Journal of Food Science Volume 74 Issue 2 2009 - S. Sathivel; H. Yin; W. Prinyawiwatkul; J.M. King -- Comparisons of Chemical and Physical Properties of Catfish

E:FoodEngineering&PhysicalProperties

JFS E: Food Engineering and Physical Properties

Comparisons of Chemical and PhysicalProperties of Catfish Oils Prepared fromDifferent Extracting ProcessesS. SATHIVEL, H. YIN, W. PRINYAWIWATKUL, AND J.M. KING

ABSTRACT: Four different catfish oil extraction processes were used to extract oil from catfish viscera: processCF1 involved a mixture of ground catfish viscera and water, no heat treatment, and centrifugation; process CF2involved ground catfish viscera (no added water), heat treatment, and centrifugation; process CF3 involved a mix-ture of ground catfish viscera and water, heat treatment, and centrifugation; process CF4 involved ground catfishviscera, enzymatic hydrolysis, and centrifugation. Chemical and physical properties of the resulting of catfish oilswere evaluated. The CF4 process recovered significantly higher amounts of crude oil from catfish viscera than theother 3 extraction methods. The CF4 oil contained a higher percent of free fatty acid and peroxide values than CF1,CF2, and CF3 oils. Oleic acid in catfish oil was the predominant fatty acid accounting for about 50% of total fattyacids. Weight loss of oils increased with increasing temperatures between 250 and 500 C. All the catfish oil sam-ples melted around 32 C regardless of the extraction methods. The flow behavior index of all the oil samples wasless than 1, which indicated that the catfish oils exhibited non-Newtonian fluid behavior. The apparent viscosity at5 and 0 C was significantly higher (P < 0.05) than those at 5, 10, 15, 20, 25, and 30 C. The average magnitude ofactivation energy for apparent viscosity of the oil was higher for CF2 than CF1, CF3, and CF4.

Keywords: catfish oil, extraction methods, rheological properties, thermal properties

Introduction

Viscera from Channel catfish (Ictalurus punctatus) is an abun-dant and underutilized by-product that can be used as aunique lipid source. Channel catfish is the 4th-most popular fishproduct consumed in the United States. The 4 major commercialcatfish producing states in the United States are Alabama, Arkansas,Louisiana, and Mississippi. In 2005, these states produced over272000 metric tons of catfish with a stable monthly production ofabout 22700 tons (NASS 2006). The by-products of catfish process-ing consists of heads, frames, skin, and viscera, which often ends upin landfills or rendering plants. The yield of catfish when processedas whole fillets is around 45%, generating about 55% waste. The av-erage weight of viscera is about 265 g, which is about 10% by weightof a live whole catfish. Much of the oil in the catfish is found in theviscera, which contains approximately 33% lipid (Sathivel 2001).The viscera can be used for recovering of catfish oil that could beconverted into edible oil or biodiesel products.

Extracting oil from viscera may add value to catfish viscera,which is currently a processing waste. For the last 2 decades, inter-est in dietary effects of marine omega-3 fatty acids has increasedbecause they play a major role in human health (Kronhout andothers 1985). Natural fish oils have been claimed to help main-tain heart and vascular health in humans (Haglund and others1998). Producing and purifying catfish oil from catfish viscera forthe growing fish oil market can benefit the catfish industry. Smallfish oil processors and entrepreneurs are interested in establishingsmall scale, cost effective oil extraction, clarification, and stabiliza-

MS 20080545 Submitted 6/21/2008, Accepted 11/14/2008. Authors are withthe Dept. of Food Science, Louisiana State Univ. Agricultural Center, BatonRouge, LA 70803-4300, U.S.A. Direct inquiries to author Sathivel (E-mail:[email protected]).

