David J. Cook

Perception of taste intensity in solutions of random-coil polysaccharides above and below c∗

Sensory paired comparison tests were used to study differences in taste intensity in solutions of hydroxypropylmethyl cellulose (HPMC) at concentrations above (1.0% w/w) and below (0.2% w/w) c*, the coil-overlap concentration (the point at which viscosity changes abruptly with increasing thickener). The sweetness intensities of aspartame (250 ppm), sucrose (5% w/w), fructose (4.5% w/w) and neohesperidin dihydrochalcone (39 ppm) and the saltiness of sodium chloride (0.35%) were all found to be significantly reduced in the more viscous HPMC solution. There was no significant effect of HPMC concentration on the acidity of citric acid (600 ppm) or the bitterness of quinine hydrochloride (26 ppm). The sweetness intensities of sucrose and aspartame were likewise investigated in two further hydrocolloid solutions, guar gum and λ-carrageenan. Experiments were designed so that the ratios of the thickener concentrations (above and below c*) to their measured c* values remained constant. The sweetness of sucrose was found to be significantly reduced in the more viscous guar gum solution (P<0.05) and that of aspartame was reduced in the λ-carrageenan above c* (P<0.001). A multiple paired comparison design was used to show that the perceived sweetness of 6.5% sucrose in 1.0% HPMC did not differ significantly from that of 5% sucrose in 0.2% HPMC. The magnitude of effect with aspartame was broadly analogous.

The prevalence and impact of Fusarium head blight pathogens and mycotoxins on malting barley quality in UK

Fusarium head blight (FHB) caused by Fusarium and Microdochium species can significantly affect the yield of barley grain as well as the quality and safety of malt and beer. The present study provides new knowledge on the impacts of the FHB pathogen complex on the malting and brewing quality parameters of naturally infected barley. Quantitative real-time PCR and liquid chromatography double mass spectrometry were used to quantify the predominant FHB pathogens and Fusarium mycotoxins, respectively, in commercially grown UK malting barley samples collected between 2007 and 2011. The predominant Fusarium species identified across the years were F. poae, F. tricinctum and F. avenaceum. Microdochium majus was the predominant Microdochium species in 2007, 2008, 2010 and 2011 whilst Microdochium nivale predominated in 2009. Deoxynivalenol and zearalenone quantified in samples collected between 2007 and 2009 were associated with F. graminearum and F. culmorum, whilst HT-2 and T-2, and nivalenol in samples collected between 2010 and 2011 correlated positively with F. langsethiae and F. poae, respectively. Analysis of the regional distribution and yearly variation in samples from 2010 to 2011 showed significant differences in the composition of the FHB species complex. In most regions (Scotland, the South and North of England) the harvest in 2010 had higher concentrations of Fusarium spp. than in 2011, although no significant difference was observed in the Midlands between the two years. Microdochium DNA was significantly higher in 2011 and in the North of England and Scotland compared to the South or Midlands regions. Pathogens of the FHB complex impacted negatively on grain yield and quality parameters. Thousand grain weight of malting barley was affected significantly by M. nivale and M. majus whilst specific weight correlated negatively with F. avenaceum and F. graminearum. To determine the impact of sub-acute infections of the identified Fusarium and Microdochium species on malting and brewing quality of naturally infected samples, selected malting barley cultivars (Optic, Quench and Tipple) were micromalted and subjected to malt and wort analysis of key quality parameters. F. poae and M. nivale decreased germinative energy and increased water sensitivity of barley. The fungal biomass of F. poae and F. langsethiae correlated with increased wort free amino nitrogen and with decreased extract of malt. DNA of M. nivale correlated with increased malt friability as well as decreased wort filtration volume. The findings of this study indicate that the impact of species such as the newly emerging F. langsethiae, as well as F. poae and the two non-toxigenic Microdochium species should be considered when evaluating the quality of malting barley.

Modification of fatty acid composition in tomato (Lycopersicon esculentum) by expression of a borage Δ6-desaturase

The improvement of nutritional quality is one potential application for the genetic modification of plants. One possible target for such manipulation is the modification of fatty acid metabolism. In this work, expression of a borage Δ6-desaturase cDNA in tomato (Lycopersicon esculentum L.) has been shown to produce γ-linolenic acid (GLA; 18:3 Δ6,9,12) and octadecatetraenoic acid (OTA; 18:4 Δ6,9,12,15) in transgenic leaf and fruit tissue. This genetic modification has also, unexpectedly, resulted in a reduction in the percentage of linoleic acid (LA 18:2 Δ9,12) and a concomitant increase in the percentage of α-linolenic acid (ALA; 18:3 Δ9,12,15) in fruit tissue. These changes in fatty acid composition are thought to be beneficial for human health.

Selection of yeast strains for bioethanol production from UK seaweeds.

