Modeling and experimental studies on intermittent starch feeding and citrate addition in simultaneous saccharification and fermentation of starch to flavor compounds

Abstract

Simultaneous saccharification and fermentation (SSF) is a combined process of saccharification of a renewable bioresource and fermentation process to produce products, such as lactic acid and ethanol. Recently, SSF has been extensively used to convert various sources of cellulose and starch into fermentative products. Here, we present a study on production of buttery flavors, namely diacetyl and acetoin, by growing Lactobacillus rhamnosus on a starch medium containing the enzyme glucoamylase. We further develop a structured kinetics for the SSF process, which includes enzyme and growth kinetics. The model was used to simulate the effect of pH and temperature on the SSF process so as to obtain optimum operating conditions. The model was experimentally verified by conducting SSF using an initial starch concentration of 100 g/L. The study demonstrated that the developed kinetic was able to suggest strategies for improved productivities. The developed model was able to accurately predict the enhanced productivity of flavors in a three stage process with intermittent addition of starch. Experimental and simulations demonstrated that citrate addition can also lead to enhanced productivity of flavors. The developed optimal model for SSF was able to capture the dynamics of SSF in batch mode as well as in a three stage process. The structured kinetics was also able to quantify the effect of multiple substrates present in the medium. The study demonstrated that structured kinetic models can be used in the future for design and optimization of SSF as a batch or a fed-batch process.

Bacterial Preservation of Pink Salmon Using Potatoes as a Carbohydrate Source

“…Homofermentative LAB, such as those used in this study, are capable of breaking starch into its monomers and then transforming the glucose into two molecules of lactic acid. However, the process is pH dependent and can be affected by inhibitors in the sample, including the build‐up of glucose, which is known to inhibit bacterial enzymic conversion of potato starch to glucose (Chavan et al . 2009).…”

“…2001). Lactic acid can be further metabolized to carbon dioxide (CO 2 ) and acetate (Chavan et al . 2009).…”

“…Homofermentative LAB, such as those used in this study, are capable of breaking starch into its monomers and then transforming the glucose into two molecules of lactic acid. However, the process is pH dependent and can be affected by inhibitors in the sample, including the build-up of glucose, which is known to inhibit bacterial enzymic conversion of potato starch to glucose (Chavan et al 2009). When the rate of conversion from starch to glucose exceeded the LAB's capacity to ferment the glucose into lactic acid, glucose may have begun to accumulate in the samples, thereby suppressing the breakdown of starch and limiting further production of lactic acid.…”

“…Bacterial contaminants, including strains of LAB, are known to degrade lactic acid, even under reduced oxygen conditions (Elferink et al 2001). Lactic acid can be further metabolized to carbon dioxide (CO2) and acetate (Chavan et al 2009). The presence of acetate, a weak base, combined with the loss of CO2 may have contributed to decreased acidity with a corresponding increase in sample pH, despite the apparent high lactic acid levels determined in Fig.…”

Interlinked population balance and cybernetic models for the simultaneous saccharification and fermentation of natural polymers

“…Evolving over the past three decades, this main feature of the CM approach has enabled it to successfully predict the growth of various microbes in complex substrate environments-from the simplest variant employed by Kompala and Ramkrishna (1986) to the more advanced variant implemented by Geng et al, (2012). Although implementations of the CM framework on simultaneous enzymatic depolymerization and fermentation had been reported (Altintas et al, 2002;Chavan et al, 2009;Ko et al, 2010;Murthy et al, 2012;Ochoa et al, 2007;Shin et al, 2006), they were interlinked to the grossly lumped M-M type of expressions for enzymatic scission, thereby, ignoring the details of enzymatic scission at the molecular level.…”