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Factors Influencing Yeast Fermentation and the Effect of LMW Sugars and Yeast Fermentation on Hearth Bread Quality

¹MATFORSK, Norwegian Food Research Institute, Osloveien 1, N -1430 Ås, Norway. ²Corresponding author. Phone: + 47 64 97 01 06. Fax: + 47 64 97 03 33. E-mail: stefan.sahlstrom@matforsk.no ³University of Nebraska, Department of Agronomy, Institute of Agriculture and Natural Resources, Lincoln, NE 68583-0915. ⁴Present address: Room 303, Leema Bldg. #146 Soosong dong Chong ku, Seoul 110-140, Korea. ⁵Present address: Wheat Marketing Center, 1200 N.W. Naito Parkway, Suite 230, Portland, OR 97209-2800.

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.