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Factors influencing characteristics of steam-flaked corn and utilization by finishing cattle¹

Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600

	Abstract

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Three experiments were conducted to identify factors influencing steam-flaked corn (SFC) characteristics and feeding value. In Exp. 1, corn samples (n = 108) were tempered for 2 h using 6, 10, or 14% moisture containing 0 or 0.67 mL of surfactant/L. Samples were steamed for 20 or 40 min and flaked to 360, 335, or 310 g/L. Treatments were arranged in a 3 x 2 x 2 x 3 factorial. No interactions existed in Exp. 1. Increasing tempering moisture linearly (P < 0.001) increased corn moisture after tempering, steaming, and flaking; however, SFC moisture was not increased (quadratic; P < 0.001) greatly by applying more than 10% water during tempering. The surfactant, steam time, and flake density had no effect (P = 0.16 to 0.93) on corn moisture after tempering, steaming, or flaking, but adding a surfactant during tempering decreased (P = 0.05) moisture loss after flaking. Starch availability was unaffected (P = 0.31 to 0.84) by tempering moisture concentration, tempering with a surfactant, or steam time but was increased (linear; P < 0.01) by decreasing flake density. Flake durability was increased by increasing tempering moisture (linear; P < 0.001), tempering with a surfactant (P = 0.04), increasing steam time (P < 0.001), and decreasing flake density (linear; P = 0.02). In Exp. 2, 89 heifers (initial BW = 350 kg) were fed 75% SFC-based diets for 108 d to determine the effects of SFC particle size on performance and carcass traits. Treatments were SFC that was mixed for 0 (4,667 µm) or 15 min (3,330 µm) before addition of other ingredients. Heifers fed 3,330-µm SFC tended (P = 0.13) to eat less DM, but ADG and G:F did not differ (P = 0.58 to 0.65) between treatments. Carcass traits did not differ, except that heifers fed 3,330-µm SFC had less (P = 0.008) KPH. In Exp. 3, 96 heifers (initial BW = 389 kg) were fed for 82 d diets containing 73% SFC that was either 18 or 36% moisture. Heifers fed 36% moisture SFC ate less DM (P = 0.02) and gained slower (P = 0.05) than heifers fed 18% moisture SFC, but G:F did not differ (P = 0.93) with SFC moisture. Heifers fed 36% moisture SFC were fatter at the 12th rib (P = 0.009), but all other carcass traits did not differ. Methods that increase moisture of SFC improved durability, but extreme moisture levels negatively affected cattle performance. Flake particle size did not affect cattle performance. Flake density is the major factor affecting starch availability in SFC.

Key Words: finishing cattle • flaked corn • grain processing

	INTRODUCTION

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The energetic improvements of processing corn by steam flaking are well known (Owens et al., 1997; Zinn et al., 2002). Limited research exists, however, regarding processing conditions that optimize flake quality and feeding value.

Moisture, heat, and pressure are essential components of the steam flaking process (Osman et al., 1970). Decreasing flake density increased the gelatinization or starch availability of steam-flaked grains (Xiong et al., 1990; Zinn, 1990a; Swingle et al., 1999), whereas moisture additions to sorghum grain increased the gelatinization and durability of flaked sorghum (McDonough et al., 1997).

Moisture in stored corn grain is typically present in small amounts (<15%). To aid in processing, moisture is often applied to grain with conditioning agents or surfactants (Zinn, 1998; Wang et al., 2003); however, their application in processing steam-flaked corn (SFC) is largely unknown. Steam conditioning before flaking typically adds up to 5 percentage units of moisture to whole grain (Zinn, 1990b), and experiments suggest that 30 min of steam are sufficient to achieve efficient starch use (Zinn, 1990b).

Lund (1984) indicated that moisture is a critical component of the gelatinization process and reported a moisture:starch of 1.5:1 is required to optimize gelatinization. If gelatinization is partially responsible for the improved energetic value of SFC (Zinn et al., 2002) and moisture in SFC is far from being optimal to maximize gelatinization, then evaluation of moisture application methods common in processing SFC seems warranted. In addition, the effects of SFC processing methods on flake durability and the effect of flake particle size on cattle performance are relatively unknown. Therefore, our objective was to evaluate the effect of processing methods involving moisture on flake quality and to identify the effect of moisture and flake particle size on the feeding value of SFC.

