Effect of Extrusion Cooking on Functional Properties and in vitro Starch Digestibility of Barley‐Based Extrudates from Fruit and Vegetable By‐Products

Abstract

Barley flour and barley flour-pomace (tomato, grape) blends were extruded through a co-rotating twin-screw extruder. The aim of the present study was to investigate the effects of die temperature, screw speed, and pomace level on water absorption index (WAI), water solubility index (WSI), degree of starch gelatinization, and in vitro starch digestibility using a response surface methodology. The selected extrudate samples were examined further using differential scanning calorimetry (DSC) and polarized light microscopy, respectively. The WAI of barley-pomace extrudates was affected by increasing pomace level. Temperature had significant effect on all types of extrudate but screw speed had significant linear effect only on barley and barley-grape pomace extrudates on degree of starch gelatinization. Although no gelatinization peak was detected, an endotherm was observed on all selected extrudates. In general, extrusion cooking significantly increased in vitro starch digestibility of extrudates. However, increasing level of both tomato and grape pomace led to reduction in starch digestibility.

Stability and Functionality of Grape Pomace Used as a Nutritive Additive During Extrusion Process

“…At 16% moisture level, WSI exhibited a direct trend with increased screw speed, and an inverse trend with 5% GP inclusion. These results are in line with the previously reported WSI range [17]. The lower WSI of GP extrudates was consistent with their higher WAI, which was further proved by the negative correlation (-0.76) between WSI and WAI ( Table 1).…”

“…As increased screw speed results in an increased SME, that would ultimately result in more breakdown of the starch. This suggests that high screw speed renders more soluble products [17]. GP contains fiber, carbohydrates, and proteins components that can provide more hydrophilic forces to compete for water than the starch [16], which could be another explanation to the higher WAI found in extrudates with GP.…”

“…The GP barley flour extrudates with 2% GP (at 160°C, 200 rpm) had higher preferences for overall product quality, while increasing GP proportion above 6% reduced expansion [16]. Extrusion processing also reduced the total phenolic content (TPC) of the GP barley flour extrudates compared to the raw material [17]. However, both of these studies lack a reasonable explanation of the positive interactions between GP and barley flour, which can greatly affect the textural properties and is evident from our recent findings on carrot and cherry pomace incorporation in cornstarch extrudates [18,19].…”

“…Briefly, 200 µl of the extracts were mixed with 12.5 µl of Folin-Ciocalteu reagent and then 37.5 µl 20% Na 2 CO 3 in a 96-well legumes, fruits, and vegetables [23]. Studies on the incorporation of pomace into extruded products showed that increased pomace levels beyond a certain level had negative effect on the expansion quality [16,17,20,27,28]. However, recent studies indicated that carrot and cherry pomace incorporation into cornstarch extrudates resulted in better expansion and nutritional quality [18,19].…”

Pelet ve Ekstrude Mamaların Köpek Beslemede Kullanılması

“…For optimal protein quality in dog food production, extrusion conditions were found to be 110-150°C, with a 300 g/kg moisture content, and 120-160°C drying temperature [3,4] . During this process, undesired enzymes are denatured, anti-nutritional factors are destroyed, and food is sterilised, all without impairing the natural odour and taste [5][6][7][8] . Extrusion also significantly increases digestible starch [9] , but may also cause undesirable effects, such as vitamin (A, E, thiamine) deficiencies, lipid oxidation, and a reduction in amino acid content through the Maillard reaction [6] .…”