Application of mannitol producing Leuconostoc citreum TR116 to reduce sugar content of barley, oat and wheat malt-based worts

Abstract

Achieving a high monosaccharide composition in malt wort is instrumental to achieve successful lactic acid bacteria fermentation of malt based beverages. The conversion of monosaccharides to alternative metabolites such as the sweet polyol, mannitol with heterofermentative strains presents a novel approach for sugar reduction and to compensate for the loss of sweetness. This work outlines the application of an adopted mashing regimen with the addition of exogenous enzymes to produce wort with high fructose content which can be applied to different malted grain types with consistently efficacious monosaccharide production for bacterial fermentation. The so produced worts are then fermented with Leuconostoc citreum TR116 a mannitol hyper-producer. Malted barley, oat and wheat were mashed to stimulate protein degradation and release of free amino acids along with the enzymatic conversion of starch to fermentable sugars. Amyloglucosidase and glucose isomerase treatment converted di- and oligo-saccharides to glucose and provided a moderate fructose concentration in malt worts which was consistent across the three cereals. Fructose was completely depleted during fermentation with Lc. Citreum TR116 and converted to mannitol with high efficiency (>90%) while overall sugar reduction was >25% in all malt worts. Differences in amino acid composition of malt worts did not significantly affect growth of Lc. Citreum TR116 but did affect the formation of the aroma compounds diacetyl and isoamyl alcohol. Organic acid production and acidification of wort was similar across cereal substrates and acetic acid formation was linked to yield of mannitol. The results suggest that differences in amino acid and fructose content of malt worts considerably change metabolite formation during fermentation with Lc. Citreum TR116, a mannitol hyper-producer. This work gives new insight into the development of consumer acceptable malt based beverages which will provide further options for the health conscious and diabetic consumer, an important step in the age of sugar overconsumption.

Keywords: Amyloglucosidase; Glucose isomerase; Heterofermentative; Mannitol; Sugar reduction.