Prediction Model Of Shelf Life Of Yoghourt To Various Parameters During Storage

Yoghourt belongs to perishable food, the amount of relevant literatures about how to extent the shelf-life of yoghourt is huge, but the relatively literatures on the prediction of shelf life of yoghourt is small. Through the Accelerated Shelf-Life Testing (ASLT) measure the quality of yoghourt indexes, this topic establish the relationship between the index values and the corresponding shelf life for accurately prediction of the shelf life of yoghourt for exploratory study when fluctuating temperature. In addition, through simulation the situation under the relatively extreme environment and the interruption of cold chain in real life, the fluctuation temperature test can record the effect of keeping quality of yoghourt during storage.By using different prediction model of shelf life, it can predict the yoghourt’s remaining shelf life in different stored temperature conditions. Through comparing, get the result about the most appropriate prediction model of shelf life for yoghourt, provide reference of the field of prediction shelf life, it also provide the basis data of changed quality for further studies in yogurt shelf life. Research contents and results are as follows:1. At ASLT and the temperature fluctuation experiment which designed in advance, according to certain rules to record the change trend of quality indexes for two brands of yoghourts, the quality’s specific indicators are acidity、viscosity、pH value、the lactobacillus colony number and sensory evaluation value. The results are as follows: yoghourts’quality, as an evaluation index, cannot be accepted by the consumers is: acidity≥120°T, viscosity≤500rap/min, sensory evaluation value≤60. In the ASLT, the acidity of yoghourts gradually increased with storage time extended, accompanied by viscosity drops, pH decreases. With the storage temperature increased, acidity, viscosity and pH value of yoghourts’rate of change will be accelerated, the rate of decreased sensory evaluation value becomes quickly, the shelf life prediction of sensory evaluation is also greatly reduced. While the index of lactobacillus colony number, during the storage period, generally follows certain laws:initially, it grown slowly; substantial growth at the medium period; reduced at last. At fluctuations temperature test, the change rate of acidity, viscosity, pH value and sensory evaluation value are bigger than the ASLT storage period of the other days. The change rule of Lactobacillus colony number in fluctuations temperature test is the same as the ASLT’s. 2. According to the measured data of former, using Arrhenius correlation prediction models to analysis the physicochemical data and sensory evaluation value of two kinds of yoghourt which obtained in ASLT and temperature fluctuation test, it can draws the following conclusion:Acidity and sensory evaluation value can accurately reflect the quality and shelf life of yoghourt, Arrhenius prediction model can obtained the result that acidity is equal to114°T when yoghourts reach at the end of shelf life. Using Arrhenius prediction model to handle the acidity data which changed with storage time in temperature fluctuation test, it can obtain the shelf life of two kinds of yoghourts:the predictive value of shelf life for G yoghourt is X1=5.163d, the predictive value of shelf life for M yoghourt is X2=5.537d. When the sensory evaluation value Y=60, the result of shelf life value is close, respectively:predictive value of shelf life for G yoghourt X1=5.229d, predictive value of shelf life for M yoghourt X2=4.975d.3. According to the above results, I select acidity and the sensory evaluation value in ASLT to conduct Weibull hazard analysis, predict the shelf life of two kinds of yoghourt in different temperature. Then use the results to conduct reliability analysis, the results are as follows:use acidity index to conduct Weibull hazard analysis, when G yoghourt storage at5℃、15℃,25℃and30℃, the prediction of shelf life were24.52d,10.75d,9.31d and8.63d respectively. when M yoghourt storage at5℃、15℃、25℃and30℃,the prediction of shelf life were23.09d,10.76d,9.31d and7.13d respectively. Through life reliability analysis, the shape parameter of the acidity is independent with temperature, the predicting shelf life and storage temperature’s relationship is conformed to Arrhenius formula, failure rate is also generally remained within the normal range. In sensory evaluation value of Weibull hazard analysis, the prediction shelf life of two kinds of yoghourt is greater than the practical shelf life value. After the life reliability analysis, the shape parameter of sensory evaluation value is independent with temperature too. However, the relationship between predicted shelf life of G yoghourt and storage temperature can’t be well fitted to Arrhenius formula (R2=0.8781), so in this experiment, it can’t use sensory evaluation value for Weibull hazard analysis.