Effects of dry matter content on trypsin inhibitors
and urease activity in heat treated soya beans
fed to weaned piglets
$
C.E. White
*, D.R. Campbell
1, L.R. McDowell
Department of Animal Sciences, Institute of Food and Agricultural Sciences, Gainesville, FL 32611, USA
Received 1 April 1999; received in revised form 28 January 2000; accepted 8 June 2000
Abstract
A nutrition study was conducted to evaluate the growth response of weaned piglets fed diets containing soya beans that had been processed into protein supplements at two different levels of dry matter (DM) and temperature. Four diets contained protein supplements prepared from whole full-fat soya beans equilibrated at 800 or 900 g kgÿ1DM prior to being heated to 110 or 1258C. An additional diet contained a protein supplement prepared from raw whole full-fat soya beans at 900 g kgÿ1DM; i.e. an unheated soya bean protein supplement. The experimental control diet was supplemented with a solvent extracted commercially processed soya bean meal (900 g kgÿ1DM) containing 480 g crude protein kgÿ1. Soya beans at 900 g kgÿ1DM prior to heat treatment at 1108C produced protein supplements, after heat treatment, that had higher residual levels of trypsin inhibitors and urease activity than measured in soya beans at 800 g kgÿ1DM prior to the same heat treatment. The moisture content of soya beans prior to heat treatment affected the level of heat necessary to lower values for trypsin inhibitors and urease activity. Soya beans at 800 g kgÿ1DM prior to heating at 1108C, produced a protein supplement with similar residual concentrations of trypsin inhibitors and urease activity to soya beans at 900 g kgÿ1DM prior to heating at 125
8C. This observation suggested that the soya beans with higher moisture content required lower heat energy to inactivate trypsin inhibitors and urease. The pen unit response of piglets fed the diet containing the soya bean protein supplement prepared from soybeans processed at 900 g kgÿ1DM and heated to 1108C was not improved when compared to piglets fed the diet containing the unheated soya bean protein supplement. Soya beans at 800 or 900 g kgÿ1DM prior to heating to 1108C, or soybeans at 900 g kgÿ1DM heated to 1258C, produced protein supplements that were inadequately heat processed as indicated by the values for residual trypsin inhibitors and urease activity, and, the depressed pen unit response of piglets when compared to those fed the control diet.
87 (2000) 105±115
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Florida Agricultural Experiment Station Journal Series no. R-06804.
*Corresponding author. Fax:1-352-392-7652
E-mail address: white@animal.u¯.edu (C.E. White).
1Present address: Roche Vitamins and Fine Chemicals, Paramus, NJ 07652, USA.
In contrast, piglets fed the protein supplement prepared from soya beans at 800 g kgÿ1DM prior to heating to 1258C, displayed an average daily feed intake and feed-to-gain ratio that did not differ signi®cantly from piglets fed the control diet. These data indicate that when whole full-fat soya beans were processed by the dry roasting method, their initial DM content of 800 or 900 g kgÿ1 affected the processing temperature necessary to denature or otherwise inactivate inherent trypsin inhibitors and urease activity.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Piglets; Soya bean; Trypsin inhibitors; Urease activity
1. Introduction
The soya bean (Glycine max (L.) Merrill) is classi®ed as an oilseed legume and inadequately heat processed soya beans contain an array of inherent anti-nutritional factors as reviewed by Liener (1988). Among these are the protease trypsin inhibitors and urease. When soya beans are subjected to adequate heat processing by any of a number of commercial or experimental laboratory methods, the trypsin inhibitors and other anti-nutritional factors are suf®ciently inactivated, and their anti-nutritional components are improved (Yoshida and Kajimoto, 1988; Marty and Chavez, 1993; Marty et al., 1994; Marsman et al., 1995; Qin et al., 1996; Zhu et al., 1996; Rajko and Szabo, 1997; Dudley-Cash, 1999).
Studies by Yoshida and Kajimoto (1988), Marsman et al. (1995), Zhu et al., (1996) and Rajko and Szabo, (1997), clearly advanced soya bean processing technologies but did not include animal feeding trials. Marty and Chavez (1993) and Marty et al. (1994) reported growth response of piglets fed experimental diets where soya beans had been prepared into protein supplements via a variety of processing methods (extrusion, jetsploding, roasting or toasting). Further, animal growth response was a criterion used to assess the quality of single batches of heat processed soybeans, but their experimental design did not permit identi®cation of the optimal processing temperature necessary to maximize the animal pen unit response within each processing method evaluated. As a result, the animal pen unit response within the two studies varied appreciably depending on the processing method used, suggesting that animal pen unit response was affected by a combination of factors which included nutritional value, palatability and digestibility, even when the soya bean protein supplements were considered by the researchers to have received adequate heat processing.
