Effects of Salting and Drying on Shark (Carcharhinus sorrah) Meat Quality Characteristics

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/263346918 Effects of Salting and Drying on Shark (Carcharhinus sorrah) Meat Quality Characteristics Article in Drying Technology · May 2008 DOI: 10.1080/07373930802046294 CITATIONS READS 15 273 4 authors, including: Nejib Guizani Mohammad Shafiur Rahman Sultan Qaboos University Sultan Qaboos University 111 PUBLICATIONS 1,012 CITATIONS 252 PUBLICATIONS 4,066 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Evaluation the Quality, Safety and Storage Stability of Traditional Fish Products in United Arab Emirates and Sultanate of Oman Ismail Al Bulushi (PI), Mohamed Shafiur, Mostafa Waly View project Food Diversification View project All content following this page was uploaded by Mohammad Shafiur Rahman on 14 December 2014 The user has requested enhancement of the downloaded file All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 Drying Technology, 26: 705–713, 2008 Copyright # 2008 Taylor & Francis Group, LLC ISSN: 0737-3937 print/1532-2300 online DOI: 10.1080/07373930802046294 Effects of Salting and Drying on Shark (Carcharhinus sorrah) Meat Quality Characteristics Nejib Guizani, Ali Obaid Al-Shoukri, Ann Mothershaw, and Mohammad Shafiur Rahman Department of Food Science and Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat, Sultanate of Oman The effect of drying method and pretreatment with salt on the properties of shark meat was investigated Water loss during the salting step was faster with dry salting than with brine salting; however, both methods led to the same final water content at the end of the drying process Moisture desorption isotherms showed that addition of salt prior to sun or air drying resulted in lower equilibrium moisture contents at the same water activity levels Salting and method of drying had significant effects on the microbial load Osmo-air-dried samples showed better microbial quality than samples treated by other methods Molds grew on all samples after two months of storage at room temperature Color and rehydration ratio were affected by the drying method Higher dehydration ratios were obtained with air drying Keywords Desorption isotherm; Drying; Quality; Salting; Shark meat INTRODUCTION Dried salted fish is consumed in many countries, especially in developing countries where they constitute an important source of low cost dietary protein.[1] The preservation activity of drying is dependent on the reduction of water activity to stop or slow down the growth of spoilage microorganisms, as well as the occurrence and rate of chemical and enzymatic reactions Fish and seafood are prone to rapid microbial spoilage; thus, adequate care must be taken in drying fish.[2] The temperature and the treatment received before drying are important factors to produce safe products Drying of highly perishable products, such as fish at low temperature, raises the risk of microorganisms and may produce an unsafe product.[3] Salting is a preliminary step in the drying process and is critical to obtain a commercial product with an adequate shelf-life and good quality Using salt before drying will Correspondence: Nejib Guizani, Department of Food Science and Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O Box 34, Al-Khod-123, Muscat, Sultanate of Oman; E-mail: guizani@squ.edu.om enhance the capability of drying to reduce water activity to lower values within a short time Osmotic dehydration is an important technology that enables both the removal of water from the product and the modification of its functional properties by impregnation of desired solutes Osmotic dehydration is commonly performed by immersion of the product in salt solutions It creates countercurrent mass transfer fluxes of water and solutes, namely water outflow from the product to the surrounding solution and solute infusion into the product In addition, leakage of the product solutes has an impact on the organoleptic properties and nutritional value of the product.[4] The preservative effect of salting is mainly attributed to the decrease in water activity (aw) inhibiting the growth of many spoilage microorganisms In addition, chloride ions are toxic for some microorganisms.[5] Dried shark (local name Uwal) is popular in Oman and other Gulf countries Traditionally, shark is sundried and is usually kept at room temperature and consumed without any further thermal treatment Before drying, fresh shark is filleted, washed, lightly salted, and then dried under the sun The process is not standardized, and variations occur in the salting method (dry vs brine), salt concentration, size and density of fish pieces, and humidity, temperature, and time of drying Consequently, there are no standard parameters for the physicochemical properties or microbiology of the product The final product is offered to the consumer in various forms including whole, skinned, and sliced It is usually distributed without packaging, although on some occasions it is sold in plastic bags The processing and the exposure of the dried shark provide many opportunities for microbial contamination Moreover, in Oman Uwal is often eaten without any heat treatment, which may increase any potential health risk The aim of this work was to optimize the individual processing steps of salting method and drying conditions involved in the production of dried shark in order to improve the quality and safety of the product This was achieved by 705 Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 706 GUIZANI studying the effect of two drying methods (sun and convection air) used alone or in combination of one salting method (brine or dry salting) on the microbiology, chemical composition, rehydration