Journal of Culinary Science & Technology
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Influence of Processing Parameters on Microbial Load, Sensory Acceptability, and Mineral Contents of Dehydrated Catfish (Clarias gariepinus) Dupe Temilade Otolowo & Abiodun Adekunle Olapade To cite this article: Dupe Temilade Otolowo & Abiodun Adekunle Olapade (2017): Influence of Processing Parameters on Microbial Load, Sensory Acceptability, and Mineral Contents of Dehydrated Catfish (Clarias gariepinus), Journal of Culinary Science & Technology, DOI: 10.1080/15428052.2017.1363106 To link to this article: http://dx.doi.org/10.1080/15428052.2017.1363106
Published online: 29 Aug 2017.
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Date: 30 August 2017, At: 03:48
JOURNAL OF CULINARY SCIENCE & TECHNOLOGY https://doi.org/10.1080/15428052.2017.1363106
Influence of Processing Parameters on Microbial Load, Sensory Acceptability, and Mineral Contents of Dehydrated Catfish (Clarias gariepinus) Dupe Temilade Otolowo and Abiodun Adekunle Olapade
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Department of Food Technology, Faculty of Technology, University of Ibadan, Ibadan, Oyo State, Nigeria ABSTRACT
ARTICLE HISTORY
Catfish was dehydrated to improve handling using Response Surface Methodology for experimental design. Brine concentration (%), brining time (min) and drying temperature (°C) as processing parameters interacted in different combinations. Influence of processing parameters on microbial load, sensory acceptability and mineral contents of dehydrated catfish was investigated. Data analysed using regression, ANOVA and average ranking grade. Low total viable and fungi counts (ranged 1.0x103-3.0x103 CFU/g) with no detection of pathogen indicates safety for consumption. Brine concentration significantly (p < 0.05) influenced the texture of catfish. The model accounted for only 29.36% of the total variation (R2 = 0.2936). The 6% brine, 90 min and 110°C treatment, significantly improved the overallacceptability. Calcium content (ranged 19.60–52.60 mg/100 g) was significantly higher which could improve the nutrient intake to facilitate development and maintenance of strong bones. Knowledge about safety, acceptability and nutrient content of dehydrated catfish could contribute positively to reshaping decision-making about catfish consumption.
Received 27 March 2017 Accepted 5 July 2017 KEYWORDS
Catfish; microbial load; mineral contents; processing parameters; sensory acceptability
Introduction Fish represents a high-quality nutritional source of food that provides much of the needed nutrients (protein, fats, minerals, etc.) and, as such, constitutes important and healthy part of the human diet (Abolagba & Melle, 2008; Ekpenyong & Ibok, 2012; Ruxton, Reed, Simpson, & Millington, 2004; Sidhu, 2003). Furthermore, the presence of Omega-3 and Omega-6 poly unsaturated fatty acid (PUFA) plays essential role in human health in preventing coronary artery diseases (Ruxton et al., 2004) and low cholesterol content in catfish when compared with red meat (Harris, 1997) are documented facts that stress the importance of fish being a healthy part of human diet (Ayeloja et al., 2013). This has greatly increased the global consumption of fish and CONTACT Dupe Temilade Otolowo
[email protected] Department of Food Technology, Faculty of Technology, University of Ibadan, Ibadan, Oyo State, Nigeria. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/WCSC. © 2017 Taylor & Francis
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derived fish products in recent decades, especially in this 21st century (Wim, Isabelle, Karen, Stefaan, & John, 2007). Hence, extensive research is required on fish processing, preparation, and quality for consumer acceptance. Catfish (Clarias gariepinus) is a freshwater fish, highly nutritious but susceptible to deterioration due largely to high moisture content that supports growth of spoilage and disease-causing microorganisms (FDA, 2001; Fellows, 2009). Therefore, processing/preservation are inevitable to prevent or limit deteriorative changes, while microbial analysis is necessary to establish the safety and quality of catfish products (Eyo, 2001; Relekar, Joshi, Gore, & Kulkarni, 2014). Although catfish is a nutrient-rich food commodity with wide consumer acceptance (Salaudeen et al., 2010), judgments as to the quality and flavor vary, with some food critics considering catfish an excellent food, while others dismiss them as watery and lacking in flavor (Baker, 1988). However, many people who do not care for fish due to the distinctive “fishy” flavor take to catfish because it lacks that essence (Baker, 1988). Thus, sensory assessment of the processed/ preserved form is necessary to affirm any improvement for acceptability. In Nigeria, restaurants where fresh fish is sold in soup sauce or pepper soup, catfish pepper soup commands a higher price and level of acceptance than other kinds of fish dishes. The Nigerian catfish pepper soup is usually eaten at exclusive bars and restaurants and referred to as “Point and Kill,” in the sense that live-catfish usually C. gariepinus is harvested into a big round bowl where the customer will go and point at his choice, which will then be made into pepper soup or fish sauce as required (Anonymous, 2016). Fresh C. gariepinus is also served as savory soup dishes in the form of home fish stew and soup sauce (Clucas & Ward, 1996). However, much drudgery of slaughtering, degutting, washing, and seasoning at every point of usage is involved in getting live catfish ready for use in making these dishes. This is time consuming and could make cooking stressful for a home maker or restaurant vendor. Processing catfish into an acceptable and ready-to-use form will build convenience into preparation of the dishes and improve the management of catfish in terms of ease of handling, quality, stability, and extended shelf-life. Catfish is processed/preserved in various forms such as fried, smoked, salted, dried-salted, or dehydrated fish (Adam & Sidahmed, 2012; Ayeloja et al., 2013). Although smoked-dried fish is the most common form of preserved catfish in Nigeria, the deposited smoke on the fish, which contains high concentrations of polycyclic aromatic hydrocarbons (PAHs), reported to be carcinogenic, poses a health risk to the consumer (Adeyeye et al., 2016) and, as such, is of low overall acceptability (Fronthea, 2003). Electrically oven-dried fish is free of such prejudice and the method of its processing is effective, simple, and inexpensive (Chukwu & Shaba, 2009). Hence, preservation by this method of dehydration/ drying to remove most of the water present in fish muscles is expected to extend the shelf-life without the need for refrigeration (Vongaswashi et al., 2008); this will improve the handling and acceptability of catfish in meal preparation.
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However, the nutritional component of dehydrated catfish (C. gariepinus), especially the mineral concentrations, varies greatly from species and one individual to another depending on age, sex, environment, season, and method of processing (Chukwu & Shaba, 2009). A study conducted by Mogobe et al. (2015) revealed that freshwater fish like catfish contain high calcium (Ca) and other mineral elements in appreciable but varying concentrations. Chukwu and Shaba (2009) reported significant differences in the proximate composition, vitamin, and mineral contents of catfish processed with different methods (kiln smoking and electric oven drying). Also, there exist significant differences in the sensory characteristics of C. gariepinus processed with different cooking methods such as boiling, frying, and smoking (Ayeloja et al., 2013), and obviously may exist in dehydrated catfish. Sensory evaluation is a scientific discipline that uses human senses (sight, smell, taste, touch, and hearing) to evaluate consumer preference for products (Iwe, 2010). It requires a panel of human assessors, on whom the products are tested, and their responses recorded. By applying statistical techniques to analyse the results (scores of the degree of likeness by the panelists), possible inferences and insights could then be made about the acceptable quality of the products under tests (Iwe, 2007). There is limited information on sensory acceptability and mineral contents of dehydrated C. gariepinus. This research is designed to investigate the microbial load, sensory acceptability, and mineral contents of dehydrated catfish as influenced by combinations of three processing parameters. Materials and methods Materials
Six-month-old catfish (Clarias gariepinus), each of an average weight and length 500 ± 20 g and 43 ± 2 cm, respectively, used in this work were obtained from the Fishery Teaching and Research Farm of the Federal University of Technology, Akure (FUTA). Table salt (NaCl, Mr ChefTM) used for the brine solution was purchased from a local market in Akure, Nigeria, while other chemicals used for the analyses were of analytical grade. The drying was achieved in an experimental convective electric fish dryer Model 2012, made in Korea and obtained from Dickem Aquatech Nigeria Ltd., Lagos, Nigeria. Methods Experimental design The design of experiment for processing catfish was done using response surface methodology (RSM). The independent variables were brine concentration (3, 6, and 9%), brining time (30, 60, and 90 min), and drying
