No abstract

A detailed kinetic study on the thermal inactivation of alkaline phosphatase (ALP) added into buffer and pasteurized milk and for ALP naturally present in raw cow's milk has been performed. Kinetic parameters (rate constant, k; decimal reduction time, D; activation energy, Ea; and z value) were evaluated based on the first‐order rate model at 50–80C. The temperature sensitivity of the kinetic parameters was evaluated considering the Arrhenius‐type Ea model. All kinetic behaviors were well described by the first‐order model (r2 > 0.91). The D values increased with increasing temperature. Higher temperatures resulted in higher rates of enzyme inactivation as indicated by lower D values and higher k values. There are significant differences (P < 0.01) among the D values for ALP in buffer and milk at treated temperatures. The rate of enzyme inactivation was much more rapid in buffer than in pasteurized milk. The evaluated Ea values for ALP added into the buffer and pasteurized milk, and for ALP naturally present in raw milk were 97.2, 149.9 and 207.8 kJ/mol, respectively. The inactivation kinetics of ALP during heat treatment was found to be dependent on the composition of the medium, and the time and temperature of the heat treatment.

Lauric acid esters of fructose were produced using immobilised lipase (EC 3.1.1.3; Novozym 435). A molecular sieve was used to shift the reaction towards the synthesis. The mono-, di-and higher esters of lauric acid with fructose were obtained and analysed qualitatively and quantitatively by highpressure liquid chromatography (HPLC). At a 5:1 molar ratio of lauric acid to fructose the amounts of monoester, diester and higher esters produced were 37, 53 and 98 mg respectively after 96 h of reaction time. After purification of the products by column chromatography the hydrophile/lipophile balance (HLB) values of fructose monolaurate and fructose dilaurate were found to be 8.95 and 5.3 respectively and their critical micelle concentration (CMC) values were calculated as 7.20 Â 10 À5 and 6.40 Â 10 À5 M respectively. The CMC values of esters obtained from the conductivity curve and the surface tension curve were significantly (P < 0.05) similar to each other. It was found that when the concentration of surfactant was increased from 0.25 to 0.50% (w/v), stabilisation of the emulsion also increased. Fructose dilaurate showed better stability than the other esters. Separation of the phases reached 70% within 30 h for the emulsion prepared with 0.50% (w/v) of this ester.

Analysis of 40 oil samples showed that 38 of them were contaminated with benzo(a)pyrene (BaP). Thirty of the 38 BaP‐contaminated edible oil samples did not have any label of a brand name. BaP content for the 38 contaminated edible oil samples were in the range of 1.22–74.89 ppb. Sixteen of the contaminated oil samples had BaP content of more than 10 ppb, which is the maximum tolerable limit for the Turkish Food Codex Regulation. BaP contents of samples for each type of oil were significantly different (P < 0.05) from each other.

The purpose of this study was to determine the effects of shear and cooling-heating rates on the rheological behavior of cocoa butter. Three different shear rates (25, 50 and 100 s -1 ) and two different cooling rates (1 and 10 °C.min -1 ) were applied for crystallization of cocoa butter at 20, 22 and 24°C. Also, effects of shear and heating-cooling rates were monitored during the cooling and heating cycle between 70-20°C. When the cooling rate was 1 °C.min -1 , viscosity reached the highest value of 0.6 Pa.s with a shear rate of 25 s -1 . A rapid rate of cooling generally led to nucleation at a lower temperature compared to slow cooling. It was observed that crystallization of Form V was improved by shear and induction time of crystallization decreased as the rate of shear increased. The longest induction period was obtained at 24°C. Effect of cooling rate was more significant at low temperatures (P < 0.05). It was also concluded that the crystallization behavior of cocoa butter was dependent on both shear and cooling rates under isothermal conditions.