Heat Treated Soybeans

Heat Treated Soybeans and Soybean Meal in Ruminant Nutrition

Chunjian Lin and Limin Kung

Introduction Amino acids required by beef and dairy cattle come both from dietary protein that escapes rumen fermentation (bypass or undegradable protein) and the microbial protein produced during rumen fermentation. Early research demonstrated that cattle fed purified diets with only non-protein nitrogen as a nitrogen source gained 65% of the weight of the cattle fed practical energy ingredients and protein supplements (Oltjen, 1969). When lactating cattle were given protein- free diets, they produced 4000 kg milk per lactation from microbial protein (Virtanen, 1969); production increased 1000 kg and 1500 kg, respectively, however, by supplying protein for 20 and 40% of nitrogen needed. The importance of dietary bypass protein in beef and dairy cattle production was soon recognized. Orskov et al. (1980) described the level of undegradable protein requirement influenced by animal age and production. The younger the animal is or the higher milk production the animal has, the more undegradable protein is required. The undegradable protein concept was then introduced by the NRC (1989) in which requirements for degradable (DIP) and undegradable protein (UIP) were separately defined. Use of undegradable protein sources in ruminant diets has become a common practice in diet formulation. Soybean meal (SBM) is the most commonly used protein supplement in beef and dairy diets. It is very palatable and has a good amino acid balance and high availability. Its bypass essential amino acid index is just next to ruminal microbial protein beating all other undegradable protein sources (Chandler, 1989). Relative to other commonly used feed proteins, Soybeans (SB) are rich in lysine but methionine, valine and isoleucine are the first, second and third limiting amino acids, respectively (Schingoethe, 1996). In fact, of the common plant proteins used in animal feeds, SBM has one of the highest percentage of essential amino acids (47.6%) as a percent of crude protein (Schwab et al., 1995). When SB are fed with corn (whose first limiting amino acid is lysine), the combination provides a well balanced protein. SB as a protein supplement are also an economical and convenient way to provide die tary fat. However, SB and SBM have a relative low protein efficiency because of extensive ruminal degradation. It is estimated that only 25% to 34% of protein in SB and SBM escapes rumen fermentation, respectively (NRC, 1989). Their use is becoming limited in diets of rapidly growing and high-producing ruminant animals. Therefore, improvement in ruminal escape characteristics of SB and SBM is of major importance to both beef and dairy producers and the soybean industry. Various methods of treating SB and SBM have been studied to alter the rate and extent of protein degradation in the rumen over the last 25 years. Some of the techniques, e.g., extrusion, roasting, expeller, lignosulfonate, formaldehyde have been successfully used to protect SB and SBM from ruminal degradation. Treating SB and SBM by these methods increases its ruminal bypass protein content up to 70% (Waltz and Stern, 1989). When dairy cattle were fed diets containing the heat-treated SB or SBM, milk production and/or feed efficiency were imp roved (Schingoethe et al., 1988; Faldet et al., 1991; Nakamura et al., 1992). Casper et al. (1994) substituted extrusion heat-treated SBM for solvent extracted SBM in a barley diet fed to fastgrowing young dairy heifers. They found increased weight gain and improved feed conversion. In the U.S.A. heat-treated SB and SBM are commercially available and rapid growth has been seen in use of these products as protein supplements for beef and dairy cattle (Satter et al. 1994). The objective of this paper is to review the major processes used to improve ruminal bypass of SB and SBM protein in ruminant production. 2