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temperature (90, 110, and 130°C), chosen based on literature and preliminary experiments. The variables were interacted using a face-centred, full factorial central composite design (CCD) of the RSM to evaluate the combined effect of the parameters. Seventeen combinations were used for the production of dehydrated catfish. Preprocessing and brining operation Catfish were slaughtered (head discarded), degutted, and washed thoroughly with tap water to remove all adhesive materials and blood. Brine solutions of appropriate concentrations (3, 6, and 9%) were prepared by dissolving 30, 60, and 90 g salt per litre of water, respectively. Headless fish (averagely 254 g) were randomly selected, immersed in brine solutions, and left for the appropriate time (Otolowo, 2017). The effect of moisture diffusion from fish muscle into the brine solution was minimized by multiple ratios of the volume of brine solution to the brining fish. Brined fish, singly arranged on mesh trays, were left for at least 1 h, for brine equilibration and drain off of excess solution. Drying operation The convective dryer was used, consists of drying chamber at the middle with eight electrical heating elements (1500 W), each enclosed in a glass tube and equidistantly fixed round the chamber, radiating heat to the drying fish. The dryer was preheated to the desired temperature (90, 110, or 130°C) and a dry bulb thermometer inserted through the vent on the top to measure the temperature. The fish were singly arranged on three-level mesh trays inside the chamber and monitored to ensure that no case hardening occurred. The initial time for drying was taken as the time the temperature stabilizes at the set temperature. The drying of catfish was done for 27 h, 24 h: 40 min, and 12 h: 49 min at 90, 110, and 130°C, respectively. The fish were cooled to room temperature (25 ± 2°C) and sealed in polyethylene bags prior analyses. The method described by Eyo (2001) was adopted for the processing of catfish. Determination of microbial load Pour plating method described by Harrigan and McCance (1976) was used in the determination of microbial load of fresh raw and dehydrated catfish. The following selective media—Nutrient Agar (Sigma-Aldrich-70148), McConkey Agar (Sigma-M7408), Desoxycholate Agar (Sigma–Aldrich - D7809), Eosin Methylene Blue (Sigma-Aldrich - 70186) Agar and Potato Dextrose Agar (Sigma-Aldrich- 70139)—were used for total viable count (TVC), Coliforms, Salmonella, Escherichia coli, and fungi growth, respectively. One gram each of blended fresh raw and ground muscle part of dehydrated catfish sample was dispersed in sterile saline solutions and homogenized. An aliquot of the
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diluents was diluted in three-fold serial dilutions (10–1 to 10–3) and pourplated on Petri dishes accordingly under aseptic conditions. Few drops of lactic acid were added to the PDA to inhibit the growth of bacteria. Incubation of bacteria and fungi plates was done at 37°C for 24 h and 25° C for 72 h, respectively. Microbial growth counts were enumerated using digital colony counter (Gallenkamp, England). Sensory evaluation Freshly produced dehydrated catfish were subjected to sensory evaluation to assess the acceptability. Each dehydrated catfish (headless) of average weight 79.35 g and 27.21 cm in length; and fresh raw fish (254 g) were cut into 3 or 4 pieces. The dehydrated fish pieces were soaked in 1 litre of water at room temperature (25 ± 2°C) for 20 min and drained. The fish was slightly seasoned with 1.5 g table salt and 10 g chopped onions, simmered in 30 mL of water for about 7 min under low fire of a gas cooker, and removed from stock into a food warmer. The fresh fish as control was equally seasoned with 6 g of salt, 40 g of chopped onions, and simmered in 120 mL of water until well cooked. The slight seasoning was necessary because catfish is majorly used in Nigeria for the preparation of savory and heavily spiced dishes such as pepper soup, fish stew, soup sauce, and Efo Riro (soup made purely with different kinds of leafy vegetable). The dehydrated fish samples were presented in three groups according to the drying temperatures. Samples of each group were compared separately with the control prepared in quantity enough to serve the three groups. Ten-man