Abstract:
Abstract: Lotus (Nelumbo nucifera), an aquatic crop, is an important economic plant in Asia and Africa. Lotus seeds are popular food ingredients to East Asian cuisine and are used extensively in traditional Chinese medicine and in Chinese desserts. There is rich source of C-type starch in lotus seeds. Starch gelatinization often occurs when starch granules are heated in an aqueous medium, a phase transition from an ordered to a disordered state. Starch gelatinization affects texture, nutritional value and porosity, which changes moisture diffusivity of porous materials significantly. On the other hand, gelatinized starch tends to an ordered crystalline structure during storage, which is termed retrogradation that affects acceptability and shelf life of starchy food. Drying is one of the major processes for dried lotus seeds, which could suppress activities of microorganisms, enzymes or ferments and maintain its nutrition content. Hot air drying is a complex process of heat and mass transfer simultaneously. A better understanding of starch thermal property and gelatinization of lotus seeds during hot air drying should help improve product quality and efficiency of drying process. The gelatinization properties of starch extracted from lotus seeds dried at different temperature (70, 80, 90 ℃) were determined at various water contents varied from 42.2% to 71.1% (g/g). and heating rates(5, 10, 15 ℃/min) by differential scanning calorimetry (DSC) in this study. DSC thermograms were determined from 40 to 120 ℃. DSC analysis revealed that a single endotherm denoted as G is observed in lower temperature region (60-80 ℃) when starch is heated in excess water of 71.1%w/w, and two combined endothermic peaks (G and M) are exhibited at 42.2% g/g. All gelatinization transition temperature, such as onset temperature (To), peak temperature (Tp) and end temperature (Te), increased with drying temperature and heating rate significantly. The gelatinization enthalpy (ΔH) of lotus seed starch increased with water content significantly and no significant difference was observed for either drying temperature or heating rate (P>0.01). The kinetic parameters (reaction order (n), frequency factor (Z) and activation energy (Ea)) were determined using Kissinger equation and Crane equation at different water. First-order reaction kinetics described non-isothermal gelatinization process of lotus seed starch well. Ea values decreased with water content from 42.2% to 71.1% were influenced by water content and drying temperature, and Ea values of lotus seed starch dried at 70 and 80 ℃, separately, were higher than those of starch extracted from fresh lotus seed dried at 20 ℃. Lotus seed starch gelatinization occurs throughout the hot air drying process, especially at higher drying temperature and at higher water content varied from 63%w.b. to 45%w.b.. This study would be helpful in optimization of lotus seeds drying process and in application of lotus starch in food industry.