Effect of Extrusion Parameters on Feed Starch Gelatinization and Protein In Vitro Digestibility

The author mainly studied the effects of extrusion parameters on the starch gelatinization degree and protein in vitro digestibility of feed from four aspects: material moisture content, feeding speed, screw speed, and barrel temperature.Effect of material moisture content on starch gelatinization degree: The starch gelatinization degree first increases rapidly with the increase of moisture content, then maintains a certain high level, but when the moisture content is too high, the gelatinization degree shows a decreasing trend.Effect of material moisture content on in vitro protein digestibility: In vitro protein digestibility increases with higher moisture content, but excessively high moisture reduces the shear friction effect on the feed, shortens the residence time in the extrusion chamber, and may decrease the degree of protein denaturation.Effect of feeding rate on starch gelatinization degree: The starch gelatinization degree increases with the increase of feeding rate, but the increase is relatively small. The in vitro protein digestibility also increases with the increase of feeding rate, but the increase is relatively small, and the pattern is similar to that of starch gelatinization degree.Effect of screw speed on starch gelatinization degree: as screw speed increases, starch gelatinization degree first increases rapidly, then slows down after 150 r/min; the effect of screw speed on protein in vitro digestibility is similar to that of starch gelatinization degree, first increasing rapidly, then slowing down after 200 r/min.The barrel temperature has a significant impact on the degree of starch gelatinization. The degree of starch gelatinization increases rapidly with the rise of barrel temperature, then levels off after 120 ℃ and remains at a high level.The barrel temperature has a significant effect on the in vitro digestibility of protein. When the temperature is below 135 °C, the in vitro digestibility of protein increases with the rise of barrel temperature; when the temperature exceeds 135 °C, it decreases with the rise of barrel temperature, and the rates of increase and decrease are similar.The author concluded that the suitable extrusion conditions for the feed are: material moisture content 26%–30%, feeding speed 30–60 r/min, screw speed 150–250 r/min, and temperatures of the middle and discharge sections of the barrel at 105–120 °C and 120–135 °C, respectively.Under these conditions, the starch gelatinization degree of the feed is 90%–92%, and the in vitro protein digestibility is 90%–92%.(Source: Cheng Yifeng et al., Fishery Modernization, 2009, 36(6): 54-59.)Anonymous editor)