Effects of extrusion cooking on physical and nutritional quality of puffed snacks made from blends of barley and green lentil flours
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This work explored the potential of using blends of a high dietary fiber cereal (i.e., barley) and a high protein pulse (i.e., green lentil) flours to produce nutritionally-dense puffed snacks using extrusion cooking. Five barley: green lentil blending ratios (100: 0, 75: 25, 60: 40, 45: 55, 0: 100, db), three feed moistures (15, 18, 21 g/100 g) and two barrel temperature profiles (60/80/100/120/130℃ and 70/90/110/130/140℃ from the feeder to the extruder die) were employed. Nutritional attributes of puffed snacks including protein content, amino acid composition, in vitro protein digestibility (IVPD), in vitro protein digestibility corrected amino acid score (IVPDCAAS), insoluble, soluble and total dietary fiber contents were tested to evaluate the nutritional value of extrudates. Physical attributes including density, expansion index, textural properties (i.e., hardness, crispness and crunchiness) and color were also investigated. Extrusion significantly (p < 0.0001) enhanced the IVPD values, especially at low feed moisture and high die temperature. Blending improved the limiting amino acid score of blended flours and their extrudates and hence increased the IVPDCAAS of extrudates, where 45: 55 barley: green lentil blend had the highest average IVPDCAAS. Extrusion (p < 0.0001) significantly decreased soluble and total dietary fiber contents of the blends 45: 55 and 60: 40. High die temperature improved the overall expansion of extrudates significantly (p < 0.0001). The effect of feed moisture on expansion varied with the blends. Extruded blend 45: 55 showed the lowest hardness and the highest crispness, followed by blend 60: 40. Compared to the flours, extrudates showed darker color, redder and yellower tones. Overall, barley and green lentil blends of 45: 55 and 60: 40 had better nutritional and physical properties compared to the other blends in this study, showing promising application in the real market. The results of this study indicated that using blends of cereal and pulse flours to replace traditional starchy materials and producing nutritious puffed snacks with acceptable physical quality is achievable.