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. / Dairy Farmers of Ontario, Natural Sciences and Engineering Research Council.

The goal of presented dissertation has been complex analysis of changes in content of fatty acids, enzymatic and low-molecular antioxidants in apples and related evaluation of perception of originators of storage diseases for apples stored in various conditions. Main part of the work has been dedicated to study of the impact of storage of apples in modified atmosphere with reduced amount of oxygen and in reference “normal” atmosphere for six months. Next part of the work has been dedicated to study how apple storage in common, consumer affordable, conditions (storage in a cellar, in a refrigerator, and in room temperature) affects content of low-molecular antioxidants. For testing has been selected apple kinds Jonagored, Golden Delicious, Idared, Šampion, and Granny Smith. Within the scope of this work has been optimized the method for determination of fatty acids in plant material with higher content of wax. The measured values imply the apples are valuable source of many important nutrition substances like vitamins, provitamins and antioxidants. During the storage process these substances exhibit considerable protective function. Long-term storage, mainly in the atmosphere with reduced amount of oxygen (FAN), enables preservation of majority of these important nutrition substances depending on the kind of apple and conditions of storage. Freezing process is conservative to apples (mainly in the presence of protective substances), while in the process of drying the values of all monitored antioxidants decrease depending on temperature and conditions of drying. Upon the choice of the storage method one must consider nutrition, sensoric characteristic and consumer demands.