Browsing by Subject "water sorption"
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(2016)Stickiness of food powders is a major issue in food industry because it causes problems during processing and it deteriorates the perceptible quality. The literature review presents different stickiness testing methods and the reasons and mechanisms for stickiness. The aim of the experimental work was to investigate stickiness of milk powders. Five different spray-dried milk powders were studied. Powders were characterized by measuring the moisture content, water activity, particle size composition, surface fatty acid composition and water sorption. Stickiness was investigated with a viscometer and with penetration test. Glass transition temperatures (Tg) were also determined. The results were analyzed with the PLSR (Partial Least Squares Regression). LF WMP contained much more surface fatty acids (42.7 mg/g) than WMP (12.4 mg/g) though the bulk fat content was same in both powders. According to the BET-sorption models, lactose-free powders adsorpt more water than conventional powders. The glass transition temperatures were much higher in lactose-containing powders (RH 0 %, 84–87 °C) than in the lactose-free powders (RH 0 %, 32–40 °C). Fat content did not affect the Tg because fat is not a water adsorbing component. Critical relative humidity is for lactose-free powders from 6 to 10 % and for lactose containing powders 40 to 42 % at room temperature (25 °C). Viscometric method was used to determine stickiness curves. Lactose-free samples became sticky at much lower temperatures than lactose-containing samples. When comparing the Tg and Tsp of skim milk powders, Tsp was 11–17 °C higher then Tg in SMP and in LF SMP the difference was 34–51 °C. In the PLSR model the coefficient of determination R2 was 90.3 %, adjusted coefficient of determination R2 adj. was 80.7 % and the coefficient of prediction Q2 was 59.9 %. Only lactose content was important according to the variables important in projection (VIP) in the PLSR model. The experimental work indicated that viscometric method is an applicable way to determine powder stickiness curve. Glass transition temperature determination is also reasonable way to predict powders stickiness and sticky point temperature is slightly above the Tg. The study showed that sugar content affected more to stickiness than fat content.
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(2013)The literature review dealed with the composition of lingonberry, manufacture of juice powder and the effects of different carriers on properties of juice powder, especially glass transition temperature and stickiness. In addition, physical, functional and nutritional properties and the effect of storage conditions on juice powders were covered. The aim of the experimental work was to investigate the effect of spray- and freeze-drying and carriers on glass transition temperature and water sorption of lingonberry juice as well as the stability of vitamin C and phenolic compounds during drying and storage. The same amounts of maltodextrin (MD), whey protein isolate (WPI) or combination of MD/WPI in equal proportions were added to each sample. All samples were spray- and freeze-dried. After storage of powders at different relative humidities, glass transition temperature, water sorption, content of L-ascorbic acid and content of phenolic compounds were examined. Water sorption was examined by static and dynamic vapour sorption methods. The small particle size of containing WPI was problematic with spray-drying because not all of the powder in the drying air could be separated in the cyclone. Adding water back into the spray-dried samples was most difficult when the samples were stored at low relative humidities (0–11%). The smallest water sorption was observed with both static and dynamic vapour sorption methods in samples which contained only MD. Water contents of freeze-dried samples were lower than those of spray-dried samples. BET sorption isotherm described the water sorption behaviour of the lingonberry juice powders well. Glass transition temperatures of all samples decreased as the relative humidity increased. During storage, the amount of phenolic compounds in samples containing WPI remained the same, whereas the amount of phenolic compounds in samples with MD decreased. Enzymatic spectrophotometric determination was un suitable for determing L-ascorbic acid in lingonberry powder because the sample colour disturbed the measurement. MD and the combination of MD and WPI were suitable carriers in lingonberry juice. The amount of phenolic compounds in lingonberry juice powders were preserved well by whey protein isolate. Therefore, the spray-drying process should be developed in a way that brings about increase in particle size of powder containing WPI.
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