CAPILLARY EXTRUSION VISCOMETER FOR THE VISCOSITY MEASUREMENT OF FISH PROTEIN PASTE

Transcription

1 CAPILLARY EXTRUSION VISCOMETER FOR THE VISCOSITY MEASUREMENT OF FISH PROTEIN PASTE BYUNG Y. KIM 1,3 and JAE W. PARK 2 1 Department of Food Science Kyung Hee University Yongin, South Korea 2 Department of Food Science and Technology and Oregon State University Seafood Laboratory Oregon State University Astoria, OR Accepted for Publication May 24, 2007 ABSTRACT To overcome various limitations of conventional viscometers in measuring salted or unsalted surimi paste, a capillary extrusion viscometer was developed. The viscosity of surimi paste was measured as a function of moisture content (MC) (75 80%), salt content (2 4%) and liquid egg white (LEW) content (2 4%). As moisture, salt and LEW contents increased, viscosity gradually decreased. The viscosity values, as affected by MCs, showed a highly negative relationship with fracture properties of surimi gel, especially shear stress from the torsion test, indicating that MC is linearly correlated to the strength of gels at fracture. This easy and quick viscosity measurement can effectively facilitate the production control of comminuted muscle foods, including surimi paste. PRACTICAL APPLICATIONS There had been a difficulty to measure the exact viscosity of comminuted muscle food pastes when conventional viscometers were used. This was due to the non-linearity between dilution rates and viscosity of muscle paste, or limited range of shear rate during viscosity measurement. New developed small capillary extrusion viscometer can measure a wide range of comminuted muscle paste viscosity. When using this capillary viscometer, flow behavior of non- Newtonian surimi paste and other comminuted muscle paste can be well defined. 3 Corresponding author. TEL: ; FAX: ; bykim@khu.ac.kr 536 Journal of Food Quality 31 (2008) The Author(s) Journal compilation 2008 Wiley Periodicals, Inc.

2 EXTRUSION VISCOMETER FOR SURIMI PASTE 537 INTRODUCTION Viscosity often determines the flow of products and controls productivity. However, because of the nature of fish muscle proteins (surimi) that easily aggregate upon mixing with salt (Lanier 1986), viscosity is not properly measured using a conventional rotational viscometer. In addition, the dilution factor of surimi paste without salt does not show a linear relationship with viscosity values. Quality control to measure the production flow is not easily maintained. Consequently, there exists a significant need for a quick and an easy method to determine the viscosity of fish muscle proteins. Rheological information obtained from surimi paste represents the gelation properties of fish proteins, in which the apparent viscosity of fish protein correlates with the degree of protein denaturation (Matsumoto 1980). According to Esturk (2003), moisture content (MC) had a good correlation with the rheological properties, such as the dynamic storage modulus, of Pacific whiting surimi. The objectives of this study were to develop a capillary extrusion viscometer to measure the viscosity of fish protein paste, and to estimate the fracture properties of surimi gels using the measured viscosity. MATERIALS AND METHODS Materials High-grade (FA) Alaska pollock (Theragra chalcogramma) surimi, containing 4% sugar, 5% sorbitol and 0.25% polyphosphate as cryoprotectants, was obtained from local manufacturers. Liquid egg white (LEW) was prepared by breaking fresh eggs obtained from a local store. Measurements of Viscosity and Dynamic Properties of Surimi Paste When salt is added to the surimi paste, salt-soluble proteins are solubilized and start to interact with each other showing a setting phenomenon. In this case, traditional viscometers like a Brookfield viscometer do not measure the viscosity of salted surimi paste well because it is extremely difficult to homogenize the set gel and make its dilution even. The viscosity of the unsalted surimi pastes, as affected by various levels of water addition ( ml), was measured using a Brookfield viscometer (model DV-I+, Stoughton, MA). The viscosity of salted surimi pastes, as affected by moisture and salt contents, was also determined using a Bohlin CS-50 dynamic test (East Brunswick, NJ) using a bob (diameter = 25 mm) and cup (diameter = 27.5 mm). The maximum stress value (10 kpa) was applied

3 538 B.Y. KIM and J.W. PARK for the viscosity measurement in the dynamic rheometer. Both tests measured the shear stress values according to the shear rates given by their operational manuals. All tests were performed at 10C. Development of Capillary Extrusion Viscometer Viscosity measurements can be made directly on the paste containing surimi, salt, water and other ingredients as a quality control tool prior to thermal processing. A small capillary extrusion viscometer was thought to be a good tool for this purpose (Fig. 1). The manufactured extrusion tubes could be interchanged to adjust the internal diameter to match the viscosity range of the surimi paste being tested, but varied in length in order to account for the entrance and exit effects. The surimi sample was extruded at several different rates by decrementing the crosshead speed. At each speed, the maximum sustained force reading was obtained. The apparent viscosity at any crosshead speed is obtained by 2 η= πr ΔP 8qΔ L (1) where h is the apparent viscosity, R is the radius of the extrusion tube, DL is the difference in extrusion tube lengths, DP is the pressure difference caused FIG. 1. DESCRIPTION OF A CAPILLARY EXTRUSION VISCOMETER