tion methods for catfish oil destined for human consumption. Fishoil can be extracted using a number of methods including render-ing, enzymatic hydrolysis, chemical extraction, mechanical press-ing, and use of centrifugal force. However, information related toquality of fish oil prepared from the different extraction methods isnot readily available. The unpurified catfish oil contains free fattyacids, primary oxidation products, minerals, pigments, moisture,phospholipids, and insoluble impurities that reduce the oil qual-ity. The amount of these impurities present in the oil may dependon the fish oil extraction methods. The longer these componentsremain in the oil, the greater their negative effects on oil quality.Finding a suitable method to extract oil from catfish viscera mayreduce some of the impurities in the oil and thus may cut downthe multiple fish oil purification steps to 1 or 2 steps. The amountof impurities present in the oil influences the rheological and ther-mal properties of fish oil (Sathivel and others 2008a, 2008b). Knowl-edge of thermal, rheological, and oxidation properties of the catfishoil is essential for the design of purifying processes, the analysis ofproduction cost, and the final quality evaluation. The objective ofstudy was to evaluate the effects of different extraction processeson chemical and physical properties of catfish oils.

Materials and Methods

Catfish oil productionCatfish viscera was obtained from a local seafood store in

Baton Rouge (La., U.S.A.), and stored at 40 C until further pro-cessed. The viscera was thawed overnight at 4 C and groundusing a Hobart grinder (K5SS, Hobart Corp., Troy, Ohio, U.S.A.)through a 7-cm diameter plate having 12-mm diameter openings,and subsequently ground through a plate with 6-mm diameteropenings. The ground viscera was used to produce catfish oil by the

E70 JOURNAL OF FOOD SCIENCEVol. 74, Nr. 2, 2009 C 2009 Institute of Food Technologists Rdoi: 10.1111/j.1750-3841.2009.01050.xFurther reproduction without permission is prohibited

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Chemical and physical properties of catfish oils . . .

following 4 different processing methods: (1) ground catfish vis-cera was added with distilled water (water: ground viscera, 1:1 v/w)and homogenized in a Waring blender (Waring Products Div., NewHartford, Conn., U.S.A.) for 2 min. The homogenized mixture wascentrifuged at 7520 g for 30 min at 23 C and catfish oil separated;(2) ground catfish viscera (no added water) was heated at 75 Cfor 30 min, centrifuged at 7520 g for 30 min at 23 C and thecatfish oil separated; (3) ground catfish viscera was added with dis-tilled water (water: ground viscera, 1:1 v/w) and homogenized. Thehomogenized mixture was heated at 75 C for 30 min, centrifuged at7520 g for 30 min at 23 C and the catfish oil removed; (4) groundcatfish viscera was enzymatically hydrolyzed (no added water),centrifuged, and the visceral oil separated. Hydrolysis conditionswere similar to those documented by Hoyle and Merritt (1994).The alcalase enzyme with the activity of 2.4 AU/g (Anson units pergram) (Novo Nordisk, Franklinton, N.C., U.S.A.) was added to theground catfish viscera at 0.5% w/w. The mixture was stirred for75 min at 50 C and then the temperature was increased to above85 C for 15 min to inactivate the enzyme. The hydrolysate was cen-trifuged at 7520 g for 30 min and the catfish oil removed. The re-sulting unrefined catfish oils were collected and stored at 70 Cuntil analyzed. The oil extracted from methods 1, 2, 3, and 4 wasreferred to as CF1, CF2, CF3, and CF4, respectively, throughout thisstudy.

Proximate composition of catfish visceraCatfish viscera samples were analyzed in triplicate for moisture

and ash contents using the AOAC standard methods 930.15 and942.05, respectively (AOAC 1999). Fat content was determined us-ing dichloromethyl ether as solvent in an automated ASE-200 fatextractor (Dionex Corp., Sunnyvale, Calif., U.S.A.). Nitrogen contentwas determined in triplicate using the Leco FP-2000 Nitrogen An-alyzer (LECO Corp., Mich., U.S.A.). The protein content was calcu-lated as percent nitrogen times 6.25.

