Chemical composition and nutritive value of Tanzanian grain sorghum varieties

J T Kaijage, S K Mutayoba¹ and A Katule¹

Ministry of Livestock and Fisheries Development, Department of Animal Production and Marketing Infrastructures
P.O. Box 9152,Dar-es-salaam, Tanzania
kaijage2000@yahoo.com
¹ Department of Animal Science and Production, Sokoine University of Agriculture
P.O. Box Morogoro, Tanzania

Abstract

Two studies were conducted to asses’ type, suitability, nutrient composition and anti-nutritional components of commercially available Tanzanian grain sorghum varieties’ (GSV) for poultry feeding. In the first study, a cross section survey was carried out the nine food markets located in the urban and peri-urban areas in three the regions of eastern central Tanzania to identify available commercial GSV.  In the second study proximate, nutritional and anti- nutritional components of GSV were analyzed. Data were analyzed using descriptive statistics. Twelve GSV were identified, most (75%) of them were landraces and few (25%) were improved. Fifty eight percent (58%) of GSV had white coat colour and the rest (42%) had red or yellow. The overall mean for the proximate components, Metabolizable energy (ME_n), starch, amino acids and anti-nutritional factors were expressed on percentage dry matter (%DM). The mean of GSV values for DM (88.3±4.5), crude protein (CP) (11.2% ± 0.68), nitrogen free extract (NFE) 78.0%±2.62, starch 70.7% and (ME_n) (13.2MJ/DM ± 0.39) were high, ether extract (EE) (3.15%±0.68) were moderate and phytates (2.42µg/100gDM) were low suggesting high nutritive value and  suitability of GSV in poultry diets. The overall mean values for crude fibers (CF) (4.10±1.76) were high with wide range were associated with tannins and could suggest the limitation of using GSV in poultry diets. The overall mean values for ash content (3.51±1.52) was high and associated with the presence contaminants among GSV from different sources. The overall mean values of the macro and micro minerals and the essential amino acids were generally low signifying the need for supplementation of minerals and amino acids in grain sorghum based diets for poultry diets. High mean values for condensed tannins (3.33%DM) as leucocyanidin equivalent and total phenolic compounds (25.0%DM) were found in some of the GSV and this could limit utilization of these grains in poultry diets. In the present study a low positive correlation was noted between color of the sorghum grains and nutrient composition, anti-nutritional components, and ME_n might suggest their similarity in nutritive values. The findings of the present showed that Tanzanian GSV have high nutritive value and could partially replace maize in poultry feeding. Their full utilization in poultry diets requires a strategic improvement to reduce anticipated effects of noted anti-nutritional factors.

Keywords: chemical composition, grain sorghum varieties, nutritive value, poultry feeds

Introduction

In Tanzania, sorghum (S. bicolor (L.) Moench), (Mtama in the local Swahili language) is a second most widely grown cereal crop with a wide genetic diversity (Bucheyeki et al 2010).  The crop is grown by majority of peasant farmers across semi-arid areas in central regions of country with substantial annual production (Minde and Mbiha 1993). Sorghum is preferred because it is drought tolerant, grows well in marginal areas, and thus yields more than maize under harsh conditions. It is also used as a food security crop in rural areas (Rohrbach and Kiriwaggulu 2007). Following these attributes sorghum has a potential of being used as an alternative feed ingredient in commercial poultry feeds.

However, in Tanzania the use of grain sorghum in poultry feeds is not preferred by commercial livestock feed processors and farmers because it is viewed as inferior crop compared to maize and as such may negatively affect poultry performance (Rohrabach and Kiriwaggulu 2007). Information on nutritive value of the existing commercial grain sorghum varieties is not well documented in Tanzania. Thus, the main objective of the present study was to evaluate and document the nutritive potential of commercial sorghum varieties for poultry in Tanzania.

Materials and methods

Study area

The study was carried out in purposively selected nine main grain markets located in urban and peri-urban areas of Singida, Dodoma and Morogoro regions, eastern central Tanzania. The regions belong to semi-arid with savannah climate characterized by short rainy period of four months between December and May with an average annual rainfall of 450mm; maximum temperature of 28^oC and minimum temperature of 17^oC, the climate which favors sorghum production. The selected regions were also the main grain sorghum producers, users and had pockets of sorghum-pearl millet groundnut based farming systems.