Methods of protecting soybeans and meal Various methods of treating proteins have been used to reduce their degradation in the rumen and they can be categorized into chemical and physical treatments. The chemical treatments can be further divided into methods in which the chemicals actually combine with the proteins, e.g. formaldehyde treatment, and those in which the chemicals denature the proteins, e.g., alcohol, sodium hydroxide and propionic acid. The most successful physical treatment has been heat. Heat facilitates the Maillard or nonenzymatic browning reaction between the sugar aldehyde groups and the free amino acid groups of protein to yield an amino-sugar complex. This complex is more resistant than normal peptides to enzymatic hydrolysis, and the reversibility of this reaction is dependent upon temperature and time of heat exposure. During the early stages of the Maillard reactions, Amadori rearrangement and Strecker degradation reactions occur forming soluble premelanoidins. In the final stage of the reactions insoluble melanoidins appear as black residues. Some precautions must be taken when heat-treating feeds, as excessive heat causes losses in sugars and amino acids. For example, in the Maillard reaction, N-terminal amino acids are most reactive followed by basic amino acids, especially the essential amino acid lysine, whose destruction can be more than 5 to 15 times greater than the other amino acids (Adrian, 1974). In SB, excess heating also causes losses of S-containing amino acids such as methionine. Furthermore, some premelanoidin compounds have been shown to toxic to microorganisms and animals. Heat treatment has a wide variation in application methods and amount of heat utilized. Extrusion and expeller processing are two protection methods involving heat. Lignosulfonate treatment utilizes wood sugars and heat to elicit the Maillard reaction. Inclusion of all chemical and physical methods in discussion is beyond the scope of this paper, thus the authors will focus on those that are most commonly used in the U.S.A. 1. Roasting There has been rapid growth in the use of heat processed SB as a protein and energy supplement for beef and dairy cattle in the U.S. Roasting and extrusion are the two commonly used methods to process full- fat SB, of which roasting of SB is the predominant process. There are about 20 millions bushels of SB roasted annually in the U.S.A. (Satter et al. 1994). Roasting of SB involves a revolving finned cylinder which lifts the beans through jets of flame. Roasting is popular because of a high through put (3 to 12 tons per h) and roasting equipment is mobile resulting in on- farm processing of beans. One drawback of this process is that often times roasting is done subjectively based on the degree color of the beans exiting the roaster. This results in a large variation in the amount of heat that SB are exposed to when processed by commercial suppliers. Faldet and Satter (1991) examined 13 commercial roasted SB. The ruminal undegradable protein contents ranged from 36% to 58% of CP with an average of 48% and the total and postruminal nutritionally available lysine (NAL) concentration from 2.1 to 2.4% and from 0.9 to 1.24% of DM, respectively. Reduction of available lysine in roasted SB is a result of excessive heat exposure. Faldet and Satter (1992a) further investigated ways to test the optimum heat exposure of SB during roasting. First, SB were roasted in a drum roaster at different temperatures for various lengths of time. The roasted

3

beans were then analysed for in vitro ruminal protein degradability and NAL content. The data showed several combinations of temperature and time (140°C-120 mm, 150°C 60 mm or 160°C-30°C) resulted in the roasted SB with an optimal or near optimal protein protection (Table 1). Secondly, roasted SB were checked for exiting temperatures and held without cooling (steeped or conditioned) for either 0,15, or 30 mm to give 12 soybean treatments. Increases in exiting temperatures and/or steeping reduced the ruminal protein degradation and improved post ruminal lysine availability (Table 2). The purpose of steeping was to allow heat to equilibrate throughout the whole soybean. In another experiment Faldet et al. (1992b) reported that steeping heated SB for at least 0.5 h post-roasting increased in vitro undegradable to 61% vs. 51% for unconditioned beans. The post ruminal available lysine (PRAL) content was highest for SB roasted and steeped, intermediate for roasted SB, and lowest for raw SB (1.23, 1.10, and 0.59% of DM). From these results they proposed that the SB would be properly roasted when they were exiting the roaster at approximately 146°C and then steeped for about 30 mm. Table 1. Effect of Roasting Temperature and Time on Ruminal Undegradable Protein (RUP) and Nutritionally Available Lysine (NAL) of Roasted Soybeans Heat Treatment Temperature, °C 0 100

Time, min

0 60 180 130 60 180 140 10 30 60 90 120 150 10 30 60 90 160 10 30 60 90 Adapted from Faldet et al., 1992.

