflora and Staph. aureus in milk. Optimized UHPH processes (five 202-MPa passes; four 232-MPa passes) defined a region where a 5-log10 reduction of total bacterial count of milk and a baroresistant pathogen are attainable, as a requisite parameter for establishing an alternative method of pasteurization. Multiple-pass UHPH optimized conditions might help in producing safe milk without the detrimental effects associated with thermal pasteurization. Significance and Impact of the Study: Milk is usually heat-preserved, but certain thermal-related modifications in nutritional, sensory and functional properties may arise. Consequently, nonthermal technologies such as ultrahigh pressure homogenization (UHPH) are currently explored. As part of the scientific criteria needed to assess UHPH equivalency to thermal pasteurization, microbial reduction of both the most baroresistant pathogen and native milk microflora must be determined and processing conditions could be defined through multiple response optimization. Results from the present study show that optimized multiple-pass UHPH treatments are capable of a 5-D reduction of both spoilage and pathogenic flora in whole milk. © 2012 The Society for Applied Microbiology.