Identification of available grain sorghum varieties

A cross section survey in these regions was carried out to identify available commercial grain sorghum varieties (GSV) in the respective food markets. About 10 key informants in each respective market were selected and interviewed using a structured questionnaire so as to obtain qualitative and quantitative data on grain sorghum marketing profile for each identified grain GSV in the market. Most of the respondents were men who were either whole sellers or retailers of grain sorghum in the respective markets.  All the types of grain sorghums sold by each interviewed whole-seller or retailer were recorded, identified based on physical characteristics and common local names. Thereafter identified varieties in markets were sampled and kept in dry paper bags for further verification and laboratory analysis.

Thereafter, the samples were ground through a 1 mm screen, packed in dry bottles, labeled and sent to the Department of Animal Science and Production (DASP) at Sokoine University of Agriculture (SUA) for the analyses of chemical composition and anti-nutritional factors.

Determination of Proximate, minerals and ME_n

Dry Matter (DM), Crude Protein (CP), Ether Extract (EE) and ash for the sorghum grain samples were determined using the (AOAC 1990) standard methods.  The minerals in grain sorghum samples were determined using atomic absorption spectro-photometric method described by (AOAC 1990).  All the analyses were done in duplicates. The values of calcium, phosphorus, magnesium and potassium were reported in percentage while sodium and iron were reported in mg/100g.  Zinc, phosphorus, manganese and copper were reported in parts per million (ppm). The calorific (energy) value was calculated by a formula: ME (kcal/kg) = (21.98 x CP) + (54.75 x EE) + (35.18 x NFE) as expressed by (Janssen 1989) and expressed as MJ/kgDM

Determination of anti-nutritional factors (condensed tannins, total phenolic compounds and Phytic acids)

The condensed tannins in the ground samples of grain sorghum were determined using Butanol/HCL method as described by Nitao et al (2001). The condensed tannins were determined as percent of leucocyanidin equivalent in accordance with the regression equation obtained from standard calibration plot. The equation expressed as Y=0.005x-0.025 (R² =0.855). Condensed tannins were expressed as mg / 100 mgDM. The total phenolic compounds in finely ground samples of grain sorghum were determined using the procedure described by Cioroi and Dumitriu (2009). Calculation of total phenols in the original sample was computed by using the equation obtained by standard calibration plot. The equation expressed as Y=0.001x-0.000 (R² =0.997). Total phenols were expressed as g/100g. The phytic acid in finely ground sorghum samples were determined based on an iron to phosphorous ratio of 4:6 using the method as described by Mustafa et al (2003). Calculation of total Phytic acids in the original sample was computed by using the equation obtained by standard calibration plot. The equation expressed as y = 1.5013x + 0.0441 R² = 0.9528.  Phytic acids were expressed as µg /100gmDM.

Statistical analysis

All the obtained data were analyzed using descriptive statistic as described by Olawuyi (1996). The Statistical values that were calculated included the means and standard deviation.

Results

Commercial grain sorghum varieties

The results of commercial GSV sold in selected food markets are presented in Table 1. A total of twelve GSV were identified in this study. Seventy five percent (75%) of the GSV were landraces and the remaining (25%) were improved varieties. Fifty eight percent (58%) of GSV had white coat colour and the rest (42%) had red or yellow. Manyiangombe, Kakera, Mkombituna, Mankumba and Mwangurungi varieties were identified as being from Singida food markets and various districts respectively. Mbangala variety was from Morogoro whereas Serena, Langalanga, Udo, Macia and Lugugu varieties were all sourced from various districts of Dodoma region. However Serena and Tegemeo varieties were also found in Morogoro region markets.

Proximate composition, energy and sugar content and some amino profile

The results for proximate composition and energy content of grain sorghum are presented in Table 1. The study revealed high DM, CP, EE and ME_n values with a slight variation across grain sorghum varieties (GSV). Moreover, the CF values were high but with a wide (5.1%) range across GSV. The highest CF values were noted in Mwankurungi and lowest in Lugugu variety. In addition, the results showed high mean NFE content but with a wide (7.7%) range across GSV. The highest NFE values were observed in Mbangala and lowest in Mwankurungi variety. However, results showed a moderate ash values with a wide range amongst GSV. The findings for starch, sugar content and profile of some amino acids are presented in Table 2. The high starch values and small proportions of sugar and amino acids were noted across GSV. The amount of lysine, tryptophan and methionine & cystine were small with insignificant variation across GSV.

