Drying characteristics and quality evaluation of dehydrated catfish ...

Nutrition & Food Science Drying characteristics and quality evaluation of dehydrated catfish (Clarias gariepinus) Dupe Temilade Otolowo, Abiodun Adekunle Olapade, Samouel Olugbenga Oladele, Felix Egbuna,

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Article information: To cite this document: Dupe Temilade Otolowo, Abiodun Adekunle Olapade, Samouel Olugbenga Oladele, Felix Egbuna, (2017) "Drying characteristics and quality evaluation of dehydrated catfish (Clarias gariepinus)", Nutrition & Food Science, Vol. 47 Issue: 6, pp.765-779, https://doi.org/10.1108/NFS-12-2016-0192 Permanent link to this document: https://doi.org/10.1108/NFS-12-2016-0192 Downloaded on: 29 November 2017, At: 05:17 (PT) References: this document contains references to 27 other documents. To copy this document: [email protected] The fulltext of this document has been downloaded 6 times since 2017* Access to this document was granted through an Emerald subscription provided by Token:Eprints:H3J6YBQYXVASRRIFQJXQ:

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Drying characteristics and quality evaluation of dehydrated catfish (Clarias gariepinus) Dupe Temilade Otolowo and Abiodun Adekunle Olapade

Evaluation of dehydrated catfish

765

Department of Food Technology, University of Ibadan, Ibadan, Nigeria


Samouel Olugbenga Oladele Department of Agricultural and Environmental Engineering, School of Engineering and Engineering Technology, Federal University of Technology, Akure, Nigeria, and

Received 24 January 2017 Revised 21 May 2017 31 May 2017 Accepted 1 June 2017

Felix Egbuna Department of Food Science and Technology, Federal University of Technology, Akure, Nigeria

Abstract Purpose – Fresh catfish (Clarias gariepinus) is highly perishable. This paper aims to investigate the drying characteristics and quality of body-mass dehydrated catfish to determine the effective dehydration parameters for preservation.

Design/methodology/approach – Brine concentration (3-9 per cent), brining time (30-90 min) and drying temperature (90-130°C) interacted using the response surface methodology. Preliminary experiments were conducted to select treatments. Moisture content and ratio and drying rate were determined and fitted into five thin-layer drying models; the goodness of fit was evaluated by average grade ranking of the regression parameters. Proximate compositions and microbial load of dehydrated catfish were determined using standard methods.

Findings – Treatments with 110°C gave initial higher drying rate (0.034-0.043 kg H2O/kg solid/h) and

shorter drying time (20-21 h). Drying occurred at two falling rate periods. Midilli model ranked first in fitting the drying data. It explained up to 99.6-99.7 per cent of the total variations in the independent variables with low values of error terms; RMSE was 0.02131-0.01794 and x 2 was 0.00037-0.00043, indicating good predictive quality. Processing parameters positively and significantly (p < 0.05) influenced the proximate compositions of dehydrated catfish. Treatment: 6 per cent brine, 90 min and 110°C presented the most effective dehydration parameters for quality preservation of body-mass catfish.

Practical implications – The dehydration technique used in this study could enhance nutritive quality and storage stability of body-mass dehydrated catfish that could serve as a useful and convenient tool for commercial application.

Social implications – Hygienically processed dehydrated catfish of good quality could be used as a source of nutrients to ameliorate malnutrition and reduce post-harvest losses of catfish.

Otolowo, D.T. gratefully acknowledges opportunity to utilise equipment provided by the Alexander von Humbolt, Germany – Courtesy OOF. Also, the Directors of Dickem Aquatech Nigeria Limited, Isashi, Odan, Lagos, Nigeria, are sincerely acknowledged for the provision of the experimental electric dryer used in this study.

Nutrition & Food Science Vol. 47 No. 6, 2017 pp. 765-779 © Emerald Publishing Limited 0034-6659 DOI 10.1108/NFS-12-2016-0192

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Originality/value – The effective processing parameters established is an important step to harness the high nutrients and economic values embedded in catfish.