4 EXTRUSION VISCOMETER FOR SURIMI PASTE 539 by force variations from using long and short tubes, respectively, and q is the volumetric flow rate. A capillary extrusion viscometer (Fig. 1) with long and short tubes was developed to attach to a texture analyzer (model TA-XT plus, Texture Technologies Corp., New York, NY). Each inner tube had the same diameter (6 mm) with the same entrance and exit design, but varied in length (10 and 30 mm). The inner tube was inserted into the cylinder (inner diameter = 38 mm; length = 152 mm). Viscosity Measurement Using a Small Capillary Extrusion Viscometer The surimi paste prepared as described later was packed into the cylinder. The surimi sample was extruded at five downward speeds of the crosshead (20, 15, 10, 5 and 1 mm/s). The maximum sustainable force readings at each speed were recorded to calculate the shear stress (Eq. 2) and shear rate (Eq. 3). τ = ( ΔP R) ( 2L ) (2) where t is the shear stress, DP is the pressure and L is the tube length. According to the Rabinowitch Mooney equation (Van Wazor et al. 1963) given for the shear rate of a non-newtonian fluid, shear rate was calculated. 3 ( dv dr)= ( 3+ b) 4 4q π R (3) { }( ) 3 b= Δlog( 4q π R ) Δlog( ΔP R 2L) (4) where (-dv/dr) is the shear rate, q is the volumetric flow rate, R is the radius and L is the tube length. Using the power law, t = C(-dv/dr)n; n (flow behavior index) and C (consistency coefficient) were obtained from the slope and y-intercept in log t and log(-dv/dr) graph, respectively (Dautant et al. 2006; Telis-Romero et al. 2006). Gel Preparation and Structural Fracture Measurement The Alaska pollock surimi was comminuted in a food processor (Hamilton Beach/Proctor-Silex, Inc., Washington, DC) with various concentrations of moisture (75~80%), salt (2~4%) or LEW (2~4%). The surimi paste was stuffed into torsion molds that gave a dumbbell-shaped geometry, and heated in a water bath (90C) for 15 min. After heating, surimi gels were removed from the torsion molds and chilled in ice water before storing overnight in a refrigerator (Hoffmann and Park 2000).

5 540 B.Y. KIM and J.W. PARK The texture properties of surimi gels in a dumbbell-shaped geometry were measured using the Hamann torsion gelometer (Gel Consultants, Inc., Raleigh, NC). The shear stress and shear strain were calculated using the torque value and angular displacement at fracture, respectively (Kim et al. 2005). Statistical Analysis The SAS statistical package was used to analyze data (version 8, SAS, Inc., Cary, NC). Least significant difference was used to determine the significant differences between mean values at P < RESULTS AND DISCUSSION Limitation of the Rotational Viscometers for Fish Protein Paste The viscosity of Alaska pollock surimi paste without salt was measured using a Brookfield rotational viscometer (Fig. 2). Viscosity decreased proportionally as water addition increased from 100 to 160 ml, but it did not decrease linearly as rotational speeds changed. The linearity between dilution mL 120mL 140mL 160mL Viscosity (poise) Speed (rpm) FIG. 2. VISCOSITY CHANGES OF UNSALTED SURIMI PASTE (100 g) WITH THE ADDITIONAL VARIOUS LEVELS OF WATER ( ml)

6 EXTRUSION VISCOMETER FOR SURIMI PASTE Shear Stress, Pa % MC 78% MC 80% MC Shear Rate, 1/s FIG. 3. VISCOSITY CHANGES OF SALTED SURIMI PASTE AT VARIOUS MOISTURE CONTENTS (MCs) USING AN OSCILLATORY DYNAMIC RHEOMETER rates and viscosity was also low. According to Sultanbawa and Li-Chan (1998), the surimi paste was diluted in a buffer and centrifuged to obtain the aliquots. However, the viscosity of these aliquots did not show any significant difference in nine different treatments, indicating that dilution did not improve the sensitivity of viscosity measurements of surimi paste. When the viscosity of surimi paste without dilution was measured using a rotational viscometer, the variation error could be significant because surimi paste cannot be homogenized without salt (Filipi and Lee 1998). The viscosity changes were measured successfully using a Bohlin dynamic rheometer. However, the results were shown only in a limited range of shear rate applied: 5/s for varied moisture concentrations (Fig. 3) and 1.6/s for varied salt concentrations (Fig. 4). This was because of the controlled movement of the cone. Determination of the Viscosity by Capillary Extrusion Viscometer Because of limited application of the two common viscosity measurement methods, a capillary extrusion viscometer was developed to measure a wide range of surimi paste viscosity. First, to determine the end effect caused by tube lengths, two different tubes (long tube length: 3 cm; short tube length: 1 cm) were used to calculate the flow behavior index (n) and consistency index (log C) (Table 1). The n values were and 0.282, while log C values ranged 3.14 and 3.60 for short and long tubes, respec-

