• Microbiology and Biotechnology Letters
• /
• v.24 no.2
• /
• pp.149-154
• /
• 1996

Effect of glucose addition to xylose medium on xylitol production was investigated by using Candida parapsilosis ATCC 21019 mutant. With increasing the ratio of glucose to xylose in total amount of 50 g/l as glucose and/or xylose, xylitol production was decreased but ethanol and glycerol production were increased. Ethanol and glycerol concentration were maxmum in 10 g/l of xylose and 40 g/l of glucose medium as 21.5 g/l and 3.6 g/l, respecti- vely. No xylitol was formed in glucose medium without xylose because xylitol could be not produced from glucose. With increasing the ratio of glucose to xylose, the activity of xylose reductase which converted xylose to xylitol were decreased. The activities of xylitol dehydrogeiiase which converted xylitol to xylulose and then cell materials were found to be constant regardless of the ratio of glucose to xylose. This results indicated that glucose addition to xylose medium on cell growth was not affected. In order to prevent the inhibitory effect of glucose on xylitol production, glucose in a fermentor was fed with low concentration and then ethanol and glycerol was critically decreased and the xylitol yield from xylose of the culture with glucose feeding was recovered the almost same as that with only 50 g/l of xylose. However, the xylitol yield from total sugars (xylose and glucose) was decreased and glucose was not contributed to xylitol production. Therefore, the fermentation at high concentration of xylose without glucose was carried out. A final xylitol concentration of 242 g/l which corresponding 80.7% of xylitol yield was obtained from 300 g/l of xylose for 273 hours.

• Korean Journal of Food Science and Technology
• /
• v.28 no.6
• /
• pp.1151-1156
• /
• 1996

Effects of xylose and glucose on the xylitol production were investigated with Candida parapsilosis KFCC 10875. With increasing the ratio of glucose to xylose, xylitol production decreased but ethanol and glycerol production increased. The maximum concentrations of ethanol and glycerol were 21.5 g/l and 3.6 g/l, respectively, in a medium consisting of 10 g/l xylose and 40 g/l glucose. No xylitol was formed in the glucose medium without xylose since xylitol could not be produced from glucose alone. The inhibitory effect of ethanol, a major by-product, on xylitol production was also studied. As the added ethanol concentration was increased, xylitol production decreased. When cells were inoculated in a xylose medium after removing the by-product (ethanol), xylitol production was not inhibited. The concentrated cells grown on xylose or glucose were inoculated in a fermentor containing the xylose medium. The total activities $(specific{\;}activities{\times}\;cell\;concentration)$ of xylose reductase and xylitol dehydrogenase in concentrated cells grown on glucose were the same as those in a normal fermentation; the specific activities of the above enzymes in the cells grown on xylose were the same as those in a normal fermentation. It indicates that the xylitol productivity of concentrated cells grown on xylose could be increased with increasing the cell concentration. By using concentrated cells of 20 g/l grown on xylose, the final xylitol concentration of 40 g/l was obtained for 18 h fermentation from 50 g/l xylose.

• Microbiology and Biotechnology Letters
• /
• v.25 no.5
• /
• pp.495-500
• /
• 1997

Xylitol production from xylose and glucose was investigated using Candida tropicalis KFCC-10960. As glucose concentration in xylose medium was increased, ethanol production increased. However, xylitol production was maximum at glucose concentration of 10 g/l. The concentrated cells grown on xylose or glucose were inoculated in xylose medium. The specific activities of xylose reductase and xylitol dehydrogenase, and xylitol production in concentrated cells grown on glucose were the same as those in concentrated cells grown on xylose. The results suggested that cells grown on glucose had the same xylitol producing activity as those grown on xylose. By feeding glucose in xylose medium, cell growth was achieved from glucose and xylitol production was obtained from xylose. By using this technique, a final xylitol concentration of 261 g/l was achieved from 300 g/l xylose in 41 hours which corresponded to a xylitol yield from xylose of 87% and a xylitol productivity of 6.37 g/1-h.

