Study Of Cleaning Process And Quality Control On Lettuce

This dissertation used chlorine dioxide （ClO₂） and ozone to investigate the effect ofwashing and disinfection on the quality of fresh-cut lettuce and find out the optimal treatmentconditions. The main results and conclusions are as follows:1. In order to select a suitable breed of vegetable, the paper investigated the changes ofseveral quality indicators on eight breeds of vegetables after washing. This result showed that:according to the microbiological, sensory quality and physic-chemical analysis （weight loss,vitamin C content, chlorophyll content）, lettuce was selected by the high nutrition value andthe difficult preservation.2. In order to study the effects of washing conditions and methods on the quality oflettuce, effects of different conditions （time, mode, temperature and dehydration process） ofwashing process on several quality indicators was evaluated. The results showed that: prolongthe washing time and decrease temperature in certain scope could effectively reduce the totalbacterial count of the lettuce. Multi-stage washing was far more effective than the continuouswashing. It could also effectively improve the sterilization rate by60s centrifugal drying afterwashing treatment. The suitable washing process was: lettuce washed at a low temperature（10℃） for60s twice after pre-wash, dried by centrifuge for60s, followed with sterilizationprocess.3. In order to study the effects of sterilizing conditions of ClO₂on the quality of lettuce,the paper found out the optimization condition by orthogonal design experiment used totalbacterial count as a factor, then investigated the changes on the quality of lettuce produttreated under the optimal sterilizing condition during preservation and monitored the residualchlorine content. According to the result of orthogonal design experiment, the suitabletreatment was: lettuce immersed in100mg/L ClO₂water for5min with a ratio of1kg lettuceto10L ClO₂solution at25℃. The lettuce’s quality was well controlled and the lettuce alsomet the limits of residual chlorine concentration （<3mg/L）.4. In order to study the effects of sterilizing conditions of ozone on the quality of lettuce,the paper first analyzed the features of ozone water solution, then investigated the changes onseveral quality indicators of lettuce after different ozone treatment. Results: ozone water had significant effects on killing the microbe on the lettuce, improving the senses evaluation, aswell as controlling the physical and chemical indicators. Moreover the concentration is moreimportant than the processing time. The optimal ozone treatment condition was: immersion in1.56mg/L ozone water for6min.