【作者】 吴昊；

【导师】 汪东风；

【作者基本信息】 中国海洋大学 ， 食品科学， 2011， 博士

【摘要】 新鲜的果蔬营养价值高,食用方便,但其在室温下货架期短,较易腐烂。虽然我国果蔬产量居世界前列,但由于受到保鲜储备能力的限制,致使水果采摘后在流通过程中损失严重。而且由于我国是一个果蔬生产大国,每年需要大量的有机磷农药用于防治果蔬病虫害。虽然有机磷农药在果蔬的增产保质上的作用很大,但是其残留带来的危害却不容忽视。因此,如何延长果蔬的贮藏期并减少果蔬表面农药残留,一直是人们十分关心的问题。壳聚糖是一种天然多糖类生物大分子,具有成膜性和其它多种优良的功能性质,被广泛应用于果蔬保鲜领域。但是,壳聚糖由于分子结构的特点,对果蔬涂膜保鲜时存在保水率较低的缺点,果实易失水萎蔫;同时,抗菌防腐也达不到保鲜的要求。壳聚糖因活泼基团氨基和羟基的存在,可以引入不同基团进行化学改性,生成多种不同的衍生物,改善壳聚糖功能性。本文利用金属离子和没食子酸对壳聚糖进行改性,提高壳聚糖的成膜性和抗氧化、抑菌能力,赋予其对有机磷农药的降解作用,并将改性后的壳聚糖应用于果蔬采后保鲜中。主要研究内容和结论如下。1.壳聚糖金属配合物的制备。以壳聚糖为原料,制备得到壳聚糖金属配合物。研究壳聚糖脱乙酰度和分子量及不同金属离子添加量对配合物成膜性和果蔬保鲜效果的影响。当壳聚糖分子量7.2×10⁵ D,脱乙酰度84%,浓度1%;锌离子起始浓度0.5mg/mL;铈离子起始浓度0.6mg/mL时,制备的壳聚糖金属配合物对果蔬有较好的保鲜效果,并且对果蔬表面有机磷农药降解率也较高。2.壳聚糖金属配合物的中试生产。中试生产的壳聚糖金属配合物为淡黄色粉末,不溶于有机溶剂,易溶于弱酸,不易溶解于强酸。分子结构主要是由壳聚糖分子上的-NH₂与Zn⁽2+0离子,-OH与Ce⁴⁺离子发生配位反应形成的。成膜性与实验室制备的壳聚糖金属配合物相比,膜的厚度、溶胀度基本没有太大变化;拉伸强度略有降低,断裂伸长百分率略有升高;水溶性和透光率明显提高;水蒸汽透过系数和氧气透过率显著下降。3.中试生产的壳聚糖金属配合物对果蔬的保鲜效果及对有机磷农药降解机理研究。壳聚糖金属配合物能很好的保持冬枣和苹果的外观、质地和营养成分,具有明显的保鲜效果;贮藏5天后,壳聚糖金属配合物对冬枣和苹果表面的有机磷农药降解率分别比空白高15%和20%以上。通过气相色谱-质谱联用、总有机碳含量分析和无机离子分析等手段对壳聚糖金属配合物降解有机磷农药的产物和机理进行了研究。结果表明,壳聚糖金属配合物对有机磷农药的降解途径主要是氧化和水解作用,包括将P=S键氧化为P=O键,将P-S、P-O键断裂等。最终的降解产物为CO₂、H₂O及一些无机离子。4.壳聚糖没食子酸衍生物的制备及对鲜切果蔬保鲜效果研究。壳聚糖没食子酸衍生物由没食子酸的羧基与壳聚糖分子上的氨基和羟基反应连接而成。在酸性、光照、低温条件下稳定,在强氧化剂、碱性和80℃以上高温条件下易分解。清除羟基自由基、DPPH自由基和超氧阴离子自由基的能力与没食子酸相当或略有提高;浓度为10 mg/mL时,对大肠杆菌抑菌圈大小达到11.44 cm。将其应用于鲜切苹果的保鲜实验中,能有效的抑制鲜切苹果酚类物质氧化,又可抑制多酚氧化酶的活性,从而达到延缓鲜切苹果褐变的效果;贮藏4天后,对鲜切苹果表面微生物生长的抑制率高于空白组30.56%。制备的壳聚糖衍生物具有安全、无毒、抑菌、可食用、可降解等多种特性,且来源广泛,能延缓果实采后衰老并降解果蔬表面的有机磷农药残留,在果蔬保鲜中具有广阔的应用前景。更多还原

