Nutritional evaluation of some varieties of sorghums (Sorghum bicolor).

Abstract

195 NUTRITIONAL EVALUATION OF SOME VARIETIES OF SORGHUMS (sorghum bicolor) DRINAH B.G. BANDA* and PRAN VOHRA* SUMMARY Significant differences were observed in the dry matter, crude protein, indigestible residue, ether extract, ash, tannins, starch and free sugar contents of number of varieties of sorghum grown in 1980 and 1981. The differences were of varietal as well as seasonal in origin. Significantly different values were obtained for the polyphenolic (tannins) content of the different varieties, and the absolute values depended upon the method of determination. Tribolium assay as well as Chicken assay were in agreement in differentiating between the best and the worse varieties, but not the intermediate quality sorghum. The growth of chickens was not correlated to either AME or ANR of the diets. A high tannin sorghum had a high AME and ANR value, but depressed the growth of chickensINTRODUCTION Grain sbrghum belong to the genus sorghwn bieolor (L,) Moench of the tribe Andropoqoneae, a member of the Gramineae family. It ranks 4th among the major cereal of the world, and is widely used for human consumption in many countries of Asia and Africa. However, it is mainly fed to animals in U.S.A. Sorghum is also called mile maize, gyp corn, grain, kafir corn in U.S.A., jowar, juar, cholam in India, Guinea corn in Nest Africa, kafir corn in South Africa, durra in Sudan, mtama in East Africa, millets in England (Rooney 1973) .and mapila in Zambia and Malawi. Sorghum, mainly a tropical or cultivated in temperate climates, producing new varieties to improve general, sorghum may be classified yellow, white, brown (high tannin subtropical plant, can also be and plant geneticists are continuously yields and pest resistance- In as follows according to their color: content or bird-resistant) and mixed. \ Different varieties of sorghum differ in their chemical composition (Neucere and Sumrell, 1980), protein content (Miller et a+ 1964, nutritive value (Breuer and Dohm 19721, and amino acid profiles (Waggle et al. 1967; Breuer and Dohxn 1972; Sikka and Johari 1979; Briley et al. 1979). The protein content and amino acids are influenced by the agronomic factors. The nutritional value of sorghums has been evaluated using chickens (Waggle et al. 1967; Armstrong . al. 1974; Luis et al. 1982a), poults ,et (Luis etX 1982b), rats (Axtell et al. 1981) and preschool children (Maclean al. 19811. Department of Avian Sciences, University of California, Davis, Ca 95616, U.S.A. 196 A lot of information on sorghums has been compiled in a recent book (Hulse et al. 1980). The present study attempts to evaluate the nutritional value of different varieties of sorghums using Ttibozi~n caskuzem larvae and chickens as the test organism. MATERIALS AND METHODS Based on an earlier study, ten varieties were selected that were the best, intennediate and the worse in supporting the growth of tribolium larvae. The selected varieties identified as in parenthesis were DeKalb , DD 50T (DD SOT), O'GoId EXP 9520 (EXP 9520), Northrup King NK 1580 (NK 1580), Northrup King NK'129 (NK 129), P.'A.G. 4432 (PAG 4432), Pioneer 8790 (P. 8790), Asgrow Corral (Corral), DeKalb A 28+ (A 28+), P. Oil POI652G (I652G), and O*SG M 0505 (M 0505). These were grown at Davis, Ca. Three high-tannin varieties NK 300, Savanna 5, and Savanna 5 X 3174 were donated by Northrup King Co., Minneapolis, Minnesota. Dry matter (DM), crude protein (% CP = % Kjeldahl N x 6.25), ether extract an'd ash were determined according to the AOAC (1970) procedures. The method developed by Hellendoorn et al. (1975) was used for the estimation of indigestible residue. Starch was determined by the method of Southgate (1969) and free sugars were determined as glucose by the glucose oxidase method using Sigma reagents. Tannins or polyphenols were measured by the vanillin-HC1 methods of Price et al. (1978), Earp et al. (1981); spectrophotometric method of Price andutler (1977), azlin-Denis method as used by Burns (1971). The first three methods use catechin as a standard, and the last method uses tannic acid. The procedure followed for the bioassay using ~I%JCJ&OI castanewn was the same as described by Vohra et al. (1981). The test samples were ground finely and fed in diets at ax1 of 90% along with 10% brewers yeast.' The larval weights were determined on the 14th day. Day-old broiler chicks obtained from A.M. hatchery, Santa Rosa, Ca were weighed, wing-banded and distributed randomly, eight birds per cage in a Petersime battery. A replicate of the experiment was set up on each side of the battery with test diets (Table 10) assigned to each cage in such a way that the same diet was not on the same level or side of the battery. The usual system of husbandry was followed. Food and water were provided ad libitum. The chicks were weighed individually twice a 240hour total collection of excreta were made during the 3rd week. week of the experiment. The corresponding food intake was also measured. The excreta were dried in a forced-air oven at 60�C. TWO From the gross energy data of food and excreta, apparent metabolizable energy (AME) of the diets was calculated. Also, from the Kjeldahl nitrogen content of a diet and the corresponding nitrogen excretion, apparent nitrogen retention (ANN of a diet was calculated. The data were subjected to analysis of variance and Duncan's (1955) new multiple range test or some other suitable statistical treatment (Steel and Torrie 1960). 