Macroalgae (seaweeds) are a promising feedstock for the production of third generation bioethanol, since they have high carbohydrate contents, contain little or no lignin and are available in abundance. However, seaweeds typically contain a more diverse array of monomeric sugars than are commonly present in feedstocks derived from lignocellulosic material which are currently used for bioethanol production. Hence, identification of a suitable fermentative microorganism that can utilise the principal sugars released from the hydrolysis of macroalgae remains a major objective. The present study used a phenotypic microarray technique to screen 24 different yeast strains for their ability to metabolise individual monosaccharides commonly found in seaweeds, as well as hydrolysates following an acid pre-treatment of five native UK seaweed species (Laminaria digitata, Fucus serratus, Chondrus crispus, Palmaria palmata and Ulva lactuca). Five strains of yeast (three Saccharomyces spp, one Pichia sp and one Candida sp) were selected and subsequently evaluated for bioethanol production during fermentation of the hydrolysates. Four out of the five selected strains converted these monomeric sugars into bioethanol, with the highest ethanol yield (13xa0gxa0L−1) resulting from a fermentation using C. crispus hydrolysate with Saccharomyces cerevisiae YPS128. This study demonstrated the novel application of a phenotypic microarray technique to screen for yeast capable of metabolising sugars present in seaweed hydrolysates; however, metabolic activity did not always imply fermentative production of ethanol.

Malt-induced premature yeast flocculation: current perspectives

Premature yeast flocculation (PYF) is a sporadic problem for the malting and brewing industries which can have significant financial and logistical implications. The condition is characterised by abnormally heavy (and sometimes early) flocculation of yeast during brewery fermentations. The resulting low suspended yeast cell counts towards the end of the fermentation can result in flavour defects and incomplete attenuation (fermentation of sugars to alcohol). Despite several decades of research into the phenomenon, its precise nature and mechanisms have not been fully elucidated. In part this is because the term PYF has become a ‘catch-all’ syndrome which can have multiple origins. Furthermore, there are complex interactions in the malting and brewing processes which together mean that the PYF status of a malt sample is hard to predict at a generic level. Whether or not PYF is observed depends not only on barley quality, but on process factors in the maltings and to a substantial extent on the brewing yeast strain concerned. This article highlights the significance of PYF, and reviews current knowledge relating to the origins of this complex phenomenon.

Rapid analysis of formic acid, acetic acid, and furfural in pretreated wheat straw hydrolysates and ethanol in a bioethanol fermentation using atmospheric pressure chemical ionisation mass spectrometry

Atmospheric pressure chemical ionisation mass spectrometry (APCI-MS) offers advantages as a rapid analytical technique for the quantification of three biomass degradation products (acetic acid, formic acid and furfural) within pretreated wheat straw hydrolysates and the analysis of ethanol during fermentation. The data we obtained using APCI-MS correlated significantly with high-performance liquid chromatography analysis whilst offering the analyst minimal sample preparation and faster sample throughput.

Development of a Predictive Controller for Use on a Direct Converter for High-Energy Physics Applications

Recently, considerable interest has been shown in direct (matrix) converter topologies as an alternative to conventional motor drives. In general, when compared with existing three-phase motor drives (rectifier-inverter types), these topologies offer advantages, such as reduced space and weight (due largely to the removal of the large electrolytic capacitor), four-quadrant operation, and high-quality current waveforms. Consequently, there is now considerable interest regarding direct converters in areas such as aerospace, where issues such as the size and weight of the converter are important. The work presented in this paper capitalizes on these advantages in power conversion for high-power radio-frequency supplies, such as those used in high-energy physics research and associated applications.

High power, high voltage, high frequency transformer / rectifier for HV industrial applications

This paper presents a high voltage (HV), high frequency (HF) transformer with voltage multiplier. The described systems employ a low profile HV, HF transformers and voltage bridge technology multiplier. A model of the converter of 150 kW is presented and verified by Saber simulator. Design considerations and models of the HV, HF transformers are presented.

Flavour generation during commercial barley and malt roasting operations: a time course study.

The roasting of barley and malt products generates colour and flavour, controlled principally by the time course of product temperature and moisture content. Samples were taken throughout the industrial manufacture of three classes of roasted product (roasted barley, crystal malt and black malt) and analysed for moisture content, colour and flavour volatiles. Despite having distinct flavour characteristics, the three products contained many compounds in common. The product concentrations through manufacture of 15 flavour compounds are used to consider the mechanisms (Maillard reaction, caramelisation, pyrolysis) by which they were formed. The use of water sprays resulted in transient increases in formation of certain compounds (e.g., 2-cyclopentene-1,4-dione) and a decrease in others (e.g., pyrrole). The study highlights rapid changes in colour and particularly flavour which occur at the end of roasting and onwards to the cooling floor. This highlights the need for commercial maltsters to ensure consistency of procedures from batch to batch.

Formulating low-fat food: the challenge of retaining flavour quality.

Publisher Summary The term, “fat” can encompass a range of different materials but throughout this chapter, the term, “fat” has been used to refer to the triglyceride molecules present in food that are composed of a glycerol backbone esterified to three fatty acids. Fats form integral elements of cell membranes and contribute to cholesterol transport, blood clotting, immune function, and the manufacture of hormones for reproductive function. Certain fatty acids, linoleic acid and alpha-linolenic acid (essential fatty acids) must also be obtained directly from the diet as they cannot be made in the body. However, there is now little doubt that a diet high in fat is linked to the chronic health problems of Western society: obesity, heart disease, diabetes, and colon cancer. Fat has a higher energy value than protein or carbohydrate but does not appear to reduce hunger or induce satiety to the same extent as these other macronutrients. Diets high in saturated fatty acids and low in unsaturated fatty acids are linked to higher blood cholesterol levels and subsequent complications, such as coronary heart disease.