Improved estimates of starch availability of steam-flaked corn and the proportion of fines could potentially lead to improved flaking consistency in commercial feedlots
By Ronald J. Trotta, Kelly K. Kreikemeier, Randy F. Royle, Todd Milton, and David L. Harmon In feedlot operations, corn is the primary grain source used for finishing diets for beef cattle and steam-flaking is the primary grain processing method. Steam-flaking is a common practice because it improves starch gelatinization and availability, nutrient utilization, and the overall feeding value. Starch availability is calculated as the amount of enzymatically-available starch divided by the total starch content of a feed. Starch availability, dry matter content, and flake density are routinely measured by commercial feedlots for quality control of flaking consistency.
A survey from commercial feeders and consulting nutritionists indicated that starch availability averaged 50.6% but ranged from 37% to 65% across 49 steam-flakers from commercial feedlots. Variation in starch availability of steam-flaked corn can occur due to factors including corn quality, moisture content, flake density, starch retrogradation, roll diameter, and steam-conditioning. Sampling and handling techniques are also thought to contribute to the variation in estimates of starch availability. Post-flaking sampling and handling techniques that involve collection of flakes, segregation of flakes and fines, and conditions influencing starch availability during transport to the laboratory have not been well-described. Thus, sampling procedures vary among feedyard personnel, leading to inconsistent estimates of starch availability. The objectives of our studies were to evaluate factors (sample handling, sifted portions of steam-flaked corn, air equilibration time, moisture, heat exposure) influencing enzymatic starch availability of steam-flaked corn. Characterizing effects of sifting, air equilibration time, and storage temperature and how that influences starch availability were necessary to improve techniques that reduce the variation of starch availability estimates, thereby developing repeatable methodology for feedyard personnel.
Figure 1. Standard testing sieve equipped with a 4-mm screen fitted with a collection pan. The top-portion of the standard testing sieve contains sifted flakes (particles greater than 4-mm). The bottom-portion of the standard testing sieve contains sifted fines (particles less than 4-mm).
Sampling and sifting of steam-flaked corn
We recommend sampling from under the rolls of the steam-flaker to obtain a fresh steam-flaked corn sample. The flake density of that sample should be measured by a trained employee. The contents within the flake density testing cup can be dumped into a standard testing sieve with a 4-mm screen that is fitted over a collection pan (Figure 1). Sieving the steam-flaked corn gently for 20 seconds will remove the fines from the sample, which will also remove moisture from the sample to better preserve the sifted flakes for starch availability analysis. The top-portion and bottom-portion of the sieves can be weighed to measure the proportion of flakes and fines in the sample, which could also be used as a measure of quality control and indicator of when rolls need to be changed.
Post-flaking preservation We tested different post-flaking preservation methods before starch availability analysis. Freeze-drying is considered the gold standard; however, we tested methods that could be utilized by feedyard personnel in a commercial setting. The methods tested were: 1) freeze-drying, 2) storing in a plastic bag for 3-d at room temperature, air equilibration for 4-h followed by storage in a plastic bag for 3-d at room temperature, or forced air oven drying at 130°F for 24-h. We found that sifting the steam-flaked corn samples or sifting the steam-flaked corn samples plus air equilibration for 4-h at room temperature resulted in equal starch availability as freeze-drying samples immediately after collection (Figure 2). However, we found that oven-drying steam-flaked corn at 130°F decreased starch availability and thus, it is not recommended to oven-dry samples before shipping. This was also an indication that heat exposure prior to starch availability analysis could potentially reduce starch availability.
Figure 2. Effects of post-flaking preservation on starch availability of sifted flakes. Sifted flakes (> 4-mm particles) were either freeze dried, stored in a plastic bag for 3-d at room temperature (no air equilibration), air equilibrated for 4-h and then stored in a plastic bag for 3-d at room temperature (air equilibration), or dried in a forced-air oven at 130°F for 24-h
Sifting and air equilibration time We tested the effects of air equilibration time for 0-h or 4-h on steam flaked corn samples that were not sifted (flakes + fines; > 4-mm and < 4-mm) or were sifted through a sieve with a 4-mm screen to retain sifted flakes (> 4-mm) and sifted fines (< 4-mm). There was a tendency for an interaction between particle size and air equilibration time (Figure 3). Our data showed that air equilibration for 4-h increased starch availability of sifted fines and flakes + fines but not sifted flakes. This indicates that the moisture content of the fines interferes with starch availability measurements and that either sifting to remove the fines or air equilibrating samples that are not sifted (flakes + fines) would both be suitable methods to achieve optimal measurements of starch availability. Also, steam-flaked corn samples that were not sifted and air equilibrated for 4-h did not differ in starch availability from sifted flakes, indicating that measuring starch availability of sifted flakes is a suitable estimate of starch availability of the entire steam-flaked corn sample. We recommend that samples of steam-flaked corn should be air equilibrated for at least 4-h at room temperature before packaging samples for shipment to the laboratory for analysis.