ratio, and color of dried shark meat METHODOLOGY Sample Preparation Fresh shark fish Carcharhinus sorrah were brought fresh from the local fish market, Al-Seeb, Sultanate of Oman, and transported within 30 in ice to Sultane Qaboos University After washing in tap water, the fish were filleted Shark fish meat samples were prepared immediately for drying by cutting into strips of approximately   cm in size The strips were then divided into two groups, one for dry salting and the other for brine salting The shark strips were then salted and dried using different methods Salting Procedures Both brine and dry salting procedures were used Brine salting was conducted in plastic containers at ambient temperature (25C approximately for days) at a ratio of 1:3 (fish:brine) The concentration of the brine was 27% (w=v) sodium chloride Dry salting was performed by coating fish samples with a layer of salt crystals at a ratio of 1:0.5 kg salt Samples of brine salted fish were removed from the brine and towel-dried at predetermined intervals to determine the water content For dry salted samples, excess salt was scraped off the surface before analysis Drying Procedures Sun Drying For sun drying, shark fish strips were exposed to sun, suspended by string with a bent hook at one end for better air circulation Shark meat samples were on the roof of a two-story building in the open sun for days All test samples were dried at the same time during the months of June to August, when the temperature ranged between 35 and 45C during the day and 30 to 35C at night and the % RH (relative humidity) was 72–81% Air Drying Shark meat strips were arranged into a single layer in a metal mesh tray and then placed inside a convection oven at 80C for 24 h The oven was constructed in the Department of Food Science and Nutrition, Sultan Qaboos University, Oman, with a control temperature and constant air flow rate (1.5 m=s) Air flowed parallel to the surface of the sample using a fan The samples were loosely spread to improve air circulation This temperature was selected for its relevance to commercially used air drying temperatures that range between 60 and 90C for food products For the drying procedure the temperature of the oven was initially set at 80C and the oven temperature was allowed to stabilize at this value for at least 30 before samples were placed inside Drying Rate Drying curves for shark meat samples were followed during the salting pretreatment and during the air drying The drying rates were determined and compared to identify the effects of salting and drying methods on the drying kinetics of shark meat The mass of each individual sample was measured using a digital balance with an accuracy of 0.001 g, immediately before salt application or insertion into the dryer Thereafter, the masses of each sample were periodically measured by briefly removing the sample from the salt (during salting period) or from the dryer (during the drying period) These measurements were used to determine the weight losses of each sample at specified time intervals Samples were salted for 48 h and dried for 48 h Moisture content values were used for drawing the drying curves (Figs and 2) Desorption Isotherm The equilibrium isotherms of dried shark meat samples were determined at room temperature (25C) by the isopiestic method.[6,7] Samples (approximately g) were placed into separate tightly closed glass jars while maintaining equilibrium relative humidity with saturated salt solutions (with a crystal layer visible at the bottom of jars) The salts were LiCl, CH3COOK, MgCl2, K2CO3, NaBr, SrCl2, and KCl (BHD, Laboratory Supplies, Poole, England) Relative humidity values for these solutions were obtained from Greenspan[8] and Spiess and Wolf.[9] The samples were sealed within the jars for weeks until a constant weight was achieved Then the dry matter content was determined by drying the equilibrated samples in an oven 100–102C for 16–18 h and from this the moisture content was estimated Beakers containing a solution of FIG Effect of salting technique on water content evolution during the salting period Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS 707 patting with tissues and were then reweighed Five samples in duplicate were performed for each treatment Rehydration ratio was defined as the ratio of weight of rehydrated samples to the weight of the sample before rehydration FIG Effect of salting techniques on water evolution during air convection drying thymol were placed open in high water activity jars to avoid microbial growth in the samples during equilibrium.[10] Chemical Composition All shark meat samples were analyzed for their water, total proteins, and ash content These chemical analyses were measured according to AOAC.[11] Five samples in duplicate were analyzed for each treatment Moisture was measured using a gravimetric method by drying the sample in an air oven at 105C until it reached constant weight Total nitrogen was determined by the Kjeldahl method Ash was determined from the residue after burning in muffle furnace at 525C for around 18 h Color Measurements Hunter aà , bà , and Là parameters were determined using a Minolta Chroma Meter (model CR-300, Minolta Co., Tokyo, Japan) in the reference mode, where Là is the lightness or darkness (black, Là ¼ 0; white, L ẳ 100), ỵa is redness,a is greenness, ỵb is yellowness, and Àbà is blueness.