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Hurdle technologies: microbial inactivation by pulsed electric fields during milk processing.

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dc.contributor.advisor Griffiths, Mansel W. Rodriguez Gonzalez, Oscar 2011-01-25T14:33:11Z 2011-01-25T14:33:11Z 2010-12 2010-12-07 2011-01-25
dc.description.abstract The application of non-thermal processes pulsed electric fields (PEF) and cross-flow micro-filtration (CFMF) continuous to be studied with the purpose of controlling microorganisms in milk. Trends suggesting increased adoption include the study of Food Safety Objectives as a safety criterion, the promotion of sustainable processing, and the implementation of hurdle strategies. While the advance of gentle processing is counteracted by the risk of enhanced resistance due to microbial stress response, several techniques can be applied to quantitatively assess its impact. The objective of this project was to evaluate the effectiveness of microbial inactivation by PEF and CFMF at various steps of milk processing including shelf-life, its comparison with high temperature short time (HTST) pasteurization, and the quantitative assessment of the cross protection resistance to PEF of Escherichia coli O157:H7. Some differences in mesophilics inactivation were observed in milks (fat contents between 1.1% and 3.1%). Increasing the PEF inlet temperature decreased the treatment time by three or two-fold. The combination of CFMF/PEF yielded similar microbial reductions as CFMF/HTST. Higher inactivation of the coliforms was achieved in homogenized cream (12% fat) compared to non-homogenized. The linear relation between electrical conductivity and nutrient content (fat and solids content) was established. In a parallel study the PEF/CFMF sequence resulted in higher inactivation of mesophilics compared to CFMF/PEF and HTST. The shelf life was acceptable for CFMF/PEF and HTST after 7 days, while enterics and psychrotrophs grew more after PEF/CFMF, thermodurics did after HTST. The growth and stress of Escherichia coli O157:H7 in lactose containing broths was monitored by absorbance and fluorescence expression of stress reporters. Growth was explained using a secondary model, and stress response using mechanistic and probabilistic models. PEF inactivation was evaluated following the Weibull distribution after the cells reached stationary phase or maximum fluorescence expression. Similar resistances were observed within the cells grown in lactose broth at 10, 25 or 40°C, as within stressed cells (starved or cold shocked). Cells grown at 45 °C were more resistant compared to the cells grown in acid, high salt concentration while the ones grown at cold temperatures were the weakest. en_US
dc.description.sponsorship Dairy Farmers of Ontario, Natural Sciences and Engineering Research Council. en_US
dc.language.iso en en_US
dc.rights.uri *
dc.subject Milk processing en_US
dc.subject Mathematical modeling en_US
dc.subject Natural microflora en_US
dc.subject Dairy products en_US
dc.subject Escherichia coli O157:H7 en_US
dc.subject Microbial inactivation en_US
dc.subject Cross-flow microfiltration en_US
dc.subject Pulsed electric fields en_US
dc.subject Milk en_US
dc.subject Hurdle technology en_US
dc.title Hurdle technologies: microbial inactivation by pulsed electric fields during milk processing. en_US
dc.type Thesis en_US Food Science en_US Doctor of Philosophy en_US Department of Food Science en_US
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