Kilning of immobilized brewers yeast cells in ca-alginate particles in fluidized bed

Abstract

The paper presents the results of testing of immobilized brewers yeast cells kilning in fluidized bed, under various temperature and air flow conditions. Yeast immobilization was carried out by method of cell retention inside the matrix of Ca-alginate support. Kilning was done by compressor air, at the temperatures t=30, 40, 50 and 60° С and at air flow rate of 3.14 m/s, during 90 minutes. Humidity of the kilned particles was within the interval of 0.1-0.2 kg/ kg, while water activity was within the range of 0.28 (t=60° C) to 0.45 (t=30° C). This level of water activity in the kilned samples prevented any biological activity and secured conservation of im- mobilized starters. Testing of the kilned particles rehydration process showed that the kilned particles can completely recover their original form and initial volume, but they expressed somewhat reduced mechanical resistance. Maximum percentage of humidity recovery was measured 24 hours after rehydration and it amounted to 92% of humidity before kilning, while particle volume increased up to four times in relation to the volume of the kilned sample. The particles conserved by the procedure of kilning after rehydration, recovered catalytic activity.

U radu su prikazani rezultati ispitivanja procesa sušenja imobilisanih ćelija pivskog kvasca u fluidizovanom sloju pri različitim režimima temperature i protoka vazduha. Imobilizacija kvasca je izvršena metodom zadržavanja delija unutar matrice nosača Ca-alginata. Sušenje je vršeno kompresorskim vaz- duhom, pri temperaturama t=30, 40, 50 i 60°C i brzini vazduha od 3.14 m/s, u trajanju od 90 minuta. Vlažnost osušenih čestica se kretala u intervalu od 0,1-0,2 kg/kg, dok se aktivnost vode nalazila u opsegu od 0.28 (t=60 °C) do 0.45 (t=30°C). Ovaj nivo aktivnosti vode u osušenim uzorcima onemogućava bilo kakvu biološku aktivnost i obezbeđuje konzervisanje imobilisanih startera. Ispitivanjem procesa rehidratacije osušenih čestica, utvrđeno je da osušene čestice mogu u potpunosti da povrate svoj prvobitni oblik i početnu zapreminu, ali ispoljavaju donekle smanjenu mehaničku otpornost. Maksimalno dostignut procenat povraćaju vlage je meren nakon 24 časa rehidratacije i iznosio je 92% vlažnosti pre sušenja, dok se zapremina čestica povećala i do 4 puta u odnosu na vrednosti osušenog uzorka. Čestice konzervisane ovim postupkom sušenja posle rehidratacije su povratile katalitičku aktivnost.