Macro and micro minerals and Anti-nutritional factors

The results for macro and micro minerals are presented in Table 3. The results showed low values of calcium, phosphorus and magnesium amongst GSV. In addition, low levels of micro-minerals were noted across GSV. The results for anti-nutritional components of GSV are presented in Table 4. The study revealed high condensed tannin values with a wide variability across GSV. The lowest condensed tannins were observed in Tegemeo and highest in Mwankurungi variety. Further, results showed high total phenolic compound values with a wide range amongst GSV. Serena had highest level of total phenolic compounds and Lugugu variety had lowest relative to their counterparts. The values of phytates observed in this study were considerably low and did not differ much across GSV.

Discussion

The high DM content observed in the present study across GSV indicates that GSV are low in moisture content. These findings suggest Tanzanian GSV could produce high valuable feed component and their use could be conducive for storage of poultry feeds. DM content below 85% leads to deterioration of feed ingredients and feed products due to growth of molds and fungi particularly in tropical countries (Hamito 2010). These observations agree with Goromela (2009) and Mutayoba et al (2011). In addition, the high CP content with a slight variability amongst GSV may indicate the GSV are grown in similar climatic and agronomic conditions such rainfall, temperature, soil fertility and time of harvest (Bryden et al 2009). These results may suggest the use of studied GSV in poultry diets could probably contribute high proportion of dietary CP and reduce the cost of supplementing high protein ingredients if could be used in poultry diets.  However, the CP quality depends on the availability of essential amino acids and their availability to the animal. In the present study low levels of amino acids such as lysine, methionine& cystine and tryptophan indicate poor quality proteins in studied GSV. These findings demonstrate that lysine and methionine are amongst the most limiting amino acids in GSV.  Thus, the utilization of studied GSV in poultry diets may require considerable use of high quality protein such as fish meal or soybeans to curb the effect of limiting amino acids. These results are congruent with the research report of Gualtieri and Rapaccini (1990) and Ebadi et al (2005).

Moreover, the moderate fat (EE) content with slight differences observed in the present study amongst studied GSV demonstrate that GSV probably GSV are grown in similar growing conditions, soil type  or are harvested within the same period of time. These findings suggest the use of studied GSV in poultry diets could relatively improve the feed keeping quality and shelf life and produce body fat and products which may pose little health risks associated with cholesterol to humans compared to maize. Unsaturated fats from cereals such as linoleic and oleic become rancid quickly and produce soft fat body fat in poultry (MacDonald et al 1999) and may influence low density lipoprotein (bad cholesterol). These results concur with results observed by Mutayoba (2011).

The ash content observed across grain sorghum varieties in the present study were within the levels reported by other authors (Kriegshauser et al 2006 and Mutayoba et al 2011). These findings indicated a wide range (1.7 to 6.9%DM) of ash content across grain sorghum varieties. The wide range of ash in grain sorghum may be attributed by various factors such as variability in soil type, storage condition, climate and contaminants of inorganic substances such as sand (Bryden 2009). The ash represents inorganic constituents of feed ingredients but contain other materials from the contamination of the feed ingredients. The ash levels in the present study was not reflected the amount of calcium, phosphorous and other minerals, thus could be an indication of contamination by soil or sand particles during harvesting and or processing.  These results suggest the use of GSV in poultry diets could require appropriate harvesting and processing methods to avoid contamination.

 The CF is used to define a variety of indigestible polysaccharides including cellulose, hemicelluloses, pectins, oligosaccharides, gums and various lignified compounds. The high CF content with a wide range across GSV observed in the present study could indicate variability of tannin content in GSV.  These findings could be reflected to high and variability of tannin content in GSV (Dykes and Rooney 2006).  This is reflected to the GSV with highest CF had highest condensed tannins in the present study. The contribution of polyphenols to the lignin fraction of the GSV fibre could be responsible for the higher values of GSV fibre in the high-tannin variety. The CF value is important in major feed ingredients in livestock diets. High CF values in feed ingredients tend to increase dietary CF values that could impair digestibility in mono-gastric animals. Further, high dietary fibre has certain adverse effects on the availability of some nutrients. These results suggest the use of studied GSV in poultry diets could negatively affect digestibility and ultimately performance. Thus, the utilization of studied GSV in poultry diets requires a strategy which could reduce tannin content and eventually lower CF content.

