Dietary fiber (DF) has drawn the attention of researchers due to its significant health benefits. Over the past decade greater DF materials from fruits and vegetables are being introduced in the market because of the presence of associated bioactive compounds and balanced compositions. The physicochemical and functional properties of DFs always depend on the food sources, extraction methods and structure of DF. Garlic bulb is consumed worldwide because of its widespread medicinal and nutritional value. During harvesting period, garlic bulb yields a considerable amount of straw which is simply thrown or disposed, causing a severe environmental problem. Garlic straw, with similar compounds to garlic bulb, might be used as a novel source of functional DF. Composition analysis reveals garlic straw consists of 7.15% soluble dietary fiber (SDF) and 72.20% insoluble dietary fiber (IDF), which exhibit different physiological effects on human health. The health effects exhibited by IDF are often not as good as that of SDF due to their different physicochemical and functional properties. Therefore, the aim of this study was to improve the functional properties of IDF from garlic straw with ultrasonic processing technology. IDF was put into a 500 mL beaker and dispersed with 300 mL deionized water. The beaker containing the sample was placed in a thermostatic water bath at initial temperatures of 25℃ for 10 min. And then the mixture was sonicated in ultrasound processor with different liquid-sample ratios, ultrasonic powers and ultrasonic time. After the pretreatment, the mixture was stored at-20℃ and freeze-dried for later analysis. The optimum ultrasonic conditions were obtained based on the responses of glucose absorption capacity from single factor experiments and response surface methodology. The functional properties including cholesterol binding capacity, water holding capacity, oil holding capacity and water swelling capacity were determined. Scanning electron microscope (SEM) and Fourier transformed infrared spectroscopy (FTIR) were used to analyze the microstructure of IDF. Results suggest that liquid-sample ratio of 30:1, ultrasonic power of 700 W and ultrasonic time of 40 min were considered as the optimum ultrasonic conditions for preparation of IDF with good glucose absorption capacity. Under these conditions, the glucose absorption capacity and cholesterol binding capacity were increased by 12.8% and 45.0% compared to those without ultrasound treatment (P＜0.05). Ultrasonic-treated IDF exhibited better color, functional and physicochemical properties than untreated IDF with significant difference (P＜0.05). FTIR of control and ultrasonic-treated IDF was basically the same. Structural analysis from SEM indicated that ultrasonic treatment destroyed the microstructure of IDF from garlic straw. Findings from structural analysis revealed that the porosity and surface area of IDF were effectively improved by ultrasound, which proved to enhance functional and physicochemical properties of modified IDF. The positive effect of ultrasound may be useful for functional modification and utilization of DF from garlic straw.%为了增强大蒜秸秆膳食纤维的功能特性,采用超声波对大蒜秸秆的不溶性膳食纤维(insoluble dietary fiber,IDF)进行改性处理.以提高葡萄糖吸附能力为目标,利用单因素试验和响应面法优化大蒜秸秆IDF的超声改性条件,通过胆固醇结合力、吸水性、持油性及膨胀能力等来评价改性后IDF的功能特性,并通过扫描电镜和红外光谱分析其结构变化.结果表明:液料质量比30:1、超声功率700 W和超声时间40 min时,大蒜秸秆IDF的葡萄糖吸附能力明显提高,比对照组提高了12.8%,胆固醇吸附力则提高了45.0%(P＜0.05);超声处理所得IDF的色泽品质和物理化学特性也明显优于对照组(P＜0.05);超声处理和对照IDF的红外吸收光谱基本相同,电镜结果显示超声波处理使IDF的组织结构变得更加疏松,其表面呈现蜂窝状,有助于表现出较强的吸附性,从而赋予大蒜秸秆IDF更强的功能品质和物理化学特性.
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