食品界

海南大学食品科学与工程学院陈卫军研究员课题组在椰青保鲜方面取得突破

近日，海南大学食品科学与工程学院陈卫军研究员课题组利用超声技术延长椰青贮存时间并保持椰子水的甜度，研究成果发表在Ultrasonics Sonochemistry（中科院1区TOP期刊，影响因子7.491），题为“Effect of Ultrasonic Treatment on the Activity of Sugar Metabolism Relative Enzymes and Quality of Coconut Water”，相关技术已申请专利《变温超声耦合密闭流体局部压差（UCP）灭酶处理的椰青保存方法》（申请号：CN202010102300.6）。

椰青中椰子水的甜度是评价椰青品质的重要标准。椰青采后贮藏过程中，由于本身代谢活动造成甜度下降是影响其保质期的主要原因。该研究利用超声(US)技术的穿透作用，结合椰青天然的封闭体系，营造一个局部高压的超声环境，降低椰青糖代谢相关酶的活性，从而达到延长椰青保质期的目的，并保持住椰子水的糖含量，提升椰青的口感甜度和商业价值，实现远距离投送的目的。

在该研究中，利用频率为20 kHz、功率为2400 W的高强度US处理嫩椰子。与对照组相比，超声处理的椰子水总可溶性固形物含量和糖酸比较高，其中蔗糖、果糖和葡萄糖含量较高，pH值和电导率较低。HS-SPME/GC-MS结果表明，US处理前后椰水中挥发性化合物含量无显著差异，风味没有明显变化。US抑制了蔗糖磷酸合酶、蔗糖合酶、酸性转化酶(AI)和中性转化酶等糖代谢酶的活性，其中AI失活最明显。圆形二色谱和荧光光谱表明，随着超声强度和时间的增加，AI分子的二级和三级结构被破坏，这一点由粒径的变化和扫描电镜证实。分子对接和分子动力学表明，US处理阻止了蔗糖和AI分子的识别和结合，从而抑制了蔗糖的分解。

图1 超声处理对AI的影响

海南大学吴纪林硕士研究生为第一作者，陈卫军研究员与张明老师为该论文的通讯作者，海南大学为主要完成单位。该研究得到海南省高层次人才项目（2019RC128）的支持。

摘要原文

Effect of ultrasonic treatment on the activity of sugar metabolism relative enzymes and quality of coconut water

Jilin Wu, Haiming Chen, Wenxue Chen, Qiuping Zhong, Ming Zhang, Weijun Chen

Abstract
In this study, tender coconuts were treated with high-intensity ultrasound (US) for 20 min at a frequency of 20 kHz and a power of 2400 W. Compared with control group, US treated coconut water had a higher content of total soluble solid and sugar/acid ratio along with a lower pH value and conductivity, and the contents of sucrose, fructose and glucose were also higher. Results from HS-SPME/GC–MS showed that there was no significant difference in the content of volatile compounds in coconut water before and after US treatment. The activities of sugar metabolism enzymes such as sucrose phosphate synthase, sucrose synthase, acid invertase (AI) and neutral invertase were inhibited by US, of which AI had the strongest inactivation. Circular dichroism and fluorescence spectra showed that the secondary and tertiary structure of AI molecule were destroyed with the increase of US intensity and time, which was confirmed by the change of particle size distribution pattern and scanning electron microscopy. Molecular docking and molecular dynamics showed that US treatment prevented the recognition and binding of sucrose and AI molecules, thereby inhibiting the decomposition of sucrose. In conclusion, our results indicate that US can inhibit the activity of AI and maintain the sugar content to increase the quality as well as extend the shelflife of coconut water, which will bring more commercial value.