[12] The instrument was calibrated with a white standard calibration plate provided by the manufacturer (Là ¼ 97.59, aà ¼ À5.06, bà ¼ 6.91) Dried shark samples were placed on flat plate, and the tip of the measuring head was pointed on the samples for measurement The color of fresh and processed (salted=dried) shark meat samples was measured The color of commercial dried shark obtained from the local market was also measured and compared with samples processed during this investigation Rehydration Ratio Rehydration ratio, which is a measure of the rehydration characteristics, was determined for dried shark fish meat by immersing about g of dried sample in tap water at 25C for h Each dried shark sample was weighed prior to immersion in the water bath Samples were removed from the water at predetermined time periods and the excess water was removed from the surface by gently Microbial Evaluation Duplicate pieces of approximately g were aseptically removed from the shark meat samples previously stored at room temperature for months and homogenized in sterile stomacher bags containing 45 mL of sterile 0.1% peptone water using a stomacher Lab 400 blender (Seward Medical, UK) Decimal serial dilutions were then prepared using 0.1% peptone water Aliquots of the dilutions were spread onto a range of media The culture media and incubation conditions used for different microbial groups were as follows: aerobic plate count (APC) on plate count agar (PCA) at 32C for 48 h;[13] Staphylococcus spp on Baird-Parker agar at 37C for 30 h;[14] and molds on potato dextrose agar (PDA) at 30C for days For presumptive identification, the macroscopic and microscopic characteristics of molds grown on PDA were observed and compared to illustrations and descriptions given by Pitt and Hocking.[15] The results were expressed as colony-forming units per gram of sample All media were purchased from Oxoid (Basingstoke, Hampshire, England, UK) Statistical Analysis Calculation of the mean values and standard deviations was performed in Excel A statistical significance test between means was conducted with Duncan’s test procedure at 5% significance level.[16] RESULTS AND DISCUSSION Effect of Salting Method on Drying Rates The effect of salting method on the evolution of water content during the salting period is shown in Fig This figure shows that initially there was a fast decrease in moisture followed by a slow decrease The rate of water loss was, however, different depending on whether fish salting was made by brining or dry salting The water content of dry salted shark meat decreased more rapidly during the first salting hours (20 h) than that of brine-salted shark meat High salt concentrations (25% w=w) and dry salting were found to lead to more protein denaturation (the myofibrillar proteins rapidly lose water due to the salting out process), resulting in changes in texture and reduced water holding capacity[17,18] and, consequently, weight loss during salting (Fig 1) The rate of water loss declined after 12 and 20 h for brine-salted and dry-salted samples, respectively The water content after 48 h of salting reached 63.6 and 73.2% for dry-salted and brine-salted shark meats, respectively The effect of the salting method on water evolution during the air convection drying period is Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 708 GUIZANI shown in Fig The results showed that the drying rate of dry-salted shark was slower than brine salt However, both drying methods led to a product of similar water content at the end of the drying period (48 h) despite the fact that the water content of brine-salted shark meat was greater at the end of the salting period The results of this study corroborate those obtained by other workers Bellagha et al.[1] reported that dry-salting sardines gave the most rapid rate of reduction in moisture content and the lowest final moisture content during salting sardine but gave a slower rate of reduction of moisture and higher final water content during drying Berhimpon et al.[19] showed that during the salting process, the yellowtail fish moisture content decreased rapidly in the first 10 h, and the higher brine concentration produced lower moisture content in the fish flesh After 28 h, the yellowtail fish moisture content became constant after salting in saturated and 21% brine, but yellowtail fish salted in 15% brine gradually increased in moisture and salt contents after 35 h, which could be due to the swelling of the flesh Jason[20] reported that water movement to the surface of the food during drying is accompanied by salt migration Water evaporation on the surface allows the formation of a crust, which is more important when the initial salt concentration is greater These crusts lessen the rate of water loss by making the surface less permeable.[21–23] Gallart-Jornet et al.[24] have studied the influence of brine concentration on weight and texture changes during the salting process of Atlantic salmon fillet Their results showed that the salting procedure significantly affected the total weight changes of the fillets The weight increase of the fillets increased with decreasing brine concentration, and the dry-salted fillets gave the lowest process yield Water Desorption Isotherm Experimental water sorption data of dried shark meat samples produced by different drying methods with or without osmotic treatment are presented in Fig As expected, equilibrium moisture content increased nonlinearly with the increasing water activity Isotherms showed that for a given water activity, equilibrium moisture content was lower for air-dried samples compared to sundried (Fig 3) This may be due to the different levels of protein denaturation affecting the nature of water binding In fact, salt concentration has an effect on the degree of protein denaturation and thus on the water adsorption by protein The use of lower brine concentration induces a lower degree of protein denaturation and hence increases waterholding capacity, resulting in a total high yield of the salting process.