Development and Characterization of Omega-3 Fortified Extruded Bean Snacks
February 21, 2007

Extrusion is a unique food processing technique which improves the quality of edible beans by inactivating anti-nutritional components and improving nutrient bioavailability. Extruded snacks are deficient in terms of fiber and omega-3 fatty acids. Thus extruding dry beans can be a means of developing health based extruded snacks by fortifying bean flour and cold milled flaxseed, which are major sources of fiber and omega-3 fatty acids respectively. The objectives of this project were i) to develop a method for producing extruded snack products from omega-3 fortified dry bean flour; ii) to assess the shelf life and sensory properties of the extruded bean snack products and iii) to establish an optimal production method (scale-up) for converting omega-3 fortified dry bean flour into an extruded snack food based on sensory feedback from potential consumers.

Pinto Snack
0% Flaxseed  5% Flaxseed  10% Falxseed   15% Flaxseed   20% Flaxseed 

Extrusion was conducted according to standard corn curl processing method developed by Wenger. Screw speed and water absorption levels were adjusted at 310 RPM and 0.128 kg/min respectively. Specific mechanical energy values decreased as the cold milled flaxseed addition increased during process. Extruded snack quality analyses indicated that 5 and 10 % cold milled flaxseed addition did not affect expansion ratio, bulk density, water activity and snack firmness parameters. Extruded snacks made with navy bean flour showed slightly lower bulk density than extruded snacks made with pinto flour. We might relate this phenomenon due to the differences in cooking and pasting properties of pinto and navy flours. However extruded pinto snacks fortified with 5 and 10% cold milled flaxseed gave higher expansion ratio scores compared to extruded navy snacks (See image above).

Linear positive relationship was observed between the snack bulk density and cold milled flaxseed fortification. Bulk density scores significantly (P<0.05) decreased as the percentage of cold milled flaxseed increased in bean snacks. This might be due to the high levels of protein, oil, fiber and gums of flaxseed which deteriorated extrusion process. In addition cold milled flaxseed fortification increased water activity (aw) values of extruded bean snacks. Extruded snacks fortified with 15 and 20% cold milled flaxseed addition significantly (P<0.05) increased water activity values of extrudates. Flaxseed oil fraction serves as a lubricant and assists extrusion by decreasing specific mechanical energy. However protein, fiber and gum fractions of flaxseed absorb water, which increases water activity of the end product. High water activity may cause gumminess and chewiness in the end product. Detrimental impact of water activity on snack texture attributes can be improved with additional drying. This phenomenon might be important for scale up, since additional drying will be required for bean snacks fortified with 15 and 20% cold milled flaxseed. Shelf life stability of extruded bean snacks was evaluated by headspace volatile analysis. Gas chromatography was conducted and secondary metabolites of lipid oxidation were analyzed. Propanal the primary aldehyde of ?-linolenic acid was not detected in all extruded bean snack samples at 8-week storage. Results indicated no lipid oxidation due to cold milled flaxseed addition. In addition antioxidant rich pinto and navy flours might have an impact on shelf life stability during storage. In conclusion extruded bean snacks could be introduced as high fiber and high omega-III products to the snack food market. Bean snacks fortified with 5 and 10% cold milled flaxseed showed superior quality parameters and shelf life stability.




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