Analysis of PV, FFA, and fatty acidcomposition of catfish oil

The peroxide value (PV) of the catfish oil samples was mea-sured by titration according to AOAC (1999). Free fatty acids (FFA)were determined using the titration procedure according to AOCS(1998). Fatty acid composition of catfish oils was determined at thePOS Pilot Plant Corp Lab., Saskatchewan, Canada. The fatty acidmethyl esters (FAME) were prepared according to the AOAC proce-dure 969.33 (AOAC 1999) and fatty acid in the catfish oil sampleswas determined according to AOAC procedure 996.06 (AOAC 1999).Triplicate determinations were performed.

Analysis of mineral, tocopherols, insolubleimpurities, and moisture content of catfish oils

Mineral, tocopherols, insoluble impurities, and moisture con-tent of oil samples were determined at the POS Pilot Plant CorpLab. Mineral content of catfish oil samples was determined ac-cording to AOCS Ca17-01 and AOCS Ca 20-99 (1998) and reportedas parts per million. Levels of tocopherols in the oil samples (al-pha, beta, gamma, and delta) were determined according to AOCSCe8-89 (1998) and reported as milligrams per gram of oil. Moisturecontent of catfish oil samples was measured using the Karl Fishertitration method (AOAC Method 984.20 (1999). Insoluble impuri-ties of catfish oil samples were measured according to AOCS Ca-46 (1998). Moisture and volatile matters were removed from the oilsample according to AOCS Ca 2b-38 (1998). The oil residue was dis-solved in kerosene and filtered through a crucible. The remainingkerosene in the crucible was removed by washing with petroleum.

The crucible was dried at 101 C until constant weight was ob-tained. Insoluble impurities value in the oil was calculated as: insol-uble impurities (%) = [gain in mass of crucible/mass of the residue] 100 triplicate determinations were performed.

Thermal properties of catfish oilsThermal stability of the unpurified catfish oil was analyzed us-

ing the Thermogravimetric Analyzer (Model Q50, TA Instruments,New Castle, Del., U.S.A.). Approximately 1 to 1.2 mg of the oil sam-ple were added to an aluminum pan, the pan was placed in thefurnace, and the exact sample weight was determined. The samplewas heated to 700 C under air atmosphere at an increasing rate of5 C/min. Sample weight differences were automatically recordedevery 0.5 s. Collected data were analyzed and plotted using the TAUniversal Analyzer Software (TA Instruments). The graph was nor-malized based on the sample weight basis.

The differential scanning calorimetric experiments were con-ducted using a differential scanning calorimetery (Model DSC 2920,TA Instruments). Approximately 0.5 to 1 mg of the unpurified cat-fish oil sample was placed in an aluminum sample vessel. An emptyaluminum vessel was placed on the reference platform. To deter-mine the phase transition of the unpurified catfish oil sample, alinear heating rate of 5 C/min over a temperature range of 75 to100 C was used. The thermogram peak was used to provide an es-timate of enthalpy (H). The thermogram peak points of the rep-resentative of the thermogram were used to determine the meltingpoints.

Rheological properties of catfish oilsRheological properties of the unpurified catfish oil samples were

measured in triplicate using an AR 2000 Rheometer (TA Instru-ments) fitted with a 2 cone-angle plate geometry (acrylic plateswith a 20-mm diameter, having a 200 m gap between the 2 plates).Each sample was placed in the temperature-controlled parallelplate and allowed to equilibrate to 5, 0, 5, 10, 15, 20, 25, or 30 C.The shear stress was measured at 5, 0, 5, 10, 15, 20, 25, and 30 Cat varying shear rates from 0 to 500/s. The mean values of triplicatesamples were reported.

The power law (Eq. 1) was used to analyze the flow behavior in-dex of the unpurified catfish oil samples.

= K n (1)

where = shear stress (Pa.s), = shear rate (s1), K = consistencyindex (Pa.sn), and n = flow behavior index. The logarithms weretaken on both sides of Eq. 1, and a plot of log against log wasconstructed. The resulting straight line yielded the magnitude oflog K (that is, intercept) and n (that is, slope).