Qin et al. (1996), showed that experimental variation in feeding steam roasted soya beans to pigs was introduced by variables such as processing temperature, length of processing time, the size and variety of the soya bean, and animal pen unit response to the diet. In the current study we report animal pen unit response of piglets resulting from the variation in nutritional value of soya bean protein supplements prepared from dry roasting whole full-fat soya beans processed at 800 or 900 g kgÿ1
DM and 110 or 1258C. The objective of this study was to compare the pen unit response of piglets fed soya bean protein supplements prepared by the dry roasting of whole full-fat soya beans at 800 or 900 g kgÿ1
DM prior to dry roasting at 110 or 1258C, using commercially available on-farm equipment.
2. Materials and methods
2.1. Dietary treatments
The composition of diets is presented in Table 1. The International Feed Number (IFN; NAS, 1971) is reported in the text herein for each major feed ingredient used as a dietary energy or protein component. Diets were formulated to contain ground maize (Zea mays) grain (IFN 4-02-935) as the primary energy source. The soya bean protein supplements prepared and used in the six dietary treatments were as follows. Diet 1, commercial solvent extracted soya bean meal (IFN 5-04-612) at 900 g kgÿ1
DM. Diets 2±6 contained the whole full-fat soya beans (IFN 5-04-610) at either 800 or 900 g kgÿ1
DM. Speci®cally, diet 2 soya beans were at 900 g kgÿ1
DM when included in the diet as a raw (unheated) protein supplement; diet 3, soya beans were at 900 g kgÿ1
DM prior to heating to a discharge temperature of 1108C; diet 4, soya beans were at 800 g kgÿ1
DM prior to heating to a discharge temperature of 1108C; diet 5, soya beans were at 900 g kgÿ1
DM prior to heating to a discharge temperature of 1258C; and diet 6, soya beans were at 800 g kgÿ1
DM prior
Table 1
Composition of experimental diets
Ingredients Control (diet 1) Soya beans (diets 2±6)
Ground maize 684 569
Soya bean meala 254 ±
Whole full-fat soya beansb ± 399
Maize oil 30 ±
Dicalcium phosphate (CaHPO4) 17 17
Limestone 8.0 8.0
Metabolizable energyg(MJ kgÿ1) 13.85 13.82 aCrude protein concentration of commercial soya bean meal, 480 g kgÿ1as fed basis. bCrude protein concentration of whole full-fat soya beans, 367 g kgÿ1as fed basis.
cCalcium Carbonate Company, Quincy, IL. Contained 200 mg zinc, 100 mg iron, 55.0 mg manganese,
11.0 mg copper, 1.5 mg iodine, 1.0 mg cobalt, 20.0 mg calcium and 0.10 mg selenium per kg of feed.
dHoffmann LaRoche Company, Nutley, NJ. Supplied 13.2 mg ribo¯avin, 44.0 mg niacin, 26.4 mg
pantothenic acid, 176.0 mg choline chloride, 22.0 ug Vitamin B12, 5500 IU Vitamin A, 880 ICU Vitamin D3
and 22.0 IU Vitamin E per kg of diet.
eAmerican Cyanamid Company, Princeton, NJ. Supplied 44.0 mg chlortetracycline, 44.0 mg sulfamethazine
and 22.0 mg penicillin per kg of complete diet.
fCalculated crude protein from nitrogen (N) analysis (N6.25) of individual grain and protein supplement
used as feed in this study, as fed basis.
gCalculated metabolizable energy based on published estimates (NRC, 1988) for grain and protein
supplements used as feed in this study.
to heating to a discharge temperature of 1258C. The appropriate levels of vitamins and minerals necessary to meet the growth requirements of piglets 5±20 kg BW (NRC, 1988), were included in each of the six dietary treatments as shown in Table 1.
