Impact of Attachment Immobilization on Yeast Physiology and Fermentation Performance

A novel bioreactor with immobilization matrices was constructed to study physiological differences between immobilized and free cells and to compare the fermentation behavior of the immobilized-cell system with that of a free-cell system. Although the yeast sample released from the immobilization matrix (immobilized cells) showed relatively low activity of glucose utilization according to the acidification power test, fermentation in the immobilized-cell system was completed 20 hr earlier than in the free-cell system. In addition, flavor-active compounds, such as fusel alcohols and esters, were produced at higher levels (23% more fusel alcohols and 22% more esters) in the immobilized-cell system compared with the free-cell system. Whole-cell immobilization induced a reduction of cellular fatty acid contents, as well as an increase of fatty acid saturation percentages. These alterations of cellular fatty acid compositions in the immobilized cells had negative effects on cellular metabolic activities and stress resistance. It is suggested that cell attachment on solid surfaces, mass transfer limitations within the immobilization matrix, or both are responsible for the modifications of cellular fatty acid contents in the immobilized yeast.