【作者】 段华伟；

【导师】 王志伟；

【作者基本信息】 江南大学 ， 包装工程， 2010， 博士

【摘要】 我国的果蔬生产量连年稳居世界首位,但由于缺乏有效的采后包装保鲜措施,每年因此而损失的果蔬产品经济价值高达数百亿元。因不使用化学试剂处理和具有高效的保鲜性能,气调包装在水果的采后贮运和销售链中得到越来越广泛的应用。气调包装的效率和性能主要取决于对被包装水果产品生理特性的正确理解和包装件自身的合理设计。虽然国内外对鲜果气调包装已进行了大量的研究并取得了卓有成效的研究成果,但目前仍存在如下限制气调包装工程化应用的理论和技术瓶颈:(1)现有的水果呼吸速率模型形式复杂、参数多、预测精度低,能预测的变量少;(2)对于部分鲜果品种在气调环境胁迫下的呼吸特性和响应尚缺乏系统性的实验研究;(3)气调包装件的设计理论和设计方法仍停留在科研层面,尚缺少面向工程应用的气调包装设计理论和方法。本论文以番石榴、杨桃、荔枝和番木瓜为研究案例,在深入理解和把握呼吸代谢本质的基础上,针对不同呼吸类型的水果,把化学动力学理论和人工神经网络建模方法引入到鲜果呼吸速率预测领域,分别构建了形式简单、预测精度高的数学呼吸速率模型和可预测四元变量的人工神经网络呼吸速率模型。此外,本论文还系统地研究了温度和气调环境对番石榴、杨桃和荔枝呼吸特性的影响,并提出了一种面向工程应用的鲜果气调包装设计方法。论文的主要内容和主要结论包括如下五个方面:1.利用化学动力学速率方程分别为番石榴、杨桃和荔枝构建了呼吸速率预测模型,该模型能高效整合温度、CO2浓度和O2浓度三个变量对鲜果呼吸速率的影响;三种水果化学动力呼吸速率模型的O2和CO2反应级数分别为——番石榴:0.46和-0.30;杨桃:0.91和-0.24;荔枝:0.98和-0.32;做为对比,分别表征了三种水果的酶动力学无竞争型M-M方程呼吸速率模型;采用三个统计学指标对三种水果的两类呼吸速率模型分别在两个温度下进行了模型性能验证;结果表明,化学动力学呼吸速率模型具有很好的预测精度和模型效率,其性能明显优于酶动力学呼吸速率模型。2.研究了番石榴、杨桃和荔枝在模拟气调包装环境下的呼吸特性;三种水果的呼吸初值与温度之间的关系均遵循Arrhenius公式,呼吸初值的表观活化能为——番石榴:48.09 kJ/mol、杨桃:54.49 kJ/mol、荔枝:70.91 kJ/mol;三种水果呼吸初值的平均温度系数分别为2.00、2.11和2.55;番石榴和杨桃的呼吸商与温度之间呈良好的线性关系,荔枝的呼吸商与温度之间的线性关系不明显;呼吸商与温度之间的拟合方程为——番石榴:RQ = 4.82×10-3T - 0.432(r = 0.988)、杨桃:RQ = 5.60×10-3T - 0.609(r = 0.998)、荔枝:RQ = 1.00×10-3T - 0.730(r = 0.606);升高温度能提高三种水果的O2发酵阈值;实验温度范围内三种水果的O2发酵阈值为——番石榴:1.68% ~ 6.88%(5 ~ 30°C)、杨桃:5.90% ~ 6.62%(15 ~ 30°C)、荔枝:5.19% ~ 7.77%(5 ~ 25°C);CO2发酵阈值为——番石榴:18.04% ~ 14.97%(5 ~ 30°C)、杨桃:15.10% ~ 15.72%(15 ~ 30°C)、荔枝:13.67% ~ 15.83%(5 ~ 25°C)。3.利用人工神经网络理论与方法为番木瓜建立了包含成熟度、温度、CO2浓度和O2浓度的四元呼吸速率预测模型,并与四元二次多项式呼吸速率模型进行了性能分析和对比;研究了番木瓜呼吸行为对四个影响因子的敏感性和响应曲线;结果表明,四元二次多项式方程的预测性能超出了可接受范围,不适合用于构建番木瓜的四元呼吸速率模型,人工神经网络呼吸速率模型具有良好的预测精度和模型效率,可以用于模拟番木瓜呼吸对四元变量综合刺激的响应;番木瓜呼吸速率对四个影响因子的敏感性依次为:温度>成熟度> O2浓度> CO2浓度;四个影响因子对番木瓜呼吸速率均呈非线性影响,呼吸速率与温度、成熟度和O2浓度正相关,与CO2浓度负相关;番木瓜呼吸速率对15 ~ 25°C之间的温度、四成熟至八成熟之间的成熟度、21% ~ 15%区间的氧气浓度以及4%以上的二氧化碳浓度变化较为敏感。4.提出了一种面向工程应用的鲜果气调包装设计方法,开发了鲜果气调包装计算机辅助设计软件;提取八个对果蔬气调包装设计有重要影响的关键参数,组成四对关键参数比例,以关键参数比例之间的相互作用机理和相关模型公式为理论指导,提出关键参数比例法气调包装设计方法和分级设计指导原则;在关键参数比例法体系的基础上,构建了操作性强的“5 + 1”鲜果气调包装设计流程;以MATLAB为平台,开发了具有气体浓度动态模拟功能的计算机辅助设计软件。5.根据所提出的鲜果气调包装设计方法和流程,为番石榴设计了气调包装技术参数,并对设计效果进行了实验验证;实验结果表明,当包装内外气体交换达到动态平衡时包装内气体浓度值能够保持在设计目标水平附近,被包装番石榴的质量指标变化慢于未包装对照样品,未包装番石榴的保质期为10 ~ 15 d,气调包装番石榴的保质期为30 ~ 35 d,保质期被延长了一倍多。更多还原

【Abstract】 The yield of fruits and vegetables in China has continuously taken the first place in the world over recent years. There was an annual money loss up to tens of billion yuan in China due to the lack of effective packaging and protection for harvested fruits and vegetables. Because of no use of chemical reagent and high effectiveness, modified atmosphere packaging (MAP) has been increasingly applied to quality keeping for fresh fruits during the postharvest distribution, storage and retail. The effectiveness and performance of MAP heavily depends upon the proper understanding of the physiological properties of packaged commodity and the accurate design of the MAP itself. Although there is already a lot of work relevant to the MAP of fresh produce in China and other countries as well, theoretical and technical bottlenecks still presently exist when applying the MAP technology to engineering projects, including: (1) current models on predicting the respiration rate of fresh produce are complex in form with too many parameters and containing fewer variables, resulting in low prediction accuracy; (2) systemic experimental research