The effect of temperature on apparent viscosity was describedthrough the Arrhenius relationship as described in Eq. 2 (Rao 1999).

k = Ae(Ea/RT) (2)

where k is the reaction rate constant, A is the frequency factor, Ea isthe activation energy (J/mol), R is the gas constant (8.314 J/mol/K),and T is the temperature (K).

Apparent viscosity of the unpurified catfish oil samples was mea-sured at 5, 0, 5, 10, 15, 20, 25, and 30 C at a shear rate of 500/susing the AR 2000 Rheometer. A plot of ln apparent viscosity com-pared with 1/T (that is, 1/absolute temperature) was constructedfor each catfish oil sample. The slope of the straight line, the inter-cept and the regression coefficient were calculated using the trendline of the plot. The magnitude of Ea was calculated as the slope of

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the plot multiply by the gas constant, and A was an exponential ofthe intercept.

Statistical analysisMeans and standard deviations of the data were reported. Anal-

ysis of variance (ANOVA) comparison was performed at the signif-icant level of P < 0.05 using SAS version 8.2 (SAS 2002). Tukeysstudentized range tests were performed to locate differencesamong the different treatments.

Results and Discussion

Yield, PV, FFA, and fatty acid compositionof catfish fish oil

The catfish viscera contained 60.9% 3.8% moisture, 10.2% 1.5% protein, 0.8% 0.01% ash, and 27.9% 3.8% fat. The fat con-tent of catfish viscera from our study was higher than that reportedby Belal and Assem (1995). CF4 process recovered a significantlyhigher amount of crude oil (14.3%) from catfish viscera than didCF1, CF2, and CF3 (Table 1). CF1 had lowest oil recovery (5.9%)while CF2 and CF3 had similar oil yield (9% to 10.8%).

The CF4 oil had higher percent FFA, while CF1 and CF3 had low-est percent FFA. Acceptable levels of FFA content in refined fish oilranges between 1.8% and 3.5% (Young 1986a). All catfish oils hadan acceptable level of FFA, except CF4, which had a slightly higherpercent FFA than recommended. Young (1986a) reported that ap-propriate fish oil processing conditions may reduce FFA up to 50%.The PV value for the oil samples indicated the amount of primaryoxidation products produced during the oil extraction. Enzymaticextraction produced a significant amount of PV than that of theother extraction methods. The enzymatic extraction process (CF4)recovered the highest amount of crude oil from catfish viscera com-pared to other extraction methods but the oil had higher FFA andPV values. CF1 process recovered a lower amount of crude oil fromcatfish viscera but the oil had lower FFA (except for CF3) and PV val-ues than did other oils. This demonstrated that extraction methodsaffected recovery of the crude oil from catfish viscera, and the FFAand PV values of the oil.

The fatty acid compositions of CF1, CF2, CF3, and CF4 are givenin Table 2. Saturated fatty acids from CF1, CF2, CF3, and CF4 oilsaccounted for 219.3, 231.6, 232.7, and 232.8 (milligrams per gramof oil), respectively. Oleic acid was the predominant fatty acid incatfish oil accounting for about 50% of the total fatty acids. Totalpolyunsaturated fatty acid present in catfish oil was slightly lowerthan total saturated fatty acid and amounted to 183.1, 177.8, 180.4,and 179.4 (milligrams per gram of oil) for CF1, CF2, CF3, and CF4,respectively. Among unsaturated fatty acids, oleic acid and linoleicacid were predominant fatty acids accounting for almost 86% of allunsaturated fatty acids. The CF1, CF2, CF3, and CF4 contained 1.9,2.1, 1.8, and 1.7 mg of DHA/g of oil, respectively. All oil samples hadslightly lower EPA content than DHA in the samples. The polyun-saturated fatty acids are considered to be of major importance interms of human health. Total omega-3 fatty acids in the CF1, CF2,

Table 1 --- Yield, FFA, and PV of catfish oil from different extraction methods.a