Keywords Catfish dehydration, Drying characteristics, Microbial quality, Processing parameters, Proximate compositions Paper type Research paper


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Introduction Fish is a major source of animal protein, providing a significant portion of the protein intake in the diets of man (Adeyeye et al., 2016a; Olagbemide, 2015). Catfish (Clarias gariepinus) is popular and widely sought-after as a delicacy in America, Europe, Asia and Africa, including Nigeria due to palatability and good taste (Adeparusi et al., 2010). Freshly harvested C. gariepinus contain high moisture content (MC) which makes it susceptible to deterioration due to microbiological and chemical reactions (Adam and Sidahmed, 2012). Thus, processing is necessary to preserve the quality and prevent post-harvest losses. Many preservation processes such as smoking, salting and dehydration attempt to eliminate spoilage in fish by reducing water available for microbial activities. However, some of these methods are not without limitations. Acceptability of smoked-dried catfish is limited for health reasons because of the presence of polycyclic aromatic hydrocarbon through the deposited smoke reported being carcinogenic, this poses a health risk to the consumer (Adeyeye et al., 2016a). Salting method operates on the principle of osmotic dehydration, which occurs by salt diffusion into fish tissue resulting in the loss of free water and reduction of water activity for the stability of the product (Fellows, 2009; Kumolu-Johnson et al., 2009); however, high concentration of salt (linked with hypertension) involved in this method is reported to be beyond the permissible level for human consumption (Graivier et al., 2006). On the other hand, fish dehydration/drying is an age-long practice across the world to obtain stable shelf life and quality of fish products (Omodara and Olaniyan, 2012); when effectively done under appropriate and acceptable conditions, dehydrated catfish is free from any health risk. Understanding of drying behaviour is very important for the control of the drying process itself, any subsequent processes and quality of the final product. Thus, drying characteristics study could give an insight into optimum drying parameters for an improved quality dried fish (Omodara and Olaniyan, 2012). Drying involves complex heat and mass transfer phenomena which are mathematically difficult to be described at a microscopic scale, and for the purpose of design and analysis, it is often sufficient to use simple semiempirical expressions, which can adequately describe the drying characteristics when the external resistance to heat and mass transfer is minimised (Midilli et al., 2002). Experimental and modelling efforts on single-layer (thin-layer) drying models of fish conducted in hot-air convective dryer/oven and solar energy drying systems have been established. These studies showed that drying parameters influence the drying rate (DR) and quality of dried fish (Bellagha et al., 2002; Omodara and Olaniyan, 2012; Guan et al., 2013), but the effective drying conditions are obscure, and tremendous effort is still required to establish the most effective dehydration parameters for improved preservation of catfish in Nigeria. Also, most of the previous studies on drying characteristics considered fillet sheets and small cuts of a portion of catfish. There is a dearth of information on that of the whole catfish for simulation of market distribution. In Nigeria, the existing market for catfish, both fresh and preserved forms, is majorly on whole fish. Hence, this study was conducted to assess the drying characteristics of body-mass (headless) catfish and evaluate the quality of dehydrated catfish as influenced by the processing parameters.


Materials and methods Materials Live catfish (Clarias gariepinus) about six months old, averagely weighed 500 6 20 g each were obtained from the Fisheries Research Farm of the Federal University of Technology, Akure (FUTA), Nigeria, and carried in a large plastic bowl half filled with water to the Food Processing Laboratory of the Department of Food Science and Technology, FUTA. An experimental electric fish dryer (Dickem Aquatech Nigeria, 2012 model) was used. Foodgrade salt (NaCl) used for brining was purchased from a local market in Akure, Ondo State, Nigeria, whereas other chemicals were of analytical grade. Methods The design of the experiment. A face-centred full factorial, central composite design of the response surface methodology was used in the design of the experiment. Runs were developed from the interaction of the independent variables, brine concentration (3-9 per cent), brining time (30-90 min) and drying temperature (90-130°C) using Design Expert software (Stat-Ease Inc., Minneapolis, USA; Version 8.0.3.1). A total of 17 runs were used in the initial dehydration of catfish. Four best runs were selected based on the preliminary sensory evaluation result on general appearance, aroma, texture, taste and overall acceptability of the dehydrated catfish samples by ten-man panelists. The panelists were used based on the familiarity with and likeness of the product. Brining operation. The fish were slaughtered, beheaded, degutted and washed thoroughly using tap water to remove extraneous materials and blood stains. Brine solutions of the selected concentrations (6 and 9 per cent) were prepared by dissolving 60 and 90 g salt/L of water at ambient temperature. The pre-processed body-mass (headless) catfish (averaged 268 g each) were randomly selected in duplicates and immersed in brine solutions within the appropriate time. Brined fish were coded and arranged singly on mesh trays, left for at least 1 h to allow brine equilibration and drain-off of the excess solution on the body surface. Determination of drying characteristics of catfish Drying procedure. Dehydration of catfish was done as described by Eyo (2001). The dryer used in this study was a type of experimental electrical heat radiating-convective system with electric heating coils enclosed in glass tubes. The thermostat on the dryer regulates the temperature. The heat radiates in all directions of the drying chamber. A dry bulb thermometer was hung in the heating chamber to monitor the drying temperature. The brined body-mass catfish arranged singly on mesh trays at the middle chamber of the dryer were dried at 90 and 110°C. To assess the effect of brining, two other samples were dried at each of the temperature factor making six treatments that were used in the study as presented in Table I. Drying characteristics determined include MC (per cent), moisture ratio (MR) (unitless), DR (kg H2O/kg solid/h) and DR period, determined by the thin-layer drying theory. The drying was done sequentially by drying samples with similar temperatures as a batch, cooled and sealed in polyethylene bag prior the quality analyses. Moisture content. The weight loss (moisture) was measured at an interval of one hour until constant weight was attained (Guan et al., 2013). The weight was determined using weighing balance (CAMRY Electric Kitchen Scale, Model: EK 5350). The average MC expressed on a percentage fresh weight basis (per cent wet basis) as a function of time were calculated and used in the construction of drying characteristics table and curves (Sankat and Mujaffar, 2006). Moisture ratio. MR was calculated as the ratio of the MC at any given time (t) to the initial MC (relative to the equilibrium MC) using equation (91):


