The objectives of this investigation were to study the effects of moisture content, screw speed and barrel temperature on physical properties of extruded soy protein isolate (SPI) with L-cysteine and xylose. SPI with L-cysteine and xylose was extruded at 30 and 35% moisture contents, screw speed 150 and 250 rpm and barrel temperatures 140 and 160℃. SPI extruded at 30% moisture content, screw speed 250 rpm and barrel temperature 140℃ was control (100% SPI). Increasing barrel temperature and moisture content decreased expansion ratio of all extrudates but increasing screw speed increased expansion ratio. Moisture content, screw speed and barrel temperature affected the color (L, a, b, ΔE) of extrudates. Water absorption index (WAI) and fat binding capacity (FBC) increased with increasing barrel temperature and screw speed. WAI and FBC were the highest at 30% moisture content. The pore structure of extrudates was a finer at barrel temperature 160℃. The increase in screw speed and moisture content showed more organized fibrous and thicker cell walls. The extrusion condition and the addition of L-cysteine and xylose may improve physical properties such as the structure-forming and textures of extruded SPI products.

The bioconversion of cellulosic biomass hydrolyzates consisting mainly of glucose and xylose requires the use of engineered Saccharomyces cerevisiae expressing a heterologous xylose pathway. However, there is concern that a fungal xylose pathway consisting of NADPH-specific xylose reductase (XR) and NAD+-specific xylitol dehydrogenase (XDH) may result in a cellular redox imbalance. However, the glycerol biosynthesis and glycerol degradation pathways of S. cerevisiae, termed here as the glycerol cycle, has the potential to balance the cofactor requirements for xylose metabolism, as it produces NADPH by consuming NADH at the expense of one mole of ATP. Therefore, this study tested if the glycerol cycle could improve the xylose metabolism of engineered S. cerevisiae by cofactor balancing, as predicted by an in-silico analysis using elementary flux mode (EFM). When the GPD1 gene, the first step of the glycerol cycle, was overexpressed in the XR/XDH-expressing S. cerevisiae, the glycerol production significantly increased, while the xylitol and ethanol yields became negligible. The reduced xylitol yield suggests that enough NAD+ was supplied for XDH by the glycerol cycle. However, the GPD1 overexpression completely shifted the carbon flux from ethanol to glycerol. Thus, moderate expression of GPD1 may be necessary to achieve improved ethanol production through the cofactor balancing.

Recently, there had been reports on ethanol fermentation from mono-saccharide and disaccharide by mushroom mycelia. This experiment was conducted to study ethanol production from xylose by mycelila of mushrooms isolated from Korea. The cultures used in this study were obtained from Culture Collection and DNA Bank of Mushrooms in the Division of Life Sciences, Incheon National University. The results showed that Neolentinus lepideus, Trametes hirsuta and Cerrena unicolor produced ethanol from xylose contained media. The ethanol concentration produced in the xylose contained media ranged from 2.5∼3.8%. The highest ethanol concentration(3.8%) was obtained from fermentation of xylose by Neolentinus lepideus mycelia. All of the mushroom mycelia used in this study showed a good ability of ethanol fermentation from glucose, fructose, mannose, cellobiose and maltose.

The objective of this study was to investigate the proper concentration of D-xylose which is expected to reduce the GI (Glycemic index) value of sucrose in the human body. When subjects took a sucrose mixture containing 5% and 10% D-xylose, the blood glucose levels were lowered by approximately 27.5% and 25.9%, respectively, compared to those of sucrose. The GI values of sucrose mixtures containing 5% and 10% D-xylose were 49.3 and 50.4, respectively. The reduction in GI value was not dependent on the D-xylose concentration, as the GI value of sucrose mixture containing 5% D-xylose (XyloSugar) was similar to that of sucrose mixture containing 10% D-xylose (XyloSugar10). D-xylose is not only more expensive but also less sweet than sucrose. So, low concentration of D-xylose has the advantage in the price and taste. It was determined that the proper concentration of D-xylose expected to reduce GI value of sucrose was 5% (w/w).