RUP, % of CP

NAL % of DM

29.7 36.7 38.7 38.2 48.0 33.9 43.9 49.4 55.0 59.2 36.6 42.4 58.4 64.2 37.4 53.2 72.0 71.1

2.43 2.27 2.21 2.36 2.14 2.44 2.20 2.17 2.01 1.89 2.39 2.19 1.99 1.56 2.33 2.07 1.41 1.14

Post ruminal NAL % of DM 0.72 0.83 0.86 0.90 1.03 8.30 0.97 1.07 1.11 1.12 0.88 0.93 1.16 1.00 0.87 1.10 1.02 0.81

Analyses for ruminal protein degradability and lysine availability are relatively complicated and time-consuming. Moreover, some of reactive lysine methods are poor indicators of lysine damage after early Maillard reactions (Hurrell and Carpenter, 1981). Traditionally, the flurodinitrobenzene (FDNB) method of estimating reactive lysine has been used widely in human foods (Hurrell and Carpenter, 1981), but not in animal feeds. However, Faldet et al. (1991b) showed that the FDNB method was useful in determining optimum heating of SB. Their results suggest that heating 4

soybean protein to achieve a loss of 15 to 22% of FDNB reactive lysine is needed to obtain optimal availability of postruminal lysine. The most commonly used method is the protein dispersibility index (PDI) for determining the amount of heat exposure SB have had. PDI is simply a measure of protein solubility in water since solubility of SB decreases as heat exposure increases. Another method uses a spectrophotometer to measure light absorbance at 420 nm of water extracts of heated SB for possible damage from excess heat exposure (Satter et al., 1993). Table 2. Effect of Exiting Temperature and Steeping Time on Ruminal Undegradable Protein (RUP) and Nutritionally Available Lysine (NAL) of Roasted Soybeans

Exiting Temperature, °C

Steeping Time, min

RUP, % of CP

NAL mg/g N

0 100

0 0 30 0 30 0 30 0 15 30 30 30

33.0 34.0 39.0 40.0 44.0 46.0 55.0 57.0 63.0 61.0 65.0 66.0

280 320 305 306 287 295 288 277 262 286 239 218

123 135 146

153 160

Post ruminal NAL mg/g N 92 109 122 122 126 136 158 158 165 174 155 144

Adapted from Faldet et al., 1992. Any increase in light absorbance above the baseline level is indicative of heat damage or over heating. This is a rather crude test, but it is extremely simple and can be run in conjunction with the PDI test. Satter et al. (1993) also concluded that acid detergent insoluble nitrogen (ADIN) was not useful as an indicator of heat exposure with SB because ADIN did not seem to change in any meaningful way with the amount of heat that SB were exposed to. However, Kung and Huber (1983) reported that heating at 149°C for 2, 4 and 6 h increased the amount of ADIN (as a percentage of total N) from 1 .9% in SBM to 4.6, 8.9 and 19.7%, respectively. The PDI procedure is relatively easy, inexpensive and fairly correlated to in vitro protein degradability although it intends to lose sensitivity as the optimum heat treatment is approached. Satter et al. (1993) suggested that SB having a PDI value of 9-11 be considered as optimally heated; those with a PDI value of 11-14 as marginally underheated, and others with a PDI value of greater than 14 as underheated. Normally underheating of SB is far more prevalent than overheating because it requires more fuel. More soybean processors are using the PDI test to help them obtain a high quality product.

