Kinetics of brewing yeast accumulation on the surface of spent grains : a biocatalyst for brewing application
Year: 2004
Type: conference-paper
Abstract: When cells come into contact with solid surfaces, the physico-chemical and/or special biochemical interactions that occur may lead to biofilm formation. Although the biofilm formation is in many places unwanted, it can also be exploited in biotechnological processes (Characklis and Marshall, 1990). Understanding the biofilm formation kinetics and the physiology of immobilized cells is relevant for increasing the productivity of a biotechnological process taking advantage of microbial biofilms. The brewing yeast Saccharomyces pastorianus (carlsbergensis), kindly supplied by a brewing company (UNICER – Bebidas de Portugal, S.A., S. Mamede de Infesta, Portugal) were immobilized on acid (HCl) and base (NaOH) treated spent grains (Branyik el al., 2002). Continuous immobilization experiments were carried out in a bubble column reactor with spent grains as carrier at different dilution rates ( D ). The immobilized cells vitality was monitored through the change of NAD(P)H fluorescence intensity (340/460 nm excitation /emission wavelength) as the response to an aerobic-anaerobic (AA) transition. NAD(P)H fluorescence was considered a good indicator of the redox state of the immobilized cells (Podrazký et al., 2003). Cell viability may be an important factor in immobilized cell reactor design and performance due to the long periods of time each immobilized cell spends in the reactor. Both the decreasing specific glucose consumption rate by the immobilized cells ( im q ) and the intracellular NAD(P)H fluorescence changes imply alterations in immobilized cell physiology with time. The changes of the physiological state of the immobilized cells can be ascribed to the aging process to which the immobilized brewing yeasts, eukaryotic cells having a finite replicative lifespan (Baker and Smart, 1996), are exposed in the continuous reactor. Thus, the existence of an actively growing fraction ( act im X ) of the total immobilized biomass ( im X ) was hypothesized and its value was estimated at act im X = 0.12 gIB gC -1 (g dry immobilized biomass per g dry carrier).
Institution: University of Minho
Language: English
Topic: Fluid Dynamics and Mixing
Subfield: Fluid Flow and Transfer Processes
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2267292898