Effect of dry-crystallization method on the engineering properties of an instant mix for rice flake-milk pudding

Abstract

An attempt was made to evaluate the engineering properties of an experimental sample of dry crystallized rice flake-milk pudding convenience mix (prepared using an in-house developed mechanical unit) against a control (prepared using manual stirring). The prepared mixes were characterized for proximate composition and engineering properties. Analysis of the proximate composition of the samples showed marginal differences; protein and starch were slightly higher in experimental sample, whereas fat and sucrose content were slightly higher in control. However, both samples reported identical water activity in the range of 0.410–0.418. Particle size analysis revealed that the average mean diameter of control and experimental sample to be 2.55 and 2.49 mm, respectively. Experimental samples reported slightly higher values of lightness and lower Browning Index, clearly indicated that the control samples were marginally darker than the experimental samples. Angle of repose of control (26.28°) and experimental samples (25.15°) indicated that the samples had good flowability, and the parameter varied linearly with moisture content of the product between 3 - 9% (d.b.). Bulk, packed and particle densities of both the samples were found to decrease with increase moisture content while, flow behaviour indices such as Hausner Ratio and Carr's Index were found to increase with moisture content. This was indicative of a marginal reduction in its flowability with moisture content. Porosity was found to be slightly higher in experimental sample (56.80%) than control sample (54.77%). Experimental samples had higher thermal conductivity and specific heat than the control samples and the thermal properties of both the samples were found to be affected by moisture. X-ray diffraction (XRD) graphs yielded sharp peaks for both the samples indicative of the crystalline nature of sugar. Scanning electron micrographs revealed an irregular surface topology for the dry-crystallized mix. Higher degradation onset temperatures (178–183 °C) and lower monolayer moisture content (2–2.5g per 100g) revealed the shelf stability of product.