5

There is also an interest in roasting SBM, but little information is available regarding optimum heating conditions for SBM (Satter et al., 1991). Plegge et al. (1982) roasted SBM in a drum roaster to 102, 128, 144, 159 and 185°C, followed by immediate cooling. Results from a chick growth bioassay and a Iamb nitrogen balance study suggested that protein availability in SBM roasted to a temperature of 128 and 144°C was not reduced relative to the control SBM. This coupled with measurement of in situ ruminal protein degradation indicated that under the roasting conditions used the optimum temperature would be between 144 and 159°C. A second study by the same group (Plegge et al., 1985) suggested that roasting SBM to 130 to 145°C increased RUP by two fold. Kung and Huber (1983) reported that oven roasting SBM at 149°C for 2 h decreased in situ nitrogen disappearance from 76.9% in untreated SBM to 36.3%. Further heating (4 to 6 h) did not further decrease rumen degradability of nitrogen. 2. Extrusion Extrusion is another commonly used method to treat full- fat SB for ruminant diets. In this method, SB are fed into an extruder barrel, where a central revolving shaft forces the beans through the extruder. The SB are treated by the heat generated through friction and/or steam which is frequently injected during the process (AAFCO, 1997). No oil is removed from the SB during extrusion. SBM can also be processed through extrusion. Extrusion usually results in a product that is more uniform in quality than does roasting but through put (1-10 tons/h) is relatively slow, mobility of the processing equipment is poor, and during times of high energy process, the cost per treated ton can be high. Extrusion has decreased soybean protein degradability in the rumen. In a study by Aldrich and Merchen (1995), SB extruded at 104°C had an in situ bypass protein content of 54.3%, a 3.4- fold higher than raw SB; further increases in extrusion temperatures up to 160°C resulted in higher protein undegradability (63.3 % at 149°C and 69.9% at 160 00). Waltz and Stern (1989) used in vitro continuous culture fermenters to evaluate extrusion and other methods in protection of SBM. They found that an extruded SBM diet had a higher non-ammonia N flow and a lower crude protein degradation than the untreated SBM diet (65.5% vs. 85.5%). However, Deacon et al. (1988) reported that extrusion did not reduce the in situ effective degradability of SBM protein. Maiga et al. (1994) replaced SBM with extruded SBM processed at 149° C in a heifer diet and failed to detect any significant improvement in in situ dietary ruminally undegradable protein. The low temperature (149 00) and short length of time that SBM was heated during extrusion were attributed to the less response for SBM protein protection (Waltz and Stern, 1989). The difference between roasting and extrusion is that the former uses a high temperature for a short period and utilizes only the moisture within the seed in contrast to extrusion with steam. Deacon, et al. (1988) compared roasting (using JetSploder) to extrusion in treatment of whole canola seeds. They found that roasting reduced ruminal protein more effectively than extrusion. The effective protein degradabilities at 0.08 h-1 of outflow were 83.5%, 83.5%, and 43.2% for untreated, extruded and roasted whole canola seeds, respectively. They concluded that use of dry heat in the Jet-Sploding process, in contrast to steam during extrusion, was a additional factor that may influence the effectiveness of heat treatment in reducing the rate of ruminal degradation. In comparison of heat 6

treatment methods: roasting (heating and steeping), Jet-Sploding (heating, unconditioning) and extrusion, Faldet et al. (1992b) reported that all three processes increased the ruminal bypass protein and PRAL content over untreated SB (53% of CP and 1.07% of DM vs. 24% and 0.55%); but the roasting showed the best protection, followed by extrusion and Jet-Sploding (64%, 1.15%; 57%, 1.17%; 39% of CR, 0.89% of DM for undegradable protein and PRAL, respectively). Adjusting the Jet-Sploder’s setting to increase the exiting temperature of heated SB up to 154°C improved the undegradable protein and PRAL concentration which were comparable to the roasted SB. 3. Expeller In this method, SB are initially cleaned, cracked, and dried. The dried SB are then transported to tempering devices and heated uniformly. From the tempering bins, the SB are fed into expeller presses. A central revolving shaft creates pressure within the press, causing the extraction of oil from the ground SB. The extracted beans leave the presses in the form of flakes, which are subsequently ground. Expeller processing is a method that involves heating to a maximum 163°C which results in the Maillard reaction between sugar aldehyde groups and free amino acids. If the extent of the reaction can be controlled by regulating the amount of heat applied ruminal protein degradation can be decreased without adversely affecting intestinal protein digestion (U.S. Patent #5225230). Expeller SBM contains 42 to 46 % of crude protein and 4.5 to 6% of fat on as- fed basis (Table 3). Table 3. Nutritional Value of Different Processed SBM and Soybeans

Soybeans 1 Soybeans, Heated 1, 2 Soybean Meal, Solvent1 Soybean Meal, Expeller3 Soybean Meal, Lignosulfonate 4

CP % DM 40.3 40.3 55.1 48.3 53.4

UIP % CP 25.0 66.0 34.0 60.0 73.5

EE % DM 18.8 20.0 1.0 5.1 1.5

NEL Mcal/kg 2.11 2.18 2.01 2.07 1.95

NEL Mcal/kg 1.64 1.64 1.48 1.45 1.43

CP = crude protein; UIP = undegradable intake protein; EE = ether extract; NEL : net energy for lactation; NEg= net energy for gain 1 NRC, 1989 2 Satter et al, 1991 3 Western-Central Coop 4 Lignotech USA, Inc. Broderick (1986) compared expeller SBM from one source to solvent SBM and found the expeller process dramatically reduced the nitrogen solubility and consequently increased in vitro undegradable protein content. The nitrogen solubility, in vitro nitrogen degradation rate and estimated escape protein were 6.44%, 3.4%/h, and 64% for expeller SBM, and 27.22%, 9.5%/h, and 39% for untreated SBM. Similar results were obtained by Waltz and Stern (1989) who used a in vitro continuous culture system and reported that expeller SBM had a lower extent and rate of ruminal protein degradation than untreated SBM. When expeller SBM replaced SBM in a diet fed to 7