	MATERIALS AND METHODS

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Experiment 1

Whole shelled corn (11% moisture) was weighed into 3.8-L glass containers (n = 12, 2 kg each), and 6, 10, or 14% water by weight containing 0 or 0.67 mL of yucca-based surfactant/L (Grain Prep; Agrichem, Inc., Ham Lake, MN) was added before lids were sealed. This process provided 0 or 63 mL of surfactant per metric ton of SFC. Samples were immediately placed on a mechanical rotary device to allow for continuous contact of corn and moisture and allowed to temper for 2 h. After tempering, samples were steam-conditioned for 20 or 40 min in a steam chamber at atmospheric pressure. After steam conditioning, samples were processed to a common flake density using 46 x 61 cm corrugated rollers. Rollers were set to the desired flake density and kept hot by flaking steamed corn that was set directly above the rollers. To flake an experimental sample, the pin feeder was turned off, and rollers were allowed to clean out before an experimental sample was placed over the rollers. Samples were collected underneath the rollers by changing the direction of an open-ended 2-way drop chute. This procedure was repeated 3 times daily using densities of 360, 335, and 310 g/L and was replicated over 3 consecutive days. The study was conducted in a 2 x 3 x 2 x 3 factorial arrangement of treatments with factors consisting of surfactant concentration (0 or 63 mL of SFC/t), tempering moisture concentration (0, 6, or 12% moisture, wt/wt), steam conditioning time (20 or 40 min), and flake density (360, 335, or 310 g/L).

Samples (as-is basis) were collected after tempering (227 g), steam conditioning (227 g), and flaking (1,550 g) and frozen daily. Subsamples of tempered, steamed, and flaked samples were analyzed for DM by oven drying at 105°C for 16 h. Subsamples were also ground to pass a 1-mm screen and analyzed for starch availability by using a gas production technique (Croka and Wagner, 1975). The gas production involved incubating 0.75 g of ground sample and 0.25 g of dry yeast in 0.067% amyloglucosidase enzyme solution for 3 h using a water bath maintained at 37°C and a mannometric apparatus to indirectly quantify gas production by water volume displacement.

To test for durability, flaked samples were sieved using a 9.5-mm screen, and 250 g of whole flakes was placed in a commercial durability tester (Continental Agra Equipment, Newton, KS) and tumbled for 10 min with six 1.27-cm, hexagonal, stainless steel nuts. The percentage of flakes retained on the 9.5-mm screen was determined by sieving after tumbling.

Data were analyzed as split-plot design using the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC). Individual samples of corn represented the experimental unit with the whole-plot consisting of flake density and the subplot represented by tempering moisture concentration, surfactant concentration, and steam conditioning duration. The model statement included effects of tempering moisture concentration, surfactant concentration, steam conditioning duration, flake density, and all interactions among factors. The random statement included effects of day and day x flake density, which served as the main-plot error. The residual error served as the split-plot error term. Linear and quadratic effects of tempering moisture concentration and flake density were tested using orthogonal contrasts.

Experiment 2

Procedures for Exp. 2 and 3 were conducted following approval of the Kansas State University Institutional Animal Care and Use Committee. After the completion of Exp. 1, an experiment was conducted using 89 cross-bred heifers (initial BW = 350 kg) to evaluate SFC particle size in finishing diets. For 14 d preceding the trial, heifers were allowed ad libitum access to a common diet to minimize differences in gastrointestinal fill. On d 0, heifers were weighed, implanted with 140 mg of trenbolone acetate and 14 mg of estradiol (Revalor-H, Intervet, Millsboro, DE), and stratified to 12 pens based on BW. On d 1, heifers were weighed and allocated to pens, and treatments were assigned randomly to pens. Shrunk (4%) initial BW on d 0 was used for calculation of performance. Heifers were offered ad libitum access to diets for 108 d.

Diets contained 76% SFC (DM basis) that was processed to 335 g/L. Treatments consisted of diets containing SFC that was mixed for 0 (4,667 µm) or 15 (3,330 µm) min before the addition of other dietary ingredients (Table 1). Flakes were mixed using a horizontal, stationary ribbon mixer (Davis Manufacturing Co., Bonner Springs, KS). After addition of the remaining dietary ingredients, complete diets were mixed in a delivery truck for 3 min before feeding. Particle size of fresh SFC and complete diets were measured throughout the trial using a Ro-Tap (W.S. Tyler, Mentor, OH) and seven sieves (ASAE, 2000; Table 2).

Data were analyzed as a completely randomized design with pen as the experimental unit. Least squares means were calculated using the GLM procedures of SAS. Categorical data such as USDA quality and yield grades and liver abscesses were analyzed using PROC GENMOD of SAS.

