Kinetics of colour and texture changes in Gulabjamun balls during deep-fat frying

Gulabjamun, a popular Indian milk sweet, is prepared by deep-fat frying of balls of dough made of khoa, wheat flour and baking powder, and subsequent dipping in sugar syrup. Kinetics of colour and texture changes in gulabjamun balls were investigated with regard to frying temperature (120, 130, 140 °C). Crust colour was evaluated in terms of CIELAB parameters L*, a*, b*, and ΔE, and rheological properties in terms of hardness, stiffness and firmness. Frying-induced surface browning was reflected in a decreasing lightness value L* as well as the ratio of yellow hue index b* and red hue index a* and total colour expressed in terms of ΔE, L* following a zero-order change whereas the other parameters, a first-order change. Increase in the texture parameters hardness and firmness followed zero-order reaction kinetics whereas stiffness rise followed a first-order reaction. The temperature dependence of reaction constants could be explained by the Arrhenius equation. Activation energy was also obtained for both the colour and texture changes, which were in the range of 24.5–77.6 kJ/mol. High correlations between colour and texture parameters were observed and it was concluded that L* alone could be used to predict the firmness of deep-fat fried gulabjamun balls.