197 RESULTS AND DISCUSSION The results of the proximate composition and the tannin content of the sorghum varieties grown in 1980 and 1981 seasons are presented in Tables 1 and-2, and of available carbohydrates in tables 3 and 4, respectively, Significant (p<O.OlJ varietal differences were observed for all the measured parameters. Table 1. Proximate composition on a dry matter basis of ten sorghum varieties grown in the 1980 season Table 2. Proximate composition of ten varieties of sorghums grown locally in 1981 and one special high tannin variety on a dry matter basis 198 The dry matter content of the different varieties was not significantly (p<o,Ol) different and the mean values were 90.7% (range, 88.b93.4%) during 1980, and 89.9% (range, 88.5-92.23) during 1981. The crude protein content showed significant varietal differences and the mean value was 12.3% (range, 10.8-13.9) for 1980 sorghum and 1,053 (range 9.3-11.23) for 1981. Indigestible residue averaged at 12.5% (range, 9.7.15.4%) for 1980 and 10.6% (range, 8.8015.3%) for 1981. Mean values for ether extract, ash and tannin content were 3.5% (range, 2.605.7%), 1.9% (range, 1.5.l-9%), and 0.23% (range, 0.1300.32%), respectively for 1980: The respective values for 1981 were 4.3% (range, 2.905,5%), 2.0% (1.702.8%) and 0.31% (range, 0.2500.36%) neglecting the high tannin variety not grown at Davis. The available carbohydrate constituents, starch and glucose also were significantly different in different varieties during both the seasons. The mean value for starch was 67.4% (range 61-l-72.6%) and for free sugars 1.63% (range, l-01-2.62%) for the 1980 samples, and the respective values for the 1981 samples were 73.6% (range, 69.0080.7%) and 1.05% (range, 0.76-1.263) which-.also included the high tannin variety. Table 3. The available carbohydrate content on a dry matter basis of ten varieties of sorghums grown in the 1980 season Different letters in a column indicate significant differences (p<o.Ol). Available carbohydrate values have been rounded to 1 decimal place. Significant differences were observed in the same parameters for the 1980 and 1981 samples as determined by t-test (Table 5). The grains were slightly smaller in 1980, had a significantly higher crude protein, indigestible residue and free sugars than the 1981 samples which were larger in size. The latter had a significantly higher ether extract, ash, starch and tannin contents. It is probable that the 1980 crop encountered some adverse agronomic factors which reduced the plumpiness of the grain, reduced their yield, starch content, but increased the protein level. 199 Table 4. The available carbohydrate content of ten varieties of locally grown sorghums in 1981 season and of the high tannin variety Table 5. The effect of growing season on the composition of ten varieties of sorghum grown in 1980 and 1981 The total protein content of cereals is controlled by the genetic potential of the plant, nitrogen fertilization and other agronomic conditions. The main increase in protein level is due to an increase in kafirin (prolamines) like storage proteins (Seckinger and Wolf, 1973) and not in the structural proteins such as glutelins which form matrices,for the starch granules. Unless the granules get plumped with starch, the protein content of the grain is relatively high. The storage proteins are deposited along with the carbohydrate deposition (Rooney 1973). The data on the varietal and seasonal differences in the composition of sorghum grain is in agreement with the values compiled by Hulse et al. (1980). 200 Table 6. A comparison of values determined by 4 methods of polyphenol (tannins) determination for 14 varieties of sorghums grown in 1981 season on a dry matter basis Tannins are polyphenolic compounds present mostly in pericarp. A high tannin content of the sorghum grains is of value against bird predation. However, we still do not have a very reliable method for the determination of tannins. The most commonly used method relies on the development of color with a vanillin solution in HCl and the color is calibrated against color produced by a known amount of catechin (Price et al. 1978). However, vanillin gives no color with tannic acid or gallic acid. Tannins were determined in 14 varieties of sorghum, 10 of which were low tannin variety of the 1981 season and 4 were of high tannin varieties. The data on the determination of tannins by four methods is given in Table 6. The Prussian blue method of Price and Butler gave lowest values of all the methods. In general, higher values were obtained by using FolinDenis reagent than vanillin-HCl, but the method is tedious and time . consuming. The data indicate significant varietal differences in the tannin contents, significant differences in the results obtained