Modeling the Heat and Mass Transfer during Frying of Gulab Jamun

Abstract

Mathematical models were developed for the heat and mass transfer phenomena during deep-fat frying of gulab jamun, a dairy dessert popular throughout the Indian subcontinent. Size, shape, core temperature, moisture and fat contents of the product were monitored at regular intervals during 8 min of frying. The heat transfer was described using both lumped capacity model and transient heat conduction equation. As the calculated Biot number for lumped capacity model was greater than 0.1, the convective heat transfer coefficient was determined using the transient heat conduction equation as 122.34, 116.12 and 94.10 W/(m2 K) at 135, 145 and 155C, respectively. The moisture transport was described using a partial differentiation equation analogous to the transient heat conduction. The moisture transfer coefficient, ranging from 10.41 × 10−6 to 14.35 × 10−6m/s, increased linearly with frying temperature. The Lewis number declined from 0.96 to 0.54 with increasing temperature, indicating that at higher frying temperatures moisture diffusivity gained predominance over thermal diffusivity. Fat uptake of the product followed fractional conversion first-order kinetic model. Practical Applications Gulab jamun, a popular dairy sweet of the Indian subcontinent, is processed by deep-fat frying of milk solids–starch dough balls, followed by soaking them in sugar syrup. Its manufacture is currently dominated by small-scale unorganized enterprises, leading to non-optimized process conditions and widely varying product quality. The present study aims at describing the heat, moisture and fat transfer during the deep-fat frying process of this product using mathematical models. The effects of process parameters, such as temperature and time, on thermal and mass transfer properties and diffusivities were evaluated. Such mathematical models provide information to food processing professionals that help in predicting and optimizing the frying process parameters of gulab jamun in order to achieve maximum energy efficiency and desired product quality.