| Arillus Longan is arillus of Sapindaceae,Dimocarpus Longan Lour,which is popular with vast comsumer for its unique flavor and high nutritional and medicinal effects.Chinese longan fruit ripening in hot and humidity season during July to September,which is subjected to browning,decay,even losing commodity value as a result of strong metabolism and infection of pathogenic microorganisms after harvest.Drying is usually used as an important way to extend the shelf life and improve added value of fresh longan fruit.Longan pulps of Fujian cultivated longan(Fuyan)as the experimental materials in this proposal.Solar Assisted Heat Pump Drying(SAHPD)Technology was applied for longan pulps drying.Color protection technology of longan pulps was firstly studied,and then drying characteristics and technologies of longan pulps by SAHPD was investigated and optimized,and packing and storge conditions were also conducted.The results as follows:1.Studies on the color protection technology of longan pulps.The effects of blanching temperature,blanching time,composite color fixative on enzymes activities of longan pulps and sensory qualities of drying product by orthogonal experimental design according to the synthetic weighted mark method.The results showed that the optimal color protection conditions of longan pulps is blanched in water at 85 oC for 4 min,and then immersed into 0.1%phytic acid and 0.2%L-ascorbic acid composite color protecting agents for 40 min,the activity of PPO was completely inactivated,POD was almost inactivated,which can get the best color protecting effect.2.Drying way selected for longan pulps.Solar assisted heat pump drying(SAHPD),microwave vacuum drying(MVD),hot air drying(HAD),heat pump drying(HPD)were applied to study the effects on sensory quality,unit energy consumption and polysaccharides of longan pulps with synthetic weighted mark method.The result showed that SAHPD was optimal and choosed for subsequent study.3.Analysis of drying characteristic of SAHPD.The drying temperature,loading density,rotary speed and slice thickness on drying characteristics of longan pulps were mainly discussed,and the drying kinetics model model was also established through model fitting during drying process.The results showed that the temperature,loading density and thickness have significant effects on the drying rate,while the rotary speed has little effects.Midilli&Kucuk model(MRF＝aexp(-ktn)+bt)was suitable for accurately predicting the change of water content ratio for longan pulps in the process of SAHPD drying.4.Optimization of longan pulps drying by SAHPD.To optimize SAHPD longan pulps parameters,a quadratic regression rotation design with three important factors,loading density,drying temperature and thickness of longan pulps,was used to investigate the response variables of drying time,specific energy consumption,polysaccharide content and sensory quality.Moreover,response surface method(RSM)was applied to optimize processing methods for SAHPD of longan pulps and to obtain a desirable product.The optimum drying conditions of SAHPD on longan pulps were as follows:the loading density was 1.48 kg·m-3,drying temperature was 65oC,thickness of longan pulps was 3.2 mm-3.6 mm.Under these optimum conditions,drying time,specific energy consumption,polysaccharide content and sensory quality were found to be 693.23 min,23.58 kJ·g-1 H2O,17.20%and 82.5,respectively.At the same time,compared with hot air drying(75℃),the energy consumption of SAHPD was saved more than 6 times and polysaccharide content was improved 30.85%.5.Discuss about packing and storge conditions of dried longan pulps.The water content,packing methods and storage conditions on total germ of longan pulps were studied.And then obtain the best packing and storge conditions by orthogonal experimental design.Dried longan pulps water content 12%,vacuum-packing method and storage temperature ℃ were the best storage conditions.When stored at 25℃,the shelf life of the untimate products was predicted to be 417 days. |
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