2.2. Laboratory preparation of soya bean protein supplements
The ®ve laboratory-prepared protein supplements fed were made from aliquots drawn from a large uniform batch of whole full-fat soya beans (183 g ether extract kgÿ1, DM basis) of the `Bragg' variety; i.e. G. max var. Bragg, grown and harvested at a single location in Alachua County, Florida during a single growing season. The entire quantity of whole raw full-fat soya beans used to prepare diets 2±6 assayed at 897 g kgÿ1
DM at ambient conditions of temperature, relative humidity and barometric pressure prior to processing. This value was rounded up to 900 g kgÿ1
DM for simplicity of reporting. The DM content of soya beans fed in diets 4 and 6 was decreased prior to dry roasting by adding 100 g kgÿ1
(w/w) distilled water to an aliquot of soya beans at 900 g kgÿ1 DM. The soya beans were equilibrated with the water overnight via gentle stirring and tumbling to ensure uniform moisture absorption. The ®nal DM concentration for soya beans used in diets 4 and 6 prior to roasting assayed at 795 g kgÿ1
DM and was rounded up to 800 g kgÿ1
DM, again for simplicity of reporting. To minimize potential deterioration from prolonged storage of soya beans at 800 g kgÿ1
DM, those used in diets 4 and 6 were heat processed the morning following overnight equilibration with water. All aliquots of raw soya beans at either 800 or 900 g kgÿ1DM were heat processed by an automated commercial Roast-A-Tron (Mix-Mill, Inc., Bluffton, IN) gas-®red roaster. Soya beans were roasted at the prescribed temperature control and transit time settings as recommended in the manufacturer's operations manual to achieve the desired discharge temperature as speci®ed in diets 3±6. The average transit time through the roaster was 60 s for soya beans processed to a discharge temperature of 1108C, or 90 s for soya beans processed to a discharge temperature of 1258C. When heat processing was completed, the soya beans returned to 90% DM at room temperature, and were ground into a meal of ®ne particle size before inclusion into their respective diets.
2.3. Commercial soya bean meal
The commercial soya bean meal used in the current study was manufactured by the solvent extraction process as outlined by Ensminger et al. (1990). Brie¯y, full-fat soya beans were crushed, then heated to 468C for 15 min. The crushed heated product was then rolled into ¯akes and passed to an extraction tower where approximately 99% of the soya oil (190 g soya oil kgÿ1
full-fat soya beans; NRC, 1988) was removed by extraction with hexane. The de-fatted soya bean meal then passed into a drier and was retained for 10 min at 988C. Thereafter, the soya bean ¯akes passed into a toaster where they were retained for 90 min at 1048C, followed by rapid cooling to 388C prior to making a pass through the grinder. The commercial soya bean meal fed in the current study had an ether extract residual of 13 g kgÿ1
DM. The fat content of the control diet containing the commercial soybean meal was adjusted to that of the diets containing full-fat soybeans by adding corn oil to the ®nal feed formulation presented in Table 1.
2.4. Analytical determinations
The DM content both before and after heat processing was determined as outlined by the American Association of Analytical Chemists (AOAC, 1980). Ether extract of the raw soya beans was also determined according to the AOAC (1980). Representative samples of the raw soya beans and the commercial soya bean meal were analyzed for crude protein (nitrogen6.25) content using the procedure for nitrogen determination set forth by Gallaher et al. (1975) for the Technicon Auto Analyzer (Technicon Industrial Systems, 1978). The residual levels of the trypsin inhibitors expressed as milligrams of protease inhibitor per gram (mg gÿ1
) of de-fatted soya bean sample was measured by the method of Hamerstrand et al. (1981) both before and after heat processing. Urease activity was measured as change in pH units (DpH) by the method of Caskey and Knapp (1944).
2.5. Animal feeding trial design
One-hundred and eight Yorkshire±HampshireDuroc crossbred piglets with an average initial body weight (BW) of 5 kg were allotted by litter origin, BW and sex to receive one of the six dietary treatments. Each treatment was replicated three times into pen units which contained six piglets each. The feeding trial was conducted over a period of 35 days. All piglets were housed in an enclosed climate controlled nursery equipped with elevated pens having expanded metal ¯oors and wire mesh side panels. Feed and water were offered ad libitum in each pen unit. The BW of individual piglets, and the feed consumption in each pen unit, were measured bi-weekly to permit calculations of average daily gain (ADG), average daily feed intake (ADFI) and the feed-to-gain ratio (F:G) used as animal pen unit response criteria for statistical analyses that compared effects of dietary treatments.
2.6. Statistical analyses
Variability in ADG of piglets was analyzed by least squares means analysis using the general linear model of the statistical analysis system (SAS, 1979). The variables ADFI and F:Gwere subjected to analysis of variance for a randomized complete block design, where blocks represented replications within dietary treatments. When calculated values forFwere signi®cant, the Duncan's new multiple range test (Steel and Torrie, 1960) was used to interpret signi®cant differences among means for ADFI andF:G. Diets 3±6 were further analyzed as a 22 factorial design evaluating animal pen unit response (ADG, ADFI and F:G) to the dry matter content of soya beans prior to dry roasting, and the effects of dry roasting soya beans at the two selected temperatures used to process the protein supplements.
