The objectives of this study were to monitor the changes in rice properties during aging and to compare kinetic parameters related to some of those changes. Paddy of three low amylose rice varieties was stored at ambient (30 ± 2ºC) and chilled (8 ± 2ºC) temperatures for 9 and 18 months, respectively. Aging led to a decrease in solid loss, peak viscosity, breakdown, and adhesiveness and an increase in head rice yield, minimum cooking time, water uptake, volume expansion, pasting temperature, final viscosity, through viscosity, setback, and hardness. Low temperature storage efficiently retarded those changes. Data of the time-dependent changes in hardness, adhesiveness, pasting temperature, peak viscosity, and breakdown of all samples stored at 30°C were fitted well with the first-order fractional conversion kinetic model (R 2 = 0.77-0.98). Higher storage temperature resulted in greater rate constant (k; up to 9 times higher) of those changes.
ABSTRACT:In this study, the production and characterization of a biosurfactant from yeast Wickerhamomyces anomalus strain PY189 was carried out. The highest efficiency for biosurfactant production was found when the organism was grown in a medium containing 4% (v/v) soya bean oil and 0.4% (w/v) NaNO 3 at 30°C and pH 5.5 for 7 days. After 7 days of cultivation, W. anomalus PY189 was able to produce up to 0.57 g/l of biosurfactant as ethyl acetate extracts. The culture supernatant was able to reduce the surface tension of the culture broth from 42.5 mN/m to 36.5 mN/m with a critical micelle concentration of 204 mg/l. The crude extract of biosurfactants was then applied to the encapsulation of lemongrass oil. Emulsions of lemongrass oil in 20 mg/dl maltodextrin solution (oil:maltodextrin solution ratios of 0.2:1, 0.15:1, and 0.1:1) containing 0.8% and 1% (w/v) crude biosurfactant extract were stable for at least 24 h and had an average oil droplet size of less than 10 µm. Lemongrass oil microcapsules were later produced using a spray drying technique. This microcapsule exhibited microbial growth inhibition activity against E. coli, S. aureus, and Salmonella at 5% (w/v) concentration.
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