【Abstract】 Fresh fruits and vegetables are rich in nutrition and can be eaten conveniently. But they are highly perishable in normal ambient conditions. The annual yield of fruits and vegetables of our country is very large. But the loss of fruit and vegetable is large too because of the poor storage capability. And the residual organophosphorus pesticides of fruits and vegetables will be a potential risk to consumers. So it is a concerned problem that how to prolong the shelf-life of fruits and vegetables and degrade the organophosphorus pesticides.Chitosan, a kind of natural polysaccharide biological macromolecule, has many outstanding properties and potential application in various areas. Chitosan could be considered as an ideal preservative coating material for fresh fruits and vegetables because of its excellent film-forming and biochemical properties. But when the chitosan is used to coat on fruits and vegetables to prolong their storage life, it has been forced to be associated with some shortcomings, such as low moisture-holding rate, fruits and vegetables dehydration due to its typical molecular structural feature. Moreover, simultaneous maintenance of quality of fruit and vegetable cannot be achieved along with the desired antimicrobial properties. Different groups of chitosan could be introduced for chemical modification to generate various derivatives due to the existence of active amino and hydroxyl groups. Therefore, chitosan was modified using metal ions and gallic acid to enhance the antioxidant and antibacterial activities and degradation ability of organophosphorus pesticides in our research.The main contents and conclusions are described as follows:1. The preparation of complex of chitosan and metal ions （CTS-M）. CTS-M was made from chitosan and some metal ions. The effects of deacetylation degree （DD） and viscosity average molecular weight （M.W） of chitosan and concentration of metal ions on film-forming property of CTS-M and the preservation quality of fruits and vegetables were investigated. The obtained results indicated that the CTS-M, which made from 1% chitosan with DD of 84%, M.W of 7.2×10⁵ D, and 0.5 mg/mL Zn²⁺, 0.6 mg/mL Ce⁴⁺, had the best fruit and vegetable fresh-keeping and organophosphorus pesticides degradation ability.2. Pilot production of CTS-M. The CTS-M prepared in pilot production was straw yellow powder. It couldn’t dissolve in organic solvent, but prone to dissolve in acidic solution. The CTS-M formation could be described as Zn²⁺ bound to amino group, and Ce⁴⁺ bound to hydroxyl groups of chitosan. Compared with the complex of chitosan and metal ions prepared in lab, the thickness and swelling ratio of CTS-M film didn’t differ significantly, tensile strength and water vapor permeability decreased, meanwhile, the dissolution ratio, oxygen resistance and transmittance increased by 10.59%, 67.39% and 5.04%, respectively.3. Effect of CTS-M on the preservation quality of fruits and vegetables and degradation mechanism of organophosphorus pesticides. The CTS-M had quite beneficial effects on the physiological quality and degradation of organophosphorus pesticides compared to chitosan and control. It could prolong the shelf-life and decrease the potential risk of jujube and apple safety. After 5 days storage, the degradation rates of organophosphorus pesticides on jujube and apple treated by CTS-M were above 15% and 20% higher than the control, respectively. Gas chromatography-mass spectrometry （GC-MS）, total organic carbon （TOC） and inorganic ions were used to analyze the degradation products and pathway of organophosphorus pesticides. Hydrolysis and oxidation were the main degradation pathway of organophosphorus pesticides by CTS-M, including the oxidation of P=S to P=O and the cleavage of P-S and P-O bonds. Complete mineralization was achieved in all cases and the final degradation products were CO₂、H₂O and some inorganic ions.4. The preparation of chitosan gallate （CTS-GA） and its effect on the preservation of fresh-cut apple. The conjugation of gallic acid （GA） on chitosan can be concluded that the gallate group of GA was successfully introduced onto chitosan via amino and hydroxyl groups. CTS-GA was stable under the conditions of acid, strong light and temperature below 80℃, whereas it was unstable under the conditions of basic, strong oxidation and high temperature. The studies on the free radical scavenging of CTS-GA clarified its significant antioxidant activity on free radicals, such as hydroxyl radical, DPPH radical and superoxide anion radical. CTS-GA showed antioxidant activity on free radicals close to or even higher than pure GA. The antibacterial ability of CTS-GA on Escherichia coli was studied. When the concentration of GTS-GA was 10 mg/mL, the antibacterial zone diameter against Escherichia coli was 11.44 cm. The effect of CTS-GA on preservation quality of fresh-cut apple was investigated. The results showed that CTS-GA had a quite beneficial effect on physicochemical and sensory quality of fresh-cut apple. And the antimicrobial activity of CTS-GA was higher than chitosan and GA. After 4 days storage of fresh-cut apple, the antimicrobial rate of CTS-GA was 30.56% higher than the control.The chitosan derivatives not only have multiple characteristics, such as, safe, non-toxic, antibacterial, edible, degradable, and the source of a wide range of easy to extract, but also control the aging of post-harvest fruits and vegetables and degrade the organophosphorus pesticides. Therefore, they have a bright prospect of application in the fresh-keeping of fruits and vegetables.更多还原