CF1 CF2 CF3 CF4

Yield (%) 5.9 1.3c 10.8 0.3b 9.0 1.0b 14.3 1.4aFFA (%) 1.17 0.06c 2.8 0.04b 1.04 0.01c 3.55 0.09aPV (meq/kg oil) 4.9 0.46d 11.4 0.18b 7.2 0.5c 36.12 0.18aaValues are means SD of triplicate determinations. abcdMeans with the same letters in each row are not significantly different (P > 0.05). CF1 = process involveda mixture of ground catfish viscera and water, no heat treatment, and centrifugation; CF2 = process involved ground catfish viscera (no added water), heattreatment, and centrifugation; CF3 = process involved a mixture of ground catfish viscera and water, heat treatment, and centrifugation; CF4 = process involvedground catfish viscera, enzymatic hydrolysis, and centrifugation.

CF3, and CF4 were 13.6, 13.8, 14, and 13.4 (milligrams per gram ofoil), respectively. The predominance of omega-6 and omega-9 incatfish oils may have been attributed to the feed fed to the catfish,especially if it was made from soy products. Diet has a major ef-fect on FA composition of lipid (Satoh and others 1989). All the oilsamples had similar fatty acids composition, which demonstratedthat extraction procedures had no affect on fatty acid composition.

Mineral, tocopherols, insoluble impurities,and moisture content of catfish oils

P, Na, Mg, Ca, and K were abundant minerals found in thecatfish oil samples (Table 3). Phosphorus levels ranged from179 ppm in CF2 to 2.76 ppm in CF3. The phosphorus present in cat-fish oil samples may be attributed to the phospholipids in the oilsample and calciumphosphate complexes (Young 1986a). All oil

Table 2 --- Fatty acid composition of catfish oil (mg/g of oil)from different extraction methods.a

Fatty acids CF1 CF2 CF3 CF4

C14 (myristic) 7.6 7.6 7.8 7.7C14:1n5 (tetradecenoic) 0.3 0.3 0.3 0.3C15 (pentadecanoic) 0.7 0.8 0.8 0.9C16 (palmitic) 149.3 156.8 159.5 159.2C16:1n7 (palmitoleic) 25.3 24.4 25.5 25.4C17 (margaric) 1.6 1.7 1.8 1.8C18 (stearic) 57.5 62.3 60.3 60.8C18:1n9 (oleic) 455.3 446.7 446.9 446.4C18:1 (octadecenoic) 8.7 6.3 7.8 6.8C18:2n6 (linoleic) 139.9 134.6 138.9 137.6C18:2 (cla isomers) 0.3 0.4 0.3 0.4C18:3n6 (gamma-linolenic) 2.9 3.0 2.7 3.1C18:3n3 (alpha-linolenic) 8.1 8.0 8.5 8.2C18:4n3 (octadecatetraenoic) 0.4 0.4 0.4 0.4C20 (arachidic) 1.7 1.8 1.8 1.8C20:1n9 (eicosenoic) 19.4 19.3 19.1 18.9C20:2n6 (eicosadienoic) 9.6 9.3 9.3 9.2C20:3n6 (homo-g-linolenic) 8.0 7.9 7.5 7.7C20:4n6 (arachidonic) 3.9 4.4 3.4 3.7C20:3n3 (meads acid) 0.4 0.3 0.4 0.4C20:4n3 (eicosatetraenoic) 0.5 0.5 0.5 0.5C20:5n3 (eicosapentaenoic) 1.1 1.0 1.1 1.0C22 (behenic) 0.7 0.7 0.7 0.7C22:1n9 (erucic) 0.7 0.8 0.7 0.7C22:2n6 (docosadienoic) 1.9 1.8 1.8 1.8C22:4n6 (docosatetraenoic) 0.9 0.7 0.7 0.8C22:5n6 (docosapentaenoic) 2.0 1.9 1.7 1.7C22:5n3 (docosapentaenoic) 1.3 1.4 1.3 1.3C22:6n3 (docosahexaenoic) 1.9 2.1 1.8 1.7C24:1n9 (nervonic) 0.3 0.3 0.3 0.3Others 16.1 16.3 15.6 15.4Total fatty acids 928.7 923.7 929.4 926.5Saturates 219.3 231.6 232.7 232.8Monounsaturates 510.2 498.0 500.6 498.9Polyunsaturates 183.1 177.8 180.4 179.4Omega 3 13.6 13.8 14.0 13.4Omega 6 169.1 163.6 166.1 165.6Omega 9 475.8 467.0 467.0 466.4aValues are means of triplicates determinations. See Table 1 for brief descriptionof CF1, CF2, CF3, and CF4.