• Microbiology and Biotechnology Letters
• /
• v.20 no.1
• /
• pp.91-95
• /
• 1992

The hydrolyzates of lignocellulosic biomass contain a mixture of glucose, xylose and cellobiose. The yeast which can produce ethanol efficiently from xylose and cellobiose was selected and its growth and ethanol formation behavior on each sugar and their mixture were investigated. Ethanol yields during batch culture of Pichia stipitis CBS 5776 were 0.4. 0.36 and 0.23 g/g substrate on glucose, xylose and cellobiose, respectively. Mixed sugar fermentation data indicate that glucose causes catabolite regulation on xylose and cellobiose utilization. However, xylose and cellobiose were utilized simultaneously. Ethanol yields on mixtures of sugars were generally additive for each of the substrates.

• Biotechnology and Bioprocess Engineering:BBE
• /
• v.5 no.1
• /
• pp.32-39
• /
• 2000

Simultaneous isomerisation and fermentation (SIF) of xylose and simultaneous isomerisation and cofermentation (SICF) of glucose-xylose mixture was carried out by the yeast Saccharomyces cerevisiae in the presence of a compatible xylose isomerase. The enzyme converted xylose to xylulose and S. cerevisiae fermented xylulose, along with glucose, to ethanol at pH 5.0 and $30^{\circ}C$. This compatible xylose isomerase from Candida boidinii, having an optimum pH and temperature range of 4.5-5.0 and $30-35^{\circ}C$ respectively, was partially purified and immobilized on an inexpensive, inert and easily available support, hen egg shell. An immobilized xylose isomerase loading of 4.5 IU/(g initial xylose) was optimum for SIF of xylose as well as SICF of glucose-xylose mixture to ethanol by S. cerevisiae. The SICF of 30 g/L glucose and 70 g xylose/L gave an ethanol concentration of 22.3 g/L with yield of 0.36 g/(g sugar consumed) and xylose conversion efficiency of $42.8\%$.

• Microbiology and Biotechnology Letters
• /
• v.16 no.6
• /
• pp.505-509
• /
• 1988

Ethanol productivity of a xylose fermenting yeast (Candida sp. X-6-4l) isolated from soil was investigated in laboratory scale using Erlenmeyer flask and mini-jar tormentor. The optimal conditions of xylose fermentation in flask experiment were pH 4, asparagine as nitrogen source, xylose 20g/$\ell$, and in these condition, ethanol yield was about 80% to theoretical yield. Using mini-jar fermentor containing 5% total sugar with 2.5% xylose and 2.5% glucose, we obtained 2.3%(v/ v) ethanol and the corresponding efficiency was 72.3% of total sugar. In this case, the consumming speed of sugar under aerobic condition was faster than that of anaerobic condition, and glucose was used previously to xylose. The optimum concentration of xylose for ethanol fermentation in mini-jar fer-mentor scale was 5%, and the efficiency was 69% of total sugar(Alc.2.2% v/v).

• KSBB Journal
• /
• v.7 no.4
• /
• pp.265-270
• /
• 1992

Low cost fermentation substrates frequently contain a mixture of carbon sources including hexoses, pentoses and disaccharides. Fermentation of such mixtures requires an understanding of how each of these substrates is utilized. During batch culture of Pichia stipitis CBS 5776 on sugar mixtures, glucose causes catabolite repression of xylose and cellobiose utilization. Also, glucose causes a permanent repression of xylose utilization as evidenced by reduced growth rates during the xylose phase of glucose/xylose fermentation. The growth model for multiple substrates is developed based on a cyclic AMP mediated catabolite repression mechanism and this model adequately described the growth and ethanol production from sugar mixtures.

• Korean Journal of Food Science and Technology
• /
• v.29 no.5
• /
• pp.1045-1051
• /
• 1997

Three kinds of model melanoidins adjusted to have the same brown color intensity were made from glucose-glycine, glucose-lysine, xylose-arginine and their antioxidative properties were determined. The antioxidative activities of these model melanoidins in linoleic acid emulsion system were determined by ferric thiocyanate method, conjugated diene contents, peroxide value and electron donating ability by DPPH. Xylose-arginine melanoidin showed the strongest antioxidative activity and electron donating ability. The antioxidative effect of melanoidin could be reliably predicted by determining peroxide value and DPPH method. Each melanoidin was separated on Sephadex G-50 column, and brown color intensity, reducing power, ninhydrin positive reaction and antioxidative activity of each fraction were determined. The antioxidative activities of melanoidin fractions showed strong correlation with their brown color intensity and especially to their reducing power. In spite of same brown color intensity, there is no big differences between these model melanoidins, thus xylose-arginine showing strongest antioxidative activity followed by glucose-lysine and glucose-glycine melanoidin. Xylose-arginine melanoidin also showed the strongest electron donating activity and broad range of reducing power when fractionated on Sephadex G-50, which was different tendency from the other model melanoidin.

