Uganda Journal of Agricultural Sciences, 2014, 15 (1): 41 - 50 ISSN 1026-0919 Printed in Uganda. All rights reserved © 2014, National Agricultural Research Organisation Proximate composition and mineral contents of Pebbly fish, Alestes baremoze (Joannis, 1835) fillets in relation to fish size N. Kasozi¹, G.I. Degu¹, D. Asizua¹, J. Mukalazi¹ and E. Kalany² ¹Livestock and Fisheries Program, Abi Zonal Agricultural Research and Development Institute, P. O. Box 219, Arua, Uganda ²Department of Food Technology and Nutrition, College of Agricultural and EnvironmentalSciences,Makerere University, P. O. Box 7062, Kampala, Uganda Author for correspondence: [email protected] Abstract Alestes baremoze (Joannis, 1835), locally known as Angara in Uganda, is native to fresh water systems in Africa, thriving well in both lacustrine and riverine conditions. It is part of the routine diets of families in northern Uganda, South Sudan, the Sudan and the Democratic Republic of Congo. The objective of this study was to determine the proximate composition and mineral contents of A. baremoze fillets according to fish size. The mineral contents of A. baremoze from Lake Albert were analysed using standard procedures. The fish samples were categorised into three size-groups; <1 kg (880–990g), 1-1.5 kg and 1.6-2.5 kg. On wet weight basis, there were no significant differences (p>0.05) in crude protein and ash content among the different fish sizes. However, there were significant differences (p<0.05) in crude fat, carbohydrate, gross energy and vitamin A. Crude fat (0.35%), carbohydrate (0.37%) and gross energy (597.6 Kcal/100 g) were significantly higher in medium sized fish (1 to 1.5 kg) compared with the larger fish category. Vitamin A contents of different fish sizes ranged from 55.1 to75.3 µµµg RAE/100g. The contents of magnesium and iron were highest in sizes <1 kg (5.34 mg/100 g) and (3.58 mg/100 g), respectively. It was observed that potassium content (339.33 mg/100 g) and calcium (29.75 mg/100 g) were significantly higher (p<0.05) in fish >1.5 kg. These findings suggest that taste, freshness and other related external appearances should not be the only factors to be considered in making choice for marketing and consumption of Alestes baremoze. Key words: Alestes baremoze, Lake Albert, mineral content, proximate composition Introduction 2007). The nutritional value of fish meat comprises the contents of moisture, Fish is known to be one of the cheapest protein, lipids, vitamins, minerals and the sources of animal protein and other caloric value (Chandrashekar and essential nutrients required by many Deosthale, 1993). Minerals components people, especially in developing countries. such as potassium, magnesium, calcium, It is widely consumed because it has high iodine, phosphorus are important for protein content, low saturated fat and also human nutrition (Erkan and Ozden, 2007). contains omega fatty acids known to However, the nutritional components of support good health (Erkan and Ozden, the fresh water fishes tend to differ 42 N. Kasozi et al. between species, sexes, sizes, seasons and Materials and methods geographical localities (Huss, 1995; Zenebe et al., 1998). The measurements Sample collection and preparation of some proximate profiles such as protein Eighteen fish of various sizes were caught contents, carbohydrates, lipids, moisture from Lake Albert, at Abok landing site (02° contents and ash percentagesare often 14.46‘N 31°19.15‘E) using 3" beach seine necessary to ensure that they meet the net. The samples were divided into three requirements of food regulations and groups according to total weight; namely commercial specifications (Watermann, <1 kg, 1-1.5 kg and 1.6-2.5 kg. Then, the 2000). samples were beheaded, gutted, washed Alestes baremoze (Joannis, 1835) is and filleted. The fish fillets were native to fresh water systems in Africa, immediately transported in ice cooled thriving well in both lacustrine and riverine boxes to the Department of Food conditions. It belongs to order Technology and Nutrition, Makerere Characiformes and family Alestidae University for laboratory analysis. All (Akinyiet al., 2010). It is highly procedures on determination of moisture marketable and highly value fish in content, crude protein, fat and minerals northern Uganda, South Sudan, Sudan and were performed in triplicate, using the the Democratic Republic of Congo method described by AOAC (2000). (Kasozi et al., 2013). In Uganda, A. baremoze gross value increased from Proximate composition US$1.2 million in 2007/08 to 1.7 in 2012, Moisture content was determined using from catches harvested from Lake Albert the dry oven method according to the (Mbabazi et al., 2012). Despite being an AOAC (2000). For each size group, 5 g important regional foreign exchange of homogenised samples were weighed earner and a delicacy in the zone, there is out in triplicate into preconditioned currently no information available on its moisture dishes. The dishes with samples nutritional