Quality Change Of Pineapple During Freezing And Storage

Pineapple is a kind of subtropical fruit which is seasonal,difficult to preserve,susceptible to blackheart.Postharvest fresh pineapple decays easily because of amounts of water and sugar with a short storage period.Cryogenic technology is one of the fruit and vegetable preservation means,which combined with osmotic dehydration could prolong the storage period of pineapple and improve freezing rate and quality.Osmotic dehydrofreezing was used to the processing of pineapple,we evaluated dehydrofreezing in pineapple in terms of different temperature,concentration,freezing temperatures.Samples were analyzed for quality parameters(mass transfers,drip loss,PPO,POD,titratable acidity,L-ascorbic acid content,color,sensory evaluation),freezing rate,thermal properties,volatile components and the quality change of osmotic dehydrofreezing pineapple in frozen storage period of five months also were evaluated.The main results obtained are as follows:(1)Glucose and sucrose were used for osmotic dehydration,and glucose was better than sucrose on the mass transfers.The best osmotic dehydration time was 2.5h,temperature was 30,and the increase of the osmotic solution temperature had a significant effect on the quality of the frozen pineapple.(2)Osmotic dehydrofreezing was better than that of traditional freezing in terms of freezing parameters and quality of samples.Sugar and pineapple flavor taste freezing permeability increasing,mainly in the osmotic dehydration could make samples' color better,improve the sensory evaluation,reduced the pineapple drip loss rate,and slowed down the degradation of L-ascorbic acid,total acid,and accelerated the polyphenol oxidase and peroxidase activity decreasing,rised samples' melting point,changed thermal parameters,improved the freezing rate.(3)Analyzd different temperature of-15,-25,-35,45,-55 and-65?,the temperature was below-35? can be quickly generated by the largest ice belt(less than 20min),considering the equipment requirements and energy consumption,the best storage temperature was-35?.Osmotic dehydrofreezing could shorten the freezing time,in which glucose was the better.(4)Compared with the traditional freezing,osmotic dehydrofreezing prevented the decrease of total phenolic content.it was the highest after the dehydration of glucose.The lower the water content was,the content of the solid content in sampleswas higher,the lower the freezing speed was.Some new volatile components were produced after different freezing treatment.Some of the volatile components diappeared after troditional freezing especialy esters.and the relative content of characteristic aroma components decreased.Osmotic dehydrofreezing could be a better way to keep the other aromatic components of pineapple.(5)In terms of color,drip loss rate,L-ascorbic acid content content,enzyme activity and sensory evaluation,the quality parameters of frozen pineapple was increased by osmotic dehydrofreezing.After 5 months of frozen storage,L-ascorbic acid C content of pineapple increased 29.58%~35.06%,juice loss rate reduced 6.66~10.97%,reduced the total color difference 18.43%~29.14%,titratable acid increased 13.895~28.18%,PPO and POD also was inhibited the enzyme activity,sensory evaluation increased compared to troditional freezing.(6)Osmotic dehydrofreezing pretreatment was of benefit on storage than troditional frozen storage.The permeate concentration can be used to maintain the quality of frozen pineapple,glucose was better for preserving the quality of pineapple than sucrose,permeate concentration of 50% was optimal conditions and the pineapple was still edible after 5 months storage on the temperature of-35?.This paper showed that osmotic dehydrofreezing is a kind of new technology,which can improve the freezing rate and quality of samples.It provided a theoretical basis and technical support for the application of osmotic dehydration pretreatment in the processing of frozen fruits.