Glucosidase inhibitors: new approaches to malting efficiency

Lead Research Organisation: John Innes Centre
Department Name: Metabolic Biology

Abstract

The brewing and distilling industries are of enormous economic importance to the UK. They have a major impact on farming because they use almost 2M tonnes of UK-grown barley (about one third of the crop, occupying one third of a million hectares of land) every year, they provide employment for tens of thousands of people, and their products are enjoyed not only in the UK but in many countries around the world. There is strong pressure on the industry to increase the efficiency with which barley grain is converted into beer and whisky. This is in part to maintain profitability, but also to reduce the production of waste and the amount of energy used in the conversion process. The basic conversion process occurs in four main stages. First, during malting, the barley grains are soaked in water then allowed to start to germinate. Inside the germinating grain, enzymes are produced that can convert the starch stored in the grain to sugars. Second, during kilning, the grain is heated to dry it out so that germination stops. Third, the grain is milled then mixed with hot water. During this mashing process, the enzymes convert the starch to sugars. Finally, the sugar-containing liquid is drained off and yeast is added. The yeast converts the sugars to alcohol. One of the major losses during the conversion of grain to beer and whisky occurs during malting. As soon as the enzymes are produced, they start to convert starch to sugars inside the seed, and the sugars fuel the growth of rootlets. Thus some of the starch store is lost before the mashing stage, reducing the potential yield of alcohol and resulting in the production of unwanted rootlets. This loss is between 5% and 10% of the starch. In the context of a market value of £20bn for the brewing industry alone, even a small reduction in the extent of starch loss during malting would have huge economic benefits. Because of the economic importance of this malting loss, several different methods to prevent rootlet growh have been tested. However these have not been applied commercially, because of cost, toxicity, or adverse effects on the quality of the malt. We have discovered that both rootlet growth and starch loss in germinating barley seeds can be reduced or prevented by the application of tiny amounts of natural plant products, called iminosugars. These products have the potential to reduce malting losses without undesirable side effects. Understanding how they work inside the seed will also provide new information that will help in developing better varieties of barley for brewing and distilling. In this project we will test natural products in a 'micromalting' system that mimics real malting, and identify which ones are suitable for commercial trials. We will use biochemical and molecular methods to discover precisely how these products prevent the growth of rootlets, and the loss of starch. This information will enable us to identify genes in barley that are important in determining the malting quality of the grain. To ensure that our research is relevant to the needs of the brewing and distilling industries, we will regularly consult an Advisory Panel that includes an expert on these industries, and also experts on barley grain germination, plant natural products, and malting.

Technical Summary

Our aim is to enhance efficiency of the malting, brewing and distilling industries by exploiting new inhibitors of barley seed germination. In malting, the seedling accumulates starch-hydrolysing enzymes in the starch-storing endosperm. Seedling growth is then stopped by drying, and the malt is milled and mixed with hot water to allow the starch-hydrolysing enzymes to convert starch to sugars. These sugars are fermented by yeast to produce alcohol. The goal of malting is to optimise accumulation of starch-hydrolysing enzymes while minimising starch degradation and rootlet growth in the seedling: these processes result in significant losses of fermentable material (5-10% of the grain dry weight). We have discovered that rootlet growth and starch degradation are strongly inhibited by low concentrations of natural compounds including the iminosugar deoxynojirimycin. These natural compounds are thus potentially exciting new tools for reducing malting losses. To exploit this discovery, we will use a library of naturally-occurring compounds to identify the most potent inhibitors of rootlet growth. Inhibitors will be applied to seeds undergoing micromalting. The impact on malting loss, malt quality, and food safety will be assessed and the commercial potential evaluated. In parallel we will use hypothesis-driven biochemical approaches to discover how iminosugars inhibit starch degradation in the endosperm. The gene(s) thus identified will be genetically mapped, and natural sequence variation assessed in a unique collection of elite barley cultivars to test, by association analysis, whether it plays a role in malting quality. This will require the collection to be phenotyped for relevant traits, including cell wall modification and starch loss during germination. The information will reveal the potential importance of gene(s) we discover, and also permit a large-scale genome-wide genetic analysis of malting quality in elite barley germplasm.