[25] It was observed in all cases that osmotic treatment prior to sun or air drying gave lower equilibrium moisture content These trends were more pronounced in the water activity region above 0.2 This is most probably due to the penetration of salt in the fish during osmotic FIG Experimental data for dried shark meat and predicted desorption isotherm curves for sun and air drying methods proceeded or not by osmotic dehydration pretreatment Salt has a strong effect on the adsorption of water by protein molecules One of the factors determining the behavior of the fish fillets in different salting media is the NaCl interaction with the protein matrix.[18] The state of the proteins in the fish muscle has been found to be mainly related to the salt concentration of its water phase.[25] At low salt concentrations, maximum muscle swelling occurs as a result of high water-protein interaction (maximum water-holding capacity) At higher salt concentrations, the proteins may have strong protein-protein bonds, resulting in dehydration.[24] The mechanism of binding of water by food materials and particularly proteins is well documented in the literature.[26–29] The sorption sigmoid-shaped isotherms of dried shark are typically divided into three parts The lower part characterizing low aw range (0.10–0.20) represents water molecules strongly bound to the hydrophilic charged and polar groups of proteins, with an enthalpy of vaporization considerably higher than pure water The high moisture at the end of this zone, called Zone I, corresponds to BET monolayer moisture At the monolayer coverage, adsorption of water to the protein surface involves binding of water molecules to both polar (ionic and hydrogen bonding) and non-polar groups on the protein surface At intermediate aw values of 0.30–0.70 (Zone II) water uptake is gradual This region characterizes water molecules that complete a monolayer coverage mostly by hydrogen bonding to preexisting bound water and, by condensation, form additional layers on top of this preexisting water layer or penetrate into newly created holes of the already swollen structure In Zone III, corresponding to aw in 0.70–0.8 ranges, uptake of water by protein is rather rapid and represents mostly multilayer water; i.e., water held in voids, crevices, capillaries, and loosely attached to protein molecules The high water uptake at these higher water activities indicates dissolution of major components of the system 709 Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS A large number of sorption isotherms have been determined and are readily available.[26] However, sorption isotherms may be affected by food composition such as fat, sugar, or salt content The shapes of isotherms showing sorption isotherms may have various forms.[29] Five types of isotherms were described by Brunauer et al.[30] Biological and food material isotherms follow the shape of the sigmoid type II or III isotherm according to the classification of Brunauer et al.[30] However, in the case of high salt concentration food, Doe et al.[31] showed a different shape for the sorption isotherm At a water activity of 0.75, which is the aw of saturated sodium chloride solution, the sorption isotherm becomes vertical for a given moisture content range, as reported previously by Smith.[32] In case of saltdried shark meat, the sorption isotherm increased steeply at a water activity of 0.75 Bellagha et al.[33] studied the brining of sardine at three different salt concentrations (15, 21, 26.5%) From their results it appeared that the sorption isotherms of salted fish had a different shape from the unsalted ones This was especially true when the aw was close to 0.75, which is the water activity of saturated salt solution Similar shapes are reported for dried salted cod[31] and for cheese.[34] Above aw of 0.75, Bellagha et al.[33] found that an increase in salt content reduced the water content The isotherm at 40C was determined for unsalted sardines (Sardinella aurita) and had a type III sigmoid pattern Isotherms of raw goat meat obtained by Singh et al.[35] at three different temperatures 10, 25, and 50C The equilibrium moisture content of goat meat rose gradually at lower aw followed by a steep rise above 0.7 aw At all aw levels, the equilibrium moisture content decreased with the increase in temperature, as is generally observed for food with high protein content.[36] Comaposada et al.[37] found that when aw of pork was above 0.75, the water content increased when the NaCl content increased However, for aw < 0.75, there was only a slight effect of NaCl content in the opposite direction, which could be explained by the increased solids due to the addition of NaCl A similar effect of NaCl above aw of 0.75 has been found in other meat experiments.[38] The NaCl solution crystallizes below aw of 0.75, which corresponds to its saturation point Thus, the crystallized NaCl absorbs little or no water Chemical Composition The chemical composition of fresh and dried shark meats used in this study is given in Table The water content of fresh shark was 75.4% and the fat content determined in this study was 0.5 g=100 g (wet basis) Shark is usually considered as non-fatty fish, since the fat content is less than 4% (wet basis).