Ambient and low temperature winemaking by immobilized cells on brewer’s spent grains: Effect on volatile composition Mallouchos Athanasios a , Loukatos Paul a , Bekatorou Argyro b , Koutinas Athanasios b , Komaitis Michael a, * a Agricultural University of Athens, Food Science and Technology Department, Iera Odos 75, 118 55 Athens, Greece b University of Patras, Department of Chemistry, Section of Analytical, Environmental and Applied Chemistry, 26500 Patras, Greece Received 16 June 2006; received in revised form 18 October 2006; accepted 19 December 2006 Abstract Repeated batch wine fermentations were conducted using immobilized yeast cells on brewer’s spent grains as well as free cells, at 25, 20, 15 and 10 °C. The operational stability of the biocatalyst was good and no decrease of its activity was observed, even at 10 °C. Eth- anol and wine productivities were high, showing the suitability of the biocatalyst for low temperature winemaking. The interaction effect of immobilization and temperature was statistically significant in most cases. Immobilized cells produced wines with a higher content of ethyl and acetate esters as well as volatile fatty acids, at temperatures of 15 and 10 °C, whereas the opposite was observed for free cells at higher temperatures. Same amounts of higher alcohols were produced by both immobilized and free cells. These amounts decreased dra- matically with temperature drop. Wines produced by immobilized cells at low fermentation temperatures (10–15 °C) were characterized by a potentially better flavour due to a better ratio of esters to alcohols. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Immobilization; Yeast; Wine; Volatiles; Esters; Acetates; Higher alcohols; Acids; Temperature; Fermentation; GC/MS; Spent grains 1. Introduction Cell immobilization in alcoholic fermentation has been extensively studied during the past three decades because of its technical and economical advantages over those of free cell systems (Dervakos & Webb, 1991; Lu, Lu, Bie, & Fujimura, 2002; Sakurai, Nishida, Saito, & Sakakibara, 2000; Shindo, Takata, Taguchi, & Yoshimura, 2001; Sree, Sridhar, Suresh, Banat, & Rao, 2000). However, for appli- cation in the wine industry, research is needed to find out an immobilization support that meets the prerequisite of food grade purity, low cost and a final product of improved aroma and taste. Particles of various synthetic or natural materials, organic and inorganic, have been used as sup- ports for cell immobilization in wine fermentations (Divies, Cachon, Cavin, & Prevost, 1994; Kourkoutas, Bekatorou, Banat, Marchant, & Koutinas, 2004). Recently, brewer’s spent grains (BSG), a by-product of the brewing industry, were used as a carrier, after treatment with acid and alkali, in order to immobilize yeast cells for pectinase production (Almeida, Bra ´nyik, Moradas-Ferreira, & Teixeira, 2003). Bra ´nyik and co- workers used the aforementioned support for continuous primary fermentation of beer (Bra ´nyik, Vicente, Cruz, & Texeira, 2004; Bra ´nyik, Vicente, Machado Cruz, & Teixeira, 2001) and suggested that it is a very efficient immobilization carrier due to its high yeast loading capacity, easy preparation, reusability, availability and inert, non-toxic nature. Wine aroma is the result of a complex combination of components that give each wine its distinctive character. 0308-8146/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2006.12.047 Abbreviations: GC/MS, gas chromatography–mass spectrometry; BSG, brewer’s spent grains; IC, immobilized cells; FC, free cells; SPME, solid phase microextraction; EERI, ethyl ester retention index; LRI, linear retention index; MCFA, medium chain length acids. * Corresponding author. Tel./fax: +30 210 5294681. E-mail address: achem@aua.gr (M. Komaitis). www.elsevier.com/locate/foodchem Food Chemistry 104 (2007) 918–927 Food Chemistry