Hemicelluloses for fuel ethanol: A review.

A literature review discusses the possible direct and indirect effects of controlled atmospheres (CA's) on the biochemical and physiological properties of fruits and vegetables during transport and storage The effects specifically discussed are those associated with: respiratory metabolism; ethylene biosynthesis and action; chemical changes affecting product color, texture, flavor, and nutritional value; growth and development; physical injuries caused by bruising; water loss; and physiological disorders alleviated, aggravated, or induced by CA's The role of CA's on controlling pathogens that promote postharvest decay also is discussed(wz)

Biochemical and physiological basis for effects of controlled and modified atmospheres on fruits and vegetables

With world reserves of petroleum fast depleting, in recent years ethanol has emerged as most important alternative resource for liquid fuel and has generated a great deal of research interest in ethanol fermentation. Research on improving ethanol production has been accelerating for both ecological and economical reasons, primarily for its use as an alternative to petroleum based fuels. Field crops offer potential source of fuel, offering promise as large-scale energy and based on its genetic diversity, climatic adaptation, biomass and sugar production. Lignocellulosic biomass is the most abundant organic raw material in the world. Production of ethanol from renewable lignocellulosic resources may improve energy availability, decrease air pollution and diminish atmospheric CO2 accumulation. The aim of the present review is to highlight on major agricultural, industrial and urban waste, which could be used for ethanol production in an ecofriendly and profitable manner. Primarily, the utilization of these wastes for ethanol production will reduce dependency on foreign oil and secondly, this will remove disposal problem of wastes and make environment safe from pollution.

Ethanol as an alternative fuel from agricultural, industrial and urban residues

1. SUMMARY The central role of the redox couples NAD+/ NADH and NADP+/NADPH in the metabolism of sugars by yeasts is discussed in relation to energy metabolism and product formation. Besides their physical compartmentation in cytosol and mitochondria, the two coenzyme systems are separated by chemical compartmentation as a consequence of the absence of transhydrogenase activity. This has considerable consequences for the redox balances of both coenzyme systems and hence for sugar metabolism in yeasts. As examples, the competition between respiration and fermentation of glucose, the Crabtree effect, the Custers effect, adaptation to anaerobiosis, the activities of the hexose monophosphate pathway, and the fermentation of xylose in yeast are discussed.

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Redox balances in the metabolism of sugars by yeasts (NAD(H); NADP(H); glucose metabolism; xylose fermentation; ethanol; Crabtree effect; Custers effect)

The central role of the redox couples NAD+/NADH and NADP+/NADPH in the metabolism of sugars by yeasts is discussed in relation to energy metabolism and product formation. Besides their physical compartmentation in cytosol and mitochondria, the two coenzyme systems are separated by chemical compartmentation as a consequence of the absence of transhydrogenase activity. This has considerable consequences for the redox balances of both coenzyme systems and hence for sugar metabolism in yeasts.

As examples, the competition between respiration and fermentation of glucose, the Crabtree effect, the Custers effect, adaptation to anaerobiosis, the activities of the hexose monophosphate pathway, and the fermentation of xylose in yeast are discussed.

Redox balances in the metabolism of sugars by yeasts

Xylose reductase from the xylose-fermenting yeast Pichia stipitis was purified to electrophoretic and spectral homogeneity via ion-exchange, affinity and high-performance gel chromatography. The enzyme was active with various aldose substrates, such as DL-glyceraldehyde, L-arabinose, D-xylose, D-ribose, D-galactose and D-glucose. Hence the xylose reductase of Pichia stipitis is an aldose reductase (EC 1.1.1.21). Unlike all aldose reductases characterized so far, the enzyme from this yeast was active with both NADPH and NADH as coenzyme. The activity with NADH was approx. 70% of that with NADPH for the various aldose substrates. NADP+ was a potent inhibitor of both the NADPH- and NADH-linked xylose reduction, whereas NAD+ showed strong inhibition only with the NADH-linked reaction. These results are discussed in the context of the possible use of Pichia stipitis and similar yeasts for the anaerobic conversion of xylose into ethanol.

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Properties of the NAD(P)H-dependent xylose reductase from the xylose-fermenting yeast Pichia stipitis.

BRUINENBERG, P. M,, VAN D1JKEN, J. P., KUENEN, J. G. and SCHEFFERS, W. A. 1985a. Critical parameters in the isolation of mitochondria from Candida utilis grown in continuous culture. J. Gen. Microbiol. 131: 1035-1042. BRUINENBERG, P. M., VAN D1JKEN, J. P., KUENEN, J. G. and SCHEFr~RS, W. A. 1985b. Oxidation of NADH and NADPH by mitochondria from the yeast Candida utilis. J. Gen. Microbiol. 131: 1043-1051.

R. van Kleef

Papers

Properties of the NAD(P)H-dependent xylose reductase from the xylose-fermenting yeast Pichia stipitis.

NAD(P)H-dependent aldose reductase from the xylose-fermenting yeast Pichia stipitis