Experimental Studies On Treatment Of Taihu Whitebait By A Combination Of Freeze Drying And Vacuum Microwave

The objective of this work was to develop a new method to process Taihuwhitebait.Three different drying methods were applied in the processing ofwhitebait,including hot air drying,vacuum freeze drying,combination of freezedrying and vacuum microwave. Before drying experiment,the nutrition and component of this fish wasanalyzed.The results shows whitebait owns a very good nutrition.The content ofprotein is nearly 85.24g/100g drying material which is much higher than otherfresh fish.Furthermore,constitutes of necessary amino acid is very rational.Acertain amount of whitebait is eaten each day will satisfy human need ofnecessary amino acid.The good nutrition of whitebait increases the value ofprocessing. Then freeze drying of heating procedure was used to dry whitebait,thedrying condition is followed:pre-freezing the whitebait at medium cooling rate(3.9cm/h),a pressure about 1 0 Pa,a condenser temperature of-45℃.Inaddition.the setting of heating plate procedure that kept the temperature inO℃ for 3 hours,then increased to 10℃for half an hour,then last half an hourat 20~C,finally kept 40"C till the temperature of sample as high as the platetemperature.The whole process last 6.5-7h.The quality of product of thismethod is much better than hot air. Though freeze drying of heating procedure can get excellent product anddecrease freeze drying time.The capital cost is still very high if it is usedin the producing of industrialization.To lower the cost further,we attempt to combinevacuum microwave drying and freeze drying.The plan is freeze drying was usedin the first stage,then whitebait was dried by vacuum microwave drying to finalmoistu re content leSs than 0.06(dry basis).The detail condition is following:the water content of white bait is lowered to 2.6±0.1 by freeze drying.microwaveoven power about 330W,pressure about 2000Pa.To compare the quality ofwhitebait dried by the current method was close to that of freeze dried whitebaitand much better than that of conventional hot.air dried ones. The cost of combination vacuum microwave drying and freeze drying wasmuch less than that offreeze drying. The result of this work show that the combination vacuum microwave drying and freeze drying may be used as an alternative to dehydrate the foodin high quality and in very low cost.