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Squid Tentacle Protein: Extraction and Its Effects on the Quality of Atlantic Pollock Surimi Gels
Can Insi. Food Sci. Technol. J. Vol. 19, No.4, pp. 158-162, 1986
RESEARCH
Squid Tentacle Protein: Extraction and Its Effects on the Quality of Atlantic Pollock Surimi Gels Tom C.S. Yang and Angela P.P. Yang Department of Food Science University of Maine 'at Orono 102 Holmes Hall, Orono, Maine 04469
water catfish have been considered as having the highest potential for economic exploitation in surimi type products (Anon., 1984). Atlantic pollock (Pollachius virens) is an underutilized species belonging to the gadoid family which includes cod, haddock, cusk, whiting, and red hake. There is an unexploited abundance of Atlantic pollock; while the estimated potential pollock catch in the Northwest Atlantic fishing area is approximately 75000 tons annually, whereas, in 1981, only 16900 tons were actually harvested (FAa, 1983). A major reason for this underutilization is the limited marketability; as with all gadoids, Atlantic pollock tends to develop an unacceptable rubbery texture during frozen storage (Lundstrom and Racicot, 1983). Although Atlantic pollock is not recommended as either frozen fillet or frozen mince, studies have shown that certain gadoid species can be used to produce surimi and surimi-based products of acceptable quality (Keay, 1980; Holmquist et al., 1984). However, a preliminary study in this laboratory indicated that a surimi made of Atlantic pollock had a weak texture and some texture enhancing ingredients were needed. While surimi products were introduced into the United States in the form of kamaboko, the products, however, are bland and rubbery by American taste standards (Hasselback, 1984). Hence, an ideal surimi for kamaboko or simulated seafoods such as crab, scallop, shrimp, and lobster, which a rubbery texture or high elasticity is essential to characterize shellfish meat, may not be most suitable for such analogs as fabricated frankfurters or patties in which a juicy and chewy texture is desirable. Squid has been used as an important and palatable source of food in the Mediterranean and Oriental countries, whereas, it has been termed as an "untapped" seafood in the U.S., partly because of the negative associations between its name and sea food buyers (Seligsohn, 1974), and its rubbery texture has limited its applicability (Kalikstein, 1974). In addition, the deepwater or shortfin squid (II/ex illecebrosus) har-
Abstract Proteins isolated from tentacles of North Atlantic squid (lIIex illecebrosus) were used to study the effects on selected quality properties of surimi gels prepared from Atlantic pollock (Pollachius virens). The yield of alkali-soluble protein was 70010 and protein concentration of the resulting freeze dried isolate was 79% (dry weight), while the yield of alkali salt-soluble protein was 49% and protein concentration of the isolate was 76% (dry weight). Addition of squid proteins significantly increased texture profiles such as fracturability, hardness, adhesiveness, springiness, gumminess, and chewiness, whereas, cohesiveness remained unchanged. The reddish pigments retained in the squid proteins also made the surimi gels darker and redder. Utilization of proteins isolated from squid tentacles could not only enhance the texture of the surimi gels prepared from Atlantic pollock, but also provide natural color to the finished products which resembled commercial frankfurters.
Resume Les effets de proteines isolees de tentacules de calmar d' Atlantique Nord (lIIex i/Iecebrosus) furent etudies en rapport avec certaines proprietes qualitatives de gels de surimi prepare a partir de goberge de I' Atlantique (Pollachius virens). Le rendement en proteine soluble al'alcali fut 70% et la concentration proteique de I'isolat Iyophilise correspondant fut 79% (base seche), tandis que Ie rendement en proteine soluble en milieu de sel alcalin fut 49% et la concentration proteique de I'isolat fut 76% (base seche). L'addition de proteines de calmar augmenta significativement les profils de la texture comme la fragilite, la durete, I'adherence, I'e!asticite, I'aptitude a coller et la mastication, tandis que la cohesion ne fut pas affectee. Les pigments rouges presents dans les proteines de calmar contribuerent a rendre les gels de surimi plus fonces et plus rouges. En plus d'accentuer la texture des gels de surimi prepares a partir de goberge de I' Atlantique, les proteines isolees de tentacules de calmar peuvent aussi contribuer ala couleur naturelle des produits finis qui ressemblerent a des saucisses de Francfort de commerce.
