壳聚糖复合涂膜在柑橘贮藏期间的结构变化及其与果实的互作机制

Coating post-harvest fruits with edible polymers such as chitosan, which may form semi-permeable film on the fruits surface, are able to reduce water loss, control gas exchange, reduce respiration rate, thus extending the shelf-life of fruits. The preservation effects can be further improved by incorporation of nano-particles into coating matrix. So far, most studies focused on the effects of polymer coating on the physiological and biochemical parameters of fruits. However, little investigation has been carried out on the structural change of coating during storage. Our preliminary experiments did discover the changes in structures of chitosan and its nano-composite coatings on Citrus fruits during storage, which were related to the incorporated nano-particles and finally affected the preservation durability of coatings. Therefore, this project will firstly characterize the composite films prepared using Citrus peels as the matrix, in order to study the effects of the interface structure and nanocellulose content on the structures and properties of chitosan composite films; Secondly, chitosan/nanocellulose composite coatings will be applied to Citrus fruits of different varieties to study the effects of Citrus variety, coating method and storage temperature on the structural changes of coatings during storage; Simultaneously, the effects of structural changes of coatings on the physiological and biochemical parameters, as well as the nutritional quality of Citrus fruits will be studied; Finally, the interactions between coatings and Citrus fruits will be discovered. The results of this study would provide theoretical basis to develop edible coating for fruits preservation with high efficiency and long-term effect.

采用壳聚糖等可食性高分子对采后水果涂膜，可在其表面形成半透膜，以减少水分散失，抑制呼吸，延长货架期。在涂膜基材中添加纳米粒子，可调节涂膜透过性以提高保鲜效果。现有研究主要关注了涂膜对果实生理生化指标的影响，却很少探究其自身在贮藏期间所发生的结构变化。前期实验结果表明在涂膜柑橘的贮藏期间，其表面的壳聚糖及其纳米复合涂膜确实会发生结构上的变化，且该变化与添加的纳米粒子有关，并最终影响保鲜效果的持久性。因此，本项目首先以柑橘皮为基底制膜并加以表征，探究柑橘皮界面和纳米纤维素含量对壳聚糖膜结构与性能的影响；其次以涂膜柑橘为对象，考察柑橘品种、贮藏温度和涂膜方式（涂膜次数与时间点）等因素对柑橘贮藏期间表面涂膜的影响，明确涂膜的结构变化规律与机制；同时，考察涂膜的结构变化对柑橘果实生理生化指标和营养品质的影响规律，最终明确涂膜与柑橘在贮藏期间的互作机制，以期为开发高效持久的天然涂膜保鲜剂提供理论依据。

纳米复合涂膜因其效果显著、简便易行等特点在采后果蔬保鲜中受到了广泛关注。现有研究大多采用平板膜来研究涂膜的性能，并重点探究涂膜材料对果实采后生理生化指标的影响，却很少关注涂膜在果实贮藏期间所发生的结构变化，而该结构变化也会对果实贮藏品质产生重要影响。.因此，为探究成膜界面对涂膜结构与性能的影响，项目首先以柑橘皮和培养皿为基底分别制备独立膜，比较其结构和性能。结果表明，两种膜中，以橘皮为基底制备的薄膜具有较低的结晶度、粗糙的形貌、较高的阻湿性和较低的吸湿率，但纳米纤维素添加量对两种薄膜性能的影响趋势较为一致。.其次，以涂膜柑橘为对象，考察了柑橘品种、贮藏温度和涂膜方式（涂膜次数与时间点）等因素对柑橘贮藏期间表面涂膜的影响，发现不同品种柑橘果实表面的涂膜在贮藏期间均会出现微孔，果实的呼吸强度越高，贮藏温度越高，则微孔出现越早，说明微孔是由于果实呼吸和蒸腾作用造成膜的结构破损。添加纳米纤维素可提高膜的稳定性，推迟微孔的出现时间；进行二次涂膜可对膜结构进行加强或修复微孔，但随着贮藏时间的延长，微孔会再次出现。.最后，探究了涂膜出现微孔对不同品种柑橘以及不同贮藏温度、不同涂膜方式处理的果实生理活动和贮藏品质的影响。结果表明，涂膜出现微孔后，对果实的保护效果降低，导致果实的衰老加快，在贮藏后期腐烂率快速上升。通过添加纳米纤维素和在微孔出现前进行二次涂膜可有效提高涂膜的稳定性，进而使涂膜保鲜效果更加持久。但对于呼吸强度较高的果实，通过二次涂膜过度抑制其呼吸反而对其品质有不利影响。.本项目探究了成膜界面对膜结构和性能的影响，并重点研究了贮藏期间涂膜的结构变化及其与果实生理活动的相互作用，明确了涂膜的结构稳定性对其保鲜作用的重要影响，为涂膜保鲜机理提供了重要补充，对高效持久、绿色环保果蔬涂膜保鲜剂的开发具有重要指导意义。