[39] Sundried and osmo-air-dried samples had the highest and the lowest water contents (35.4 and 27.1%, respectively) The water content was significantly affected ( p < 0.05) by the drying method An osmotic predrying step had a significant effect ( p < 0.05) on the water content of the final dried samples Water content of commercial dried shark was significantly higher than all shark samples dried in this study, except those sundried The protein content of dried shark samples ranged from 93.32% (db) for osmo-air-dried samples to 95.14% (db) for sundried samples The drying method and the use of salt (osmotic treatment) had no significant (p > 0.05) effect on the protein content of the dried samples Ash content of dried shark was not affected by the drying method or application of an osmotic treatment and ranged between 4.62% (db) for sundried samples and 5.01% (db) for air-dried samples Microbiological Quality The effect of different drying techniques on the microflora present on the fresh shark meat samples is shown in Table The data are expressed as the ratio of the count on newly processed fish (L) to the count on fresh fish (Lo), (Log L=Lo) The microbial log counts of fresh shark meat were APC 4.20, Staphylococcus spp 3.02; and molds 2.12 The results indicate that the different salting=drying techniques varied in their lethality to the microflora Samples that had been air dried at 80C showed significantly TABLE Chemical composition of fresh and dried shark meat Composition (g=100 g) Sample Fresh Sun drying (osmotic) Sun drying Air drying (osmotic) Air drying a Water (g=100 g) of dried shark samples Proteina Asha 75.37b Ỉ (0.37) 34.35d Ỉ (1.76) 35.45c Ỉ (1.13) 27.11f Ỉ (1.65) 28.00e Ỉ (1.60) 94.69b Ỉ (0.96) 95.14b Æ (1.25) 95.13b Æ (1.19) 93.32b Æ (1.22) 93.46b Æ (1.09) 4.73b Ỉ (0.34) 4.8b Ỉ (0.51) 4.62b Ỉ (0.53) 4.97b Ỉ (0.48) 5.01b Ỉ (0.59) Dry basis (g=100 g solids) Note: Values in brackets are the standard deviations Means with the same column with different letters were significantly different (p < 0.05) Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 710 GUIZANI TABLE Effect of different drying processes on the microflora of shark meat samples expressed as the ratio of log count immediately after processing to the count on the fresh meat immediately before drying Ratio log L=Loà Sample APC Staphylococcus spp Molds Osmo-sundried Sundried Osmo-air-dried Air-dried 0.94 0.98 0.57 0.84 0.75 0.91 0.34 1.23 1.63 0.60 L is the count immediately after processing and Lo is the count of fresh fish samples immediately prior to the drying process Ratios greater than indicate that the count has increased; ratios below indicate a decrease in the count (p < 0.05) lower total aerobic plate counts and levels of Staphylococcus spp compared to sundried samples In addition, osmotic treatment of shark meat samples prior to drying also significantly lowered the staphylococci and aerobic plate counts of the dried samples A decrease in the number of molds was also seen when samples were air dried; however, in contrast, the level of mold contamination increased when the samples were dried in the sun Drying is the most commonly selected process for prohibiting fungal growth.[40] The presence of Staphylococcus spp in food is used as an indicator of inadequacies during food preparation.[41] The count of Staphylococcus spp in dried shark meat samples used in the present study is shown in Table The data indicated that the method of drying significantly affected the number of Staphylococcus spp with lower numbers being recovered from air-dried shark samples In addition, osmotic treatments significantly reduced counts of Staphylococcus spp.; the lowest values were observed for osmo-dried samples Staphylococci were particularly resistant to sun drying; their numbers were significantly higher in sundried samples when compared to air-dried samples Many Staphylococcus spp are enterotoxigenic and it has been estimated that the minimum number of cells required to produce sufficient enterotoxin to induce food poisoning is about 107.[42,43] In addition, such species can multiply to an extremely high number on meat products without producing significant changes in color, odor, or flavor.[44] Rodriguez et al.[45] isolated Staphylococcus aureus from ready-to-eat meat at levels of 106 cfu=g of meat; they also detected enterotoxin To simulate the normal use of the product, the microbiological analysis was repeated after the dried samples had been stored for two months at room temperature (Table 3) In general, the level of microbial contamination increased during storage; only the counts of mold on samples that had been air dried demonstrated a decrease in numbers Commercial dried shark meat samples had significantly higher aerobic bacterial and staphylococci counts (Table 3) This could be explained by the higher moisture level in these samples, which has been reported to be the most important factors influencing the microbial load of dried food.[46] A positive correlation (r2 ¼ 0.81) was found between aerobic plate counts and the water content of the dried shark meat (Fig 4): the higher the moisture content, the higher the total aerobic count However, other factors such as salting, size of meat samples, temperature, humidity, and sunlight intensity during drying can all influence the rate at which water activity declines and, hence, microbial growth Mold counts in the commercial samples were also significantly higher than the other dried samples Identification studies on molds isolated in the current study suggested that Penicillium and Aspergillus spp were the predominant species on dried shark meat samples More than 83% of molds isolated from the commercial dried shark were Aspergillus spp All molds isolated from air dried samples were Penicillium spp Sundried samples TABLE Microbial analysis of shark meat dried by different methods and fresh samples APC Sample Osmo-sundried Sundried Osmo-air-dried Air-dried Commercial samples Staphylococcus spp Log N Molds After drying (L) After storage After drying (L) After storage After drying (L) After storage 3.94a 4.11a 2.38c 3.54b NA 4.48c 4.85b 2.70e 4.00d 5.48a 2.25b 2.74a ND 1.04c NA 2.90c 3.30b ND 2.70d 4.00a 2.61b 3.46a ND 1.28c NA 2.30c 2.48b ND 1.48d 2.70a Means within the same column with different letters are significantly different ( p < 0.05) Five samples in duplicate ND means not detected NA means data not available 711 Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS FIG The relationship between the moisture content and aerobic plate count of dried shark meat samples contained about 74 and 26% of molds belonging to Penicillium and Aspergillus spp., respectively More than 90% of molds isolated from osmotic-treated sundried shark meat were Aspergillus spp Mold species of Penicillium, Aspergillus, and Cladosporium have been shown to be among the most prevalent species on dried fish[47] and dried meat products.