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ABSTRACT
The purpose of this study was to investigate how wheat cultivar, growth location, type of mill, LMW sugar composition of wheat flours, mixing time, and type of mixer affected yeast fermentation. Also studied was the effect of yeast fermentation and LMW sugar composition on hearth bread quality. To achieve this, 36 different flours were produced from two different mills using six different wheat cultivars grown at three locations. Yeast fermentation in doughs, measured as gas production, was determined using realtime pressure measurements and GasSmart software. A short mixograph mixing or spatula mixing was not efficient enough to rehydrate instant dry yeast. Compressed yeast and a short mixing time were enough to reach maximum fermentation rate. Maximum pressure after 210 min of fermentation was higher for instant dry yeast than for compressed yeast. Wheat cultivar, and growth location had a significant effect on LMW sugar composition. Wheat cultivar, growth location, and type of mill used significantly affected pressure curve parameters. Oligosaccharides and damaged starch were positively correlated, and ash content and flour yield were negatively correlated with pressure curve parameters. Hearth bread characteristic crumb structure was positively correlated with all pressure curve characteristics except fast fermentation rate. Increased levels of mono- and disaccharides in wheat flour gave hearth breads with a more round shape.
The characteristic structure and volume of yeast-fermented products depend on the production of carbon dioxide by the yeast (Eliasson and Larson 1993). A desirable loaf volume is achieved only if the dough provides a favorable environment for yeast growth and gas generation and, at the same time, possesses a gluten matrix capable of maximum gas retention. The latter attribute is most conveniently determined by measuring the volume increase of fermenting dough, whereas gas production can be estimated by any of several available procedures such as the oven rise recorder method (Brabender OHG, Duisburg, Germany), alveograph method (Approved Method 54-30, AACC 2000), and pressure meter methods.
AACC Approved Methods describe a pressure meter method (Approved Method 22-11) and a volumetric method (Approved Method 22-14) for measuring the gas production that is an index of diastatic activity. The former employs the pressure meter described by Sandsledt and Blish (1934) and Malloch (1939) in which the pressure produced in a fermentation vessel...