气氛条件对玉米淀粉辐射改性的影响

为提高玉米淀粉的使用性能,采用⁶⁰Co-γ射线在氧气、空气和氮气条件下对玉米淀粉进行辐照处理,辐照剂量分别为1、3、5、7、10 kGy,测定玉米淀粉的粘度、羧基含量,并采用傅里叶红外(FTIR)和扫描电镜(SEM)进行表征分析。结果表明,随着辐照剂量的增加,玉米淀粉粘度逐渐下降,而羧基含量逐渐升高,其中,辐照剂量为1~5 kGy时,粘度下降较快,最大达到70%以上;辐照剂量为5~10 kGy时,粘度降低减缓。不同气氛条件辐照对玉米淀粉粘度的降低速度和羧基含量的增加速度有明显影响,且其影响程度按照氮气、空气和氧气次序逐渐增强,辐照为5 kGy时,与充氮辐照组相比,充氧辐照组玉米淀粉粘度值降低12.0%,而羧基含量相对增加比率达到107.7%;与原淀粉相比,在3种气氛条件下经5、10 kGy剂量辐照处理后,玉米淀粉分子结构和表面颗粒形貌皆无可见变化,但表征淀粉有序结构的FTIR量化指标1 047 cm^-1/1 022 cm^-1比值总体上呈下降趋势。综合考虑,辐照引起淀粉分子结构的变化主要发生在无定型区域,而氧气对此有促进作用,氧含量的增加有利于增强该区域内淀粉大分子的辐射裂解与氧化。通过调节辐射剂量和气氛条件,可以节约辐照加工成本,制备性能优良的变性淀粉,从而促进辐照技术在淀粉改性上的推广应用。

Influence of Atmosphere Conditions on the Radiative Modification of Corn Starch

In order to improve the performance of corn starch, corn starch was irradiated by ⁶⁰Co-γ rays under oxygen, air and nitrogen conditions. The adopted irradiation doses were 1, 3, 5, 7 and 10 kGy, respectively. The variation of viscosity and carboxyl content of corn starch were investigated. The morphology and crystalline structure changes were analyzed using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The results showed that the viscosity of corn starch decreased gradually while the content of carboxyl group increased gradually with the increase of irradiation dose. The viscosity decreased rapidly as much as 70% when the irradiation dose in the range of 1~5 kGy. The viscosity decreased much slower in the range of 5~10 kGy. Irradiation under different atmospheric conditions also had a significant effect on the viscosity and the carboxyl content of corn starch, and the influence of atmosphere was increased in the order of nitrogen, air and oxygen. With irradiation at 5 kGy under oxygen, the viscosity was 12.0% lower than that under nitrogen; meanwhile, the carboxyl content of relative increase ratio was 107.7% higher. As compared with the original starch, there were no visible changes in respects of the molecular structure and surface morphology among the three different atmospheres (irradiation dose = 5/10 kGy), but the quantitative index, which characterizes the order of corn starch structure via the FTIR peak ratio of 1 047 cm^-1/1 022 cm^-1,was generally decreased. The change of starch molecular structure caused by irradiation mainly occurred within the amorphous region, which can be promoted by the oxygen environment. The increase of oxygen content may enhance the cracking and oxidation of starch macromolecules in the amorphous region via radiation. By optimizing the radiation dose and the atmospheric conditions, it would save the irradiation processing cost and show higher yield of the modified starch. This study will provide technique support for the further practical application of irradiation.