Introduction Surimi is a Japanese term for mechanically deboned fish flesh that has been washed with water and mixed with cryoprotectants for a good frozen shelf life and is used as an intermediate product for a variety of fabricated seafoods (Lee, 1984). Fishes such as Alaska pollock, red hake, menhaden, gulf croaker and freshCopyright
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1986 Canadian Institute of Food Science and Technology
158
vested along the eastern coast of the U.S. and Canada, is considered very leathery (Otwell and Hamann, 1979b). Compared to other marine animals eaten by man, however, squid meat is equal to fish meat in protein content (l6-20OJo) and amino acid composition, and can be considered as an excellent source of protein (Takahashi, 1965). The edible portion, which consists of the mantle, fins, and tentacles, comprises 60 to 80010 of the weight, compared to 20-50% of vertebrate fishes and 20-40% in the commonly eaten shellfish (Ampola, 1974). Unlike most vertebrate fishes, squid contains no remaining bones to concern the processor and the consumer (Anon., 1977). Presently, most studies on squid and its utilization are centered in mantle and fins (Hunt et al., 1970; Saffle, 1973; Kahn et al., 1974; Seligsohn, 1974; Otwell and Hamann, 1979a, b; Slabyj et al., 1981; Stanley and Hultin, 1982; Rodger et al., 1984), few have been on tentacles which also contain a considerable amount of protein. Squid contains a high proportion of both water-soluble protein (Matsumoto, 1958) and saltsoluble protein (Saffle, 1973), and the latter is considered to be helpful in emulsion and texture properties. However, Saffle (l973) found that the squid protein was so soluble in salt solution that most of the squid would go into solution and leave very little material for structure or texture and eventually, an extremely soft and mushy fish sausage product was obtained as the squid was used directly as an emulsifying agent. Similar problems might occur in surimi preparation due to this high proteolytic activity of the squid muscle under normal conditions of surimi preparation (Suzuki, 1981; Rodger et al., 1984). The objective of this study was, therefore, to extract both types of protein from the squid tentacles and examine the effects of these proteins on the quality of Atlantic pollock surimi gels.
Materials and Methods Raw material Fresh (less than 24 h post-harvest) Atlantic pollock fillets were purchased from Stinson Canning Co., Prospect Harbor, ME in February, 1985. The iced fillets were transported to the Department of Food Science, University of Maine, Orono, and processed immediately. Frozen squid tentacles were supplied by National Sea Products Co., Portsmouth, NH. They had been obtained from commercial vessels, frozen and stored at -22°C for 3 mo prior to use. Commercial frankfurters, namely beef, chicken, and regular (contained beef, pork, and chicken meats), were purchased from local stores.
10:1 (v/w) was used. Ground slurry was then mixed in a beaker for 45 min at 25°C using a magnetic stirrer. The pH was kept constant during extraction by addition of 004 M NaOH or 2M HC!. Following extraction, the slurry was centrifuged at 3,000 x G for 10 min. The supernatant was collected and then protein was precipitated by lowering the pH to 5 with 2M HC!. The precipitate was recovered by centrifugation at 3,000 x G for 10 min, and was subsequently mixed with a minimal volume of distilled water. The pH of the slurry was readjusted to 7 before freeze drying. A 24 h membrane desalination (Fisher Spectrapor 1.8 cm-dia. membrane tubing with 12,000 molecular weight cut-off) was performed on the alkali salt-soluble protein prior to freeze drying. The dried protein (s 2% moisture) was ground through a 40 mesh screen and packaged in air-tight bags and stored at 5°C until used. The extraction was repeated three times.
Surimi preparation The fillets were ground through a 6 mm plate in a Hobart Food Cutter (Model 84141) and washed with six parts of icy water for 30 min with a propeller mixer. The water was decanted after the mince settled. The washing cycle was repeated four times; a 0.1 % NaC! (w/w) solution was used for the last washing to ease the removal of the water. Excess water was removed by a Carver Laboratory press (Model C) at 10,000 psi pressure, and the mince was chopped with 4% sugar, 4% sorbitol, and 0.2% sodium tripolyphosphate (w/w) for 10 min. The process temperature was kept below 10°C at all times. The resulting surimi was packed in 400g portions in polyethylene bags. The bags were placed in waxed freezer boxes and quickly frozen in a blast freezer (-40°C) and stored at -22°C until used.
Surimi gel preparation The frozen surimi was thawed overnight in a 2°C cooler and then was placed in a Hobart Food Cutter and chopped for 2 min with 3% (by weight of surimi) NaC!. The fish paste was kept below 10°C at all times. lo4i(---FIRST biTE
~
~
SECONO BITE
---+
_OOWNSTROKE~~ UPSTROKE ~ ~ OOWNSTROKE---+ ~UPSTROKE-+
H2 ...
Squid protein extraction An optimized extraction method suggested by Kahn et al. (1974) and Saffle and Galbreath (l964) was used with some modifications. Frozen squid tentacles were thawed overnight at 5°C, and were then rinsed and ground with either alkali water or 4% (w/w) salt alkali solution (both were adjusted with OAM NaOH to pH 11) in a Waring blender. A solvent-to-squid ratio of Can. Insl. Food Sci. Techno!. J. Vol. 19, No.4, 1986
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DISTANCE (CI:1)
Fig. I. Typical Instron texture profile curve for surimi gels. (HI :fracturability; H 2:hardness; AI :area of first downstroke; A 2 :area of second downstroke; A 3 :adhesiveness; A 21Al :cohesiveness; d 2/d l :springiness; hardness x cohesiveness:gumminess;gumminess x springiness:chewiness).
