Measurement of Transport Properties for The Dried Layer of Several Food Materials Udergoing Freeze-Drying

Abstract

The transport properties of several food materials have beet? presented us ,fundc2.nzenial irfortnurion to determine the drying rate ofpeeze-drying process. As un exatrzple, the nleasuring method of thermal condtrctivity and permeability hcrs been demonstrated for the samples of sliced and nzashed apples undergoing freezedrying. Both samples were Ji-eeze-dried at constant surface ten~peratzn-csr anging porn -10 to 70 under the usual pressure range of comniercial operations. A tnatheniaticul model, based on a quasi-steady state analysis, was Jormtrluted and then applied to the drying data to deternzine these transport properties for the ~lriedlt ryer of the sunzple undergoing,fi.eeze-dryingV. alzres of thermal condzlctivity were ,foz,rtid to be alnlost the same between sliced and mashed .sanlples. Howevei: the perrneubility datcz of the tnashed apples were more thun 4 titnes greater th~ril that of sliced apples. Both tenzperatzire and pressure dependences on these transport properties were not recognizecl uppuretitly, and the effects of Jreezing rate on transport properties were found to be criticaljor the mashed saniples. The results indicated that the drying rate of sliced suniples MIUS limited by the trtmsJir rate of water vapor flowing through the dried Iuyer The trunsport properties for raw beeJ mi~icedb eej shritnp crnd coffee solutior~s \z3ere ~xl,soy t-esented indicating the effects of operating conditions us well 'a the str~ictt~rpa~l ~runzeterosf the satnples on these values.