Analysis of dietary value of the soft tissue of the freshwater crab Travancoriana schirnerae

The present study determined the nutritional status of claw and body meat in adult male and female of the freshwater crab, Travancoriana schirnerae with respect to the proximate composition, free amino acids (FAA) and cholesterol contents. Biochemical analyses were done in pentaplicate samples of the homogenate and the data obtained were analyzed using Student’s t-test and correlation analysis. The mean protein, oligo and polysaccharides, moisture, lipid, FAA and cholesterol contents of crab meat were found to be 19.39%, 0.38%, 0.51%, 83.02%, 369.5 mg, 1469 mg and 21.3 mg/100 g respectively. Only the fat content showed significant differences between the body parts analyzed. Furthermore, female crab meat had significantly higher levels of protein, carbohydrate and FAA than males indicating females are better than males nutritionally. This study revealed that T. schirnerae meat being low in fat, yet high in protein, is an excellent option to include in a healthy diet. Introduction Edible crustaceans such as crabs, prawns, shrimps, crayfishes and lobsters comprise one of the major sources of nutritious food for human beings. The nutritive value of crustaceans depends on their biochemical constituents such as proteins, carbohydrates, lipids, amino acids, vitamins and minerals. Crabs have exceptional and scrumptious taste as compared to fish and mollusc and rank third after shrimps and lobsters for their revered delicacy and the value of fishery they support (Savad and Raghavan, 2001). Crab meat contains many nutrients and is an excellent source of high quality proteins, vitamins and minerals. Many curative properties are attributed to crab meat in view of the fact that it is used to treat asthma and chronic fever (Raja, 1981). It has been reported that large numbers of potamids and parathelphusids are consumed in Thailand. Yeo et al. (2008) reported that potamids are consumed by the natives of South America to improve health, to treat digestive disorders and to cure physical injuries. Crab fishery in India is fast developing and there is immense scope for crab meat due to its delicacy and nutritional richness. Because of their delicacy and larger size, crabs are in greater demand and gain lofty price in both national and international markets. In India, a total of 12 marine/brackish water species belonging to six genera, viz., Scylla, Portunus, Charybdis, Matuta, Varuna and Podophthalmus are of commercial value. Proximate composition, amino acid and cholesterol contents have been extensively studied in marine crabs from India (Srinivasagam, 1979; Sudhakar et al., 2009; Sudhakar et al., 2011) and abroad (Kucukgulmez et al., 2006; Dima et al., 2009; Jimmy and Arazu, 2012). However, limited research has focused on freshwater crabs (Sayyad et al., 2008; Sengul and Zeliha, 2011). The freshwater crab, Travancoriana schirnerae (Bott, 1969), abundant in the wetlands of Wayanad, Kerala, India, forms a cheap source of animal protein to the poor, malnourished tribes. The natives consume the ovary alone during the breeding season. In spite of abundance and commercial value, no studies have been conducted to determine its nutrient value. The knowledge of the biochemical composition of any edible organism is extremely important since the nutritive value is reflected in biochemical contents as stated by Nagabhushanam and Mane (1978). In the present study, an attempt has been made to evaluate the nutritive value of claw and body meat of adult male and female T. schirnerae, thereby to encourage its large scale production and consumption. Materials and Methods Adult intermoult males (n=15) and females (n=15) (carapace width 5.5-6 cm) were collected from the paddy fields near the College campus, Mananthavady during April 2010-June 2011. The collected specimens were brought immediately to the laboratory. Their carapace widths (CW) and wet weights were recorded. Meat from the body and claw portions of crabs was removed manually, weighed and analyzed fresh. Care was taken not to desiccate the tissue during dissection. All analyses were conducted on pentaplicate samples of tissue homogenates. Total protein content was determined by Lowry et al. (1951) method. The oligo and polysaccharide fractions were extracted following the procedure of Johnston and Davies (1972) and estimated by phenol-sulphuric acid method (Dubois et al., 1956). The green colour developed on addition of phenol and sulphuric acid was read at 490 nm in a UV-Vis spectrophotometer-117 (Systronics). Lee and Takahashi (1966) method was adopted for the determination of total free amino acids (FAA). The absorbance of the bluish-purple colour developed was read at 570 nm spectrophotometrically within one hour. The total lipid was extracted following Folch et al. (1957) and estimated by the Sulphovanillin method (Frings et al., 1972). Zlatkis et al. (1953) method was adopted for the estimation of cholesterol. Moisture analysis For determination of the moisture content, fresh tissues of claw and body meat were weighed and kept in an oven heated to 1050C. The tissues were taken out and weighed at regular intervals until constant weights were reached. Moisture content was calculated as the difference between wet weight and dry weight of the tissue and this difference has been expressed as percentage of the wet weight of the tissue. Statistical analysis The recorded data were subjected to Student’s t-test and correlation analysis. Significant differences between means were determined by Student’s t-test. Correlation analysis was conducted to find out the relation between protein, carbohydrate, lipid and moisture values.