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Effect of Extrusion Process Parameters on the Quality of Buckwheat Flour Mixes¹

¹Published with the approval of the Director of the Agricultural Experiment Station, North Dakota State University, Fargo. ²Associate professor and statistical consultant, respectively, Department of Cereal Science and Information Technology Services, North Dakota State University, Fargo, ND 58105. ³Corresponding author. E-mail: rayasdu@okway.okstate.edu Present address: Food and Agricultural Products Research and Technology Center, Oklahoma State University, Stillwater, OK 74078. Fax: 405-744-6313. ⁴Researcher, Department of Plant Products, Food Technology, University of Agriculture and Technology, Olsztyn-Kortowo, Poland.

A response surface analysis using a second-order central composite design was used to study the effect of extrusion process parameters on the extrudate quality of three blends containing buckwheat flour. The extrudates were prepared as three blends. Blend 1 was a 55:40:5 (w/w) mix of light buckwheat flour, wheat flour, and nonfat dry milk (NFDM). Blend 2 was a 40:55:5 mix of light buckwheat flour, corn meal, and NFDM. Blend 3 was a 30:60:10 mix of light buckwheat flour, corn meal, and NFDM. The blends were processed in a twin-screw extruder with factorial combinations of the parameters including: process temperatures of 95–150°C, dough moisture of 15–22%, and screw speeds of 260–390 rpm. The linear components alone significantly explained most of the variation of expansion index, bulk density, water absorption, and breaking strength. The greatest amount of variability was explained by process temperature for blend 1. Dough moisture accounted for the greatest amount of variation for blends 2 and 3. Maximum predicted expansion index values and high water absorption percentages were obtained at low dough moisture levels. Dough moisture and process temperatures were the most important factors predicting bulk density. Sensory evaluation of texture, color, flavor, and general acceptability scores of selected samples ranked blend 3 > blend 2 > blend 1. The in vitro protein digestibility values ranked blend 1 > blend 2 > blend 3. An increase of up to 9.5% units in the protein digestibility values was observed when compared to the nonextruded raw blends.