[44,48] Mycotoxins are secondary metabolites produced by molds belonging mainly to the Penicillium and Aspergillus genera Foods contaminated with mycotoxins may cause serious health problems when consumed Color Measurements The effect of drying method and osmotic treatment on shark meat lightness (Là ), redness (aà ), and yellowness (bà ) was investigated Table shows the color parameters of fresh shark meat and the different dried shark samples Yellowness of the shark meat was significantly affected (p < 0.05) by the drying method with higher bà values being determined for air-dried samples The redness of dried shark meat was significantly lower than fresh meat, suggesting more extensive degradation of fish proteins that contribute to the color of fish Color changes are related to TABLE Colour parameter estimate of fresh and dried shark meat samples Lightness L Fresh Osmo-air drying Air drying Osmo-sun drying Sun drying Dried commercial à Redness a à Yellowness 55.5d Æ 0.49 12.9a Æ 0.58 8.8C Æ 0.41 61.2c Æ 1.21 5.1d Ỉ 2.41 14.7a Ỉ 4.60 64.8b Ỉ 1.05 5.9cd Ỉ 1.24 16.0a Ỉ 2.29 56.2d Ỉ 2.78 6.0c Æ 0.83 12.0b Æ 2.67 71.8a Æ 2.00 6.9b Æ 2.48 12.9b Ỉ 3.00 41.2e Ỉ 3.02 5.6cd Ỉ 2.37 8.0C Ỉ 2.58 Means within the same column with different letters were significantly different ( p < 0.05) Means are of five samples in duplicate the degree of protein structural changes, which cause a difference in the light-scattering properties of the surface of the shark meat.[49] Myoglobin is a major contributor to the color of muscle, the color being dependent on both its derivatives and concentration.[50,51] Hemoglobin is lost easily during bleeding of the fish, while myoglobin is retained by the muscle intracellular structure.[52] In addition, moisture content may affect the color of the dried products In this study, the maximum variation in water content between samples is 8%; however, it is expected that different drying methods will result in different levels of moisture content During the handling and storage of fish, a number of biochemical, chemical, and microbiological changes take place, leading to discoloration.[50,53,54] Discoloration of tuna during frozen storage is caused by the formation of metmyoglobin, as has been reported by Haard.[55] This phenomenon can be influenced by many factors, such as pH, temperature, ionic strength, and oxygen consumption reaction.[49] Osmotic pretreatment using NaCl solution significantly affected the lightness of shark meat samples Osmotic treatment enhances the removal of heme proteins from shark fish meat, leading to increased whiteness of the flesh However, heme proteins become less soluble as the fish undergoes deterioration.[56] Higher myoglobin removal by NaCl solution and distilled water could result in a lower redness of washed mince Rehydration Ratio The effects of different drying methods on the rehydration ratios of dried shark meat samples are illustrated in Table The data indicated significant differences (p < 0.05) in rehydration ratios among the drying methods, with significantly higher rehydration values for air-dried samples Osmotic dehydration significantly affected the rehydration ratios of sundried samples Rehydration ratio values of commercial dried shark meat samples were significantly lower when compared to other dried shark samples The basic objective in drying food products is the removal of water from the solids, up to a certain level, at which microbial spoilage is minimized Most dehydrated TABLE Rehydration ratios of dried shark meat samples Drying method Sun drying Osmo-sun drying Air drying Osmo-air drying Commercial samples Rehydration ratio 37.0c Ỉ 0.39 38.7b Ỉ 0.87 42.6a Ỉ 0.27 42.5a Ỉ 0.77 28.3d Ỉ 3.60 Means within the same column with different letters were significantly different (p < 0.05) Means are of five samples in duplicate Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 712 GUIZANI products are rehydrated before use Rehydration can be considered as a measure of the injury to the material caused by drying and treatment preceding dehydration.[57,58] Variations in rehydration ratio values between samples from different drying methods revealed a degree of reducing space between both groups of muscle fibers and individual fibers as well as by a progressive reduction in muscle fiber diameter.[59] In this study, the rehydration was conducted for the final dried fish; thus, the rehydration is a combined effect of osmotic followed by air or sun drying It would be interesting to separate these two processes to study the rehydration in a future study The rehydration ratio had a correlation with the juiciness of food during consumption, which might affect the acceptability of such products by the consumer Rehydration of dried tissues is composed of three simultaneous processes: the imbibition of water into dried material, the swelling, and the leaching of solubles.[60,61] Steffe and Singh[62] showed that the volume changes (swelling) of biological materials are often proportional to the amount of absorbed water Fan et al.