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MR ¼

M Me M0 Me

(1)

where M, Mo and Me = present, initial and equilibrium MCs, respectively. This can be simplified into equation (2) (Darvishi et al., 2013):

768

MR ¼

Mt M0

(2)


where MR = Moisture ratio, Mt = Moisture content at any time t; Mo = Initial moisture content. Drying rate. DRs were calculated by estimating the change in MC with time, expressed in kg H2O/kg solid/h on a wet basis. The DR can be expressed as shown in equation (3) (Sobukola and Olatunde, 2011): DR ¼

Mt þ dt Mt dt

(3)

where DR = drying rate (kg H2O/kg solid/h); Mt þ dt = moisture content at t þ dt; Mt = moisture content at time t (drying time) and dt = change in time. Modelling the drying characteristics of catfish. The data obtained for the MR, computed from MC at time ‘t’ (equations (1) and (2)) of different treatments during drying was fitted into five thin-layer drying models, namely, Page (MR = exp (kt n)); Midilli (MR = a exp (ktn) þ bt); Logarithmic (MR = a exp (ktn) þ b); Parabolic (MR = c þ bt þ at2); Wang and Singh (MR = 1 þ bt þ at2); as given by different authors and chosen for their simplicity (source: Darvishi et al., 2013), where MR = moisture ratio; k = drying constant; t = time (h); a, b, c and n are model constants. The non-linear regression statistical analysis of the experimental data was performed using Microsoft Excel Solver (2013) software. The coefficient of determination (R2) was used as the primary criteria for selecting the best-fitted model in describing the drying characteristics of catfish; values close to 1 denotes good predictive quality. The error terms; root mean square error (RMSE) and reduced chi-square ( x 2) were used to determine the quality of fit (values near zero indicated good fit). The bestfitted model was taken as the one with the highest R2, lowest RMSE and x 2 values. The least average ranking value of the rating parameters ascertains the selection of the best model.

Table I. Selected treatments used for the study based on preliminary result of single factor ANOVA (p < 0.05) for sensory evaluation scores of the dehydrated catfish

Process parameter/ Treatment Treatment 1 Treatment 2 Treatment 3 Treatment 4 Treatment 5 Treatment 6

Brine concentration Brining time Drying temperature (%) (min) (°C) 9 6 0 6 6 0

90 60 0 60 90 0

90 90 90 110 110 110

Overall acceptability Variance 4.22 4.13 – 4.04 4.31 –

0.2 0.3 – 0.2 0.1 –

Note: Superscripts 1, 2, 3 and 4 indicated ranking grades of overall acceptability scores in each treatment by a ten-man panel using average ranking test

The rating parameters were calculated as stated in regression equations (4)-(6) below (Sacilik and Elicin, 2005) for each of the treatment used: XN

MRi MRpre;i MRi MRexp;i R ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi nX XN 2 2 o N MR MR MR MR i pre;i i pre;i i¼1 i¼1 2

i¼1

(4)

