Freezing-Point Storage Of Lettuce And The Preliminary Establishment Of Prediction Model Of Microorganisms

The post-harvested lettuce has a strong metabolism. So it requires an effective reservation way to keep it fresh. The research applied the lettuce as the experiment material and using the technology of freezing-point temperature storage to preserve the lettuce, aim at finding out the effect of the freezing-point temperature on the lettuce’s preservation quality and its antioxidant capacity. Meanwhile, it also preliminarily studied the microbes’ growth in the lettuce under the storage condition of the low and the freezing-point temperature. Hope it could provide some ideas and theoretical reference to ensure the storage quality of lettuce and the microbes’ safety as well as the prediction model. And the main research results are shown as below:1. Lettuce were packed into micro porous PE bags and stored at(-0.5℃) for 15 days after the pre cooling at 4℃ for 8 hours. Changes in weight losses rate, respiration intensity, chlorophyll content, TA, TSS and Sensory valuation were measured. Compared with the traditional storage, the results indicated that freezing-point storage postponed the decrease of weight losses rate, respiration intensity, chlorophyll content, TA, TSS and Sensory valuation scords. These results suggest that freezing-point storage may inhibition the metabolic rate and improve the effect of storage.2. To investigate the effect of freezing-point storage on antioxidation capacity of post-harvested lettuce, Changes in APX, CAT activity, ASA content, H2O2 content, superoxide anion radical formation rate, MDA content, and membrane permeability were measured. Compared with the traditional storage, the results indicated that freezing-point storage induced an increase in endogenous H2O2 content at the beginning of storage, enhanced the activities of APX, CAT, postponed the decrease of ASA content, inhibiting the accumulation of superoxide anion radical, MDA content. These results suggest that freezing-point storage may inhibition the metabolic rate and enhance the antioxidation capacity of lettuce, improve the time and effect of storage.3. With the modified Gompertz equation, the growth model of the total number of microorganisms was made. At the storage condition of freezing-point(-0.5℃),the model was made as log(Nt/N0)=0.818exp(-exp(1.937-0.413×t)),R2=0.9819. the model was remarkable significantly at the 0.01 level; At the storage condition of 4℃,the model was made as log(Nt/N0)=2.323exp(-exp(1.937-0.495×t)),R2=0.9874, the model was remarkable significantly at the 0.05 level. The models could describe the growth kinetics of the total number of microorganisms during the time of preservation. Combining the minimal spoilage level 4.2 × 107 cfu/g and total number of microorganisms’ growth model, the shelf life predictive model was established. We can predict the shelf life of the lettuce rapidly by calculating the number counted by microscope direct count method.