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Analysis of functional properties of protein isolates
Vojtasová, Tereza ; Diviš, Pavel (referee) ; Pořízka, Jaromír (advisor)
Proteins are an important part of the human diet, and a lack of them can lead to many health problems. Therefore, they are often added to enrich foods. For food applications, it is desirable to know the functional properties of the proteins used, as they can significantly affect the resulting quality of the final product. This bachelor thesis was focused on the determination of functional properties of some commercially available protein powders: pea, beef, hemp, rice, egg, soy, whey, and laboratory-prepared wheat bran protein powder, and their possible application in food industry. The theoretical part of the thesis described proteins, their functional properties, production, quality assessment, then plant and animal proteins and methods of characterization of protein isolates and concentrates. In the experimental part, individual determinations of functional properties were performed and their applications in food industry were discussed. The solubility of tested protein powders was variable, with the highest solubility observed in powders of animal origin. The lowest solubility was found at pH 3–5, where the isoelectric point of most proteins was located. Soy protein isolate showed the best water-holding capacity of 10.65 gH2O/g, foaming capacity of 109.6% and emulsion properties. It was followed by pea protein with a WHC of 5.32 gH2O/g. Wheat bran concentrate had the best oil holding capacity of 2.18 goil/g. Foaming properties varied considerably but showed a positive correlation with water-holding capacity. The emulsion activity was very similar for most of the protein powders, except for beef, hemp and rice protein which exhibited no good functional properties. Only the beef hydrolyzed collagen was fully soluble. The emulsion layer increased slightly after heat treatment for the proteins, which already formed quite stable emulsions, except for wheat bran powder. Hemp and bran protein powders were the most distinctive in color, while egg and beef protein powders were the lightest. Soy and pea protein isolates showed foaming and emulsion properties similar to egg white proteins, indicating their potential use as partial or total replacements for egg white proteins in food products. In conclusion, selecting protein isolates with suitable functional and sensory properties for a specific food application is crucial for successful consumer acceptance of the protein-enriched product.
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Senzorické vlastnosti sladiny
Piechová, Hana
Beer foaminess is one of the main sensory properties of beer. Polypeptides have a positive effect on foam formation, while lipids have a negative effect. The wort contains both types of substances, but it does not foam by itself due to a lack of carbon dioxide. The aim of the thesis is to find out whether there is any influence of a particular variety and year on the foaminess of the wort. 14 varieties of spring malting barley were monitored at nine locations from the harvest between the years 2020 and 2022. The foaming of the wort was measured on a 1-CUBE type FA device at the Research Institute of Brewing and Malting (Výzkumný ústav pivovarský a sladařský, a. s.). The found foaminess values of the wort were clearly influenced by 30% by year and by 33% by variety. What is statistically significant is that the lowest foaming rate of the varieties was found in the 2020 harvest. The average stability of the wort foaming was 170 s and for individual varieties it ranged from 111–220 s. The statistically significantly lowest foaming stability of the wort was observed in the Overture and KWS Amadora varieties, the highest values of the wort foaming were found in the LG Ester and Spitfire varieties. The KWS Amadora variety showed the greatest foaming variability (70%), the LG Stamgast showed the lowest variability (18.5%). The foaminess of the wort can potentially predict the foaminess of beer.
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