| 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.
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