摘要
为探究澳洲坚果(Macadamia ternifolia F.Muell.)干燥过程中水分的变化规律,测定其干燥过程中的含水率,利用低场核磁共振技术研究了干燥过程中澳洲坚果的水分态及其分布,建立含水率与低场核磁总信号幅度的关系。结果表明:温度越高,澳洲坚果的干燥速率越大,达到恒质量的时间越短,但是比较干燥后澳洲坚果的品质发现变温干燥方式(30℃2 d→38℃2 d→45℃至结束)相对较好;在干燥过程中,自由水、半结合水的含量逐渐降低,结合水的含量先下降后有所上升;干燥过程中澳洲坚果内水分分布不均匀,水分由内向外扩散;拟合得到澳洲坚果含水率与低场核磁总信号幅度的线性关系方程的决定系数R2为0.904,经检验该曲线预测性较好(平均相对误差为5.89%),结果表明低场核磁共振技术可以用作澳洲坚果含水率的快速无损检测。
A moisture content of macadamia nuts needs to be reduced from the harvested approximately 25%to 5%or less for efficient storage and processing.Drying strategy can be widely used to produce macadamia nuts,while detecting the moisture change in real time.In this study,Low-Field Nuclear Magnetic Resonance(LF-NMR)and Magnetic Resonance Imaging(MRI)techniques were used to investigate the water conditions and distribution during drying.A relationship between moisture content and total signal amplitude of LF-NMR was established to systematically analyze the dry characteristics of macadamia nuts during drying.The results showed that the high drying rate and short time can be achieved to reach the constant weight for the macadamia nuts as the increase of temperature.The drying rate was high in the early stage(0-36 h),and decreased rapidly during a whole drying processing.Specifically,the drying rate decreased slowly in the middle stage(36-72 h),and then become constant in the later stage(72 h to the end),even close to 0.The high initial drying temperature can be easier to cause the cracking of the macadamia nuts’shell.Therefore,it is necessary to comprehensively evaluate the influence of various drying methods on quality indexes,the change of macadamia nuts’shell and commodity value.After evaluation,the variable temperature drying was better than the other four drying methods,where the specific process was:30℃2 d→38℃2 d→45℃to the end.MRI analysis revealed that the internal moisture distribution of macadamia nuts was uneven,and the water diffused outwards during the drying process.The water on the surface of macadamia nuts evaporated fast as the drying time increased.This change can cause a low moisture content on the surface,while a high moisture content inside the macadamia nuts.In any case,the overall moisture content of macadamia nuts can decrease for the purpose of drying,because the water inside the macadamia nuts can diffuse fast to the surface due to the presence of a water gradient.There were three states of water in macadamia nuts:free water,semi-bound water,and bound water.The content and state of three kinds of water indicated different changes during the drying process.Compared with bound water,free water and semi-bound water were easier to evaporate in the process of macadamia nuts drying.In addition,the drying rate also decreased rapidly with the decrease content of free water and bound water within 0-24 h.The bound water evaporated fast and the content of bound water was reduced at the early stage of drying.In the later stage of drying,the drying shrinkage made the semi-bound water closely bound with macromolecules,part of which was converted into bound water,indicating the increase in the content of bound water.The absorption peak shifted to the left because the water with weak binding force in macadamia nuts was dispersed,whereas the remaining water showed relatively strong binding force,with the increase of drying time.There was an obvious linear relationship between the moisture content of macadamia nuts and the total signal amplitude of the low-field nuclear magnetic resonance.The coefficient of determination R2 was 0.904,indicating good predictability.The findings demonstrated that the LF-NMR can be served as a rapid and noninvasive method to accurately predict the water content of macadamia nuts during drying process.
作者
陈文玉
穆宏磊
吴伟杰
房祥军
韩延超
陈杭君
郜海燕
金龙
Chen Wenyu;Mu Honglei;Wu Weijie;Fang Xiangjun;Han Yanchao;Chen Hangjun;Gao Haiyan;Jin Long(Institute of Food Science,Zhejiang Academy of Agricultural Science,Key Laboratory of Post-Harvest Handling of Fruits,Ministry of Agriculture and Rural Affairs,Key Laboratory of Fruits and Vegetables Postharvest and Processing,Technology Research of Zhejiang Province Key Laboratory of Postharvest Preservation and Processing of Fruits and Vegetables,China National Light Industry,Hangzhou 310021,China;Qiaqia Food Co.,Ltd,Hefei 260301,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2020年第11期303-309,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
浙江省重点研发计划项目(2018C02006)
国家自然科学基金(31571907)。
关键词
干燥
含水率
澳洲坚果
低场核磁共振技术
水分分布
drying
moisture content
macadamia nuts
LF-NMR(Low-field nuclear magnetic resonance)
moisture-distribution
