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The influence of five different emulsifying salts on casein peptization (dissociation) and apparent viscosity of processed Gouda cheese was studied. Casein peptization was evaluated as peptization coefficient in the final product, while apparent viscosity was determined as flow behavior and consistency indices in the product during processing before cooling. Increasing moisture content and pH of processed cheese samples generally increases peptization coefficient, however the type of emulsifying salt showed to play an important role also. On the contrary, independently of the type of emulsifying salt, predictive regression models were suggested in order to express flow behavior index and consistency index versus chemical composition and pH. Increasing moisture content or reducing pH increases the flow behavior index. Consistency index, and thus the apparent viscosity, of processed cheese samples was increased when the moisture content was reduced, and when pH and the soluble casein content were increased.

This work focuses on the evaluation of commercially available rapid methods for determining frying oil quality. Five rapid methods differing in principle were selected: FOM320 (Ebro), PCT120 (3M), LRSM (3M), Fritest (Merck) and Viscofrit (Viscofrit). The performance of the methods was examined by use of 184 oil samples produced by controlled frying experiments. Twelve series of frying experiments (45 batches each) were performed in which the oil type (palm, sunflower and olive) and the food type (potatoes, zucchini and minced beef meat) varied. Control thermal oxidation experiments with the same oil types were also performed. Results of the rapid methods were compared to results of analytical methods determining legislation criteria. Namely, the total polar compounds and total polymer compounds were determined using High Pressure Size Exclusion Chromatography with and without prior separation of the polar fraction. Furthermore, determination of the free fatty acid concentration, acidity, viscosity and level of oxidation of the oils using UV spectroscopy were carried out. Principal component analysis and linear regression analysis were used in order to assess the obtained results. Comparison of the results of the rapid methods with the analytical ones showed differences in most examined cases. For many of the examined rapid methods the agreement of the results versus those of analytical methods depended on the food‐oil combination used in the frying experiments.

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