Planned Impact

This project addresses the main focus of CIRC: it will elucidate molecular and biochemical mechanisms behind the major trait of commercial interest in barley. The project is central to both the Seed Structure and Composition and Germination Properties research challenges of CIRC. It specifically addresses the call to increase malt yield and quality. The project will directly benefit the malting, brewing and distilling industries by providing means to reduce malting losses and thus increase efficiency and profitability. These industries are major exporters (Scotch whisky exports are worth £3bn a year) so the project will contribute to the economic competitiveness of the United Kingdom. It will have positive environmental impacts, by reducing waste and energy consumption involved in removing rootlets and increasing the amount of fermentable material generated from a given level of inputs into malting. The research will also identify new targets to improve barley malting quality through breeding, providing direct benefit to the barley breeding sector, and indirect benefit to growers and the malting / brewing / distilling industries. The project falls within several BBSRC priorities in addition to CIRC. It is relevant to Bioenergy, both because cereal grains are the main source of first generation biofuels in the UK and because it can potentially provide new information on cell wall degradation. It is also highly relevant to two Policy Priorities: Increased international collaboration (collaboration with Birte Svensson and William Willats, both in Denmark, is central to the project) and Economic and social impact. The project has potential impacts in a wide range of other public and commercial sectors. 1. Pre-harvest sprouting and related problems. Premature production of starch-hydrolysing enzymes and consequent germination prior to harvest can cause huge crop losses in wheat. Better understanding of endosperm carbohydrate metabolism and rootlet growth incereal seeds will underpin rational attempts to solve this problem. 2. Industrial applications of carbohydrate-active enzymes. New information about diversity and properties of these enzymes could improve or extend their applications in industries as diverse as food processing, medical diagnostics and textiles. 3. Medical applications. Inhibitors of carbohydrate-active enzymes are used in the treatment of diabetes, obesity and various diseases including cancers and pathogen infections. Our project will provide new inhibitors as lead compounds for drug discovery. The project provides excellent training for the postdoctoral researcher, and opportunities for public engagement and teaching. Lay people are generally interested in how alcoholic beverages are produced, and our project deals with simple but important aspects of chemistry and biology relevant to everyday life. We will contribute informative and entertaining displays and presentations of our work to public events and as teaching materials for schools.
 
Description During the germination of barley grains, starch in the grain is broken down to provide sugars for the growth of the emerging seedling. During malting - the initial stage of brewing and distilling in which barley grains are allowed to germinate for a few days - starch breakdown and seedling growth are undesirable because they reduce the amount of starch available for fermentation to produce alcohol.
We discovered that naturally-occurring compounds (iminosugars) can reduce starch breakdown when applied to germinating barley grains. We established that the iminosugars inhibit a specific enzyme that breaks down the cell walls within which the starch is contained. If cell wall breakdown is prevented, the starch is inaccessible to the enzymes that normally convert it to sugars. Iminosugars also reduce root growth of barley seedlings. Our work provides new information about processes important for controlling the rate of barley grain germination and seedling growth.
We investigated whether iminosugars could be used during malting to reduce starch breakdown and seedling growth. In a scaled-down version of the malting process, these compounds had significant, positive effects on malting efficiency. Our result establishes that low concentrations of naturally occurring compounds can be used to influence the malting process. This information will be of interest to the malting industry
In a parallel approach, we measured the malting performance of grains from a large number of different, genetically characterised types of barley. The results reveal that several genes are important for malting efficiency. Further work is being done to identify precisely which genes are involved. This information will be of direct used to barley breeders.
Exploitation Route Our results are of use to the malting and barley breeding industries. We have already worked closely with colleagues in these industries, and will be putting out further information in papers, via contacts, and through the BBSRC Crop Industry Club.
Sectors Agriculture, Food and Drink

 
Description Findings from this research have been made available to R+D staff in malting, brewing and barley breeding companies. The findings 1. raise awareness of the potential for using natural plant and microbial products to enhance the malting process in various ways 2. identify new, specific enzyme targets for breeding and chemical interventions to increase malting efficiency
First Year Of Impact 2015
Sector Agriculture, Food and Drink
Impact Types Economic