Influence And Control Of The Quality Of The Freezing Process On Papaya

Carica Papaya, a famous tropical and subtropical fruit which is rich in a variety of nutrients. It can be eaten raw and also can be cook, even used as medicine material. Papaya born more than a year, the production is very high, but it is easy to soften and corruption after picking, so it’s storage period is short. Currently, cool or modified atmosphere technology is applied to the postharvest storage of papaya, and there are certain extend of the storage period, but the decay rate remains high. Studies have shown that for some suitable fruit refrigerated and quick-frozen can well improve the storage quality of fruit, extend the storage period, low decay rate, etc. In this study, the papaya of Zhan Jiang were used as raw material, the feasibility of quick-frozen papaya process were studied. The main results were as follows:(1)The influences of maturity of the quality of the quick-frozen papaya have been studied. S1, S2, S3, S4, S5 five maturity papaya was selected, the degree of moisture loss 、L value were used as index, And through the sensory evaluation to analyze the quality characteristics of quick-frozen papaya block and papaya juice of papaya after frozen block. The results show that with the increase of maturity the moisture loss of quick-frozen papaya is increased, the moisture loss of S1, S2 maturity papaya is small, S4 maturity papaya is the largest;The L value of different maturity papaya were reduced as the extension of storage period, and make the overall retained the L value decreases with the increase of maturity. But the low maturity S1 and S2’s reduction of L value were bigger, it were reduced by 19.15% and 17.17% after storage of four months; The score of quick-frozen papaya block and the papaya juice of quick-frozen papaya were high by sensory evaluation on the color, smell, taste. Comprehensive above, the S3 was determined the most appropriate feedstock maturity.(2)The process of obtaining the optimal blanching technology of Carica papaya was studied. On the basis of the results of single factor experiment, the response surface regression with Design-expert 8.0 was used to optimize the blanching condition that could gain higher Vc retention rate and lower peroxidase(POD) activity.The test results indicated that at the blanching temperature of 100℃, 1.26 min blanching time,2.7 cm cutting size, the papaya Vc loss rate was 12.64%, relative activity of POD was 6.68%.After blanching treatment the quick-frozen papaya had a good Vc reserve level in storage period. By useing predicting optimum process conditions of testto verify the feasibility of the response surface method. Through the three groups of parallel experiment, the average of papaya enzyme activity relatively is 6.57%, Vc loss rate is 12.18%, within 5% error. Therefore the model accord with the actual basic, the response surface method can be applied to papaya blanching process optimization research.(3)The freeze features(freezing curve、freezing rate、the time through the largest ice crystals、freezing point) and the quality change of Carica Papaya under the different freezing conditions were investigated. Results showed that, Papaya’s freezing curve accord with general freezing characteristics of fruits and vegetables, can be divided into three stages; the freezing point is changed with the freezing rate, it is ranges from-1.1℃ to-1.7℃。The time through the largest ice crystals were all reduced with the increase of the freeing rate. The PH of the Papaya were all reduced after freezing, and with the increase of the freezing rate, riploss, whiteness and browning degree decreased. And the freezing rate of VC, soluble solids content of papaya have little impact. Freeze on papaya PPO and POD enzyme activity has certain inhibitory effect, with the increase of freezing rate both of the enzyme activity are the trend of first increases and then decreases. According to the results of physical and chemical index and sensory evaluation, the high freezing rate to be helpful for maintaining the quality of the papaya.(4)The quality change of the quick-frozen papaya block under storage period was studied. with the extension of storage time the moisture loss rate of quick-frozen papaya is increased under different storage temperatures, and under the same storage time, the low storage temperature, the moisture loss rate is smaller, the moisture loss rate- 30℃<-25℃<-18℃(p < 0.05);Because of the oxidation of enzyme and the decomposition of nutrients, papaya browning degree increased with the extension of storage time, the lower the storage temperature, the smaller increase of papaya browning degree. As the extension of storage period, papaya sensory score under different freezing temperature is declined(p < 0.05), and the overall observation of quick-frozen papaya sensory score-30℃>-25℃>- 18℃, and the difference increases with the extension of storage period, four months after storage. Because of a shortage of fragrance,juice less, color becomes dark the quick-frozen papaya under-18℃ temperature got low sensory score, and the quick-frozen papaya block under-30℃ still has good eating quality; the Vc degradation activation energy E0 of papaya is 30.6898 kJ/mol, at-18℃ temperature storage of frozen the shelf period was 5.897 months,-25℃ environment storage shelf period was 7.1247 months, under- 30℃ storage shelf life for 12.2300 months. The aroma components of quick-frozen papaya under different storage period were studied, by using headspace solid phase microextraction combined with gc. With the extension of storage period, the kinds of alcohols and acids of the fragrance ingredient of papaya were reduced, the kinds of alkanes were increasing.