The kinetics of yeast growth and nicotinic acid production

Phenotypic evaluation and characterization of 21 industrial Saccharomyces cerevisiae yeast strains

Microorganisms have been studied and used extensively to produce value-added fuels and chemicals. Yeasts, specifically Saccharomyces cerevisiae, receive industrial attention because of their well-known ability to ferment glucose and produce ethanol. Thousands of natural or genetically modified S. cerevisiae have been found in industrial environments for various purposes. These industrial strains are isolated from industrial fermentation sites, and they are considered as potential host strains for superior fermentation processes. In many cases, industrial yeast strains have higher thermotolerance, increased resistances towards fermentation inhibitors and increased glucose fermentation rates under anaerobic conditions when compared with laboratory yeast strains. Despite the advantages of industrial strains, they are often not well characterized. Through screening and phenotypic characterization of commercially available industrial yeast strains, industrial fermentation processes requiring specific environmental conditions may be able to select an ideal starting yeast strain to be further engineered. Here, we have characterized and compared 21 industrial S. cerevisiae strains under multiple conditions, including their tolerance to varying pH conditions, resistance to fermentation inhibitors, sporulation efficiency and ability to ferment lignocellulosic sugars. These data may be useful for the selection of a parental strain for specific biotechnological applications of engineered yeast.

Determination of tryptophan derivatives in kynurenine pathway in fermented foods using liquid chromatography tandem mass spectrometry

This study aimed to develop an analytical method for the determination of tryptophan and its derivatives in kynurenine pathway using tandem mass spectrometry in various fermented food products (bread, beer, red wine, white cheese, yoghurt, kefir and cocoa powder). The method entails an aqueous extraction and reversed phase chromatographic separation using pentafluorophenyl (PFP) column. It allowed quantitation of low ppb levels of tryptophan and its derivatives in different fermented food matrices. It was found that beer samples were found to contain kynurenine within the range of 28.7±0.7μg/L and 86.3±0.5μg/L. Moreover, dairy products (yoghurt, white cheese and kefir) contained kynurenine ranging from 30.3 to 763.8μg/kg d.w. Though bread samples analyzed did not contain kynurenic acid, beer and red wine samples as yeast-fermented foods were found to contain kynurenic acid. Among foods analyzed, cacao powder had the highest amounts of kynurenic acid (4486.2±165.6μg/kgd.w), which is a neuroprotective compound.

Nicotinic acid controls lactate production by K1-LDH: a Saccharomyces cerevisiae strain expressing a bacterial LDH gene

Industrial applications for lactate, such as the production of chemicals, has led to interest in producing this organic acid by metabolically engineered a yeast such as Saccharomyces cerevisiae, which is more acid tolerant than lactic acid bacteria. This paper deals with lactate production by S. cerevisiae K1-LDH, in which the Lactobacillus plantarum lactate dehydrogenase (LDH) gene is integrated into the genome of the wine yeast strain K1. We show that a vitamin, nicotinic acid (NiA), was the limiting factor for lactate production during fermentation with the K1-LDH strain. Increasing the NiA concentration in batch conditions or in the medium used to feed chemostats affected the lactate yield. Moreover, the addition of pulses of NiA or the exponential addition of NiA made it possible to control the lactate production kinetics throughout the fermentation process. The results point to the role of NiA in the regulation of metabolic pathways, but the physiological mechanisms remain poorly understood.