Storage temperature Frequently, steam-flaked corn samples are mailed to a laboratory for analysis of starch availability. During shipping, temperatures in summer months could potentially reach over 130°F and this could increase retrogradation of starch. We evaluated the effects of storage temperature on starch availability for flakes + fines (> 4-mm and < 4-mm). Steam-flaked corn samples were stored in foil bags and heat-sealed to prevent moisture loss. The bags were stored at room temperature (73°F) or placed into a forced-air oven at 130°F for 3-d to simulate shipping time. We found that storage temperature of 130°F for 3-d decreased starch availability by 28.9% (Figure 4). The decrease in starch availability was most likely due to starch retrogradation, which makes the starch less accessible for enzymatic hydrolysis. We recommend measuring flake density at the feedyard along with starch availability at the laboratory. If there is consistency in flake density measurements but not in starch availability, it may be an indication of starch retrogradation during the shipping process. Future research is necessary to find the best preparation method to prevent starch retrogradation during shipping.
Figure 3. Effects of air equilibration time at room temperature (0-h or 4-h) of steam flaked corn samples that were not sifted (flakes + fines; > 4-mm and < 4-mm particles) or were sifted through a sieve with a 4-mm screen to retain sifted flakes (> 4-mm) and sifted fines (< 4-mm).
Figure 4. Effects of storing steam-flaked corn (flakes + fines) in foil bags that were heat-sealed for 3-d at either room temperature or 130°F on starch availability.
Overall recommendations We recommend sampling fresh steam-flaked corn from under the rolls of the steam-flaker. Steam-flaked corn samples can be sifted using a standard testing sieve with a 4-mm screen to separate flakes and fines. We recommend that samples for laboratory analysis are allowed to air equilibrate for at least 4-h before processing for shipment. Sifting and air equilibration can achieve starch availability that is equivalent to freeze-drying. Measuring starch availability, dry matter content, and flake density should be done for multiple indicators of quality control of steam-flaked corn production. Avoiding exposure to high temperatures post-flaking is recommended to avoid possible retrogradation of starch. Adoption of the strategies discussed can lead to more consistent estimates of enzymatic starch availability. Improved estimates of starch availability of steam-flaked corn and the proportion of fines could potentially lead to improved flaking consistency in commercial feedlots.
References
Trotta, R. J., K. K. Kreikemeier, R. F. Royle, T. Milton, and D. L. Harmon. 2021. Influence of air equilibration time, sampling techniques, and storage temperature on enzymatic starch availability of steam-flaked corn. J. Anim. Sci. 99:skab162. doi:10.1093/jas/skab162
Trotta, R. J., K. K. Kreikemeier, R. F. Royle, T. Milton, and D. L. Harmon. 2021. Flake density and starch retrogradation influence in situ ruminal degradability characteristics of steam-flaked corn and predicted starch digestibility and energetic efficiency. J. Anim. Sci. 99:skab298. doi:10.1093/jas/skab298
Trotta, R. J., K. K. Kreikemeier, R. F. Royle, T. Milton, and D. L. Harmon. 2022. Corn processing, flake density, and starch retrogradation influence ruminal solubility of starch, fiber, protein, and minerals. J. Anim. Sci. 100:skac149. doi:10.1093/skac149
Trotta is with the Department of Animal and Food Sciences, University of Kentucky, Lexington, Ky.; Kreikemeier is with Hoxie Feedyard, Foote Cattle Co., Hoxie, Kan.; Royle is with ServiTech Inc., Dodge City, Kan., and Harmon is with Midwest PMS, Firestone, Colo.