Experiment 3

A second performance study was conducted to compare the effects of feeding 36% moisture SFC to that of conventional, 18% moisture SFC. On d 0, 96 crossbred heifers (initial BW = 389 kg) were implanted with Revalor-H and stratified by BW to 12 pens (6 per treatment). On d 1, heifers were weighed and allocated to pens, and treatments were assigned randomly to pens. Ad libitum access to experimental diets was provided for 82 d (Table 3).

	RESULTS

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Experiment 1

No interactions existed (P = 0.11 to 0.96) between tempering moisture concentration, surfactant concentration, steam conditioning duration, and flake density with respect to moisture content of tempered, steamed, and flaked corn; therefore, only main effects are presented in Table 4. As expected, increasing tempering moisture concentration linearly increased corn moisture content after tempering (P < 0.001), steam conditioning (P < 0.001), and flaking (P < 0.001). Tempering with 14% moisture did not appreciably increase (quadratic; P < 0.001) moisture content of corn after flaking. Adding the surfactant did not alter corn moisture content after tempering (P = 0.36), steam conditioning (P = 0.16), or flaking (P = 0.38). Moisture content of steamed corn was not affected by steam conditioning duration (P = 0.42). Likewise moisture of SFC was not affected by steam conditioning duration (P = 0.17) or flake density (P = 0.86).

No interactions existed (P = 0.20 to 0.95) between tempering moisture concentration, surfactant concentration, steam conditioning duration, or flake density for starch availability measured using a gas production procedure; therefore, main effects are presented (Table 5). Starch availability was not affected by tempering moisture concentration (P = 0.62), surfactant concentration (P = 0.31), or steam conditioning duration (P = 0.33). Increasing the degree of processing (decreased flake density) increased (linear; P = 0.009) starch availability of SFC.

Experiment 2

Limited performance responses were observed because of differences in flake particle size (Table 6). Cattle fed 3,330-µm SFC tended (P = 0.13) to consume less DM; however, ADG, G:F, and NE_m and NE_g (predicted from animal performance) did not differ between particle sizes (P = 0.34 to 0.65). Carcass traits, including HCW, dressing percent, LM area, 12th rib fat, marbling score, USDA yield grades, and liver abscesses did not differ (P = 0.16 to 0.98) for heifers fed 4,667 and 3,330 µm SFC. Heifers fed 4,667 µm SFC had greater (P = 0.008) KPH than heifers fed 3,330 µm SFC, and heifers fed 4,667 µm SFC tended (P = 0.10) to have more USDA Choice carcasses and tended (P = 0.10) to have fewer USDA Select carcasses.

As shown in Table 7, heifers fed 36% moisture SFC consumed less DM (P = 0.02) and gained slower (P = 0.05) than heifers fed 18% moisture SFC; however, G:F was not affected (P = 0.93) by moisture content of SFC. Additionally, dietary NE densities and carcass characteristics for heifers fed the high- and low-moisture flakes did not differ (P = 0.11 to 1.0), with the exception that heifers fed the 36% moisture SFC were fatter (P = 0.009) over the 12th rib.

	DISCUSSION

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Our results suggest that moisture (via increasing tempering moisture concentration, increasing steam conditioning duration, or adding a surfactant during tempering) increased flake durability and caused flakes to be more resilient to breakage, but these changes had little influence on starch availability. These results are supported by other research that found that adding moisture during tempering increased flaked sorghum durability (McDonough et al., 1997) but are not consistent with reports indicating that addition of moisture during tempering increased starch availability or gelatinization of flaked sorghum (McDonough et al., 1997). These differences may be attributable to differences in grain type. Sorghum starch is known to be tightly bound with endosperm protein and often responds more favorably to extensive processing than does corn (Rooney and Pflugfelder, 1986). Applying moisture to sorghum before processing may provide for greater disruption of the protein-starch matrix and render starch more accessible to enzymatic attack. Because the protein-starch matrix is less extensive in corn, the effects of tempering may be less profound.

Moisture concentration of corn after tempering, steam conditioning, and flaking was unaltered by adding the surfactant during tempering. Tempering with a surfactant is commonly done to facilitate moisture absorption (Zinn, 1998; Wang et al., 2003). The advantage of using a surfactant may be attributed to its ability to decrease the time needed for moisture absorption. The time provided to temper corn in this experiment (2 h) may have exceeded the advantage of the surfactant to facilitate quick moisture absorption. Additionally, adding the surfactant during tempering decreased the moisture lost after flaking. The surfactant may have allowed more moisture to migrate internally and decreased the surface moisture found on the outer kernel that would be lost quickly during flaking.