panelists (judges) were used for the evaluation. The panelists were selected randomly from the staff and students of the Department of Food Science and Technology, Federal University of Technology, Akure, Nigeria based on their familiarity with catfish (fresh and dried). They were made to carry out the test under the controlled environment to avoid biased results and were instructed on the prerequisites of sensory evaluation before the analysis was performed. The panelists were presented with stainless forks and a bowl of water to rinse the cutlery after each evaluation. Potable water was also provided for them to rinse their mouth in-between evaluation. The fish were served on uniform coded flat plates and rated for general appearance, texture, aroma, taste, and overall acceptability on a 5-point hedonic scale; where 1 = dislike very much; 3 = neither like nor dislike; and 5 = like very much, as described by Aworh, Okparanta, and Oyedokun (2002). Response surface modelling /statistical analysis The data obtained from sensory evaluation were analyzed using response surface methodology (RSM) so as to fit the quadratic polynomial equation generated by the Design-Expert software version 8.0.3.1 (Stat-Ease Inc.,
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Minneapolis, USA). The qualities of the fit of the models were evaluated using analysis of variance (ANOVA); backward regression was used to improve the fit of the model. Single factor ANOVA with average ranking grade was also done as a form of descriptive test aimed at evaluating the overall acceptability of dehydrated catfish samples. The fitted quadratic response model is as described in Equation 1. y ¼ bo þ
k X i¼1
bi Xi þ
k X i¼1
bij Xi2
þ
k X k X i1 < j
bi Xi Xj þ e
(1)
j
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where y is the response; i and j denote linear and quadratic coefficients, respectively; bo is the intercept, bi is the first order model coefficient, k is the number of factors, and e is a random number. Determination of mineral elements The analysis of mineral elements was carried out on the ground muscle part of dehydrated catfish using the dry ashing procedure of AOAC (2003). Data analysis/software Analysis of variance (ANOVA) was used to establish differences among treatments. Duncan’s multiple range tests were used to separate treatment means where differences exist (p < 0.05). Statistical Package for Social Science version 18 was used (SPSS, 2009). Design expert DX 8.0.3.1, USA was used for the RSM analysis and modelling of the sensory evaluation data.
Results and discussions Microbiological load of fresh raw and dehydrated catfish
The result of microbiological analysis is presented in Table 1. The result showed that total viable counts (TVC) in a few of the dehydrated fish samples ranged from 1.0 x 103 to 3.0 x 103 CFU/g, while only one treatment (6% brine, 90 min, and 110°C) gave the sample with fungal growth (1.0 x 103 CFU/g). However the growth counts both for the TVC and fungi were far below the maximum permissible level in dried fish products, which are 5.0 x 105 CFU/g TVC and 1.0 x 106 CFU/g fungi (ICMSF, 1986). There were no growths of Coliforms, Salmonella, and E. coli in all the treatments indicating the safety of the products. This implies that brining as well as the thermal processing employed for catfish preserve the quality in the dehydrated fish, thus the dehydration technique was effective. This is similar to the report of Da Silva et al. (2008) on the effect of preservatives on microbial safety and quality of smoked blue catfish (Ictalurus furcatus) steaks during room-temperature storage. However, since the fresh raw fish had no growth, the
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Table 1. Microbiological load of fresh-raw and dehydrated catfish samples RSM run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 RAW
Treatment
Total viable
Coliform
Salmonella
E. coli
Fungi
ABC 6 60 110 6 90 110 3 60 110 3 30 90 6 30 110 9 90 130 9 60 110 6 60 110 9 90 90 6 60 130 3 90 130 6 60 110 6 60 90 3 90 90 3 30 130 9 30 130 9 30 90 FRESH FISH
count (cfu/g) ND ND ND ND 1.0 x 103 ND 1.0 x 103 ND 2.0 x 103 ND 2.0 x 103 ND ND ND 3.0 x 103 ND ND ND
(cfu/g) ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
(cfu/g) ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
(cfu/g) ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
(cfu/g) ND 1.0 x 103 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND
Key: RSM = Response surface methodology; A = Brine concentration (%); B = Brining time (min); C = Drying temperature (°C); ND = Not detected.
