Studies On Technologies Of Hot-air Combined Microwave Vacuum Drying Of Papaya Fruits

Papaya(Carica Papaya L.)is known as "fruit of the King",with its smooth and beautiful skin,rich aroma,abundant juice,sweet taste and rich nutrition.This thesis applied the hot air drying and microwave vacuum drying(MVD)technologies for drying papaya,studied the drying characteristics and dynamic models,optimized the hot air combined with microwave vacuum drying process,explored the law of adsorption and desorption isotherms and applied of HACCP(Hazard Analysis and Critical Control Point)principles for hazard analysis.1.The hot air drying process of papaya was studied systematically and it indicated that:The hot air drying process was affected by the hot air temperature,air velocity and thickness,the affect of the loadage was not obvious.It had only falling rate stage and drying rate of decline,without increasing rate and constant rate stages.The Page equation MR=exp(-rtn)could accurately describe the hot air drying process of papaya.2.The microwave vacuum drying rocess of papaya could be characterized three distinct drying rate regions:increasing rate region,constant rate region and falling rate region.Most of the time was concentrated in the constant rate stage.The whole process was affected by the microwave power,vacuum degree,thickness and loadage.The comparision of dry-basis moisture and MR between experimental and predicted date at the same condition were basically fitted,so the Page equation could be used to accurately describe the microwave vacuum drying process.3.The orthogonal test was carried out to inverstigate the optimum method of the hot air combined with microwave vacuum drying process,that was determined as follows:the hot air temperature was 60?,conversed moisture content was 40%,microwave power was 3 kW,vacuum degree was-80 kPa.Meanwhile,it compared the advantages and disadvantages of the hot air drying,microwave vacuum drying,hot air combined with microwave vacuum drying and vacuum drying and inferred that the hot air combined with microwave vacuum drying is a kind of popularization of drying technology.4.The equilibrium moisture content was affected by the temperature and equilibrium relative humidity.Equilibrium moisture content increased with increasing relative humidity at the same temperature and decreased with increasing temperature.The absorption and desorption equilibrium moisture content curves were almost end to end.Differences between the equilibrium moisture content range due to lag effct was 0%-5%(d.b).The Modified-Halsey equation could accurately describe the moisture isotherms of papaya and the Modified-Oswin equation could describe the desorption isotherms.5.HACCP principles were applied for hazard analysis and established five critical control points:acceptance of the raw fruit,peeling and seeding,drying,packing and storing-distributing-selling.In response to these critical control points,this paper developed the HACCP schedule,established the critical limits and corrective measures to ensure quality and safety.