Effect of particle size, concentration, temperature and pH on rheological properties of shallots flour
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ORIGINAL ARTICLE
Effect of particle size, concentration, temperature and pH on rheological properties of shallots flour S. Khushbu1 • C. K. Sunil1
Revised: 4 March 2020 / Accepted: 1 April 2020 Ó Association of Food Scientists & Technologists (India) 2020
Abstract Shallot flour was prepared and sieved into three different particle sizes of \ 180 lm (sample A), 180 lm (sample B) and 250 lm (sample C). Effect of concentration [0.5%, 1.0%, 1.5% and 2.0% (w/w)], temperature (20, 30, 40, 60 and 80 °C), pH (4, 7 and 10) and freezing (- 20 °C) on rheological properties of shallot flour were studied at increasing shear of 0.1–100 s-1. Effect of dynamic change in temperature (15–95 °C) was also measured at constant shear rate of 50 s-1. Power law (Eq. 2) model with coefficient of determination (R2) above 0.90, well described the rheological behavior of the shallot flour as a shear thinning, non-Newtonian fluid at different concentration, temperature and pH. All the samples had n values below 1 and increase in viscosity or consistency index (k) value with increase in concentration of the sample was observed, while inverse relation was observed when temperature was increased. All samples showed increase in k value when the pH of the dispersion was varied from acidic to alkaline condition. Viscosity of samples were found unaffected even after freezing in freeze–thaw cycle. These data show sample A to be most suitable for their application as thickener, having highest k value. The obtained research provides information for utilization of shallot as a thickener in various food industries. Keywords Shallot flour Shear thinning Consistency index Flow behavior index Thickener
& C. K. Sunil [email protected] 1
Department of Food Engineering, Indian Institute of Food Processing Technology, Thanjavur 613005, India
Introduction Shallot (Allium cepa var. aggregatum) is a type of onion which is widely cultivated globally in China, Asia and Europe. Onion bulb which is a primary edible portion that could be served as ethno-medicine and as a functional food, due to its unique taste, pungent flavor and nutritional properties (Dini et al. 2008). The fresh onion (Allium cepa) bulbs gets softened due to the presence of inherent enzymes, such as polygalacturonase and pectin methyl esterase and are also prone to pathogens during post-harvest (Coolong et al. 2008). Shelf life of onion can be effectively extended by drying of fresh onions to powder as well as chips. Various methods of drying were studied for preparing the dried form of onion like onion powder, strips etc., among these tray drying was found to be most effective, economical and feasible method. The composition of onion powder is very complex because of its nutritional and functional properties which holds better for its prospective sources of antioxidant, food ingredient, antibrowning and bioactive compounds. Major compound like polysaccharides in onion not only have strong biological activity, such as antioxidant property (Shi 2016) but also have anti-cancerous, an
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