769


2

where R is the coefficient of determination, MRexp,i is the experimental MR, MRpre,i is the predicted MR and N is the total number of observations: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi XN 2 MR MR exp;i cal;i i¼1 (5) RMSE ¼ n where RMSE is the root mean square error which signifies the noise in the data (Demir et al., 2007): XN

x ¼ 2

i¼1

MRexp;i MRcal;i N n


2 (6)

where x 2 is the reduced chi-square; N is a number of observations, whereas n is the number of constants in the model (Kingsley and Singh, 2007). Determination of proximate composition. The proximate composition of the muscle parts of the dehydrated catfish was determined using the method of AOAC (2012), whereas the carbohydrate content was calculated by difference. Determination of microbial load. Pour plating method described by Harrigan and McCance (1976) was used in the determination of microbial load analysis. The following selective media were used: Nutrient Agar (Sigma-Aldrich-70148), McConkey Agar (SigmaM7408), Desoxycholate Agar (Sigma-Aldrich-D7809), Eosin Methylene Blue (Sigma-Aldrich70186) 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 of ground muscle part of the fresh and dehydrated catfish was dissolved in three-fold serial dilutions (101 to 103) in sterile saline solutions. An aliquot of the diluted sample was pour-plated 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 counts were enumerated using digital colony counter (Gallenkamp, England). Further statistical analysis. Data obtained for the proximate compositions was subjected to analysis of variance (ANOVA) at p < 0.05 using Statistical Package for Social Sciences (SPSS) version 22 (IBM Corp, 2013). Duncan multiple range tests were used to separate the means. Results and discussion Effect of treatment on drying characteristics of catfish The drying characteristics study is necessary to determine the drying parameters that could prevent extended drying time which may impair the quality of dried fish. Effect of processing parameters on MC and MR relative to drying time is presented in Table II, whereas DR and the relationship between DR and MC curve patterns (to determine the

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DR period) are represented in Figures 1 and 2, respectively. Drying time in all treatments approximately ranged from 20-28 h. The MC of samples after brining at drying time zero ranged from 68-78.9 per cent. The higher the brine concentration, the lower the MC of samples. Sample of catfish in Treatment 1, involving the higher brine concentration (9 per cent) and brining time (90 min) before the actual drying (at time

770 1

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Table II. The variations in MC 30

and MR with drying time in drying bodymass catfish of different treatments

Drying treatments at 90°C 2

68.4 (1) 62.8 (0.9) 57.8 (0.8) 54.4 (0.8) 50.3 (0.7) 44.7 (0.7) 38.2 (0.6) 31.0 (0.5) 24.6 (0.4) 21.2 (0.3) 16.8 (0.3) 13.6 (0.2) 11.0 (0.2) 8.3 (0.1) 5.3 (0.1) 2.2.0 (0)

75.1 (1) 69.4 (0.9) 64.4 (0.9) 60.1 (0.8) 55.3 (0.7) 48.2 (0.6) 39.7 (0.5) 30.5 (0.4) 21.0 (0.3) 17.0 (0.2) 10.8 (0.1) 7.0 (0.1) 4.4 (0) 1.5 (0)

Drying treatments at 110°C 5 6

3

4

77.0 (1) 71.1 (0.9) 66.4 (0.9) 61.7 (0.8) 56.9 (0.7) 49.5 (0.6) 40.5 (0.5) 30.7 (0.4) 20.9 (0.3) 15.9 (0.2) 9.4 (0.1) 3.6 (0.1) 1.9 (0) 0.4 (0)

77.0 (1) 70.7 (0.7) 58.5 (0.4) 51.0 (0.3) 44.9 (0.2) 38.4 (0.2) 27.7 (0.1) 17.1 (0.1) 10.4 (0) 5.2 (0) 1.4 (0)

75.5 (1) 69.2 (0.9) 56.8 (0.8) 48.9 (0.6) 42.8 (0.6) 36.2 (0.5) 26.5 (0.3) 17.3 (0.2) 11.5 (0.1) 6.7 (0.1) 2.1 (0)

78.9 (1) 73.2 (0.9) 62.1 (0.8) 54.9 (0.7) 48.4 (0.6) 41.5 (0.5) 30.5 (0.4) 19.7 (0.2) 13.0 (0.2) 6.6 (0.1) 1.7 (0)

Notes: Data presented as MCs and MRs are in parentheses; Values are means of duplicate determinations; Key: h = Hour; 1 = Treatment with processing parameters; 9% brine concentration, 90 min brining time, 90°C drying temperature; 2 = 6% brine, 60 min, 90°C; 3 = 0% brine, 0 min, 90°C; 4 = 6% brine, 60 min, 110°C; 5 = 6% brine, 90 min, 110°C; 6 = 0% brine, 0 min, 110°C

0.045 0.040 Tr4 (6% brine, 60 min, 110 oC) Drying rate (kg H2O/kg solid/h)


Time (h)

Figure 1. Effect of treatments on drying rate versus drying time of catfish

0.035

Tr5 (6% brine, 90 min, 110 oC) Tr6 (0% brine, 0 min, 110 oC)

