Influence of air equilibration time, sampling techniques, and storage temperature on enzymatic starch availability of...

Measuring enzymatic starch availability is commonly used as a quality control method to ensure steam-flaked corn manufacturing consistency in commercial cattle feeding operations. However, starch availability estimates can be variable. We conducted five experiments to evaluate factors influencing starch availability estimates of steam-flaked corn. In Exp. 1, sample handling methods were evaluated. Sifted flakes were immediately placed into a plastic bag, air equilibrated for 240 min, oven-dried, or freeze-dried. Directly oven-drying samples at 55°C decreased (P < 0.01) starch availability compared to other sample handling methods. In Exp. 2, sifted flakes were air equilibrated for 0, 15, 30, 60, 120, or 240 min. Air equilibration time did not influence (P ≥ 0.54) starch availability. In Exp. 3, samples were evaluated for effects of sifting through a 4-mm screen (flakes + fines vs. sifted flakes) and air equilibration time (0 vs. 240 min). Both sifting steam-flaked corn samples and air equilibration for 240 min increased starch availability (P < 0.01 and P = 0.02, respectively). In Exp. 4, we evaluated the effects of air equilibration time (0 vs. 240 min) on the two sifted portions (sifted flakes vs. sifted fines). There was an air equilibration time × sifted portion interaction for starch availability because air equilibration time increased (P < 0.01) starch availability of sifted fines but did not influence starch availability of sifted flakes. Concentrations of crude protein, soluble crude protein, neutral and acid detergent fiber, ether extract, and acid-hydrolyzed fat, Ca, P, K, Mg, S, Fe, Zn, Mg, and Cu were greater (P < 0.01) for sifted fines compared to sifted flakes. Starch availability and total starch concentration were greater (P < 0.01) for sifted flakes compared to sifted fines. In Exp. 5, effects of air equilibration time (0 vs. 240 min) and storage temperature (23°C vs. 55°ºC) on flakes + fines were evaluated. Storage of flakes + fines in heat-sealed foil bags at 55°C for 3-d decreased (P < 0.01) starch availability by 40.7%. Sifted flakes contained less moisture, greater total starch concentrations, and greater starch availability than sifted fines. Moisture, sifting, air equilibration time, and storage temperature influence starch availability of steam-flaked corn. Adoption of the strategies discussed in the current study will lead to more consistent estimates of starch availability.