recorded microbial counts in few of dehydrated fish samples could have had its source from handling during processing; hence the practice of high standard hygiene is required in fish processing and handling.
Sensory acceptability of fresh and dehydrated catfish
The data for the sensory evaluation by 10 judges of the attributes of appearance, aroma, texture, taste, and overall acceptability presented in Table 2 were imputed into the response surface, full factorial face-centered central composite design (CCD) for analysis. The attributes, except the texture, could not be predicted from second order response surface regression equations. This probably could be due to the subjective nature of panelists’ preferential responses in the evaluation. Effect of treatments on texture attribute of dehydrated catfish Only the texture attribute found the reduced linear (RLinear) model that fits the description of the effect of processing parameters on the sensory quality of dehydrated catfish (C. gariepinus), as presented in Table 3. This could mean that the effect of treatments was significant (p < 0.05) on the texture of dehydrated catfish, although with low regression coefficients. This concords with the report of Ayeloja et al. (2013) on the effects of processing methods on the texture attribute of C. gariepinus. The model was significant (p < 0.05) with p-value of 0.0247 but accounted for only 29.36% of the total variations
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Table 2. Average scores for sensory evaluation of dehydrated catfish RSM run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 FRF
A 6 6 3 3 6 9 9 6 9 6 3 6 6 3 3 9 9 -
B 60 90 60 30 30 90 60 60 90 60 90 60 60 90 30 30 30 -
C 110 110 110 90 110 130 110 110 90 130 130 110 90 90 130 130 90 -
Appearance 4.0 4.2 3.7 4.0 4.2 3.8 4.1 4.1 4.2 3.5 4.4 3.3 4.2 3.4 3.4 3.8 2.8 3.0
Texture 4.0 4.4 4.0 3.7 3.7 4.1 4.1 3.9 4.2 3.3 3.4 3.5 4.0 3.8 3.1 4.5 3.7 4.0
Aroma 3.9 4.3 3.9 4.0 4.0 3.8 4.0 3.5 4.0 3.0 4.1 3.3 3.6 3.2 3.2 3.6 3.3 3.0
Taste 4.0 4.4 4.1 3.7 3.8 3.9 3.9 3.3 4.5 3.4 4.0 3.5 4.3 3.0 3.4 4.1 3.9 3.3
Overall Acceptability 4.0 4.3 3.9 3.8 3.9 3.9 4.0 3.8 4.2 3.4 4.0 3.4 4.1 3.2 3.2 3.8 3.3 3.4
Key: RSM = Response surface methodology; A = Brine concentration (%); B = Brining time (min); C = Drying temperature (°C); FRF = Fresh raw-fish.
Table 3. Response surface ANOVA determinant factors for sensory evaluation of dehydrated catfish Sensory attributes RSM model Model (p-value) Model term A (p-value) Lack of fit p-value R2 Adj R2 Pred R2 Adeq Precision
Appearance Mean 0.0000 0.0000 0.6238 0.0000 0.0000 −0.1289 0.0000
Texture RLinear 0.0247 0.0247 0.4429 0.2936 0.2465 0.1001 4.6040
Aroma Mean 0.0000 0.0000 0.4415 0.0000 0.0000 −0.1289 0.0000
Taste Mean 0.0000 0.0000 0.5117 0.0000 0.0000 −0.1289 0.0000
Overall acceptability Mean 0.0000 0.0000 0.5110 0.0000 0.0000 −0.1289 0.0000
Key: A = Brine concentration; RLinear = Reduced Linear model; R2 = Coefficient of determination; Adj = Adjusted; Pred = Predicted; Adeq = Adequate.