7 542 B.Y. KIM and J.W. PARK Shear Stress, Pa % Salt 3% Salt 4% Salt Shear Rate, 1/s FIG. 4. VISCOSITY OF SURIMI PASTES MEASURED AT VARIOUS SALT CONTENTS USING AN OSCILLATORY DYNAMIC RHEOMETER The final moisture content was 78%. TABLE 1. COMPARISON OF FLOW BEHAVIOR INDEX (n) AND CONSISTENCY INDEX (LOG C) AS AFFECTED BY THE LENGTH OF THE TUBE Short tube Long tube Length (mm) Flow behavior index (n) a a Consistency index (log C) 3.60 b 3.14 b The same superscript in the same row indicates they are not different statistically (P > 0.05). tively. Because the n value was not significantly different (P < 0.05) between the long and short tubes, the long tube was then selected for use in the capillary extrusion viscometer to determine the viscosity of Alaska pollock surimi paste as a function of moisture concentration (Fig. 5), salt concentration (Fig. 6) and egg white concentration (Fig. 7). Viscosity is the slope of shear stress over shear rate, and decreased as the concentration of moisture, salt and LEW increased (Figs. 5 7). Moisture is the most significant factor affecting the viscosity changes (Filipi and Lee 1998) and rheological properties (Yoon et al. 1998) in surimi seafood products. According to Filipi and Lee (1998), the addition of preactivated iota-carrageenan in surimi paste increased the viscosity of surimi paste probably because water-soluble carrageenan absorbed the moisture. The main function of salt is to help solu-

8 EXTRUSION VISCOMETER FOR SURIMI PASTE % MC Shear Stress, Pa % MC 80% MC Shear Rate, 1/s FIG. 5. VISCOSITY OF SALTED (3%) SURIMI PASTE MEASURED AT VARIOUS MOISTURE CONTENTS (MCs) USING A CAPILLARY EXTRUSION VISCOMETER bilize the myofibrillar proteins like a surimi, thus improving gel formation paste (Suzuki 1981; Stone and Stanley 1992). The solubilization is affected by salt concentration and is represented by viscosity value as shown in Fig. 6. Usually, 3% salt concentration shows the maximum solubilization (Suzuki 1981). Additives like an egg white increase the viscosity of the paste and enhance the final gel properties. LEW, however, was used in the study, and lower viscosity values were produced as higher LEW concentrations were added. Correlation Between Viscosity and Structural Fracture Property The structural fracture properties of surimi gels made with different conditions are shown in Fig. 8. As the moisture concentration increased from 75 to 80%, shear stress decreased from 47.5 to 12 kpa. Shear stress changed significantly as moisture concentration changed, indicating a strong linear relationship with shear stress and moisture concentration (Yoon et al. 1997). However, shear strain values did not correspond linearly to the change of moisture concentration. Yoon et al. (1997) reported the same observation for the trend of shear strain of Pacific whiting gel. However, the linear reduction of shear strain was observed when the MC of Alaska pollock gel exceeded

9 544 B.Y. KIM and J.W. PARK % Salt % Salt Shear Stress, Pa % Salt Shear Rate, 1/s FIG. 6. VISCOSITY OF SURIMI PASTE MEASURED AT VARIOUS SALT CONTENTS USING A CAPILLARY EXTRUSION VISCOMETER Egg white 2% 3% 4% Shear Stress, Pa Shear Rate, 1/s FIG. 7. VISCOSITY OF SALTED (3%) SURIMI PASTE WITH THE ADDITION OF VARIOUS CONTENTS OF LIQUID EGG WHITE USING A CAPILLARY EXTRUSION VISCOMETER

10 EXTRUSION VISCOMETER FOR SURIMI PASTE 545 Shear Stress Shear Strain Shear Stress (kpa) Shear Strain 0 75M 78M 80M 2S 3S 4S 2E 3E 4E 0.0 FIG. 8. FRACTURE PROPERTIES OF SURIMI GELS PREPARED AT DIFFERENT CONDITIONS M, moisture concentration (%); S, salt concentration (%); E, liquid egg white concentration (%). 81.5%. A linear relationship between moisture concentration and shear stress (Fig. 9) was calculated as shown in the following equation: Y = X (5) where Y is the shear stress at fracture, and X is the moisture concentration. Unlike gels made with different moisture concentrations, neither shear stress nor shear strain of gels made with salt or LEW linearly corresponded with concentration. The moisture concentration also showed a strong linear relationship with viscosity measured with an extrusion viscometer as shown in the following equation: Z = X (6) where Z is the viscosity, and X is the moisture concentration. Using Eqs. (5) and (6), a simple linear equation (Eq. 7) could be developed for the relationship between viscosity and shear stress value.

