Application of pulsed electric field treated milk on cheese processing: Coagulation properties and flavor development

Raw milk cheeses have unique flavor and texture not obtainable in cheeses from pasteurized milk. However, cheeses made from pasteurized milk are widespread for public health reasons. Pulsed electric field (PEF) treatment as a non-thermal pasteurization method has shown its advantage over conventional heat processing. Understanding the effect of PEF on cheese making is crucial. This study firstly determined the effect of fat content in milk on the microbial inactivation by PEF treatment. Fat content showed different behavior on microbial inactivation by PEF at different temperature levels. At 5 to 35°C, milk fat content did not affect the microbial inactivation by PEF. However, from 45 to 55°C, microbial reduction in whole milk was lower than that in skim and 2% fat milk. Secondly, this study investigated the effects of PEF parameters and temperature on the inactivation of pathogenic microorganisms (E. coli O157:H7 and Salmonella enteritidis) in whole milk. PEF treatment indicated effective inactivation of E. coli O157:H7 and S. enteritidis in whole milk. The maximum reduction of E. coli O157:H7 and S. enteritidis was 4.1 and 5.2 logs, respectively at 30 kV/cm and 50°C. The inactivation kinetics for both bacteria was primarily exponential, except in some cases with some tailing. E. coli O157:H7 in whole milk was more resistant to heat-PEF treatment compared to S. enteritidis. Further on, this study determined the effects of PEF and temperature on the rennet coagulation properties (curd firmness, CF, and rennet coagulation time, RCT) of raw milk using the rheological approach. PEF treated milk showed better rennetability compared to thermally pasteurized milk in terms of CF and RCT. Finally, this work investigated the effects of PEF and temperature on the ripening properties (proteolysis) of raw milk cheese curd using the RP-HPLC technique and Cd-Ninhydrin method. Peptide and free amino acid analysis showed that PEF treated milk could give similar flavor to cheddar cheese as raw milk, superior to that of pasteurized milk. These indicated that PEF treatment could have a chance to supplement or replace traditional pasteurization process with minimum impact on cheese quality.