Abstract
Studies were conducted on the quality assessment and improvement of traditionally dried small indigenous fish of Bangladesh using low cost solar drier. The survey on the present status showed that among the SIS mola (Amblypharyngodon mola), dhela (Osteobrama cotio cotio), puti (Barbodes sarana), tit puti (Puntius ticto), tengra (Mystus vitatus), chapila (Gudusia chapra), batashi (Pseudotropius atherinoides), buzuri tengra (Mystus tengra), katchki (Corika soborna), gol chanda (Chanda ranga), lamba chanda (Chanda nama), phul chela (Chela phulo) and lata (Channa punctatus) are most common. Puti was top of the list in percentage (7-9%), followed by mola (7-8%), tengra (6-7%) and chapila (5-6%). There are three levels of SIS marketing chains: primary, secondary/higher secondary and final consuming markets. Major gears used for catching the SIS are monofilament gill nets, traps, line nets and seine nets and the traditional boats used for harvesting SIS are kari dingi, konai dingi, jaila dingi, bhedi dingi, bhedi nauka, kosa nauka and dexco. The price of chapila, batashi, mola, tengra and dhela are in the range of Tk. 80.00-100/kg at consumer market, Tk 50.00-70.00/kg in secondary/wholesale and Tk. 30.00-35.00/kg in primary market. The highest percentage of quality loss (35%) occurs due to keeping the fish for longer period at high ambient temperature followed by 25% due to rough handling and excessive pressure during loading and unloading at various stages of marketing chains. Highest percentage of quality losses occur in village assembly point (25%) followed by during transportation (20%). The highest percentage of SIS are marketed in fresh condition (80%) followed by dried (18%) and semi fermented (2%). The processing steps are grading, dressing, de-scaling, gutting, washing and drying. SIS normally takes 4-5 days for proper drying in the normal shining day but it exclusively depends on the weather condition and other related factors. There is widespread use of insecticides such as nogos, basudin and rubral during processing and subsequent storage. The main causes of quality loss is beetle larvae infestation (35%) followed by (20%) due to rough handling and transportation, 15% due to poor quality of raw material, (10%) for spoilage and (5.0%) due to meteorological reasons. The fresh SIS were found in acceptable condition for 6-8 days in ice storage. In fresh fish moisture, protein, lipid and ash contents were found in the range of 73.78% to 75.33%, 15.22% to 18.80%, 4.98% to 5.85% and 2.55 to 4.80%, respectively. Sarcoplasmic, myofibrillar, stroma and alkali soluble protein fractions of chapila, puti, dhela and chela were 19.17 to 34.00%, 56.31 to 72.27%, 1.31 to 3.03% and 7.18 to 12.76%, respectively. At the end of 8 days ice storage, the percentage of sarcoplasmic, stroma and alkali soluble protein fraction decreased, while myofibrillar fraction increased. The initial pH was 6.44 to 6.48 immediately after catch and increased gradually with the lapse of storage period. The initial TVB-N values were 10 to 11 mg/100g and gradually increased to over 30mg/100g in 8 days of storage. The initial PO values were below 5 meq/kg oil and increased gradually with the lapse of storage period. There was large fall in Ca²⁺- and Mg²⁺-ATPase activity during 8 days of ice storage. A low cost solar drier was constructed using locally available materials. The size of the drier was 20' × 3.6' × 3' having drying capacity of 80 kg of SIS (w/w). The optimum temperature for producing high quality dried products was 45-50°C in solar tunnel drier. The moisture, protein, lipid and ash contents of the solar dried products were 14.38 to 18.48%, 67.57 to 71.90%, 11.73 to 21.98% and 10.71 to 14.97%, respectively.Maximum reconstitution of solar dried products was obtained at 80°C in all samples and was in the range of 65.26 to 70.51% where the percentage of reconstitution increases with the increase of socking time and reach maximum at the end of up to 60 min. The TVB-N content of solar dried fish is low compared with traditional one ranging from 20.30 to 28.40mg/100g and peroxide value in the range of 12. 54 to 19.20meq./kg oil. The TVB-N of traditionally dried products were in the range of 32.50 to 45.45mg/100g and PO values of the traditionally dried products were in the range of 30.00 to 36.00meq./kg oil.The bacterial load of the solar dried products wase in the range of 4.0×10³/g to 3.6×10⁵CFU/g and of the traditionally dried products ranged from 1.45×10⁵ to 2.52×10⁶ CFU/g. Among all amino acids analyzes, glutamic acid content was found quite high in all the samples ranging from 5.76 to 6.96% and cysteine content was quite low ranging from 0.20 to 0.31%. Among the free amino acids, the predominant ones were glutamic acid, alanine, valine, leucine, lysine and histidine. The potassium level ranged between 520 to 920mg100⁻¹g, magnesium 100-200mg100⁻¹g and calcium 100-400mg100⁻¹g. Micro nutrients such as zinc, copper, manganese and iron contents were quite high. The colour of solar tunnel dried mola, dhela, puti, chela and chapila became whitish to slightly brown colour, Texture was firm and flexible and odour was very natural in all samples. No insect infestation or broken pieces were found around the products. The overall quality of all the products was excellent The overall quality of five SIS products stored under various polythene packaging conditions were found in good condition for 2 months as determined by organoleptic, biochemical and bacteriological analysis. On the other hand, the quality of the products stored in open air without packaging conditions was found in acceptable conditions for 5 days. The moisture content, TVB-N and PO values of dried SIS products slightly increased during 60 days of storage.