11 546 B.Y. KIM and J.W. PARK Shear stress (kpa) Shear stress Viscosity y = x R 2 = y = x R 2 = Moisture concentration (%) FIG. 9. VISCOSITY OF SURIMI PASTE AND FRACTURE PROPERTY OF SURIMI GEL AS AFFECTED BY MOISTURE CONTENTS Viscosity (Pa. sec) Y = Z (7) where Y is the shear stress at fracture, and Z is the viscosity. The glass capillary viscometer is designed for the Newtonian fluids (Van Wazor et al. 1963). Specific assumptions are typically given for the capillary viscometer such as steady flow, no end effects and no radial and tangential components of velocity in the capillary viscometer (Rao 1977). However, the flow behavior of non-newtonian surimi paste with or without salt could be well defined using the capillary viscometer. CONCLUSION Viscosity measurement using a capillary extrusion viscometer can be effectively used as an easy tool for controlling the production flow of surimi, surimi seafood paste and other comminuted muscle food paste. Even though textural properties and viscosity of surimi seafood depend on various factors such as moisture, salt, starch and protein additive, the results demonstrate that

12 EXTRUSION VISCOMETER FOR SURIMI PASTE 547 good prediction was obtained using a simple linear equation only as a function of MC, but not other factors. Thus, the prediction of final gel textural properties from paste viscosity could be somewhat limited. ACKNOWLEDGMENT This research was supported by the Kyung Hee University Research Fund in REFERENCES DAUTANT, F.J., SIMANCAS, K., SANDOVAL, A.J. and MULER, A.J Effect of temperature, moisture and lipid content on the rhelogical properties of rice flour. J. Food Eng. (in press). ESTURK, O Characterization of rheological properties and thermal stability of fish myofibrillar proteins. PhD Dissertation, Oregon State University, Astoria, OR. FILIPI, I. and LEE, C.M Preactivated iota-carrageenan and its rheological effects in composite surimi gel. Lebensm.-Wiss. Technol. 31, HOFFMANN, J. and PARK, J.W Improved torsion testing using molded surimi gels. J. Aquat. Food Proc. Technol. 10, KIM, B.Y., YOON, W.B. and PARK, J.W Texture and rheological properties of surimi gels. In Surimi and Surimi Seafood, 2nd Ed. (J.W. Park, ed.) pp , CRC Press, Boca Raton, FL. LANIER, T.C Functional perperties of surimi. Food Technol. 40, MATSUMOTO, J.J Chemical deterioration of muscle proteins during frozen storage. In Chemical Deterioration of Proteins, ACS Symposium series 123 (J.R. Whitaker and M. Fujimoto, eds.) American Chemical Society, Washington, DC. RAO, M.A Measurement of flow properties of fluid foods developments, limitations, and interpretation of phenomena. J. Texture Studies 8, STONE, A.P. and STANLEY, D.W Mechanism of fish muscle gelation. Food Res. Int. 25, SULTANBAWA, Y. and LI-CHAN, E.C.Y Cryoprotective effects of sugar and polyol blends in ling cod surimi during frozen storage. Food Res. Int. 31,

13 548 B.Y. KIM and J.W. PARK SUZUKI, T Fish and Krill Protein; Processing Technology, p. 260, Applied Science Publishers Ltd., London, England. TELIS-ROMERO, J., THOMAZ, C.E.P., BERMARDI, M., TELIS, V.R.N. and GABAS, A.L Rheological properties and fluid dynamics of egg yolk. J. Food Eng. 74, VAN WAZOR, J.R., LYON, J.W., KIM, K.Y. and COLWELL, R.E Viscosity and Flow Measurement, Interscience Publishers, Inc., New York, NY. YOON, W.B., PARK, J.W. and KIM, B.Y Linear programming in blending various components in surimi seafood. J. Food Sci. 62, , 567. YOON, W.B., PARK, J.W., KIM, B.Y. and KIM, M.H Dynamic properties of surimi-based seafood product as a function of moisture. Korean Food Eng. Prog. 2,