Decreasing flake density increased the durability of SFC. Processing to a greater degree would seem to increase fine and small particles; however, we evaluated the durability of the whole flakes that were produced during flaking and did not measure the amount of fine particles produced by flaking to different flake density. Other researchers (Xiong et al., 1990; Reinhardt et al., 1997; Swingle et al., 1999) have found that decreasing flake density caused greater disruption of starch granules and increased the gelatinization of flaked grains. Increasing gelatinization likely contributes to greater durability by binding more of the starch and protein that are disrupted during the flaking process.

Experiment 2

Particle size of SFC did not appreciably affect cattle performance. We are not aware of other published reports in the literature of cattle fed flakes of differing particle sizes. Methods that increase flake integrity and decrease breakage may be of little interest to cattle feeders if bunk management is adequate to ensure that broken flakes/fines do not contribute to ingredient sorting and excessive feed wastage.

Differences in the mean particle sizes of the complete diets became smaller during the mixing of the complete diets (Table 2). The mixer used in mixing the complete diets was rather aggressive, which may have caused performance to be similar due to smaller differences in particle sizes of the experimental diets. Alternatively, attempts to improve flake durability may be futile because normal mixing action may eliminate the advantage created by improving durability and may suggest that variation in dietary fines is not markedly affected by mixing time of steam-flaked corn finishing diets. Whether performance differences exist for SFC having particle sizes different from our experiment is unknown.

Experiment 3

The moisture concentrations that we evaluated did not influence starch availability in vitro nor did they improve cattle performance. Dry matter intake and ADG were actually decreased by feeding 36% moisture SFC in Exp. 3. Zinn et al. (2002) reported that tempering grain using 7.5% water and a surfactant before steam conditioning and flaking did not alter growth performance or NE value of the corn. We used an extreme concentration of moisture that is considerably greater than flaking mills would target, but knowing that steam flaking is a low-moisture system and that moisture is essential for complete starch gelatinization, we targeted a high level of moisture addition to ascertain whether moisture level of SFC affected cattle performance. This high concentration of moisture yielded flakes with a translucent appearance and flake integrity and resiliency seemed superior to that of 18% moisture SFC (our unpublished observations). It is unknown why cattle ate and gained less by feeding 36% moisture SFC, but the added moisture may have caused flakes to be over-processed because the weight of added water increased the corn density and caused flakes to be thinner because water was adding weight to the density tester. Likewise, Brown et al. (2000) reported that over-processing corn by flaking to lighter densities decreased cattle performance.

Moisture is required in some amount to swell starch and aid in the flake manufacturing process, but this requirement may not be more than what is added during short periods of steam conditioning. Zinn (1990b) found that total tract starch digestion from SFC that was steam conditioned for 30 min was similar to SFC that had been steam conditioned for 60 min. In our Exp. 1, 20 min of steam conditioning seemed to be as effective as 40 min. All our corn had been tempered using at least 6% moisture. It is unknown whether 20 min or less of steam conditioning would suffice to process SFC with <6% added moisture, but by tempering corn before steam conditioning, the requirement for steam conditioning may be shortened. Having sufficient moisture present in the kernel before steam conditioning may allow steam to more effectively heat the grain and decrease the requirements for steam. However, duration of steam conditioning is often associated with the size of the steam chamber, degree of processing, and throughput demands and/or limitations. All things being equal, decreasing the requirement for steam will undoubtedly decrease processing costs associated with flaking corn.

	IMPLICATIONS

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Processing methods involving the manufacturing of steam-flaked corn were evaluated. Flake durability can be improved by increasing corn moisture, increasing steam duration, applying a surfactant, or decreasing flake density, but flake particle size may have little influence on cattle performance. Flake density is the most effective means of altering starch availability of flaked grains if adequate amounts of heat and moisture are present. Applying moisture by tempering grain before flaking is an effective means of adding moisture to flaked corn and may decrease the need for long periods of steam conditioning; however, excessive moisture levels in steam-flaked corn may be detrimental to cattle performance.

	Footnotes

 
¹ Article No. 05-213-J from the Kansas Agric. Exp. Stn.

² Present address: Nutri-Tech, Inc., 1435 Ave. N, Lyons, KS 67554.

³ Corresponding author: jdrouill{at}oznet.ksu.edu

Received for publication March 9, 2005. Accepted for publication August 22, 2005.

	LITERATURE CITED

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