is absent with regards to the respiratory responses of some fresh fruit varieties to modified atmospheres; (3) the theory and method of MAP design still remain on the level of scientific research and theory and method oriented to engineering application is lacking.Taking guava, carambola, litchi and papaya as case study, the dissertation developed mathematical respiration rate prediction models with simple form and high prediction precision and an ANN respiration rate prediction model that was capable of describing respiration rate as a function of four influencing variables, for fruits with different respiration patterns by introducing the chemical kinetics principle and the artificial neural network (ANN) into the field of respiratory prediction for fresh fruits on the basis of deep understanding and grasp of the essence of respiratory methmolism. Moreover, research work was carried out systemically to examine the effect of temperature and modified-atmospheric conditions on the respiratory characteristics of guava, carambola and litchi, and a new method on how to design the MAP for fresh produce was proposed with emphasis on engineering application. The main contents and research results of the dissertation consist of five parts as described below.1. Models that are able to easily incorporate effects of temperature, CO2 concentration and O2 concentration on the respiration rate were developed for guava, carambola and litchi by using the reaction rate equation of the chemical kinetics theory. The reaction orders of O2 and CO2 in the respiration models developed for the three fruits were: 0.46 and -0.30 for guava, 0.91 and -0.24 for carambola, 0.98 and -0.32 for litchi, respectively. As contrasts, respiration models based on the Michaelis-Menten equation of enzyme kinetics with uncompetitive mechanism were also parameterised for these three fruits. The performances of the two types of respiration rate model of the three fruit were validated at two temperatures through use of three statistical indicators. Results showed that the respiration rate models based on the chemical kinetics were of very good prediction accuracy and model efficiency, significantly better than those created on the enzyme kinetics.2. The respiratory characteristics of guava, carambola and litchi were studied under the environmental simulations of MAP. Relationships between temperature and the initial respiration rates of each of the three fruits were found in accordance with the Arrhenius equation. The apparent activation energies of the initial respirations for guava, carambola and litchi were 48.09, 54.49 and 70.91 kJ/mol, respectively, and the averages of the temperature coefficients were 2.00, 2.11 and 2.55 for guava, carambola and litchi, respectively. There was a good linear fitness between temperature and the respiratory quotient (RQ) for guava and carambola, and such a linear relationship was unobvious to litchi. The regression equations fitted for the respiratory quotients and temperatures were: guava: RQ = 4.82×10-3T - 0.432 (r = 0.988), carambola: RQ = 5.60×10-3T - 0.609 (r = 0.998), litchi: RQ = 1.00×10-3T - 0.730 (r = 0.606). Increases in temperature can enhance O2 fermentative thresholds of the three fruits. Oxygen fermentative thresholds of respirations of guava, carambola and litchi in the temperature range studied were 1.68% ~ 6.88% (5 ~ 30°C), 5.90% ~ 6.62% (15 ~ 30°C), 5.19% ~ 7.77% (5 ~ 25°C), respectively. Fermentative thresholds of CO2 of the three fruits’respiration were: guava:18.04% ~ 14.97%(5 ~ 30°C)、carambola:15.10% ~ 15.72%(15 ~ 30°C)、litchi:13.67% ~ 15.83%(5 ~ 25°C)。