Study On The Safety Reliability Of Food Cold Chain Logistics

Aiming at the problem of lacking safety quantitative index in the research of food cold chain logistics system, based on related theories and methods of food science and system reliability, this dissertation builds up the safety reliability models of food cold chain, and applies these models to the design assessment and optimization of food cold chain logistics system.(1) Safety reliability models of food cold chain. It puts forward the concept of safety reliability of food cold chain, and constructs the safety reliability models of cold chain logistics unit (R= R0-d△T2t) and cold chain logistics system (Ri= R0-d(?)△Tj2tj), based on microbial growth model and dose-response curve. These models show that the failure rate of cold chain unit is proportional to the time and the square of temperature; the safety reliability of cold chain units are mutually independent, it only relats to their respective time and temperature yet unrelated to initial state of system and the other units. The system model also reveals that the safety reliability of cold chain system reduces gradually and irreveribly. Finally, it verifies the models by pasteurized milk cold chain experiment; the results indicate that this model can represent the safety of food cold chain.(2) The allocation design of safety reliability of food cold chain system. Non-cost constrained optimization model and cost constrained optimization model have been built on the basis of safety reliability model and the function of temperature and energy consumption. Moreover, a new heuristic algorithm has been designed to find the solution. Further, it studies the reallocation dicision of safety reliability of system. Safety factors of cold chain units are in accordance with their component importance.(3) Safety analysis and assessment of cold chain system based on safety reliability. The concept and model of safety reliability can be applied to determine the key unit of cold chain, shelf life and use-by date of food. It also can assess the safety of cold chain logistics system based on GO-FLOW method. With the sensitivity analysis of safety factors of food cold chain system, it draws a conclusion that the unit having maximum safety factor is just the key unit of cold chain. The safety reliability model also provides a new method to predict the shelf life and use-by date of food. Based on pasteurized milk cold chain experiment, it is known that use-by date of food is quickly shortened with the temperature rising and the sale is the key safety unit. It is necessary to control the temperature of refrigerated display cabinet not exceed 10℃and outer milk and inner milk should change position every day.(4) Food distribution optimization based on safety reliability. Through a comparative analysis of fixed quantity distribution and fixed time distribution, some intensive distribution operation strategies have been provided. Fixed time distribution model is better than fixed quantity distribution model for those foods that require high service level, however, fixed quantity distribution model is better than fixed time distribution model for those foods with low timeliness. A model of vehicle route problem with time window based on safety reliability has been built, and solved using max-min ant colony optimization algorithms. Used the safety reliability model and dateof pasteurized milk experiment, it studies distribution time, distribution temperature, stacked and reception of food. The results show that the milk temperature at the doorway and in the middle of carriage is lower than the milk temperature in the innermost of carriage. So, milk should not be stacked in the innermost of carriage but loaded at the doorway and the middle of carriage; distribution time of milk should be limited to no more than 12 hours; reception time should be shorten as possible and cold chain breaking must be avoided.(5) Food inventory optimization based on safety reliability. By means of safety reliability of fresh food, a food ordering model integerated with penalty function of expiration is put forward to study the ordering policies. A. The higher food safety requirement is, the shorter food ordering cycle needed. Perishables require the shortest ordering cycle under same storing condition. B. The larger food demand rate is, the shorter ordering cycle needed. Fresh food at high demand rate must take high frequency ordering rule. Yet, it is proper to prolong ordering cycle for those at low demand rate. C. The better food storing condition is the longer ordering cycle could be. As regards out-stock strategy, the safety of two rules, which are first in first out (FIFO) rule and minimum safety reliability first out(MSFO) rule, have been compared by the means of simulation. The conclusion shows that minimum safety reliability first out rule is much safer than first in first out rule.