| Old stems of bamboo shoots, the residues after industrial processing, account for more than 50% of total bamboo shoots, and they are often disposed as waste materials, which has caused a great waste of resources. According to tests, old stems of bamboo shoots contained 71.73%(on a dry basis)total dietary fiber(TDF),which is a natural, safe and high quality source of dietary fiber. As people pay more attention to health, dietary fiber food will become one of the indispensable functional foods in our daily life. So there is a broad market prospect to develop products with dietary fiber. In this paper, old stems of bamboo shoots were used as raw materials. The following three aspects were involved:first, conditions to extract insoluble dietary fiber(IDF)from old stems of bamboo shoots; second, the physical and chemical properties of IDF modified by superfine grinding; and last, ultra-micronization IDF application in bread. The main results were shown as follows:1. The IDF from old stems of bamboo shoots was extracted by double enzymatic processing which was optimized by Box-Behnken central composite design experiments. The optimal conditions analyzed by Design-Expert 8.0.6 were shown: neutral protease addition 3278.96 U·g-1,hydrolyzing temperature 40.69?, and time 136.77min.The extraction ratio was 92.1%,and the purity of IDF was 90.6%.2. The influences on IDF with four different drying methods were studied. Results showed that the quality of IDF after freeze-drying process was superior, but it took a long time and cost much. The superheated steam combined with hot air drying was the most energy efficient and environmentally friendly process. Moreover, the quality and appearance of IDF processed by this way were better than those by the hot air drying, so it was an ideal drying method to process IDF from old stems of bamboo shoots.3. The IDF was crushed by vibratory crusher, and then the influences on its physical and chemical properties as well as its microstructure through superfine grinding were researched. The main results were shown as follows:(1)The water-holding capacity, oil-holding capacity and swelling capacity of the IDF treated with coarse grinding reduced by 28.17%,61.33% and 29.36% respectively, Its adsorption capacity of cholesterol and scavenging activity towards NO2- were decreased, but its cation-exchange capacity increased by 203.7%. The superfine grinding had little effect on the adsorption capacity of IDF to metal ions Cu2+and Cd2+, from 122ug·g-1 to 118 ug·g-1,from 224.6ug·g-1 to 220.1ug·g-1, respectively.(2)The picture of SEM showed that the ultrastructure of IDF shaped like small pieces, which had been destructed after treated with superfine grinding. And the infrared spectrograms of IDF showed there were characteristic absorption peaks of polysaccharides, so superfine grinding had no effect on the molecular structure of IDF.4. The application of the IDF treated with superfine grinding in bread was studied. The results were as follows:(1)Dietary fiber had negative effects on bread volume and texture, but had positive effects on the water ratio. Meanwhile, it could enhance the economic benefits. Through the sensory evaluation, the bread adding different amounts of dietary fiber was compared with the whole wheat bread on the market. It was found that comprehensive evaluation value of bread adding 3% and 6% of dietary fiber was higher than the whole wheat bread's. And high fiber bread owned high acceptance and good texture preserving.(2)The orthogonal experiment including three factors and three levels was conducted by selecting the addition of dietary fiber, the addition of bread improver and fermentation time. The optimal conditions statistically analyzed by Excel 2003 and DPS software were:The addition of dietary fiber 6%; the addition of bread improver 0.3%; and fermentation time 75min. Under these conditions, the specific volume of bread was 5.42 mL·g-1, comprehensive score was 90.15 points and the whole acceptability was good. |
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