0.030

Tr1 (9% brine, 90 min, 90 oC) 0.025


0.020 0.015 0.010 0.005 0.000 0

5

10

15 Time (hour)

20

25

30


0.045 0.040


Drying rate (kg H2O/kg solid/h)


0.035 0.030


771

Tr5 (6% brine, 90 min, 110 oC) 0.025

Tr6 (0% brine, 0 min, 110 oC)

0.020 0.015 0.010 0.005 0.000 0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

Moisture content (%w.b)

zero), had a lower MC (68 per cent) than the determined initial value (76.34 per cent), but a range of values, 77 and 78.9 per cent, close to the initial MC value was observed for the unbrined samples, in Treatments 3 and 6, respectively. This implies that brining aids osmotic removal of free water from fish tissues. Omodara and Olaniyan (2012) made a similar observation in studying the effect of pre-treatments (blanching; salting; sugaring) and drying temperatures (40-55°C) on DR and quality of small cuts of C. gariepinus. Equal MR value (1.0) was obtained in all treatments at time zero contrary to MC pattern. This is so because assuming the equilibrium MC; Me is negligibly small and tends to zero, the MR; (Mt Me)/(Mo Me) was simplified to Mt/Mo [equations (1) and (2)]. Therefore, at time t = o; Mt = Mo implies Mt/Mo (MR) will always be 1, indicating that neither moisture reduction nor drying has occurred before heating. However, as the drying time increased, both MC and MR decreased, showing that drying was in progress; the decrease was more with the temperature increase as a result of more heat transfer. A similar trend was reported by Sobukola and Olatunde (2011) for the drying characteristics of catfish fillet sheets brined in 0.21 g/g salt solution and dried at 60°C. As shown in Figure 1, the DR was highest during the first 2 h of drying at both temperatures. This could be as a result of the initial high MC of the drying catfish. The initial value ranged from 0.022-0.025 kg H2O/kg solid/h at 90°C, and increased rapidly to a range of 0.034-0.043 kg H2O/kg solid/h at 110°C, implied that there was more heat transfer to the catfish muscle at a higher temperature for a faster moisture removed. The drying time, 20-21 h, was shorter at 110°C in Treatments 4-6 than, approximately, 26-28 h in Treatments 1-3 at 90°C for the same reason of a faster rate of removing moisture at a higher temperature. This finding is consistent with the reports on the DR at 30-60°C and 40-55°C of salted fillets and brined small cuts of catfish (C. gariepinus) in a hot air convective dryer by Sankat and Mujaffar (2006) and Omodara and Olaniyan (2012), respectively. Drying took place in two falling rate periods as shown in Figure 2. There was no constant rate period during the drying of catfish like in other agricultural

Figure 2. Effect of treatments on drying rate period of catfish

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772

materials. This implies an internal mass transfer mechanism may be responsible for the falling DR in the samples. A similar trend was reported by Bellagha et al. (2002) in the drying of whole sardine fish (30 g) at 35-50°C. As could be observed in Figure 2, the rate of moisture reduction was faster at 110°C than at 90°C, irrespective of the treatment. Also, the DR decreased with reduction in MC as less heat is absorbed by the fish muscle which actually caused the fall in the DR period. This agreed with the report of Darvishi et al. (2013). Treatment with higher brine concentration (9 per cent) and longer brining time (90 min), dried at 90°C (Tr1) had the longest second falling rate with the least DR of about 0.006 kg H2O/kg solid/h towards the equilibrium. During drying, water accompanied by salt migrates from tissues to the surface of fish and evaporates, leaving salt particles clogging the pores on fish surfaces, thus, making the surface less permeable. This phenomenon was more pronounced at higher brine concentration. Thus, brine concentration and brining time affects drying characteristics of catfish, which is in agreement with the report of Sobukola and Olatunde (2011). The two unbrined samples (Treatments 3 and 6), dried at each temperature (110 and 90°C), attained the falling rate period and moisture equilibrium (at about 2 and 5 per cent, respectively) faster than the corresponding brined samples. This may be due to no barrier to moisture diffusion as observed in the brined samples, similar to the report of Omodara and Olaniyan (2012). Generally, the rate of change in MC was influenced by drying temperature. Result of modelling the drying characteristics of catfish The non-linear regression statistical result obtained from fitting the experimental MR with that of the tested thin-drying models ranked Midilli model as best-fitted for drying characteristics of catfish in Treatments, 1, 2, 3, 4 and 6 (brining for 90 min in 9 per cent brine concentration before drying at 90°C; brining for 60 min in 6 per cent brine concentration before drying at 90°C; no brining, only dried at 90°C; brining for 60 min in 6 per cent brine concentration before drying at 110°C; and no brining, only dried at 110°C, respectively). The Parabolic model presented the best fit in Treatment 5 (brining for 90 min in 6 per cent brine concentration before drying at 110°C), having the R2 value of 0.9962 with a negligible difference in the corresponding R2 value (0.9961) of Midilli model. Therefore, Midilli was chosen as the best model that described the drying characteristics of the body-mass catfish with high R2 values ranged from 0.996-0.997, implying that the model explained up to 99.6-99.7 per cent of the total variations in the independent variables of the treatments. The low values of error terms: RMSE (0.021310.01794) and x 2 (0.00037-0.00043) indicated a good predictive quality of Midilli model. High R2 and low error terms are indications of a better predictive quality of a model (Makanjuola et al., 2015). This corroborates the findings of Darvishi et al. (2013) in which Midilli was reported to be the best model that described the drying characteristics of sardine fish dried with microwave heating power between 200-500 W. The obtained values for DR constant (k) in different treatments at the two temperatures of Midilli model increased from the range 0.00202-0.010114 h1 (in treatments involving drying at 90°C) to a range of 0.0.017573-0.038173 h1 (in treatments involving drying at 110°C) implies that increasing the drying temperature from 90°C to 110°C enhanced the DR. This is in agreement with the report of Sankat and Mujaffar (2006) in modelling the drying behaviour of salted catfish (Arius sp.) fillets at four drying temperatures (30, 40, 50 and 60°C). The fitness of experimental MR curves of Midilli model in the Treatments 1-6 (Treatments 1-6) is expressed in Figure 3. The data banded along the dotted straight line at 45° indicated good agreement between the predicted and experimental data,