3. Results
3.1. Pen unit response
Table 2 presents the growth response data of piglets assigned the six dietary treatments. The ADG of piglets fed diet 1, containing the commercial soya bean meal as a protein
supplement was greater (P<0.05) than that of other dietary treatments. By contrast, piglets fed diet 2, containing the unheated raw soya bean meal at 900 g kgÿ1
DM, or diet 3 with soya beans at 900 g kgÿ1
DM and heated to a discharge temperature of 1108C, had the lowest ADG in the feeding trial. Piglets fed diet 3 also showed similar ADFI andF:G to piglets fed diet 2. When DM content of soya beans was reduced to 800 g kgÿ1
and heated to a discharge temperature of 1108C, the resulting protein supplement used in diet 4 signi®cantly improved (P<0.05) ADG compared with piglets fed diets 2 and 3. TheF:G of piglets fed diet 4 also was signi®cantly improved (P<0.05) compared with that of piglets fed diet 3, but not those fed diet 2. The ADG of piglets fed diet 5, which contained soya beans at 900 g kgÿ1
DM and heated to a discharge temperature of 1258C, was signi®cantly improved (P<0.05) compared to the ADG measured for piglets fed diets 2 and 3, but did not differ from those fed diet 4. The ADFI of piglets fed diets 2±5 did not differ signi®cantly. The F:G of piglets fed diet 5 was signi®cantly improved (P<0.05) when compared to those fed diets 2 and 3, but not diet 4. TheF:Gof piglets fed diets 5 and 6 did not differ. Piglets fed diet 6, where soya beans at 800 g kgÿ1
DM were heated to a discharge temperature 1258C, gave the best overall pen unit response among groups fed the laboratory prepared protein supplements. Average daily feed intake was highest and F:Gwas lowest for piglets fed diets 1 and 6, which did not differ signi®cantly from each other.
3.2. Effects of dry matter and temperature
The 22 factorial analysis for main effects of DM content of soya beans prior to dry roasting, and processing temperatures on subsequent pen unit response of piglets fed diets 3±6 is presented in Table 3. Piglets fed diets 5 and 6 containing the protein supplements prepared from soya beans heated to a discharge temperature of 1258C had higher ADG (P<0.05), ADFI (P<0.05) and trends for improved F:G than piglets fed diets 3 and 4
Table 2
Pen unit response of piglets fed diets containing protein supplements from commercial soya bean meal (SBM, diet 1) or full fat Bragg variety soya beans (diets 2±6) processed at different levels of dry matter and temperaturea,b
Dietary treatment, diet S.E.M.c
1 2 3 4 5 6
Process temperature (8C) n/a Ambient 110 110 125 125 Soya bean dry matter (g kgÿ1) 900 900 900 800 900 800
Average initial weight (kg) 5.04 5.03 5.02 5.03 5.03 5.03 ± Average ®nal weight (kg) 16.80 7.87 7.56 9.75 11.03 13.71 ± Average daily gainb(kg) 0.33 a 0.08 d 0.06 d 0.13 c 0.17 c 0.25 b 0.02
Average daily feed intake (kg) 0.59 a 0.33 b 0.32 b 0.41 b 0.39 b 0.55 a 0.02 Average feed-to-gain ratio,F:G 1.76 c 4.45 ab 5.23 a 3.09 b 2.33 c 2.21 c 0.41
aMeans in the same row with different letters are signi®cantly different (P<0.05).
bPen unit least squares means for average daily gain, and means of average daily feed intake and the
feed-to-gain ratio as calculated from the randomized complete block statistical analysis of treatments.
cStandard error of mean.
where protein supplements were prepared from soya beans heated to a discharge temperature of 1108C. The main effect of lowering DM from 900 to 800 g kgÿ1
prior to dry roasting soybeans used to prepare protein supplements fed to piglets in diets 4 and 6, was to improve ADG (P<0.05) and ADFI (P<0.05). Lowering the DM content of soya beans prior to dry roasting and preparation of protein supplements fed to pigs in diets 4 and 6 had a tendency to improved theF:G, but mean differences among treatments were not signi®cant.
