| The raw material used is Fujian Dioscorea opposita Thunb., and it is extruded by Twin-Screw Extruder under different condition of processes. The change of the pasting degrees and the radial expansion ratio、WSI、WAI of the samples are studied under the different materiel moisture content、the middle of barrel temperature、feed speed and screw speed. The physic-chemical characteristics and structure characteristics of the Dioscorea opposita Thunb. before and after the extrusion are studied. Based on these results, and combining with quality requirements (GB/T 30645-2014) of traditional cloud chip cake, the process and formula of yam cloud chip cake which use yam puffing powder have been explored. The main results are as follow:(1) Using yam powder as raw material, the technical parameters which influence puffed yam powder processing were studied. The effect of different screw speed, feeding speed, barrel middle the middle of barrel temperature, material moisture content on yam puffing extrusion rate, water soluble index, water absorption index and pasting degrees were considered.The results showed that the optimal parameters of each single factor are:the screw speed was 25Hz, the feed rate was 15Hz, the middle of barrel temperature was 170℃ and the raw materials water was 14%.(2)Using the RSM experimental design to optimized yam powder extrusion process parameters, and study the radial extrusion rate and the degree of gelatimzation of products. Using Design Expert 8.0.6 software to build a mathematical model, and determine the best process parameters of yam powder extrusion process and study how the interaction of factors affect the radial expansion rate and pasting degrees.The results showed that:the interaction of screw speed and feed rate、the interaction of screw speed and material moisture content and the interaction of the middle of barrel temperature and material moisture content have significantly effects on radial expansion rate;the interaction of screw speed and feed rate、the interaction of screw speed and the middle of barrel temperature、the interaction of screw speed and material moisture content and the interaction of feed rate and the middle of barrel temperature have significant impacts on pasting degrees. The optimum Response surface design optimization of process parameters:the screw speed was 25Hz, the feed rate was 16Hz, the middle of barrel temperature was 168℃, the material moisture content was 13.98%, under the best conditions radial expansion rate of was 3.65%, the pasting degrees was 89.38%.(3) The contents of water, starch, fat and protein of the yam powder have declined, and ash content basically unchanged after yam powder extrusion. The angle of repose and the angle of slid raised as the particle sizes decreasing, the angle of repose and the angle of slide after extrusion were increased compared with the originals, and they showed that yam powder is a general mobility powder. After extrusion, the water absorption capacity and the solubility of yam powder have greatly increased, as well as the pasting degrees, however its oil absorption capacity turned out to decline. The stability of puffed yam powder suspensions is better than the original. The absorption peak of the DSC gelatinization endotherm curves of puffed yam powder was lower than the original, showing that the extrusion processing can make it fully gelatinize. The yam powder paste before and after extrusion are pseudo plastic fluid, and the viscosity decreased significantly after extrusion. Extrusion make the structure of starch from elliptical one turn into a mutual adhesion irregular blocky structure. Extrusion is a physical change, and doesn’t change the original group. The puffed yam powder has an absorption peak at 1019.32 which the yam powder doesn’t have. The yam powder and puffed yam powder belong to the B-type crystal structure, extrusion may destroy the double helix stability of the original crystal structure.(4) The processing technology and formula about adding puffed yam powder to make yam cloud chip cake were researched. Experimental results showed the best formula of yam cloud chip cake is as follows:100g glutinous rice flour at baseline, the best accessories for each added were puffed powder 11%, sugar 60%, water 20%,sesame oil 1%, honey 5%. Using the optimal formula to produce yam cloud chip cake, the high sense value and the textural value can be got. Obtaining a more scientific and objective results by fuzzy sensory evaluation, then provide a theoretical basis and scientific guidance for industrial production. |
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