From Field Barley to Malt: Detection and Specification of Microbial Activity for Quality Aspects

167

While beer provides a very stable microbiological environment, a few niche microorganisms are capable of growth in malt, wort and beer. Growth of mycotoxin‐producing fungi during malting, production of off‐flavours and development of turbidity in the packaged product due to the growth and metabolic activity of wild yeasts, certain lactic acid bacteria (LAB) and anaerobic Gram negative bacteria, impact negatively on beer quality. It follows that any means by which microbial contamination can be reduced or controlled would be of great economic interest to the brewing industry and would serve the public interest. There has been an increasing effort to develop novel approaches to minimal processing, such as the exploitation of inhibitory components natural to raw materials, to enhance the microbiological stability of beer. LAB species, which occur as part of the natural barley microbiota, persist during malting and mashing, and can play a positive role in the beer‐manufacturing process by their contribution to wort bioacidification or the elimination of undesirable microorganisms. Other naturally occurring components of beer that have been valued for their preservative properties are hop compounds. It may be possible to enhance the antimicrobial activities of these compounds during brewing. Some yeast strains produce and excrete extracellular toxins called zymocins, which are lethal to sensitive yeast strains. Yeast strains resistant to zymocins have been constructed. Imparting zymocinogenic activity to brewing yeast would offer a defence against wild yeasts in the brewery. Thus, the antimicrobial properties of naturally occurring components of raw materials can be exploited to enhance the microbial stability of beer.

Section: Antifungal Compoundsmentioning

confidence: 99%

Enhancing the Microbiological Stability of Malt and Beer - A Review

Vaughan

O'Sullivan

Sinderen

2005

167

“…Conditions that enable grain germination also favour microbial growth. Imbibed water rapidly activates the dormant microbes present in barley and therefore steeping can be regarded as a crucial step in malting with respect to microbial activity 32,41,45 . Microbial activity remains high during germination.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to germinating barley, the malting process involves another metabolically active component: the diverse microbial community that naturally colonizes the grains. The indigenous community harbours a wide range of microbes including numerous species of Gram-negative and -positive bacteria, yeasts and filamentous fungi 17,20,32,41,46 . In addition, each process step can be a source of additional microbes and their metabolites 32,45 .…”

Section: Introductionmentioning

confidence: 99%

Indigenous Microbial Community of Barley Greatly Influences Grain Germination and Malt Quality

Laitila

Kotaviita

Peltola³

et al. 2007

The present study was carried out to investigate the impacts of bacterial and fungal communities on grain germination and on the malting properties of good‐quality two‐row barley. In order to suppress the growth of bacterial and/or fungal communities, various antibiotics were added to the first steeping water of barley. This study was also designed to explore the dynamics of the bacterial community in the malting process after antimicrobial treatments by polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE). The diverse microbial community played an active role in the malting ecosystem. Even previously undescribed bacterial species were found in the malting ecosystem. Suppression of the bacterial community mainly consisting of Gram‐negative bacteria was advantageous with respect to grain germination and wort separation. In addition, more extract was obtained after antibacterial treatments. The fungal community significantly contributed to the production of microbial β‐glucanases and xylanases, and was also involved in proteolysis. An improved understanding of the complex microbial community and its role in malting enables a more controlled process management and the production of high quality malt with tailored properties.

“…Synthesis of bacteriocins 3,10,22 and antifungal compounds 28 and depletion of nutrients can also play a role 20 . Of significance with respect to sorghum malting is that many anti-microbialproducing lactic acid bacteria have been isolated from samples of raw sorghum 12 .…”

Section: Introductionmentioning

confidence: 99%

Control of the Growth of Coliforms and Moulds in Sorghum Malting by Bacterial and Yeast Cultures

Lefyedi

Taylor

2007

Traditional outdoor floor malted sorghum can be contaminated with high levels of coliform bacteria and moulds that can potentially produce mycotoxins. The effect of steeping with the addition of bacterial and yeast starter cultures on microbial contamination, toxicity and diastatic power (DP) of sorghum malt was investigated. Lactobacillus plantarum, Pedicococcus pentosaceus and Saccharomyces species were selected on the basis of inhibition of fungal species using the disc diffusion assay. Steeping the sorghum with the addition of these cultures at 10 7 -10 8 cfu /mL reduced the level of moulds by one to two log cycles, with the Saccharomyces culture appearing to be the more effective and L. plantarum the least effective. Coliforms, where present in significant numbers, were reduced to levels of <10 1 -10 2 by steeping with the cultures, with the P. pentosaceus culture appearing to be the most effective and Saccharomyces the least effective. There were no detectable amounts of mycotoxins and no significant cytotoxicity in the malts in either the controls or the culture-steeped malts. Steeping with the cultures did not affect malt DP. The use of such P. pentosaceus and Saccharomyces sp. cultures could be an alternative to chemical treatment for the control of microbial contamination in sorghum malt.