Study On Cooling-Type Drying By Hot-Air And Controlled Storage Conditions Of Diospyros Lotus Linn

Diospyros lotus Linn is one of the main wild fruits in China,which has rich nutritional value and health function.In this paper,Diospyros lotus L.in Hebei Province is used as the test material to investigate different kinds of cooling-type drying process by hot-air,storage process parameters and the mechanism of frost.The aim is to provide a theoretical basis for the commercialization and storage of Diospyros lotus L.,and reduce its rot and quality decline in postharvest.The main conclusions are as follows:(1)The drying rate of Diospyros lotus L.was significantly improved,the drying time was shorten,energy was saved and the quality of products was aiso maintained by cooling-type drying process by hot-air.The appropriate cooling-type drying process of Diospyros lotus L.: Diospyros lotus L.is firstly preheated at(40±1)? for 15 min,then dried to moisture content(41±0.5)% at(68±1)?,and dried to moisture content(37±0.5)% at(63±1)? and finally dried to moisturer content(35±0.5)% at(55±1)?.Compared with constant temperature(65±1)? drying,time can be shortened about 1.5 h,and the contents of total sugar,total phenolics and vatamin C,the rehydration rate and sensory quality of dried products were obviously higher.And the nutritional ingredients of Diospyros lotus L.were better preserved.(2)The appropriate storage process of Diospyros lotus L.: dried after the classification,packaged with the thickness of 0.12 mm polyethylene bag,and stored under the conditions of(0±1)? and relative humidity of 75%~80%.The moisture contents of Diospyros lotus L.were controlled in(39±0.5)%,(41±0.5)% and(43±0.5)% can achieve the effect of no moldiness and no frosting at 270 d,And their weight loss rates were respectively(0.93±0.25)%,(1.33±0.44)% and(1.05±0.47)%.(3)During storage at(0±1)?,The respiration rate,soluble solids,total sugar,total acid and total phenolics of Diospyros lotus L.showed a trend of increasing first and then decreasing gradually,but the content of Vc showed a decreasing trend all the time.When the moisture content was controlled at(39±0.5)%,(41±0.5)% and(43±0.5)%,the changes of physiological and nutritional indexes can be maintained at a high level and the quality declined slowly at 270 d.Moreover,when the moisturer content was reduced to(35±0.5)%,the hardness,chewiness,gumminess and adhesiveness of Diospyros lotus L.changed significantly,and the moisture content was controlled between(37 ± 0.5)% and(43 ± 0.5)%can be better to maintain the organization and taste of Diospyros lotus L..(4)The main ingredient of Diospyros lotus L.frost is carbohydrate.The contents of total sugar,fructose,glucose and mannitol were(600.28 ± 4.58)mg/g,(93.11 ± 2.10)mg/g,(387.61 ± 3.11)mg/g and(337.15 ± 10.19)mg/g.And its suitable frost-forming condition:(0±1)?,the moisture content of(35 ± 0.5)%,packaged with the thickness of 0.15 mm polyethylene bag,and tile placed.(5)The frost-forming mechanism of Diospyros lotus L.: Diospyros lotus L.that moisture content is(35±0.5)% was packed in 0.15 mm polyethylene bags and tile placed at(0±1)?for 60 days.Under this condition,the sugars of Diospyros lotus L.migrated from the inside to outside with the evaporation of water,and condensed into white frost under the conditions of low temperature and low humidity.And accompanied by the hydrolysis and conversion of sugars at the same time.In the acidic environment,sucrose was hydrolyzed to glucose and fructose and fructose was converted to mannitol partly.