1

Midilli (TR- 1-6)

0.9

Predicted moisture ratio


0.8 0.7

773

0.6 TR1 (9% brine, 90 min, 90 oC)

0.5

TR2 (6% brine, 60 min, 90 oC)

0.4

TR3 (0% brine, 0 min, 90 oC) 0.3

TR4 (6% brine, 60 min, 110 oC) TR5 (6% brine, 90 min, 110 oC)

0.2

Figure 3. Variations in the predicted and experimental MRs for drying catfish of 1 different treatments

TR6 (0% brine, 0 min, 110 oC)

0.1 0 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Experimental moisture ratio

0.8

0.9

hence, the suitability of Midilli model in describing drying characteristics of body-mass catfish.

Comparative analysis of drying characteristics The drying characteristics of body-mass catfish (C. gariepinus) expressed in Table II; Figures 1 and Figure 2 followed the same pattern as the fillets and small cuts of portions of fish found in the literature. The major disparity was observed only in drying duration. While drying time approximately ranged from 20-28 h in the present study, Sobukola and Olatunde (2011) reported a drying time of 215 min (about 3.6 h). However, the range of drying time recorded in the present work was shorter than the observed time (36 and 72 h) for drying small cuts and fillets of salted catfish (C. gariepinus and Arius macalatus) at 50°C and 30°C in the works of Omodara and Olaniyan (2012); and Sankat and Mujaffar (2006), respectively. Shorter drying time will enhance good quality. The variation observed in these findings could be due to the differences in the species, size, shape, form of fish, and the treatments used. The best-fitted models; Midilli and Page which described the drying characteristics of catfish in the present and the work of Sobukola and Olatunde (2011) had highest R2 values of 0.997 and 0.999; lowest RMSE (0.0179 and 0.0205) and x 2 (0.000365 and 0.000105), respectively, showing a comparable result. The model constants obtained were also comparable with the values reported by Darvishi et al. (2013). Therefore, considering the applied treatments with the dryer used, the determined drying characteristics of the body-mass catfish could adequately be described by the thin-layer drying models as obtained for fillet sheets and small cuts of a portion of fish common in the literature.