(R2 = 0.2936). Non-significant lack of fit p-value of 0.4429 was obtained. Brine concentration (A) was the only significant model term. The response surface curve (3D plot), of the effects of brine concentration and brining time at a fixed temperature (110°C) on the texture attribute is presented in Figure 1. The result showed that the panelists’ preference for texture increased with increasing brine concentration, while brining time showed no significant effect. A desirable adequate precision value greater than four (4.604) was obtained as an indication that the model predictions on the texture attribute of dehydrated catfish were adequate and agreed with the experimental. Thus processing, especially with the dehydration technique employed, significantly improved the texture attribute of catfish for better consumer acceptability. Negative values of predicted R2 (coefficient of
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4.6 4.4 4.2 4
Texture
3.8 3.6 3.4 3.2
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3
90
9
80
8
70
7
60
6
50
B: Brining Time (min)
5
40 30
4 3
A: Concentration (%)
Figure 1. Response surface 3D plot presenting the effects of brine concentration and brining time at a fixed temperature (110°C) on texture attribute of dehydrated catfish.
determination) for all other sensory attributes implies that they could only be described by their means. Therefore, mean scores of the judges for the overall acceptability was analyzed using ANOVA single factor with average ranking grade. Effect of processing parameters on overall acceptability of dehydrated catfish The result of average scores of the judges for the overall acceptability analyzed using ANOVA single factor with the average ranking grade is presented in Table 4. The average scores ranged from 3.2 to 4.325. The high-rated samples (ranked 1, 2, and 3) had the mean overall acceptability scores of 4.325, 4.225, and 4.100, respectively. The scores were above the rating scale 4 (like moderately) but below the highest scale 5 (like very much) in the 5-point preferential hedonic scale used, indicating that all the high rated dehydrated catfish samples were well acceptable and at the same level. The same level of acceptability of these samples could mean that the differences in the combinations of the processing parameters were complementary in effect. However, 6% brine, 90 min, and 110°C treatment that gave the most preferred sample with ranking value one (1) and highest rating score (4.325) in overall acceptability could be recommended for overall sensory quality of dehydrated catfish. The lower level of brine concentration (6%) and longer
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Table 4. The ANOVA single factor of the overall acceptability of fresh and dehydrated catfish sample RSM run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fresh fish
ABC 6 60 110 6 90 110 3 60 110 3 30 90 6 30 110 9 90 130 9 60 110 6 60 110 9 90 90 6 60 130 3 90 130 6 60 110 6 60 90 3 90 90 3 30 130 9 30 130 9 30 90 ---
Average 4.025 4.325 3.935 3.825 3.925 3.850 4.025 3.775 4.225 3.425 4.025 3.400 4.100 3.200 3.275 3.825 3.325 3.425
Variance 0.242361 0.111806 0.272806 0.292361 0.667361 0.336111 0.145139 0.700694 0.186806 0.861806 0.422917 0.419444 0.308333 0.525000 0.867361 0.153472 0.542361 0.861806
Ranking 4 1 7 10 8 9 4 12 2 13 4 14 3 17 16 10 15 13
Key: RSM = Response surface methodology; A = Brine concentration (%); B = Brining time (min); C = Drying temperature (°C)