3.3. Trypsin inhibitors and urease activity
The levels of trypsin inhibitors and urease activity of soya bean protein supplements used in each of the six diets are presented in Table 4. Soya bean meal with a urease activity between 0.05 and 0.20DpH units is considered to have received optimum heat processing for feeding all animals species regardless of age (Smith, 1977). Neither heat treatment (110 or 1258C) during the roasting process, nor lowering the DM content of soya beans was effective in lowering the urease activity of the laboratory-prepared soya bean protein supplements used in diets 3±6 to less than 0.25DpH units. Heating an aliquot of whole soya beans at 900 g kgÿ1
DM to a temperature of 1108C was effective in
Table 3
Pen unit response analyzed as a 22 factoral analysis of piglets fed diets containing soya bean protein supplements processed at different dry matter and temperature levelsa
Temperature (8C) Dry matter (%) S.E.M.b
110 125 90 80
Average initial weight (kg) 5.02 5.02 5.02 5.02 ± Average ®nal weight (kg) 8.69 12.41 9.35 11.78 ± Average daily gain (kg) 0.10 a 0.21 b 0.12 a 0.19 b 0.04 Average daily feed intake (kg) 0.37 a 0.47 b 0.35 a 0.48 b 0.03 Average feed-to-gain ratio,F:G 4.16 2.27 3.78 2.65 0.79
aMeans for pen unit response in rows within main effects (temperature and dry matter) with different letters
are signi®cantly different (P<0.05).
bStandard error of mean.
Table 4
Values for trypsin inhibitors and urease activities of soya bean protein supplements processed at different levels of dry matter and temperature
Diet, dry matter, process temperature in8C Trypsin inhibitors in mg gÿ1de-fatted sample
Urease activity in units ofDpH Diet 2, 900 g kgÿ1DM, raw unprocessed 53.95 1.97
Diet 3, 900 g kgÿ1DM, heated to 110
8C 40.00 1.82
Diet 4, 800 g kgÿ1DM, heated to 110
8C 24.00 1.30
Diet 5, 900 g kgÿ1DM, heated to 125
8C 22.88 0.55
Diet 6, 800 g kgÿ1DM, heated to 125
8C 9.18 0.25
Diet 1, 900 g kgÿ1DM, commercial SBM 3.11 0.10
lowering the trypsin inhibitors and urease activity by 26.0 and 7.6%, respectively. Heating an aliquot of soya beans at 900 g kgÿ1
DM to a temperature of 1258C or heating an aliquot of soya beans at 800 g kgÿ1
DM to a temperature of 1108C had the similar effect of lowering the trypsin inhibitors by an average of 57.4%, while the DpH for urease activity of soya beans heated to a temperature of 1258C was two-fold less than soya beans at 800 g kgÿ1
DM heated to a temperature of 1108C. Heating an aliquot of soya beans at 800 g kgÿ1
DM to a temperature of 1258C prior to processing the protein supplement used in diet 6, resulted in reductions of trypsin inhibitors and urease activity of 83.0 and 87.3%, respectively. Of the ®ve laboratory-prepared protein supplements, the supplement fed in diet 6 had the lowest residual trypsin inhibitors and urease activity, but, these values remained two-fold higher than those of the commercial solvent extracted soya bean meal fed in diet 1.
4. Discussion
4.1. Processing of soya beans
The technologies currently available for on-farm processing of whole soya beans consist of; extrusion, jetsploding, microwave heating, micronizing, roasting and toasting (Yoshida and Kajimoto, 1988; Marty and Chavez, 1993; Marty et al., 1994). Each technology differs in application, but all employ energy in the form of heat to inactivate trypsin and chymotrypsin inhibitors, urease, and lectins which represent the more thermolabile anti-nutritive constituents in soya beans (Liener, 1988). The most plausible mechanism by which heat inactivates anti-nutritional factors in legume seeds is by denaturation (Grant, 1989). According to Rackis et al. (1986), a minimum absorbed energy of 1200 J gÿ1
was suf®cient to inactivate the total amount of urease enzyme and an energy of 1670 J gÿ1
was required to destroy over 95% of the trypsin inhibitor in soya beans. In addition to inactivation of anti-nutritional factors, adequate heat processing improves the digestibility of legume proteins by denaturation which opens the polymerized structures of proteins (van der Poel et al., 1990) and starches (Marty and Chavez, 1993). Inadequately heated soya beans affect digestibility as trypsin and chymotrypsin inhibitors form insoluble complexes in the ileum of piglets and inhibit the action of the proteolytic enzyme trypsin (Rajko and Szabo, 1997).