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Table 3 --- Mineral content of catfish oil from different ex-traction methods.a

Mineral (ppm) CF1 CF2 CF3 CF4

Aluminum



This reaction is usually identified by an increase in the initial sam-ple mass (Hassel 1976). In this study, no weight gain was observedin the TG curves for all catfish oils that were analyzed under airatmosphere, indicating that thermal decomposition of catfish oilswas not related to oxygen absorption. The weight loss between 250and 550C was 88.8%, 87.3%, 86.4%, and 84.6% for CF3, CF1, CF4,and CF2, respectively. Sathivel and others (2003a) reported that theweight loss of fish oils due to thermal decomposition was higher inrefined oils than crude or unrefined oils. The higher thermal de-composition implies higher quality of oil. Unrefined oils containimpurities such as phospholipids, complexed metals and minerals,free fatty acids, and peroxides and their breakdown products, thatare highly interactive with the oil (Wiedermann 1981). This studydemonstrated the extraction process affected the amount of im-purities and mineral contents in the oil samples. The presence ofimpurities reduces effectiveness of heat transfer to unrefined oils,and, therefore, resulting in less energy available to evaporate thevolatiles (Wesolowski and Erecinska 1998). Based on this study, theTG analysis can be used to determine the quality of fish oils.

Figure 2 shows typical melting curves of CF1, CF2, CF3, and CF4catfish oils. The melting points of catfish oil ranged from 32.7 to9.9 C for CF1, 32.7 to 11.4 C for CF2, 33 to 11.6 C for CF3,and 33.4 to 12 C for CF4. This indicated that extraction proce-dures affected melting points of crude oils from catfish viscera. Fiveendothermic peaks, considered as melting points, were observedin the DSC thermogram for all unpurified catfish oils (Figure 2).The melting point of the unpurified catfish oil was relatively narrowcompared to the reported melting point range of 69.6 to 0.36 C,64.7 to 20.8 C, and 64.5 to 14.86 C for red salmon andpink salmon oils (Sathivel 2005), and pollock oil (Sathivel and

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-50 -40 -30 -20 -10 0 10 20 30 40 50

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CF1.001 CF2.001 CF3.001 CF4.001

Exo Up Universal V4.3A TA Instruments

Figure 2 --- DSC thermogram of catfish oil from different extraction methods. See Table 1 for brief description of CF1,CF2, CF3, and CF4.

others 2008a), respectively. The negative melting points of catfishoil may be attributed to triacylglycerol, which contained unsat-urated fatty acids (Tan and Che Man 2002). The 1st peak at themelting point of 32 C may be attributed to the presence ofpolyunsaturated fatty acids (Sathivel 2001). Oil samples with ahigher degree of unsaturated fatty acids melt at lower temperatures,whereas those with a higher degree of saturated fatty acids melt athigher temperatures. The 2nd, 3rd, and 4th peaks appeared around22 and 11 C; this may be attributed to the presence of linolenicacid (C18:3) and linoleic acid (C18:2), whose melting points rangefrom 4 to 21 C (Sathivel 2001). The 3rd peak appeared closerto 0 C, which might be attributed to the moisture present in thesample (Berjak and others 1992; Connor and Bonner 2001). Physi-cal properties of triglycerides are more complex than those of theindividual fatty acids because they contain 3 fatty acid groups. Inthis study, we did not analyze the triglyceride composition of thecatfish oil. However, the trends in melting points observed for cat-fish oils would likely reflect its fatty acid composition. Fatty acidsfound in catfish visceral oil were C14:0, C16:0, C16:1, C18:0, C18:0,C18:1, C18:2, C18:3, C20:0, C20:1, C20:2, C20:4, and C22:6, and thecatfish visceral oil contained more than 77% of total unsaturatedfatty acids (Table 2). All 5 peaks for the unpurified catfish oils werenot sharp; this might be attributed to the presence of impurities,such as phospholipids, ketones, and other materials in the unpuri-fied fish oil (Sathivel 2005). A similar DSC thermogram was reportedfor pollock oil by Sathivel and others (2008a). Those impurities meltuncharacteristically compared to pure fatty acids; therefore, sharppeaks were not observed for the oil. Sathivel (2001) reported thatthe DSC thermograms of purified catfish oil showed sharper andnarrower peaks than unpurified fish oil.