continuous cultures, they found lower dietary CP degradation, bacterial N flow and efficiency of bacterial synthesis and higher dietary N flow. The decrease in bacterial synthesis may have been due to less soluble N available in the diet containing expeller SBM. Broderick (1987) determined in vitro ruminal protein degradation of various commercial expeller SBM products and reported a great variation in bypass protein contents ranging from 38.5 to 69.8%. Even in samples from a same source, undegradable protein contents varied from 54.1 to 69.8% with an average of 61.4% and standard deviation of 4.4%. This suggests that care should be taken when heattreated SBM is used.

4. Lignosulfonate Treatment In this method, SBM is treated with 7% (wt./wt.) calcium lignosulfonate and then heated at 95°C for 1 h before it is dried (Standford et al., 1995). A higher temperature (100°C) for 30 mm is used in a commercial process of lignosulfonate-treated SBM (Winowiski, personal communication). Lignosulfonate is a term to describe any product derived from the spent sulfite liquor that is generated during the sulfite digestion of wood and containing a percentage of lignosulfonic acid or its salt as well as hemicellulose and sugars. Calcium lignosulfonate is produced from hardwoods via the acid-sulfite wood pulping process and contains a variety of wood sugars, main sugar being xylose (Windschitl and Stern, 1988). Initially, lignin present in the spent liquor was thought to protect the protein in the feed from ruminal microbial degradation that was mixed with 0.25-3.0% spent sulfite liquor (U.S. Patent No. 4377596). However, Winowiski and Stern (1987) examined various factors involved in lignosulfonate treated SBM and concluded that calcium lignosulfonate itself does not play any active role, rather heat and the presence of wood sugars, mainly xylose, are necessary for protein protection. In this process, the amount of sugar added, temperature, pH, moisture and time of reaction are critical to obtain the optimal effect (U.S. Patent No. 4957748). Windschitl and Stern (1988) described a processing procedure in which either 5% calcium lignosulfonate or 1% xylose (by weight) was added along with 10% additional water to SBM, the mixture heated at 95 to 100°C for 3 mm, and then held at 90 to 95°C for 45 mm before it was air-dried. A water treatment was processed the same as above without addition of xylose or calcium lignosulfonate. They reported that in situ ruminal protein degradabilities and N digestion rate were 40.6% and 2.7%/h for xylose treated SBM; 40.6% and 2.7% for calcium lignosulfonate treated SBM; 67.8% and 8.4%/h for water treated SBM; and 70.6% and 9.4% for untreated SBM, respectively. Lignosulfonate treatment provides protection of SBM protein from ruminal degradation without affecting the total protein digestion. When SBM was treated with calcium lignosulfonate and compared to untreated SBM, the former reduced the in situ ruminal N digestion rate (2.05 vs. 4.70%/h), increased bypass protein content (65.3 vs. 41.9%) (Stanford et al., 1995). Calsamiglia et al. (1995) reported tha t the in situ extent and rate of SBM protein degradation was reduced from 77.5 to 23% and from 14.7 to 1.4%/h by calcium lignosulfonate treatment, and the intestinal digestion of undegradable protein was not affected (93.4 vs. 92.1%) which resulted in increased intestinally absorbable dietary protein (LADP) (20.7 vs. 70.8%). When lignosulfonate treated SBM replaced SBM in a diet fed to lactating cows, the dietary protein degradation was dramatically reduced, but intestinal digestion of dietary undegradable protein and LADP were increased (Calsamiglia et al., 1995). 8

Heat-treated soybeans and soybean meal in beef and dairy cattle production According to the NRC, most diets containing only SBM as the supplemental protein source might be expected to increase milk yields or weight gain by supplementing a high UIP source e.g., heat-treated SB or SBM. 1. Heat-treated Soybeans As early as 60’s, feeding heat-treated SB to lactating dairy cows was the subject of much research (Loosli et al., 1961). Dairy cows in early lactation (