J Stuart Swanston

Starch production and industrial use

This review of starch is concerned with its industrial uses, origins and structure. The current demand for starch is met by a restricted range of crops, the most important of which are potatoes, maize, wheat and tapioca. Improvements in the properties of starches for industrial uses can be achieved through chemical and physical modification of extracted starch and through the manipulation of starch biosynthesis in the plant itself. We examine starch structure and composition in relation to its use and exploitation by industry. The current understanding of physiological and biochemical mechanisms influencing starch formation in higher plants is described. This information is set in the context of the need to know the physical/chemical specification for each individual starch and to understand the genetic control of these characteristics in order to identify target genes for manipulation.

Using molecular markers to determine barleys most suitable for malt whisky distilling

Two barley quality characters of specific interest to whisky distillers are fermentability and production of the ethyl carbamate precursor, epi-heterodendrin. The former is a quantitative trait, while the latter may be determined by a single Mendelian genetic factor. Molecular markers have been used to map, to barley chromosome 5(1H), the locus responsible for epi-heterodendrin synthesis and the inheritance of this character and a closely linked microsatellite have been followed through the pedigrees of several contemporary cultivars. Six loci, which affected fermentability in random inbred lines from a barley cross, have been mapped to chromosomes 2(2H), 3(3H) and 7(5H). This would permit the use of molecular markers in a breeding programme, to select barleys best suited for distilling. In addition, one of the loci related to fermentability mapped to an area of the genome indicated, by a previous study, to affect the activity of β-amylase, a character likely to influence fermentability. Molecular markers may, therefore, be powerful tools in exploring the contribution and detecting the mode of action of the genetical components influencing malt whisky distilling.

Mixtures of UK wheat as an efficient and environmentally friendly source for bioethanol

Summary Concerns about access to oil supplies have encouraged the exploration of renewable fuel and energy sources. Industrial ecology offers tools to compare the energy implications and benefits of differing strategies, but using botanical sources of raw materials to replace nonrenewable ones also requires appreciation of plant science, especially the variation in genetic potential within species. Whereas cultivation methods determine whether genetic potential is realized, different methods impact the environment to varying degrees. Experience with barley variety mixtures, aimed at reducing chemical input, has shown them to improve yield and reduce disease, while maintaining or even enhancing quality. Yield improvements still occurred in the absence of disease and increased in proportion to the number of component varieties. Because other research showed mixtures to be similarly effective in wheat, a protocol to grow and exploit a complex mixture of soft wheat is proposed, offering a cost-effective and energy efficient feedstock for a possible bioethanol industry in the United Kingdom. Ethanol would be produced initially from grain, with the straw used for heating or electricity generation. Fertilizer production and use and vehicle fuels have been shown as the main forms of energy consumption in growing a crop, and targets for enhancing the energy balance, by growing mixtures under an integrated farming system, are postulated. A close but negative association between grain protein and alcohol yield is demonstrated and a mixture giving comparable grain yield, but superior alcohol yield, to its best component is identified. Mixing varieties differing in plant morphology may also increase total biomass yield and, therefore, the energy generated from the crop. Pesticide reduction has another positive, though small, effect on the energy balance, from using mixtures. Eliminating prophylactic spraying also reduces vehicle fuel consumption, and may provide the low-toxicity benefits of organic agriculture without the yield penalty. A range of alternative uses for straw and other by-products is also discussed.

Limit dextrinase from germinating barley has endotransglycosylase activity, which explains its activation by maltodextrins

Limit dextrinase (EC 3.2.1.41) from germinating barley (Hordeum vulgare L) can be activated by millimolar concentrations of linear maltodextrins with a degree of polymerisation ≥ 2. The activation was assay-dependent; it was detected using assays based on the solubilisation of cross-linked dyed pullulan but not in assays that directly measured cleavage events such as the formation of new reducing termini. This strongly suggested that maltodextrins did not increase the catalytic rate of limit dextrinase i.e. this is not a true activation. On the other hand, considerable activation was noted in assays that measured pullulan degradation by reduction in viscosity. Taken together, this suggested that maltodextrins altered the mode of action of limit dextrinase, causing more rapid decreases in viscosity or greater solubilisation of dye-linked pullulan fragments per cleavage event. The proposed mechanism of activation by alteration in action pattern was reminiscent of initial work in the discovery of xyloglucan endotransglycosylase. Therefore, the ability of limit dextrinase to catalyse transglycosylation reactions into pullulan was tested and confirmed by an assay based on the incorporation of a fluorescently labelled maltotriose derivative into higher-molecular-weight products. The transglycosylation reaction was dependent on limit dextrinase activity and was enhanced in more highly purified preparations of limit dextrinase. Transglycosylation was inhibited by unlabelled maltotriose. How transglycosylation accounts for the apparent activation of limit dextrinase by maltodextrins and the physiological relevance of this novel reaction are discussed.