| Mechanically activated starch has many properties such as greater cold-water solubility, transparency and chemical reaction activity, lower viscosity and so on. At present, studies about mechanical activation are mainly on effects of technologcial conditions (such as rotational speed, ball milling time, ratio of starch to ball and so on) on physicochemical properties of mechanically activated starches, while there are few reports describing effects of starch varieties and moisture contents of starches on physicochemical properties of mechanically activated starches. In this present study, effects of starch varieties on the physicochemical properties and chemical reaction activity of cassava starch, maize starch and indica rice starch were studied. Moreover, effects of moisture content of starches on the agglomeration and physicochemical properties of maize starch and cassava starch during ball milling were studied, in order to understand differences of mechanical activation properties of starch varieties. The main results were as follows:1. Effect of ball milling treatment on the physicochemical properties of three kinds of starchAs the ball milling time prolonged, the starch granules were damaged and the particle size decreased gradually, thus causing the increase of reducing power, coldwater solubility and transparency and the decrease of apparent viscosity and crystallinity. Coldwater solubility, transparency and apparent viscosity of three kinds of starch had significant difference (p<0.05) under the same ball milling time. Reducing power of maize starch and indica rice starch had no significant difference before 75 h but had significant difference (p<0.05) at 100 h. Moreover, ball milling treatment had the most effect on the physicochemical properties of indica rice starch compared with cassava and maize starch.2. Effect of mechanical activation on the chemical reaction activity of three kinds of starchAs the ball milling time prolonged, the structure of starch granules were damaged and the particle size decreased gradually, thus causing the increase of reducing power and coldwater solubility and the decrease of molecular weight, apparent viscosity and crystallinity. The degrees of substitution (DS) of OSA starch esters were higher than that of native starch esters. After mechanical activation 5 h and 10 h, the DS of OSA maize starch esters and indica rice starch esters reached a peak. Interestingly, mechanical activation beyond 10 h had little further effect on the chemical reaction activity. As the ball milling time prolonged, the DS of OSA cassava starch esters first increased then decreased. The cold water solubility of OSA starch esters were as high as 40% and 92%. Therefore, mechanical activation proved a good method to improve starch reaction activity and prepare cold-water soluble compound modified starch.3. Effect of moisture contents on the physicochemical properties of mechanically activated cassava starch and maize starchCassava starch, maize starch with different moisture contents were mechanically treated 25 h with a ball mill. Effects of moisture content of starches on the agglomeration and physicochemical properties of starches during ball milling were studied and suitable moisture content for ball milling of cassava starch and maize starch was obtained. Starch granules agglomeration appeared more easily with higher moisture content. When maize starch and cassava starch were treated by ball milling with the moisture content of 6%～8% and 8%～13% respectively, the physicochemical properties changed most sharply. |
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