 The high ME_n with a narrow range observed in this study across GSV agree with Donkoh and Attoh- Kotoku (2009). These results indicate that the GSV are either grown in similar climate or agronomical conditions. Energy in GSV content depends on the availability of starch. However, the availability of starch is influenced by the interaction between proteins, cell walls, non-starch polysaccharides, kaffirins and tannins (Chandrasheker and Kirleis, 1988; Kavitha and Chandrasheker, 1997 and Duodu et al 2003). All these factors are either genetically or environmentally controlled.

These findings suggest the high ability of studied GSV to supply substantial energy in poultry diets.   

The phenolic compounds may include simple phenols, phenolic acids, flavonoids, hydrolysable tannins, condensed tannins and lignin (Hahn et al 1984).The high total phenolic compounds with a wide range across GSV observed in the present study might indicate high genetic differences amongst GSV.  These findings suggest the utilization of studied GSV in poultry diets could be produce stable concentrates (Dykes and Rooney, 2006). However, high total phenolic compounds may limit the use of GSV in poultry feeds due to the presence of condensed tannins and lignin which impair utilization of nutrients and eventually could negatively affect performance in poultry.  Moreover, the high content of condensed tannins with a wide range across GSV might indicate that the GSV are genetically different  (Etuk, 2008). These results indicate that the studied GSV belong to type III containing high tannins content (Dykes and Rooney 2006). The high condensed tannins might limit their use in poultry diets. Tannins are polyphenolic compounds, which have ability to form complexes with metal ions and with macro-molecules such as proteins and polysaccharide and eventually impair digestion and make them unavailable to poultry (Dei et al 2007). Dietary tannins reduce feed efficiency and weight gain in chicks (Armstrong et al 1994). However, tannins are tolerable up to 1% in poultry diets (Ravindran et al 2006). Thus, the use of studied GSV in poultry diets might require a strategic improvement to reduce negative effects of tannins such as chemical and physical treatment of GSV or supplementation of nutrients bound or denatured by tannins (Gualtieri and Rapaccini 2009). These observations were consistent with the results reported by Tabosa et al (1995) and Medugu et al (2010).

The low of phytates observed across GSV in the present study conflict with other research reports (Wanisca and Rooney 2000 and Mustafa et al 2003). The reasons for these results are not clear but could indicate GSV are grown in dry climatic conditions without phosphorus fertilizer applications (Bassiri and Nahapetion 1977 and Asada et al1969).

The low phytic content observed in this study across GSV could suggest that GSV are high in non-Phytic phosphorus and availability minerals. There is a negative correlation between phytates content and bioavailability of phosphorus (Ahmad and Sattar 2003). About 30-90% of total phosphorous is form of phytates (MacDonald et al 1999). Moreover, phytic acid is not desirable dietary agent because chelates multi-valent metal ions, particularly phosphorus, zinc, calcium and iron and proteins which results in insoluble salts leading to unavailability of those minerals (Bryden et al 2007). These results suggest the utilization of GSV in poultry diets could minimize supplementation of minerals particularly phosphorous and calcium or use of Phytase to curb the anti-nutritional effect of phytates in poultry.

Conclusions

• It can be concluded that Tanzanian GSV have high nutritive value and quality and could partially replace maize in poultry feeding. But supplementation of mineral and amino acids is essential to optimize their nutritive value for poultry. However, their full utilization in poultry diets could require a strategic improvement to reduce anticipated effects of noted anti-nutritional factors to improve their feeding value.

Acknowledgement

The authors greatly acknowledge the Ministry of Livestock and Fisheries Development (MLDF), the Government of United Republic of Tanzania for funding the research project.

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Received 5 June 2014; Accepted 7 September 2014; Published 3 October 2014

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