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Quality assessment of the dehydrated catfish Proximate composition of fresh raw and dehydrated catfish The proximate composition of fresh raw and dehydrated catfish is presented in Table III. The treatments used produced dehydrated catfish of low MC ranged from 7.43-10.87 per cent which could enhance good storage stability (Kumolu-Johnson et al., 2009). This reduction in MC from the initial value (76.34 per cent) in all the treatments is a confirmation that fresh raw C. gariepinus is high in water content which predisposes it to spoilage if not well processed immediately after harvest (Effiong and Mohammed, 2008). The range of values for MC was much lower than the value (15.62 per cent) reported by Chukwu and Shaba (2009) for electrically oven dried C. gariepinus at 120°C without brining. Thus, brining enhanced the removal of free moisture in the present work. The significant (p < 0.05) increase in crude protein (ranged; 60.12 to 70.28 per cent) in the dehydrated catfish samples compared to the fresh raw fish (15.3 per cent), suggested good nutritional quality, that protein nitrogen was not lost during processing, and as a result of concentration through drying. The highest protein content value (70.28 per cent) in Treatment 2; 6 per cent brine, 60 min and 90°C could be due to the lower limits of all the process parameters in this treatment which might have retarded the process of the protein modification of the catfish sample by the combined effect of salt and heat. This is similar to the report of Bellagha et al. (2002), in studying the drying kinetics and characteristics drying curve of lightly dry salted sardine (Sardinella aurita) of 30 g each, at 35-50°C. The effect of variation in the combinations of processing parameters on protein contents in treatment 1 and 5 was not significant; this could mean that the differences in the parameters were complementary. Also, the two un-brined samples (Treatments 3 and 6) were not significantly (p < 0.05) different in protein content, indicating that the difference in drying temperatures between 90 and 110°C does not constitute a source of significant variation in protein content of unbrined dried catfish. However, the un-brined catfish, that was dried, at 90°C (Treatment 3) gave higher MC (10.87 per cent) than that, dried at 110°C (Treatment 6) which had 9.33 per cent MC, indicating that higher drying temperature is synonymous with more heat transfer for a higher moisture loss. The crude fat and ash contents of the dehydrated catfish samples were significantly (p < 0.05) different in all the treatments. These showed that there was a significant influence of processing parameters on proximate compositions of the dehydrated catfish in the present study. This agreed with the reports of Adeyeye et al. (2016b) in assessing the quality and safety of traditional smoked spotted tilapia fish (Tilapia mariae) from Lagos State, Nigeria, and Chukwu and Shaba (2009) studied the effects of drying methods (kiln smoking at 60-70°C and electric oven drying at 120°C) on proximate compositions of whole catfish (Clarias gariepinus) of about 278 g each. However, Treatment 5 that gave the lowest MC (7.43 per cent) in this study could enhance the maintenance of quality during storage and the first ranking in overall acceptability of the corresponding dehydrated catfish sample in the preliminary sensory evaluation result (Table I) suggested this combination of processing parameters (6 per cent brine, 90 min and 110°C) as the best conditions for the production of good quality dehydrated catfish. Microbial load of dehydrated catfish The microbial counts (cfu/g) of dehydrated catfish are presented in Table IV. The observed TVC ranged from 1.0 103 to 3.0 103cfu/g were quite low compared to the recommended acceptable limits (5.0 105 cfu/g) for good quality dried fish. The fungi count in treatment 6 (2.0 103 cfu/g) was within the standard (1.0 106 cfu/g)

90 60 – 60 90 – –

9 6 – 6 6 – –

90 90 90 110 110 110 –

Drying temperature (°C) 12.6 6 0.6 11.6b 6 0.6 11.7b 6 0.1 10.8c 6 0.6 12.5a 6 0.4 9.5d 6 0.3 2.6e 6 0.2

9.5 6 0.3 6.5c 6 0.3 6.5c 6 0.3 8.0b 6 0.6 10.0a 6 0.0 8.0b 6 0.0 1.5d 6 0.0 a

Fat

a

Ash 9.5 6 0.1 7.7e 6 0.2 10.9b 6 0.7 9.8c 6 0.7 7.4e 6 0.3 9.3d 6 0.7 76.3a 6 0.1

MC cd

65.7 6 1.3 70.3a 6 0.4 60.1d 6 2.5 66.9b 6 2.5 62.1c 6 1.3 60.3d 6 1.3 15.3e 6 0.2 bc

Protein

2.8e 6 0.4 3.9de 6 0.1 10.9b 6 2.8 4.5d 6 2.6 8.1c 6 0.6 12.9a 6 1.9 4.5d 6 0.0

CHO

Notes: Values are means of three replicates 6 standard deviation from ANOVA (p < 0.05); means with different superscripts along the same column are significantly different using Duncan’s multiple range tests; Key: dw = Dry weight basis; FRF = Fresh-raw fish; – = No brining/drying; CHO = Carbohydrate

1 2 3 4 5 6 FRF

Treatment

Brining time (min)

Brine concentration (%)



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Table III. Proximate compositions of fresh raw and dehydrated catfish (% dw)