[63] found that the gain in volume due to water sorption equalled the volume of imbibed water It is generally accepted that the degree of rehydration is dependent on the degree of cellular and structural disruption CONCLUSION This study showed that dry salting was faster than brine salting in removing water during the same salting period However, this trend is inverted during drying and both methods led to the same water content at the end of the drying process Moisture sorption isotherms showed that addition of salt prior to sun or air drying gave lower equilibrium moisture contents at the same water activity levels Salting and method of drying had a significant effect on the microbial load Lower total aerobic and staphylococci counts were obtained for osmo-air-dried samples Molds grew on all samples during storage at room temperature Method of drying had an effect on the color and rehydration ratio Considering all the characteristics studied, 80C air drying could be recommended in Uwal drying Brine salting at 27% could be considered the best condition for uniform water loss REFERENCES Bellagha, S.; Sahli, A.; Farhat, A.; Kechaou, N.; Glenza, A Studies on salting and drying of sardine (Sardinella aurita): Experimental kinetics and modelling Journal of Food Engineering 2006, 78, 947–952 Rahman, M.S.; Guizani, N.; Al-Ruzeiki, M.H D- and Z-values of microfloara in tuna mince during moist- and dry-heating LebensmittelWissenschaft und-Technologie 2004, 37, 93–98 Rahman, M.S.; Guizani, N.; Al-Ruzeiki, M.H.; Al-Khalasi, S Microflora changes in tuna during convection air drying Drying Technology 2000, 18, 2369–2379 Torreggiani, D Osmotic dehydration in fruit and vegetable processing Food Research International 1993, 26, 59–68 Leroi J.; Joffraud, J.J.; Chevalier, F Effect of salt and smoke on the microbiological quality of cold-smoked salmon during storage at 5 C as estimated by the factorial design method Journal of Food Protection 2000, 63, 502–508 Sablani, S.S.; Myhara, R.M.; Mahgoob, Al-Attabi, Z.H.; Al-Mugheiri, M.M Water sorption isotherms of freeze dried fish sardines Drying Technology 2001, 19 (3), 673–680 Sablani, S.S.; Rahman, M.S.; Labuza, T.P Measurement of water activity using isopiestic method In Current Protocols in Food Analytical Chemistry, Vol 1; Wrolstad, R.E., Ed.; John Wiley & Sons: New York, 2001; A2.3.1–A2.3.10 Greenspan, L Humidity fixed points of binary saturated aqueous solutions Journal of Research and National Bureau of Standards [A]: Physics and Chemistry 1977, 81A (1), 89–96 Spiess, W.E.L.; Wolf, W Critical evaluation of methods to determine moisture sorption isotherms In Water Activity: Theory and Applications to Foods; Rockland, L.B., Beuchat, L.R., Eds.; Marcel Dekker: New York, 1987; 215–234 10 Rahman, M.S.; Al-Belushi, R.H Dynamic isopiestic method (DIM): Measuring moisture sorption isotherm of freeze-dried garlic powder and other potential use of DIM International Journal of Food Properties 2006, 9, 421–437 11 AOAC Official Methods of Analysis of the AOAC; Association of Official Analytical Chemists: Arlington, VA, 2000 12 Francis, F.J Colour analysis In Food Analysis; Nielsen, S.S., Ed.; Aspen: Gaithersburg, 1998, 599–612 13 FDA Aerobic plate count In Food and Drug Administration Bacteriological Analytical Manual, 7th Ed; Arlington, VA, 1992, 17–26 14 Baird-Parker, A.C An improved diagnostic and selective medium for isolating coagulase positive staphylococci Journal of Applied Bacteriology 1962, 25 (1), 12–19 15 Pitt, J.I.; Hocking, A.D Fungi and Food Spoilage; Academic Press: Sydney, 1985 16 SAS SAS Users’ Guide; SAS Institute: Raleigh, NC, 2001 17 Cheftel, J.Q.; Cuq, J.L.; Lorient, D Proteı´nas Alimentarias; Acribia S.A.: Zaragoza, Spain: 1989 18 Offer, G.; Trinick, J On the mechanism of water holding capacity in meat: The swelling and shrinking of myofibrils Meat Science 1983, 8, 245–281 19 Berhimpon, S.; Souness, R.H.; Buckle, K.A.; Edwards, R.A Salting and drying of yellowtail (Tachuru mcculochi Nichols) International Journal of Food Science and Technology 1990, 25, 409–419 20 Jason, A Physical properties and processes In Advances in Fish Sciences and Technology; Conell, J.J., Ed.; Fish News Books Ltd.: Farnham, 1980 21 Poernomo, A Drying behavior of salted sardines I Model fitting of drying curves Journal of Post-Harvest Fisheries Research 1986, 53, 27–32 22 Poernomo, A Salting behavior of sardines Journal of Post-Harvest Fisheries Research 1986, 51, 23–29 23 Zuggarainundi, A.; Lupin, H.M A model to explain observed behaviour on fish salting Journal of Food Science 1980, 45, 1305–1311 24 Gallart-Jornet, L.; Barat, J.M.; Rustad, T.; Erikson, U.; Escriche, I.; Fito, P Influence of brine concentration on Atlantic salmon fillet salting Journal of Food Engineering 2007, 80, 267–275 25 Barat, J.M.; Rodrı´guez-Barona, S.; Andre´, A.; Fito, P Influence of increasing brine concentration in the cod salting process Journal of Food Science 2002, 65, 1922–1925 26 Iglesias, H.A.; Chirife, J Equilibrium moisture content of air dried beef—Dependence on drying temperature Journal of Food Technology 1976, 11, 565–573 27 Kapsalis, J.G Moisture sorption hysteresis In Water Activity Influences on Food Quality; Rockland, L.B.; Stewart, G.F., Eds.; Academic Press: New York, 1981, 143–177 Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS 28 Kinsella, J.E.; Fox P.F Water sorption by proteins: milk and whey proteins CRC Critical Reviews in Food Science and Nutrition 1986, 24, 139–144 29 Basu, S.; Shivhare, U.S.; Mujumdar, A.S Models for sorption isotherms for foods: A review Drying Technology 2006, 24, 917–930 30 Brunauer, S.; Emmet, P.H.; Teller, E Adsorption of gases in multimolecular layers Journal of the American Chemical Society 1938, 60, 309–319 31 Doe, P.E.; Hashmi, R.; Poulter, R.G.; Ocley, J Isohalic sorption isotherms: I Determination for dried salted cod Journal of Food Technology 1982, 17, 125–129 32 Smith, S.E