以毛竹为原料,在160,180,200,220 ℃下分别进行2,4,6,8 h的热处理,重点分析总糖、还原糖、游离糖,pH、吸湿性的变化,结合黑曲霉的霉变测试,揭示高温热处理竹材的霉变机理。研究显示:竹材中总糖和还原糖的质量浓度总体呈现出下降的趋势,总糖与还原糖的最低质量浓度分别为0.83和0.05 g/L,相比未处理竹材分别降低了68.7%和95.3%。同时,游离糖中的葡萄糖相比未处理竹材降低了13.5%; 木糖与阿拉伯糖分别下降了73.1%和77.9%。而且,竹材的pH呈现出逐渐上升的趋势,维持在5.07～6.13,呈现出有利于霉菌生长的弱酸性环境。但是,高温热处理增大了竹材的接触角,润湿性降低,能阻碍霉菌生长的水分供应。黑曲霉测试显示:热处理能在一定程度上延缓竹材的霉变速率,但在160,180,200 ℃时竹材的感染面积占比均超过了75%,防治效力为0。即使在220 ℃时,霉菌感染面积仍接近50%,防治效力仅为50.0%。研究表明,尽管高温热处理降低了竹材的润湿性,糖分也明显减少,在一定程度上抑制了霉菌生长的营养物质和水分供给,延缓了霉菌的生长速率,但是竹材中保留的葡萄糖、木糖及阿拉伯糖等,以及适宜的pH仍为霉菌生长提供了充足条件,导致高温热处理对竹材霉变影响不明显。
Because of its fast growth rate, renewable, high strength and easy processing, bamboo has been widely used in many fields of daily life, such as furniture manufacturing, building materials, craft supplies. However, due to its rich nutrients, such as sugar, protein and starch, bamboo is susceptible to fungi, bacteria and pests, resulting in the drawbacks of easy mold, decay and deformation, which limit the application fields of bamboo to a certain extent. Therefore, the mildew mechanism of heat-treated bamboo was explored by studying the changes of mass concentration, hygroscopicity and pH of residual total sugars, reducing sugars and free sugars in bamboo by high-temperature heat treatment process, and the mildew performance of the heat-treated bamboo on Aspergillus niger. As a type of raw material, the moso bamboo samples were heat-treated at 160, 180, 200 and 220 ℃ for 2, 4, 6 and 8 h, respectively, to analyze the changes of the total sugar, reduced sugar, free sugar, pH and hygroscopicity, and the mold mechanism of high temperature heat-treated bamboo combined with the Aspergillus niger mold test was investigated. This study revealed that the contents of the total and reducing sugars of bamboo displayed a decreasing trend, in which the lowest values were 0.83 and 0.05 g/L, respectively, which were reduced by 68.7% and 95.3% compared with the untreaded bamboo. Meanwhile, glucose in free sugars, xylose and arabinose were decreased by 13.5%, 73.1% and 77.9% compared to the nature bamboo, respectively. Moreover, the pH of bamboo gradually increased and maintained in the range of 5.07-6.13, providing a weak acidic environment favorable to the growth of mold fungi. However, the high-temperature heat treatment increased the contact angle and reduced the wettability of the bamboo, which can hinder the water supply for mold growth. The Aspergillus niger test showed that the heat treatment could delay the rate of the mold of bamboo to a certain extent, but the infected areas percent of the bamboo at 160, 180 and 200 ℃ were more than 75%, and the effectiveness of control was zero. The area infected by mold was still close to 50% even at 220 ℃, and the efficacy of control was only 50.0%. This study indicated that the high-temperature heat treatment reduced the wettability and the sugar content of the bamboo, which inhibited the nutrient and water supply for mold growth to some extent and retarded the growth rate of mold. However, the glucose, xylose and arabinose were retained in the bamboo and the suitable pH still provided sufficient conditions for mold growth, resulting in an insignificant effect of the high-temperature heat treatment on bamboo mold.
