Min Wu

Optimization of twin-screw extrusion process to produce okara-maize snack foods using response surface methodology

Okara-maize flour blends were extruded in a co-rotating twin-screw extruder in order to assess their suitability as snack foods. Response surface methodology (RSM) using a central composite design was used to evaluate the effects of process variables (extrusion temperature (120-180°C), screw speed (100-180 rpm) and feed composition (20-40 percent ww) and moisture content (14-22 percent ww)). Multiple regression equations were developed to describe the effects of each variable on product responses. The product characteristics such as bulk density, expansion index, appearance (colour, porosity), flavor (aroma, grittiness and off-odor), texture (hardness, crispness and brittleness) and overall acceptability were determined through experiments and sensory analyses. Through superimposed RSM contour map, it was found that the feed composition with 30 percent okara content, 14.5-19.3 percent moisture content and the extrusion temperature 120.0-171.2°C and screw speed of 140 rpm, respectively to be the optimum extrusion conditions. The sensory tests showed that the products extruded at the optimized condition had the best appearance, taste, texture and overall acceptability. These results show that the okara-maize blends can be extruded into acceptable snack foods.

Removal of Flaxseed Mucilage by Extrusion and Enzyme Treatments

Mixture of flaxseed meal and corn flour (90/10, w/w) was extruded at a feeding rate of 33.1kg h-1 and different die temperatures (80-160 oC), screw speeds (300-900 rpm), and initial moisture contents(18.8-35.1%) on a co-rotating twin-screw extruder. Extrudates with the maximum removal rate of mucilage of 60.3% and lesser bulk density of 0.647 g cm-3 were obtained at screw speed of 500rpm, temperature of 140°C and initial moisture content of 25.1%. The micrographs of the extrudates showed that the greater structure dispersal occurred at higher temperature and lower initial moisture content. Mucilage extracts of enzyme-treated extrudates contained less viscosity than that of unextruded meals. The solubilization of mucilage increased with the increase in soaking time. 82.3% of the removal rate of mucilage was obtained after treatment with Pectinex Smash XXL at enzymatic loading of 200µl kg-1 for 6 h.

The digestibility and thermal properties of fermented flaxseed protein

Abstract The effects of solid fermentation conditions such as the incubation period, fermentation temperature, initial pH, and inoculum concentration on protease production and in vitro digestibility of flaxseed protein with Aspergillus oryzae 3.951 were reported. From 72h of fermentation at 30 °C, protease activity and protein digestibility were significantly increased. Maximum protease activity was obtained for high temperature-pressed flaxseed meal (HFM) and cold-pressed flaxseed meal (CFM) with initial pH 4.4-5.2, inoculum concentration 0.5×106 spores /mL. The results showed that the melting temperature (Td) increased by 4.8 °C and 7.6 °C for fermented CFM and HFM, respectively. In DSC tests, the enthalpy value is defined as the quantity of heat absorbed by samples during warming process. Results indicate that the enthalpy value of fermented samples significantly reduced from 186.5 J/g to 148.9 J/g (CFM) and from 187.0 J/g to 163.3 J/g (HFM). The result suggests that the lower molecular weight protein was degraded by protease, and the remaining were globulin with greater thermal stability and higher molecular weight.

Effect of Flaxseed Meal Addition on Dynamic Mechanical Properties of Rice Starch Films

Starch-based films have promising application on food packaging due to their outstanding performance with flexibility and transparency. On the other hand, the mechanical properties of starch films should be improved. The aim of this work is to enhance the mechanical performance of starch films by reinforcing the films with flaxseed meal (flaxseed fiber and protein). Films were prepared by casting technique, from film-forming suspensions of rice starch, flaxseed meal, glycerol and water. The dynamic mechanical method was used for measurement of the starch film samples. Films reinforced with flaxseed meal showed higher tensile strength, lower deformation capacity and higher the glass transition temperature (Tg) than films without flaxseed meal.