The sorption of water vapor by high polymers Journal of American Chemical Society 1947, 69, 646–651 33 Bellagha, S.; Sahli, A.; Glenza, A.; Kechaou, N Isohalic sorption isotherm of sardine (Sardinella aurita): Experimental determination and modeling Journal of Food Engineering 2004, 68, 105–1011 34 Hardy, J L’activite´ de l’eau, le sel et les moisissures des fromages Revue Laitie`re Franc¸aise 1979, 377, 19–23 35 Singh, R.R.B.; Rao, K.H.; Anjaneyulu, A.S.R.; Patil, G.R Water desorption characteristics of raw goat meat: Effect of temperature Journal of Food Engineering 2005, 75, 228–234 36 Delgado, A.E.; Sun, D.W Desorption isotherms and glass transition temperature for chicken meat Journal of Food Engineering 2002, 51, 1–8 37 Comaposada, J.; Gou, P.; Arnau, J The effect of sodium chloride content and temperature on pork meat isotherms Meat Science 2000, 55, 291–295 38 Lioutas, T.S.; Bechtel, P.J.; Steinberg, M.P Desorption and adsorption isotherms of meat-salt mixtures Journal of Agricultural and Food Chemistry 1984, 32, 1382–1385 39 Økland, H.M.W.; Stoknes, I.S.; Remme, J.F.; Kjerstad, M.; Synnes, M Proximate composition, fatty acid and lipid class composition of the muscle from deep-sea teleosts and elasmobranchs Comparative Biochemistry and Physiology 2005, 140, 437–440 40 Pearson, A.M.; Dutson, T.R Advances in Meat Research: Meat and Poultry Microbiology; Macmillan Publishers: New York, 1986 41 Hambleton, P.; Broster, M.G.; Dennis, P.J.; Henstridge, R.; Fitzgeorge, R.; Conlan, J.W Survival of virulent Legionella pneumophila in aerosols Journal of Hygiene 1983, 90, 451–460 42 Lotter, L.P.; Leistner, L Minimal water activity for enterotoxin A production and growth of Staphylococcus aureus Applied and Environmental Microbiology 1978, 36, 377–380 43 Mossel, D.A.; van Netten, P Staphylococcus aureus and related staphylococci in food: Ecology, proliferation, toxinogenesis, control and monitoring Journal of Applied Bacteriology 1990, 19 (Suppl.), 123–145 44 Jay, J.M Modern Food Microbiology, 5th Ed; Aspen: New York, 1998 45 Rodriguez, M.; Nunez, F.; Cordoba, J.J.; Bermudez, E.; Asensio, M.A Gram-positive Catalase-positive cocci from dry cured View publication stats 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 713 Iberian ham and their enterotoxigenic potential Applied and Environmental Microbiology 1996, 62, 1897–1902 Bennani, L.; Faid, M.; Bouseta, A Experimental manufacturing of kaddid, a salted dried meat product: Control of the microorganisms European Food Research and Technology 2000, 11, 153–157 Atapattu, R.; Samarajeewa, U Fungi associated with dried fish in Sri Lanka Mycopathologia 1990, 111 (11), 55–59 Rahman, M.S.; Salman, Z.; Kadim, T.K.; Mothershaw, A.; Al-Ruzeiki, M.H.; Guizani, N.; Mahgoub, O.; Ali, A Microbial and physico-chemical characteristics of dried meat processed by different methods International Journal of Food Engineering 2005, 1, 1–14 Renerre, M.; Labas, R Biochemical factors influencing metmyoglobin formation in beef muscles Meat Science 1987, 19, 151–165 Faustman, C.; Yin, M.C.; Nadeau, D.B Color stability, lipid stability, and nutrient composition of red and white veal Journal of Food Science 1992, 57, 302–305 Postnikova, G.B.; Tselikova, S.V.; Kolaeva, S.G.; Solomonov, N.G Myoglobin content in skeletal muscles of hibernating ground squirrels rises in autumn and winter Comparative Biochemistry and Physiology, Part B 1999, 124, 35–37 Livingston, D.J.; Brown, W.D The chemistry of myoglobin and its reactions Food Technology 1981, 25, 244–252 O’Grady, M.N.; Monahan, F.J.; Brunton, N.P Oxymyoglobin oxidation in bovine muscle-mechanistic studies Journal of Food Science 2001, 66, 386–391 Pacheco-Aguilar, R.; Lugo-Sanchez, M.E.; Robles-Burgueno, M.R Postmortem biochemical characteristic of Monterey sardine muscle stored at 0C Journal of Food Science 2000, 65, 40–47 Haard, N.F Biochemistry and chemistry of color and color change in seafoods In Advances in Seafood Biochemistry; Flick, G.J., Martin, R.E., Eds.; Technomic Publishing Co.: New York, 1992, 305–360 Chen, H.H Effect of cold storage on the stability of chub and horse mackerel myoglobins Journal of Food Science 2003, 68, 1416–1419 McMinn, W.A.M.; Magee, T.R Physical characteristic of dehydrated potatoes—Part II Journal of Food Engineering 1997, 33, 49–55 Okos, M.R.; Narishman, G.; Singh, R.K.; Weitnauer, A.C Handbook of Food Engineering; Marcel Dekker: New York, 1992 Lawrie, R.A The storage and preservation of meat II Moisture control In Lawrie’s Meat Science, sixth edition; Lawrie, R A., Ed.; Woodhead Publishing: Cambridge, England, 1988; 178–199 Lewicki, P.P Effect of pre-drying treatment, drying and rehydration on plant tissue properties: A review International Journal of Food Properties 1998, 1, 1–22 McMinn, W.A.M.; Magee, T.R.A Quality and physical structure of dehydrated starch based system Drying Technology 1997, 15, 49–55 Steffe, J.R.; Singh, R.P Note of volumetric reduction of short grain rice during drying Cereal Chemistry 1980, 57, 148–150 Fan, L.T.; Chun, P.S.; Schellenberger, I.A Volume increase of kernels of corn and sorghum accompanying absorption of liquid water Biotechnology and Bioengineering 1962, 4, 311–322  ... 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS FIG The relationship between the moisture content and aerobic plate count of dried shark meat samples contained about 74 and. .. dissolution of major components of the system 709 Downloaded By: [sultan qaboos university] At: 06:12 14 May 2008 EFFECTS OF SALTING AND DRYING ON SHARK MEAT QUALITY CHARACTERISTICS A large number of. .. effect of two drying methods (sun and convection air) used alone or in combination of one salting method (brine or dry salting) on the microbiology, chemical composition, rehydration ratio, and