การเตรียมและการประยุกต์ใช้ starch nanocrystals เพื่อเสริมแรงในฟิล์มสตาร์ชข้าวเจ้า

บทคัดย่อ

Rice starch nanocrystals were prepared by acid hydrolysis of rice starch with sulfuric acid at various concentration (2, 3, 4 and 5 M) at 40 ?C for 5 days. The optimal conditions of sulfuric acid hydrolysis to be obtained in the highest yield and smallest median size particle of starch nanocrystals was obtained when 3 M sulfuric and was used. Starch nanocrystals are generally observed in the form of aggregates having an average size around 3.97 ?m and higher crystallinity value in structure of the starch nanocrystals obtained from X-ray diffraction. Starch nanocrystals was used as a reinforced for rice starch film. The properties of the rice starch films were improved through the addition of starch nanocrystals. The result showed that the mechanical properties of the rice starch film were enhanced by the addition of starch nanocrystals indicated that introduction of starch nanocrystals increased the crystalline peak structure of rice starch film. Furthermore, increasing of starch nanocrystals content, the water barrier properties of the rice starch films was also improved. The glass transition temperature (Tg) shifted towards higher temperature with increasing amount of nanocrystals and the char yield of rice starch films was enhanced as starch nanocrystals increased. Therefore, addition of starch nanocrystals into the rice starch films can be improved the thermal stability of rice starch films. The results demonstrated that addition of starch nanocrystals 15% showed better properties including mechanical, water barrier and thermal properties. The properties of the rice starch films were improved through the addition of kaolin. The result showed that the mechanical properties, thermal properties and barrier properties of the rice starch film were enhanced by the addition of kaolin. Because of the introduction of kaolin increased the crystalline peak structure of rice starch film. The results demonstrated that addition of kaolin 15% showed better properties including mechanical, water barrier and thermal properties. Thus, the addition of kaolin can improve the properties of rice starch film like as the addition of starch nanocrystals at the same level. The influence of types (Palm oil, Margarine and Rice bran oil) and content (3, 6, 9, 12 and 15%) of lipids on water vapor permeability, mechanical properties and water uptake of rice starch films reinforced with starch nanocrystals at 15% were investigated. The barrier properties and water uptake of the rice starch films were improved through the incorporation of lipid. The results showed that the addition and increasing concentration of lipid resulted in a reduction in water vapor permeability of the rice starch films, due to the fact that, the water vapor permeability decreases with increasing hydrophobicity of the added lipid materials. However, increasing of lipid content, the mechanical properties were lower and reduced its ability to stretch. The incorporation of palm oil 3% showed better properties including water barrier and mechanical properties than other lipids. Moisture adsorption was more rapidly in the initial stage of moisture adsorption and a little of moisture was adsorbed when adsorption time increased. The incorporation of palm oil 3% showed significantly reduces the moisture sorption of rice starch film reinforced with starch nanocrystals 15% and the lowest value was observed when lower relative humidity and applied. Moreover, the lowest tensile strength of rice starch film was obtained when a high relative humidity was used. For application of rice starch films by wrapped around crackers and conditioned at 75% RH and room temperature (27?3?C) by placing them in desiccators over a saturated solution of sodium chloride. The results showed that when the storage time increased resulted in an increase of compression load of crackers in all cases. The grow is associated with a loss of crispness due to the hydration. Cracker wrapped with rice starch films reinforced with starch nanocrystals 15% and containing palm oil 3% showed lower reducing of crispness than rice starch film. Hence, cracker wrapped with rice starch film reinforced with starch nanocrystal 15% and containing palm oil 3% exhibited higher shelf-life (9 days) than cracker wrapped with rice starch films (6 days). Moisture content and water activity of cracker wrapped with all films increased when the storage time increased. However, the result demonstrate that moisture content and water activity of cracker wrapped with rice starch film reinforced with starch nanocrystals 15% and containing palm oil 3% were significantly (p<0.05) lower than cracker wrapped with rice starch film all storage time.

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