brining time (90 min) may be attributed to the highest overall acceptability rating of this sample among the high rated ones. However, other dehydrated catfish samples (except few) were also rated higher than the control (fresh catfish), implying that the dehydrated catfish were generally preferred to the control sample. Hence, people who dismiss fresh catfish as watery and lacking in flavor could now find pleasure in eating dehydrated catfish to derive the nutrients contained for healthy living. Mineral contents of dehydrated catfish
The mineral content of dehydrated catfish samples is presented in Table 5. The result showed calcium (Ca) and magnesium (Mg) as the most abundant elements, which ranged from 19.6 to 52.60 and 15.30 to 48.60 mg/100 g, respectively, and were significantly higher than other elements in all treatments. This is similar to the report of Adeniyi, Orikwe, Ehiagbonare, and Joshia (2012), who reported a high amount of Ca in catfish, which is good for maintenance of strong bones and teeth (Turan, Kordali, Zengin, Dursun, & Sezen, 2003). Mogobe, Mosepele, and Masamba (2015) equally reported that freshwater fish like catfish contain a high concentration of Ca and Mg. Sodium (Na) content reduced with reducing brine concentration, buttressing the fact that ash content increases with increasing brine concentration and vice versa (Jittinandana, Kenney, Slider, & Kiser, 2002). Low concentration of Na is desirable as its intake is directly related to hypertension in human (Adeniyi et al., 2012). Iron (Fe) and Zinc (Zn) were within tolerable limits
A 6 6 3 3 6 9 9 6 9 6 3 6 6 3 3 9 9
B 60 90 60 30 30 90 60 60 90 60 90 60 60 90 30 30 30
Treatment
C 110 110 110 90 110 130 110 110 90 130 130 110 90 90 130 130 90
Ca mg/100 g 24.50 ± 0.01f 22.30 ± 0.00i 19.60 ± 0.01p 29.80 ± 0.09b 20.60 ± 0.05m 21.90 ± 0.09k 22.00 ± 0.19j 52.60 ± 0.07a 21.60 ± 0.07l 21.90 ± 0.02k 27.80 ± 0.02d 20.20 ± 0.00n 22.80 ± 0.01g 22.60 ± 0.00h 20.30 ± 0.01n 26.10 ± 0.04e 29.70 ± 0.02c
K mg/100 g 8.83 ± 0.00c 8.24 ± 0.00h 7.99 ± 0.00n 8.07 ± 0.00m 8.67 ± 0.00e 7.20 ± 0.02q 8.57 ± 0.00g 8.97 ± 0.00b 7.92 ± 0.00° 8.59 ± 0.00f 8.10 ± 0.00l 8.81 ± 0.00d 8.21 ± 0.00i 8.14 ± 0.00k 8.19 ± 0.00j 7.80 ± 0.02p 9.12 ± 0.00a
Na mg/100 g 10.10 ± 0.01d 11.40 ± 0.01b 7.00 ± 0.01m 6.40 ± 0.02n 9.20 ± 0.02h 10.10 ± 0.02d 9.18 ± 0.00i 10.40 ± 0.04c 9.80 ± 0.01f 8.99 ± 0.00j 11.80 ± 0.02a 9.62 ± 0.00d 8.21 ± 0.00k 7.00 ± 0.02m 6.26 ± 0.00° 10.00 ± 0.01e 7.44 ± 0.00l
Mg mg/100 g 32.00 ± 0.01e 26.60 ± 0.02k 48.60 ± 0.04a 35.10 ± 0.02b 28.80 ± 0.02h 15.30 ± 0.01p 30.40 ± 0.02f 26.40 ± 0.02m 17.20 ± 0.02° 27.40 ± 0.01i 19.70 ± 0.01n 32.70 ± 0.03d 32.70 ± 0.00d 34.20 ± 0.01c 29.20 ± 0.00g 27.30 ± 0.01j 26.50 ± 0.02l
Fe mg/100 g 10.20 ± 0.00j 10.40 ± 0.00h 8.50 ± 0.01m 11.20 ± 0.00g 10.20 ± 0.02i 17.70 ± 0.00b 4.90 ± 0.01p 9.10 ± 0.01l 9.90 ± 0.01k 7.40 ± 0.00n 11.70 ± 0.03f 12.50 ± 0.01d 7.10 ± 0.01° 12.40 ± 0.02e 12.90 ± 0.01c 28.30 ± 0.01a 9.00 ± 0.01m
Zn mg/100 g 16.40 ± 0.11c 14.60 ± 0.01i 14.90 ± 0.12g 15.10 ± 0.04f 17.30 ± 0.35b 4.10 ± 0.00n 8.60 ± 0.02k 14.70 ± 0.02h 1.30 ± 0.02q 3.10 ± 0.03p 14.20 ± 0.03j 27.60 ± 1.79a 7.50 ± 0.01l 16.10 ± 0.15d 3.20 ± 0.00° 4.90 ± 0.02m 15.60 ± 0.01e
Values are means of triplicate determinations ± standard deviation. Means with different superscripts within the same column are significantly (p < 0.05) different. Key: RSM = Response surface methodology; A = Brine concentration (%); B = Brining time (min); C = Drying temperature (°C).