composition, yet consumers are were placed in oven and dried for 16 hours interested not only in whether this fish at 98 °C, as this temperature avoids loses tastes good, but also its nutritional value. of volatile food components (Pearson, With the anticipated development of A. 1976). After the 16 hr of drying, the dishes baremoze aquaculture in Uganda, were cooled down in desiccators and the generating knowledge on the nutrient moisture content of the samples calculated composition will become of significant accordingly. practical interest. It is, therefore, Crude protein was determined by the important to generate nutritional data on Kjeldahl methods using sulphuric acid for this fish in order to make use of it as food sample digestion. Total nitrogen was and also develop suitable processing quantified by titrating the distillate against method. This study determined the 0.05 M hydrochloric acid. Methylene blue proximate composition and mineral and methyl red mixture was used as contents of A. baremoze fillets based on indicator. Crude protein was determined fish size. by multiplying the nitrogen value by the Proximate composition and mineral contents of Alestes baremoze fillets 43 conversion factor of 6.25. Crude fat was cold reduction vaporisationAtomic obtained by exhaustively extracting 2.0 g absorption spectrophotometric Method of each sample in a Soxhlet apparatus (Shimadzu AAS, Model AA-6300 and using petroleum ether (b.p. 40 - 60 °C) as Mercury Vapor Unit, MVU-1A). the extractant (AOAC, 2000). Carbohydrate was hydrolysedwith acid Statistical analysis and the absorbance was read in Results were subjected to analysis of spectrophotometer at the specific wave variance (ANOVA) using SAS statistical length of 470 nm. Ash content was software (Stata Corporation, Texas, and determined by igniting the sample for 12 USA). Multiple comparisons of means hr in a furnace at 525°C. For vitamin A were done using the Duncan method and content, total carotenoids content were p-values<0.05 were considered statistically determined using the Harvest Plus method significant. Data are expressed as and the absorbance of the carotenoids milligram per 100 gramme wet samples. were read in spectrophotometer at the specific wave length of 450 nm. This value Results and discussion was then converted to Vitamin A by dividing it with12 conversion factor. Proximate composition Vitamin A was expressed asretinol activity The proximate composition of the analysed equivalent (RAE). samples is shown in Table I. There were significant differences (p<0.05) in gross Mineral analyses energy, vitamin A, carbohydrate, moisture The preparation of samples for mineral and crude fat among the different sizes. elements analysis followed a method In comparison with other fresh water described by AOAC (2000). species, Okeyo et al. (2009) reported that Approximately 5 g of each sample (wet the chemical composition of Nile perch weight) were placed in a Teflon digestion from Kenya was 78.5% moisture, 19.8% vessel and double acid digested with nitric protein and 0.63% ash. Effiong and acid (HNO3) and perchloric acid Fakunle (2013) found proximate (HCLO4). Samples were then analysed composition of experimental samples from for mineral contents of iron (Fe), Nigeria to comprise 78.19% moisture; manganese (Mn), zinc (Zn), potassium 17.38% crude protein for lates niloticus, (K), calcium (Ca) magnesium (Mg) 78.17% moisture; 19.83% for Clarias andmanganese (Mn) using the Atomic gariepinus and 79.40% moisture; 18.38% Absorption Spectrophotometer (Shimadzu crude protein for Oreochromis niloticus. AAS, AA-6300). Total phosphorus was The main constituent of fish flesh is determined by spectrophotometric water, which usually accounts for about vanadium phoshomolyb date method. The 80% of the weight of a fresh white fish concentration of iodine was determined fillet (Murray and Burt, 1969). The highest by iodo-titrimetric method. The samples moisture content of 75.5% in thisstudy was for total mercury analysis were treated recorded from fish <1 kg weight. There with conc. nitric acid, sulphuric acid, were significant differences (p<0.05) in hydrogen peroxide, potassium moisture contents between different sizes. permanganate and Hydroxylamine Moisture content decreased with hydrochloride before being analysed by increased size of the fish. In comparison 44 N. Kasozi et al. Table 1. Proximate analysis of A. baremoze fillets according to sample sizes in a study in Uganda Chemical composition Fish size classes (kg) Below – 1 1–1.5 1.6–2.5 Moisture content (%) 75.54±0.11a 74.56±0.36b 72.17±0.13c Crude protein (%) 18.01±0.51a 17.77±0.27a 18.44±0.37a Crude fat (%) 0.21±0.06ab 0.35±0.1a 0.13±0.1b Ash content (%) 7.56±0.30a 7.34±0.44a 7.25±0.12a Carbohydrate (%) 0.06±0.008a 0.37±0.021b 0.27±0.01c Gross energy (Kcal/100g) 546.5±1.7a 597.69±1.3b 576.08±3.3c Vitamin A µµµg RAE/100g 55.10±0.56a 74.70±0.42b 75.3±0.10b Means with the different letters in the same row are significantly different (P<0.05).