• Nutrition Research and Practice
• /
• v.10 no.1
• /
• pp.11-18
• /
• 2016

BACKGROUND/OBJECTIVES: Type 2 diabetes (T2D) is more frequently diagnosed and is characterized by hyperglycemia and insulin resistance. $\small{D}$-xylose, a sucrase inhibitor, may be useful as a functional sugar complement to inhibit increases in blood glucose levels. The objective of this study was to investigate the anti-diabetic effects of $\small{D}$-xylose both in vitro and stretpozotocin (STZ)-nicotinamide (NA)-induced models in vivo. MATERIALS/METHODS: Wistar rats were divided into the following groups: (i) normal control; (ii) diabetic control; (iii) diabetic rats supplemented with a diet where 5% of the total sucrose content in the diet was replaced with $\small{D}$-xylose; and (iv) diabetic rats supplemented with a diet where 10% of the total sucrose content in the diet was replaced with $\small{D}$-xylose. These groups were maintained for two weeks. The effects of $\small{D}$-xylose on blood glucose levels were examined using oral glucose tolerance test, insulin secretion assays, histology of liver and pancreas tissues, and analysis of phosphoenolpyruvate carboxylase (PEPCK) expression in liver tissues of a STZ-NA-induced experimental rat model. Levels of glucose uptake and insulin secretion by differentiated C2C12 muscle cells and INS-1 pancreatic ${\beta}$-cells were analyzed. RESULTS: In vivo, $\small{D}$-xylose supplementation significantly reduced fasting serum glucose levels (P < 0.05), it slightly reduced the area under the glucose curve, and increased insulin levels compared to the diabetic controls. $\small{D}$-xylose supplementation enhanced the regeneration of pancreas tissue and improved the arrangement of hepatocytes compared to the diabetic controls. Lower levels of PEPCK were detected in the liver tissues of $\small{D}$-xylose-supplemented rats (P < 0.05). In vitro, both 2-NBDG uptake by C2C12 cells and insulin secretion by INS-1 cells were increased with $\small{D}$-xylose supplementation in a dose-dependent manner compared to treatment with glucose alone. CONCLUSIONS: In this study, $\small{D}$-xylose exerted anti-diabetic effects in vivo by regulating blood glucose levels via regeneration of damaged pancreas and liver tissues and regulation of PEPCK, a key rate-limiting enzyme in the process of gluconeogenesis. In vitro, $\small{D}$-xylose induced the uptake of glucose by muscle cells and the secretion of insulin cells by ${\beta}$-cells. These mechanistic insights will facilitate the development of highly effective strategy for T2D.

• Journal of Microbiology and Biotechnology
• /
• v.13 no.5
• /
• pp.725-730
• /
• 2003

Three recombinant Saccharomyces cerevisiae strains showing different levels of xylose reductase activity were constructed to investigate the effects of xylose reductase activity and glucose feed rate on xylitol production. Conversion of xylose to xylitol is catalyzed by xylose reductase of Pichia stipitis with cofactor NAD(P)H. A two-substrate fermentation strategy has been employed where glucose is used as an energy source for NADPH regeneration and xylose as substrate for xylitol production. All recombinant S. cerevisiae strains Yielded similar specific xylitol productivity, indicating that xylitol production in the recombinant S. cerevisiae was more profoundly affected by the glucose supply and concomitant It generation of cofactor than the xylose reductase activity itself. It was confirmed in a continuous culture that the elevation of the glucose feeding level in the xylose-conversion period enhanced the xylitol productivity in the recombinant S. cerevisiae.