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Table 5 --- Apparent viscosity (Pa.s) at different temperatures for catfish oils.

Temperature (C) CF1 CF2 CF3 CF4

5 0.64 0.02aD 2.70 0.01aA 1.55 0.01aB 0.93 0.07aC0 0.35 0.05bD 2.15 0.06bA 1.09 0.02bB 0.58 0.01bC5 0.16 0.00cD 0.32 0.01cB 0.78 0.01cA 0.20 0.02cC10 0.12 0.00cdB 0.12 0.00dB 0.23 0.06dA 0.12 0.00dB15 0.10 0.00deB 0.10 0.00dB 0.14 0.00eA 0.09 0.00dC20 0.08 0.00deB 0.08 0.00dB 0.11 0.00efA 0.08 0.00dC25 0.07 0.00deB 0.07 0.00dB 0.08 0.00efA 0.07 0.00dC30 0.06 0.00eA 0.06 0.00dA 0.06 0.00fA 0.06 0.00dAValues are means SD of triplicate determinations. ABCDMeans with the same letters in each row are not significantly different (P > 0.05). abcdefMeans with thesame letters in each column are not significantly different (P > 0.05). See Table 1 for brief description of CF1, CF2, CF3, and CF4.

Table 6 --- Flow behavior index (n) at different temperatures for catfish oils.


5 0.84 0.01abA 0.71 0.01bcB 0.80 0.04abAB 0.73 0.03bB0 0.79 0.01bcAB 0.61 0.12cB 0.74 0.07abAB 0.80 0.01abA5 0.75 0.07cA 0.78 0.13abcA 0.58 0.23bA 0.80 0.15abA10 0.90 0.01aA 0.90 0.00aA 0.81 0.08abA 0.91 0.01aA15 0.89 0.01aA 0.89 0.00abA 0.83 0.01abB 0.89 0.00aA20 0.87 0.00aA 0.88 0.00abA 0.78 0.01abB 0.87 0.00abA25 0.86 0.00abA 0.85 0.01abA 0.80 0.01abB 0.85 0.01abA30 0.84 0.01abAB 0.84 0.00abAB 0.85 0.00aA 0.83 0.00abBValues are means SD of triplicate determinations. ABMeans with the same letters in each row are not significantly different (P > 0.05). abcMeans with the sameletters in each column are not significantly different (P > 0.05). See Table 1 for brief description of CF1, CF2, CF3, and CF4.

Table 7 --- Consistency index (K) at different temperatures for catfish oils.


5 1.44 0.04aC 12.35 0.76aA 4.39 0.91aB 3.67 0.42aB0 0.92 0.06bC 7.80 0.04bA 4.42 1.85aAB 1.58 0.05bBC5 0.68 0.01cB 1.43 0.43cB 3.70 1.06aA 0.62 0.36cB10 0.20 0.01dA 0.21 0.00dA 0.68 0.49bA 0.19 0.01cA15 0.17 0.01dB 0.18 0.00dB 0.34 0.01bA 0.16 0.00cB20 0.15 0.00dB 0.15 0.00dB 0.35 0.01bA 0.15 0.00cB25 0.14 0.00dB 0.15 0.01dB 0.23 0.02bA 0.14 0.00cB30 0.13 0.00dAB 0.13 0.00dAB 0.13 0.00bA 0.13 0.00cBValues are means SD of triplicate determinations. ABCMeans with the same letters in each row are not significantly different (P > 0.05). abcdMeans with the sameletters in column row are not significantly different (P > 0.05). See Table 1 for brief description of CF1, CF2, CF3, and CF4.

