Studies On Thermal-expansion Property Of Millet Starch And Manufacture Of Cracker From Millet

The internal and external factors that affected thermal-expansion property of millet starch were systematically studied after the obtainment of quality indicators through statistical analysis. The possibility of making cracker from millet was discussed so as to provide a theoretical basis for the comprehensive utilization and improvement of industrial value of millet.Firstly, the correlation between sensory evaluation and measured parameters was analyzed after the determination of texture of crackers through both sensory evaluation and instrumental measurement. Results showed that there was a significant correlation between fracture energy and all indicators of sensory evaluation as well as the composite scores (P<0.01), which indicated that fracture energy could be used as an objective indicator to reflect the textural properties of crackers.Secondly, the processing conditions for thermal expansion of millet starch were studied. The impacts of degree of gelatinization, relative crystallinity, moisture content, expansion temperature and expansion duration on thermal-expansion property were investigated through single factor experiments using expansion ratio and fracture energy as indicators. Orthogonal array test based on single factor experiments was designed and optimal conditions for starch expansion were: gelatinization duration 25 min under 100℃steam, without retrogradation, moisture content 8%, expansion temperature 310℃and expansion duration 50 s.The effect of basic composition on thermal-expansion property was then researched and results demonstrated that both the presence of protein and lipid had negative impacts on expansion of starch. Overall, starch with amylose content of around 20% was most suitable for production of rice cracker. The quality showed a downward trend with the decrease in degree of polymerization of starch molecules. Starch that excessively hydrolyzed was not suitable for making cracker any more.Afterwards, the influences of common supplementary (sucrose, salt and bicarb) on thermal-expansion property of starch were investigated. We came to the conclusion that high dosage of salt and bicarb had negative impact on both taste and color of crackers although moderate adding amount could significantly improve the quality of product. 2% of salt and 0.2% of bicarb was appropriate. The addition of sucrose would inhibit the expansion of starch, which in turn influenced the texture of product.The thermal-expansion properties of starch esterifiable and crosslinked starch were also studied after chemical modification. The quality was significantly improved because of esterification. Starch with low degree of crosslingking showed better performance compared with native starch. However, product made from starch with high degree of crosslinking showed even poorer quality than that from native starch. In summary, moderate degree of chemical modification could improve the thermal-expansion property of starch, while excessive degree of modification had an opposite effect.Finally, we proposed two feasible options for industrial production of crackers from millet:①The millet was milled in a colloid mill after soaking in 30℃water for 24 h with changing the solution at intervals of 6 h. The precipitate after centrifugation was then mixed with 2% sodium chloride and 0.2% bicarb. The quality of product that made from above mixture was comparable to cracker on the market. The upper yellow material that was rich in protein could be used as raw material for protein recycling.②In order to retain the nutrition of millet to the greatest extent under the promise of ensuring product quality, we discussed the feasibility of making crackers with different proportions of rice, glutinous rice as well as starch acetate. Experimental results indicated that the quality of product could reach the standard of crackers on the market when the addition amount of rice, glutinous rice or starch acetate was 20%, 10% or 5%, respectively. The product could be accepted by consumers.