RSM run 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Table 5. Mineral composition of dehydrated catfish samples
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comparable to the Recommended Dietary Allowance (RDA), which is averagely 15 and 11 mg per day, respectively (Lenntech, n.d.). The form of occurrence of Fe and Zn in the dehydrated catfish samples is also in consonance with Fe and Zn values expressed as RDA for adults (Lenntech, n.d.). Iron is an important constituent of haemoglobin, while Zn is equally important in the management of diabetes (Onwordi, Ogungbade, & Wusu, 2009). Potassium (K) was the least abundant of all the mineral elements, with values ranged from 7.20 to 9.12 mg/100 g; K is important in maintaining a balance with Na in the body to prevent hypertension. The results imply that dehydrated catfish could serve as a good source of the determined mineral elements except K, which could be sourced from generous consumption of fruits and vegetables; thus using dehydrated catfish in vegetable soup preparation could make a meal of perfect source of all the determined mineral elements. The order of occurrence of the mineral composition in the present work was rather a reverse case of the report of Ersoy and Özeren (2009), who found K to be the most abundance followed by Na, Mg, and Ca in that order in fresh C. gariepinus cooked with different methods. The variation could be attributed to different sources and processing methods employed. Also, significant (p ≤ 0.05) differences exist in each of the mineral composition of the samples in all the treatments. Usydus, Szlinder, Adamczyk, and Szatkowska (2011) reported a high variation in the mineral contents of fish tissues, both inter- and intra-species. However, based on the significant high Ca content obtained in the present work, incorporating dehydrated catfish in the formulation of calcium-enriched products and preparation of assorted dishes could improve the nutrient intake that will facilitate the development and maintenance of strong bones. Conclusions The dehydration technique based on the combinations of processing parameters employed significantly improved the overall sensory acceptability of catfish and the products were microbiological safe. Dehydrated catfish processed with 6% brine concentration, 90 min brining time, and drying temperature of 110°C that was most preferred could be a better alternative to fresh catfish especially in areas where fresh catfish is naturally less accessible. Generally, appreciable concentrations of the determined mineral elements obtained in the result could indicate that dehydrated catfish could serve as a good source of these minerals, except K. Also based on significantly higher concentrations of Ca than other elements, dehydrated catfish could be employed in the formulation of calcium-enriched products needed for the formation of strong bones and teeth in infants/toddlers and maintenance of strong bones in adults. Finally, knowledge about the safety, high level of acceptability, and nutrients contained in dehydrated catfish could contribute
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positively to reshaping decision-making process about eating or using catfish in meal preparation.
Acknowledgment The authors gratefully acknowledged the director and staff of Multidisciplinary Central Research Laboratory (MCRL), University of Ibadan, Ibadan, Oyo State, Nigeria for the use of their equipment; opportunity to utilize equipment provided by the Alexander von Humbolt, Germany is also appreciated—Courtesy OOF. The director of Dickem Aquatech Nigeria is as well acknowledged for the provision of the experimental dryer used in this work.
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