Design and experiment of aseptic packaging line of staple wheat food with analytic hierarchy process method

Abstract: A design of aseptic packaging system integrated as the end part of the staple wheat food product line is studied, in order to keep the quality of the staple wheat food in the period of the distribution and sale. There are 3 basic parts in the aseptic packaging system, i.e. drying unit, compound sterilization units and packaging unit, considering influence factors for the food quality during storage and circulation as well as fresh-keeping packaging technology. Three basic parts can be freely used for different kinds of staple wheat food. Four technical schemes of aseptic packaging line are established according to different kinds of drying, sterilization and packaging techniques. The 4 schemes are studied with the analytic hierarchy process (AHP) method. In the AHP analysis process, the hierarchy with 3 criteria i.e. working performance, economic efficiency and reliability, and 9 sub-criteria is established. Through evaluation and priority considering, the optimum scheme is chosen. The aseptic packaging line is carefully designed, which is composed of the infrared drying unit, compound sterilization units of ultraviolet (UV), low temperature, Ozone, packaging machine, and reasonable product flow. In order to achieve industrial production of aseptic packaging for different kinds of staple wheat food, the line can be program-controlled with adjustable parameters, such as drying time, drying temperature, sterilization time, UV illumination intensity and Ozone intensity. The aseptic packaging system is set up in accordance with the above optimum scheme by the AHP method. Chinese steamed bread made of flour with primary moisture content of 43% have been processed by the compound sterilization units of aseptic packaging system under the condition of 4℃, relative humidity (RH) of 50%-70%, UV illumination intensity of 90-100 μW/m2 and Ozone intensity of 40-60 mg/m3. For processed and the naturally placed Chinese steamed bread, the comparative tests of color, texture and bacterial quantity have been conducted. For color comparison, lightness, contrast by red to green, yellow to blue are determined, while hardness, elasticity and recoverability are for texture comparison. The results show that the Chinese steamed bread processed by the packaging line has better quality and less bacterial quantity than that naturally placed under 25℃ and 50%-70% RH. The processed Chinese bread is stored in the environment with 4℃ temperature and 50%-70% RH for the expected guarantee period of 20 d, and the total number of bacteria within it is 3.5 lg(CFU/g), which is lower than the upper limit 4 lg(CFU/g) of the defined by standard, so it can keep the good quality of steamed bread in the expected guarantee period.