The effect of lactic acid bacteria and fungi on the malting of barley

Hattingh, Melanie (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Barley malt is the predominant raw material for beer brewing world-wide. To meet consumer demand, a constant high quality malt product is required. Malt quality is determined by the degree of substrate hydrolysis during germination and mashing which serves as fermentable substrates for alcoholic fermentation during brewing. It is often difficult to sustain malt of high quality due to inconsistent malt batches and poor germination capacities of dormant barley. External additives such as chemicals and gibberellic acid have been used to overcome these difficulties but are unwanted in the beverage industry. Maltsters are consequently always in search of alternative solutions. Microbes produce diverse enzymes which can contribute to substrate hydrolysis during germination. The development of such starter cultures might provide a natural and economically feasible alternative to augment barley germination. Starter culture technology has been employed in the malting industry, although the main focus has been to improve the microbial stability of malt. The exploitation of cultures with hydrolytic capabilities to augment barley germination is consequently largely unexplored. The aim of this study was to develop a starter culture which can contribute to the enzymatic degradation of barley polymers. Geotrichum spp. and Lactobacillus plantarum were isolated from substrates rich in polymers present in barley and screened for enzymatic capabilities. Geotrichum spp. produced cellulase, xylanase, protease and β-glucanase activities, while L. plantarum harboured cell-bound and extracellular α-amylase activities. These cultures were added in different combinations during the malting of Erica and SSG 564 cultivars, but did not enhance germination significantly. Improved malt parameters did not correlate with microbial enzyme activities and the data were not repeatable. Preliminary plate assays could thus not be used to predict enzyme production in a malting environment. Cell-free supernatants with known enzyme activities of Aspergillus sp., Trichoderma reesei and Rhizopus sp. significantly enhanced malt quality. To our knowledge, the use of fungal supernatant to augment malt modification is a novel concept. Supernatant is more convenient than starter cultures and will aid to deliver more constant malt products than live cultures, as known enzyme levels are added.

AFRIKAANSE OPSOMMING: Garsmout is wêreldwyd die oorheersende roumateriaal vir bier brou. Om die aanvraag van verbruikers te bevredig, word 'n konstante hoë gehalte mout produk vereis. Die kwailiteit van mout word bepaal deur die graad van substraathidrolise gedurende ontkieming, wat dien as fermenteerbare substraat vir alkoholiese fermentasie tydens verbrouing. Dit is dikwels moeilik om ʼn konstante, hoë gehalte, moutproduk te lewer as gevolg van variasie in mout en die swak ontkiemingsvermoë van dormante gars. Hierdie probleem kan oorbrug word met eksterne toevoegings soos chemikalieë en gibberelliensuur, maar dit is nie ʼn gewensde praktyk in die broubedryf nie. Vermouters is gevolglik gedurig op soek na alternatiewe oplossings. Mikroörganismes produseer diverse ensieme wat kan bydra tot substraathidrolise gedurende ontkieming. Die ontwikkeling van sodanige suurselkulture is moontlik 'n natuurlike en ekonomies praktiese alternatief om die ontkieming van gars te stimuleer. Suurselkulture is reeds in die moutindustrie gebruik, alhoewel die fokus hoofsaaklik was om die mikrobiese stabiliteit van mout te verbeter. Die konsep om kulture met hidrolitiese vermoëns te gebruik om garsontkieming aan te vul is gevolglik grootliks onverken. Die doel van hierdie studie was om 'n suurselkultuur te ontwikkel wat kan bydra tot 'n ensiematiese afbraak van die polimere in gars. Geotrichum spp. en Lactobacillus plantarum is uit substrate ryk aan polimere teenwoordig in gars geïsoleer en vir hul ensiem aktiwiteite getoets. Geotrichum spp. het sellulase, xylanase, protease en β-glukanase aktiwiteit getoon, terwyl L. plantarum sel-gebonde en ekstrasellulêre α-amilase aktiwiteit getoon het. Hierdie kulture is in verskillende kombinasies tydens die vermouting van Erica en SSG 564 kultivars bygevoeg, maar het nie tot ʼn verbetering in die ontkieming van die gars gelei nie. Geen korrelasie is gevind tussen verbeterde mout parameters en mikrobiese ensiemaktiwiteit nie. Die resultate was ook nie herhaalbaar nie. Voorlopige plaattoetse kan dus nie as 'n maatstaf gebruik word om ensiem produksie deur suurselkulture in vermounting te voorspel nie. Sel-vrye supernatante van Aspergillus sp., Trichoderma reesei en Rhizopus sp., met bekende ensiem aktiwiteit, het die gehalte van mout aansienlik verbeter. Sover ons kennis strek is die gebruik van supernatante van fungi om die ontkieming van gars te stimuleer ʼn nuwe konsep. Supernatant is meer gerieflik as suurselkulture en sal help om konstante mout produkte te lewer aangesien ensiemvlakke beter beheer kan word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/79911
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