Table 8 --- Activation energy (Ea) and frequency factor ()for different catfish oil extraction methods.

Sample Ea (J/mol)

CF1 5.4E-09 3.8E-10a 45955.64 29.39dCF2 8.1E-16 6.1E-17c 78869.38 187.01aCF3 1.1E-13 2.9E-15c 67587.28 97.1bCF4 2.1E-11 7.5E-12b 53941.23 928.7cValues are means SD of triplicate determinations. abcMeans with the sameletters in each column are not significantly different (P > 0.05). See Table 1 forbrief description of CF1, CF2, CF3, and CF4.

Rheological propertiesApparent viscosity for all of catfish oils increased significantly

(P < 0.05) with decreased temperature (Table 5). CF2 had higherapparent viscosity (P < 0.05) at 5 to 0 C than CF1, CF3, andCF4 samples. Wiedermann (1981) reported that unpurified fish oilcontained a large amount of impurities including Mg, Ca, Fe, P,free fatty acids, and peroxides, insoluble impurities, and moisture,which were present in catfish oil; these impurities are highly in-teractive with the oil, while Sathivel and others (2003b) reportedchanges of catfish oil rheological properties during the purifica-tion processes. The interface between impurities and oil may beattributed to the development of an aggregated colloidal dispersionsystem, which might be a reason for different apparent viscosity ex-hibited in the oil samples at lower temperatures.

The power law parameters for the catfish oils at 5, 0, 5, 10, 15,20, 25, and 30 C are given in Table 6 and 7. The flow behavior index(n) of the catfish oil samples ranged from 0.58 to 0.91. The flow be-havior index (n) of the oil samples was lower than 1 indicating thatthe oils were non-Newtonian fluids. The n-value for all the sam-ples at 5 to 5 C behaved as pseudoplastic fluids regardless of thecatfish oil extraction methods (Table 5). The consistency index (K )value for the catfish oils was higher at lower temperatures. CF2 hadhigher K values at 5 and 0 C than the CF1, CF3, and CF4.

The Arrhenius equation (Eq. 2) was employed to calculate theaverage magnitude of activation energy of the catfish oil. CF2 had ahigher magnitude of Ea than that CF1, CF3, and CF4 (Table 8). TheEa indicates the energy barrier that must be overcome before theelementary flow process can occur (Rao 1999). This study showedthat the magnitude of the apparent viscosity of the catfish oil wasgreatly influenced by temperatures, regardless of the oil extractionmethods.

Conclusions

This study demonstrated the effect of the extraction meth-ods on chemical, nutritional, thermal, and rheologicalproperties of catfish oil, which is useful for designing thepurification process of the oil. The CF4 oil had higher percentFFA and PV value than other oil samples. All oil samples hadslightly lower EPA content than DHA. CF2 and CF4 had higher iron

Vol. 74, Nr. 2, 2009JOURNAL OF FOOD SCIENCE E75



and copper contents. All oil samples had slightly different thermalproperties. The catfish oils exhibited non-Newtonian fluid behav-ior at lower temperature regardless of extraction methods. Theapparent viscosity of all oil samples was significantly increasedwith decreased temperature. Information on thermal, rheological,and oxidation properties from this study can be used for the designof a purification process to produce catfish oil destined for humanconsumption.

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Documents

Journal of Food Science Volume 74 Issue 2 2009 - S. Sathivel; H. Yin; W. Prinyawiwatkul; J.M. King -- Comparisons of Chemical and Physical Properties of Catfish