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Ultrasonication, Microwave and Heat Moisture Treatments to Accelerate the Formation of Resistant Starch in Broken and Brewer Rice Flour
Thesis Abstract:
Broken and brewer rice, the by-products of rice milling, was developed into modified flour, which is expected to enhance its functional properties as well as economic value—namely, high-resistant starch (RS) rice flour. This research aimed to reveal the ability of combined microwave assisted processing, ultrasound assisted processing, and heat moisture treatments (HMT) to enhance RS contents and study its associated changes in the microstructural, crystalline, thermal, and pasting characteristics of the Ciherang variety’s broken and brewer rice mix flour.
Ciherang’s broken and brewer rice mix was chosen because Ciherang variety was one of the most cultivated rice varieties in Indonesia. A completely randomized design was used to obtain the best treatment combinations of ultrasound assisted, microwave assisted, and HMT processing, i.e., time, temperature, and moisture treatments each at three levels, in increasing RS content of rice flour. The best processing conditions for each ultrasound assisted, microwave, and HMT processing were selected further and combined to obtain the optimum RS contents of the flours. The changes in the microstructure, crystalline, thermal, and pasting properties of the five best modified flours with high RS content were analyzed.
The results showed that five best treatment combinations effectively increased RS of the native flours (1.89% d.b.). Ultrasound assisted processing of the flour with 20 percent moisture content with 10 hours of HMT increased the RS content up to 6.89 percent d.b., and with 12 hours of HMT flour 6.50 percent d.b. (p < .05). Combination of microwave assisted process of the flour with 20 percent moisture content and 10 hours of HMT increased RS up to 8.04 percent d.b. The use of microwave assisted process at moisture content of 50 percent for two minutes combined with eight hours of HMT at 90°C increased the RS content up to 7.22 percent d.b. and the use of 10 hours HMT at 90°C increased the RS content up to 9.25 percent d.b.
Significant structural changes of those modified flours were noticeable from the disappearance or reduced amount of non-starch particulates from the flour’s surfaces, more porous, and larger size matrices formation. Significant changes also occurred in the increased pasting temperature and the decreased peak viscosity. Modified flours showed lower breakdown viscosity (137.00–192.50 cP) and setback value (725.50– 1209 cP). Significant structural changes occurred as shown from the FTIR data that the combined treatment caused the decrease of crystalline area, with crystallinity ratio from 0.94 (native flour) to 0.86–0.91 (combined treated flours). The XRD data, however, showed only the combination of microwave and HMT flours experienced the decrease of crystalinity, with crystalinity percentage from 36.35 percent (native flour) to 32.55–35.20 (microwaved and HMT flours).