An indicator of adequately heat processed soya beans is the near complete inactivation of urease, but some trypsin inhibitor activity usually remains following the complete inactivation of urease (Smith, 1977), and, as previously stated, soya bean meal having urease activity in the range of 0.05±0.2DpH has been adequately heat treated for feeding all animal species regardless of age. Therefore, it seems reasonable that this range of urease activity would be acceptable for adequately dry roasted, whole full-fat soya beans fed to piglets in the present study. Other factors are involved in producing acceptable soya bean protein supplements from whole full-fat soya beans. The optimization of temperature, moisture content, particle size and cultivar of soya beans are mentioned as important variables by Melcion and van der Poel (1993), but the desired product is a soya bean protein supplement with inactivated anti-nutritional factors having high
availability of essential amino acids (Van Barneveld, 1993). In the current study dry roasting soya beans to a discharge temperature of 110 or 1258C, was more effective in lowering trypsin inhibitors and urease activities when DM content was decreased from 900 to 800 g kgÿ1
by overnight equilibration with water. These observations are in agreement with those of Yoshida and Kajimoto (1988) who showed that increasing moisture content of soya beans also increased the ef®ciency of microwave heating. Similarly, Zhu et al. (1996) showed that increasing the moisture content lowered the protein dispersibility index (PDI), and temperature necessary to inactivate three inherent lipoxygenases in extruded full-fat soya beans. Heat transfer in foods or feeds that are dry roasted occurs by the physical process of conduction (Holman, 1986). The heat energy conducted into the soya beans by the process of dry roasting increased the molecular motion of water molecules and the molecules of other nutrients present. The heat transfer was more ef®cient in soya beans with the higher moisture content because water is an excellent conductor of heat. Therefore, with the additional water molecules in motion during the dry roasting of soybeans at 800 g kgÿ1
DM, as opposed to soybeans at 900 g kgÿ1
DM, the conductive energy (110 or 1258C) supplied by the roasting equipment was more effective in inactivating trypsin inhibitors and urease.
4.2. Effects of temperature and moisture
Data presented in Table 4 suggested that the Bragg variety of full-fat soya beans requires a dry roasting discharge temperature that is1258C and (or) a heating period of greater than 90 s to inactivate trypsin inhibitors and urease to the extent measured in the 480 g kgÿ1
crude protein commercial soybean meal fed as a protein supplement in diet 1. The laboratory prepared protein supplements having values for trypsin inhibitors greater than 9.18 mg gÿ1
or urease activities higher than 0.25DpH had not received the level of heat treatment necessary to denature trypsin inhibitors adequately and otherwise improve the nutritional value of soya beans to acceptable levels for feeding piglets from 5 to 20 kg BW. Since other experimental parameters were held constant, it is concluded that the depressed ADG response of piglets fed diets 2±5, resulted from protein supplements prepared from inadequately heated soya beans.
Decreasing DM content to achieve 800 g kgÿ1
prior to heating whole soybeans to a temperature of 1258C, was the most effective DM to heat combination of treatments used in the current study for lowering values for trypsin inhibitors and urease activities to levels near those recommended by the American Feed Manufacturer's Association (Smith, 1977). Piglets fed diet 6 displayed signi®cantly (P<0.05) lower ADG, but similar and acceptable growth response in terms of ADFI and theF:Gratio as piglets fed the diet 1 containing the commercial soybean meal.
5. Conclusions
The DM content of whole full-fat soya beans prior to heat treatment had a signi®cant effect on the temperature necessary to adequately denature inherent trypsin inhibitors and lower urease activity. Decreasing the DM content prior to heat treatment represents a
relatively inexpensive but potentially cost effective method (in terms of lowered energy requirement) for non-commercial, on-farm heat processing of full-fat soya beans. Some potential bene®ts of this study were; farmers on combination grain and livestock farms where both soya beans and pigs are produced have the option of processing their soya beans into protein supplements and especially during economic cycles when commercial soya bean meal is expensive, demand for whole full-fat soya beans is high, and the available supply is low. Alternately, when the market demand for soya beans is depressed, but market demand and economics for pork production are favorable, on-farm processing of soya bean protein supplements fed to piglets is an option that could add value to the soya bean crop. Finally, the Bragg variety of soya beans used in this study is genetically related to several other soya bean cultivars (Campbell, 1986). Therefore, data generated from the heat processing requirements and subsequent nutrient value of dry roasted Bragg variety soya beans as reported herein might also pertain to the application of the dry roasting process for adequately heat treating related varieties of soya beans.
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