by different methods, and a significant interaction between the methods of determination of tannins and the varieties of sorghums. These data are in 201 agreement with of the results of Earp et al. (1981) who also found wide differences in values depending upon tizthod used. The amino. acid profiles of the 1980 varieties of sorghums are given in Table 7. The data could not be evaluated statistically because only a single sample of each variety was analyzed. Table 7. Amino acid profiles of ten varieties of sorghums grown in the 1981 season The different varieties suggest differences in amino acid profiles and the results are within the range of values reported by Sikka and Johari (19791, and Badi et al. (1978). The composition of the diets used for bioassy with tribolium larvae is given in Table 8. The samples were first assayed in 1980 and 3 times in 1981. The data on the growth response of tribolium larvae over a 14 day period is given in Table 9. The data were analyzed by a 2-way analysis of variance and the Least significance difference (LSD) for the data was calculated. 202 Table 8. The composition of the diet to screen the relative nutritive value of different varieties of sorghums using TtiboZim castanewn as test organism Table 9. The average larval weight of Tz6boZiwn castanewn at 14 days of age fed various varieties of sorghums of the 1980 and 1981 seasons Significant,differences were observed in the growth response of the tribolium larvae to different varieties of 1980. The varieties NK 1580, NK 129, Pioneer 8790, DeKalb A 28+ and O'SG M 0505 were significantly inferior to the other varieties. This was the basis for planting these varieties in 1981. However, these differences disappeared in the first test in December 1981 on fresh samples. The 2nd and 3rd tests were run on these stored samples during June and December 1982. Some significant differences were observed and the variety Pioneer 8790 was still the poorest and DeKalb DD SOT was still the best variety in supporting larval 203 growth. The ranking of other varieties was different in 1981 than in 1980, Seasonal differences in weights of tribolium larvae have also been recorded by Rogel et al. (1983). Tribolium larvae respond to amino acid balances Wohra et al, 1978) I complex carbohydrates (Vohra et al. 1979a, 1979b; Rogel and Vohra, 1981) and some other heat labile antinutrients (Shariff et al. 1981). The 1980 grains we,re'not as large as those of 1981. Theagronomic factors may have reduced the antinutrients in 1981 crop. The effect of storage on nutritional quality deserves further study. In the studies with chickens diets were fed based on sorghums and soybean meal containing 24% crude protein and supplemented with 0.45% DL-methionine (Table 10). To obtain this level of protein, neither sorghums nor soybean meal could be kept sat a constant level. Table 10.' The main constituents of the chicken diets fed various varieties of sorghums (g/kg diet) . The results of feeding these diets to chickens are presented in Table 11. The data indicate significant differences in the growth of chickens fed diets containing different varieties of sorghums. The diet 1580 incorporated the highest level of soybean meal followed by diet 8790. The diets 4432 and 300 contained the same level and Corral had the lowest level. If the growth of chickens was a reflection of the..incorporation of soybean meal, maximum growth should have been for birds fed the diets NK 1580, and Pioneer 8790, and poorest on Asgrow Corral. Actually, the growth on P.A.G. 4432 was not significantly different from that on NK 1580 variety which had a much higher inclusioti of soybean meal. The growth of chickens was not correlated to the level of soybean meal in the diets. The data suggest varietal differences in the nutritive value of sorghums for chickens. The adverse effedts of high tannin sorghums as reported by other workers (Armstrong et al. 1973) are also confirmed.Apparent metabolizable energies of diets containing different varieties of sorghums differed significantly. AME of the diet was not dependent upon the level of soybean inclusion. Unexpectedly, AME of the diet containing high tannin sorghum (NK 300) was significantly higher than of any other diet even when the growth of chickens ,was significantly depressed. No correlation was observed between the AME of the diets and the growth-of chickens. 204 Table 11. The effect of diets containing 24% crude protein based on different varieties of sorghums on the body weights of chicks at 3 weeks of age, and on apparent metabolizable energy (AME) and apparent nitrogen retention of the diets (16 birds/diet) Apparent nitrogen retention was also different for the diets containing different varieties of sorghums, and the highest value was observed for the high-tannin variety NK 300, contrary to our expectations. No significant correlation was observed between the growth of chickens and ANR, or between AME and ANR. Tribolium assay on 1981 samples also suggested that NK 1580 was significantly superior than Agrow Corral. The intermediate values are harder to predict. . 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