3. The theory and method related to ANN technology were adopted to create respiration rate prediction model for papaya, which taken into account four variables that have impacts on papaya’s respiration, namely, maturity degree, temperature, CO2 concentration and O2 concentration. The performance of ANN model was compared with that of a second-order polynomial model. The respiratory behaviours of papaya were analysed for its sensitivity and response to each of the four influencing factor studied. Verification result showed that the prediction performance of the second-order polynomial equation with four variables exceeded the limit of acceptance, and was thus not appropriate for the creation of multivariate respiration rate model for papaya. By contrast, the ANN model yielded a very satisfactory prediction result to predict the respiration rate of papaya subjected to the four influencing factors. The sensitivities of papaya’s respiration rate to the four factors in a descending order follow as: temperature > maturity degree > O2 concentration > CO2 concentration. Nonlinear correlations were observed between each of the four factors and the respiration rate of papaya. The papaya’s respiration rate was directly proportional to temperature, maturity degree and O2 concentration and inversely proportional to CO2 concentration. The respiration rate of papaya was more sensitive to temperatures between 15 ~ 25°C, maturity degrees of 40% ~ 80%, O2 concentrations ranging 21% ~ 15%, and CO2 concentrations higher than 4%.4. An approach for MAP design for fresh produce was proposed with emphasis on the engineering application. Based on which, computer-aided software of fresh produce MAP design was developed. Eight key parameters that have vital impacts on the MAP’s performance were extracted and four ratio pairs thereof were obtained. A method named key parameter ratio and a principle called grading-design for the MAP design of fresh produce were suggested in terms of the underlying mechanism of those parameter ratioes and related mathematical formulae. On the basis of the new design system, an operable routine called“5 + 1”procedure to design the MAP package for fresh produce was proposed. A computer-aided software pack desiged with the function of simulating time-varying gas concentrations within MAP was developed on the platform provided by MATLAB.5. Dimensional parameters of guava’s MAP were calculated according to the design method and procedure recommended in this dissertation. Experiments were carried out to verify the performance of the designed MAP. Results showed that the gas concentrations within the MAP were maintained around the expected gaseous levels when the gas exchanges across the MAP wall reached to dynamic equilibrium, and the packaged fruit samples senesced much slower than the unpackaged controls indicated by several quality indexes examined. The unpackaged fruit samples were found having shelf-life periods of 10 ~ 15 d, and the packaged ones 30 ~ 35 d, two times more than that of the unpackaged fruit.更多还原