Table IV. Microbial quality of dehydrated and fresh-raw catfish

9 6 – 6 6 – –

90 60 – 60 90 – –

90 90 90 110 110 110 –

Dying temperature (°C) 3

1.0 10 Nil 1.0 103 1.0 103 Nil 3.0 103 Nil 5.0 105

TVC (cfu/g) Nil Nil Nil Nil Nil Nil Nil

Coliform (cfu/g)

Nil Nil Nil Nil Nil Nil Nil

Salmonella (cfu/g)

Nil Nil Nil Nil Nil Nil Nil

E. coli (cfu/g)

Nil Nil Nil Nil Nil 2.0 103 Nil 1.0 106

Fungi (cfu/g)

Notes: Values are means of duplicate microbial counts; Treatments 1-6 corresponds to the combinations of brine concentration, brining time and drying temperature, respectively; Key: TVC = Total viable count; cfu/g = colony forming unit per gram; Nil = No growth count; FRF = Fresh-raw fish; - = No brining/ drying; STD = Standard [ICMSF (International Commission on Microbiology Safety for Foods), 2002]

1 2 3 4 5 6 FRF STD

Brining time (min)

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Treatments

Brine concentration (%)


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according to ICMSF (International Commission on Microbiology Safety for Foods) (2002). There was no growth count of pathogenic bacteria, indicating the safety of the products. This showed that brining, as well as the thermal processing, could prevent the growth of spoilage and pathogenic organisms. This agreed with the report of da Silva et al. (2008) in studying the “effect of preservatives on microbial safety and quality of smoked blue catfish (Ictalurus furcatus) steaks during room-temperature storage”. The results of the microbiological analysis in the present study showed that dehydration technique used could be an adequate processing method for catfish, which is better than the convective smoking kiln method that gave the higher TVC range (1.0 103-8.6 103 cfu/g) reported by Adeyeye et al. (2016b). Generally, the highest MC (10.87 per cent) in Treatment 3; highest TVC (3.0 103 cfu/g) and fungi counts (2.0 103 cfu/g) in the sample of Treatment 6 (both unbrined samples) underscores the positive influence of brining operation on the preservation of quality in dehydrated catfish. Conclusion The DR, as well as quality of dehydrated catfish, was enhanced by processing parameters. The drying of catfish occurred in two falling rate periods. Midilli model best described the drying characteristics of catfish; hence, this study has shown the possibility of explaining the drying behaviour of body-mass catfish under the singlelayer drying models. Modelling the drying characteristics of brined and unbrined bodymass catfish could provide necessary data for the design of drying process and equipment. Dehydration of body-mass catfish with 6 per cent brine concentration, 90 min brining time and 110°C drying temperature gave the lowest MC and no viable organism, which could make a stable dehydrated catfish upon storage. Thus, this study provides a simple and effective method for dehydrating catfish that may be useful and convenient for a commercial application; this, in turn, could boost the economic value of catfish. Hygienically processed dehydrated catfish of good quality could be a source of nutrients to ameliorate malnutrition and reduce post-harvest losses of catfish. Creation of awareness for consumer acceptability will be necessary to harness these values. Finally, this study provides baseline data necessary for the further study to establish standards for studying drying characteristics of body-mass catfish under the thin-layer drying theory. References Adam, S.H.M. and Sidahmed, M.A. (2012), “Effect of drying system on chemical and physical attributes of dried catfish (Clarias Sp.)”, World’s Veterinary Journal, Vol. 2 No. 1, p. 1. Adeparusi, E.O., Dada, A.A. and Alele, O.V. (2010), “Effects of medicinal plant (Kigelia Africana) on sperm quality of African catfish (Clarias gariepinus, Burchell, 1822) brood stock”, Journal of Agricultural Science, Vol. 2 No. 1, pp. 193-199. Adeyeye, S.A.O., Oyewole, O.B., Obadina, O., Adeniran, O.E., Oyedele, H.A., Olugbile, A. and Omemu, A.M. (2016a), “Effect of smoking methods on microbial, polycyclic aromatic hydrocarbon, and heavy metal concentrations of traditional smoked fish from Lagos state, Nigeria”, Journal of Culinary Science & Technology, Vol. 14 No. 2, pp. 91-106. Adeyeye, S.A.O., Oyewole, O.B., Obadina, A.O., Omemu, A.M., Adeniran, O.E. and Oyedele, H.A. (2016b), “Assessment of quality and safety of traditional smoked spotted tilapia fish (Tilapia mariae) from Lagos State, Nigeria”, Nutrition and Food Science, Vol. 46 No. 1, pp. 142-155, doi: 10.1108/NFS-05-2015-0059.


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Corresponding author Dupe Temilade Otolowo can be contacted at: [email protected]

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