Preservation, risk of contamination, transportation and storage costs (e.g. refrigeration) are the main problems associated with wet, active starter cultures such as yeast. To deal with these ...aspects, drying of commercial cultures is required. A thermally dried biocatalyst has been prepared by immobilization of the psychrotolerant yeast strain Saccharomyces cerevisiae AXAZ-1 on delignified brewer's spent grains, followed by simple thermal drying or by air stream at 30 and 35 °C. Repeated batch fermentations of grape must (11.5 °Be, corresponding to 196 g/L of fermentable sugar) using the dried biocatalysts were performed at successively reduced temperatures (15, 10 and 5 °C). The fermented samples were analyzed for residual sugar, alcohol and free cell concentrations. The alcohol yield, alcohol productivity and sugar conversion were calculated in order to estimate the optimum conditions of drying. The volatile constituents in the produced wines were analysed by GC analysis. The results showed that drying of immobilized cells by the proposed techniques did not affect their viability and fermentative activity. High alcohol productivity, increased esters and lower concentrations of higher alcohols obtained by low-temperature fermentation using the dried biocatalysts indicate a potential improvement of product quality. Key words: brewer's spent grains, immobilization, thermal drying, winemaking
Konzerviranje, rizik od onečišćenja, te cijena transporta i skladištenja (npr. hlađenja) najčešći su problemi pri korištenju vlažnih, aktivnih starter-kultura, tj. kvasaca. Stoga komercijalne kulture ...kvasaca treba osušiti. Sušeni je biokatalizator pripremljen imobilizacijom psihrotolerantnoga soja kvasca Saccharomyces cerevisiae AXAZ-1 na pivskom tropu, iz kojeg je prethodno uklonjen lignin, a zatim sušenjem toplinom ili strujom zraka pri 30 i 35 °C. Pomoću tako pripremljenog kvasca uspješno je provedeno nekoliko uzastopnih šaržnih postupaka vrenja mošta (11,5 °Be, proporcionalno 196 g/L fermentabilnog šećera) pri nižim temperaturama (15, 10 i 5 °C). Ispitana je koncentracija preostalog šećera, dobivenog alkohola i slobodnih stanica u fermentiranim uzorcima. Da bi se procijenili optimalni uvjeti sušenja, izračunati su ovi parametri: udio i produktivnost alkohola te konverzija šećera. Volatilni su sastojci vina analizirani plinskom kromatografijom. Rezultati pokazuju da sušenje imobiliziranih stanica kvasca predloženim metodama ne utječe na njegovu vitalnost i fermentacijsku aktivnost. Kakvoća se proizvoda može poboljšati korištenjem sušenih stanica kvasca pri nižim temperaturama, što je uočeno iz većeg udjela alkohola, veće koncentracije estera i manje koncentracije viših alkohola u vinu.