Yang and Yang / 159
Table I. Results of squid tentade protein extraction. I •2 Extraction Protein Yield Concentration (070) (070) Alkali-Soluble Alkali Salt -Soluble
70a
79a
Color measurements
Hunter Color
Lab 57.97 b 14.13 a 12.16a
A Hunter LabScan II Spectrocolorimeter was used to measure the Hunter L, a, and b readings of surimi gel samples prepared the same way as for texture measurement. A sensor with a 1.27 cm aperture was used.
61.89 a 12.ll b 7.35 b
49 b
I. Mean of three replications. 2. Means within columns having a common superscript are not significantly different (P oS 0.05).
Squid protein isolates were added at 5010, 10%, and 15% levels (w/w) with additional water in each batch to maintain the moisture constant. The slurry was then chopped for an additional 3 min. The finished paste was stuffed into aluminum dishes (5 cm-dia., 2.3 cm height) lined with aluminum foil to facilitate gel removal after cooking. The weight of the paste in each dish was kept constant. Dishes, with lids on, were clamped and placed in a preheated oven at 95°e for 40 min. The finished surimi gels were then cooled in an ice bath for 10 min before being removed from the dishes and stored at 2°e until evaluation.
Analytical procedures Moisture was determined by the AOAe method (1980) and nitrogen was determined by the macroKjeldahl method. Extraction yields were computed as follows: g N in total vol of extract x 100070 g N in squid sample
= extraction
yield
Statistical analyses The data were analyzed by the Waller-Duncan Kratio (100) T test using the Statistical Analysis System (SAS, 1982).
Results and Discussion
Extraction of squid tentacle proteins Texture profile analyses Texture was measured according to Yang et al. (1983) and Bourne (1978) with some modifications. An Instron Universal Testing machine (Model 1000) was used and a plunger with a diameter of 5 mm was attached to the moving crosshead. The speed of the crosshead was set at 20 mm/min in both the upward and downward directions. The recording chart speed was set at 20 mm/min. The sample was obtained by using a cork borer with a 20 mm inside diameter, shaped with a sharp knife to a 20 mm height. The penetration of the plunger into the sample was set for 16 mm (80% deformation). A full scale load range of 1000 g was used and two consecutive bites were taken. Seven parameters, i.e., fracturability, hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness, were obtained from the resulting curve (Figure I). The measurements were conducted at 25 ± loe, and four replications were made. Table 2a. Moisture content and color of squid-pollock surimi gels. 1.2
Sample Control Alkali-soluble protein 5070 10070 15070 Alkali salt-soluble protein 5070 10070 15070
Hunter Color
Moisture (070)
L
78.45 a
76.60"
75.42 b 73.57 c 71.5l d
59.66 c 53.84 d 49.76 f
9.27 d 11.90b 13.56a
1O.44c 1O.69 b 10.62c
76.22 b 73.91" 70.75 d
60.83 b 52.7ge 49.96 f
8.65 e 11.l3 c 13.16a
8.44d 7.18 e 7.3ge
a
b
The extraction yield, protein concentration, and the Hunter color of both alkali-soluble and alkali saltsoluble proteins of squid tentacles are listed in Table I. Alkali-soluble protein had a significantly higher yield than the alkali salt-soluble protein, while both yields were lower than that of squid mantles reported by Kahn et al. (1974). A greater proportion of nonprotein materials (such as mouth beak, eyes, suckers, and cartilage) existing in the tentacle part might explain this lack of agreement. In surimi processing, a pH ranging from 6 to 7 is suggested for strong gel texture (Lee, 1984). This pH, however, is not the optimum condition for squid protein extraction (Kahn et al., 1974). Using a squid protein isolate obtained from a separate extraction at higher pH, followed b~ isoelectric precipitation would seem to be more practIcal than the direct incorporation of squid meat during the surimi processing. The protein concentration of both alkali- and alkali salt-soluble proteins was similar to that of protein isolated from fish frame (Montecalvo et al., 1984). Alkali-soluble protein was significantly darker, redder, and yellower than alkali salt-soluble protein, and both would provide a reddish-pink color which resembled the color of red meat products such as frankfurters (to be discussed later)'.
11.99a Table 2b. Moisture content and color of commercial frankfurters.1.2 Sample
I. Mean of four replications 2. Means within columns having a common superscript are not significantly different (P oS 0.05).
160/ Yang and Yang
Regular Beef Chicken'
Moisture (070) 53.8 b 54.3 b 56.2a
Hunter Color
Lab 1O.45c 14.35 b 15.46a 15.44 a /3.81 b 13.58 c
58.84 a 54.62 b 50.73 c
I. Mean of four replications . 2. Means within columns having a common superscript are not sIgnificantly different (P oS 0.05). J. Inst. Can. Sci. Technol. Aliment. Vol. 19. No.4. 1986
Table 3a. Texture profile analyses of squid-pollock surimi gels. J.2 Fract. (g)
Sample
Hard. (g) 202.0e
190.0f Control Alkali-sol protein 299.7 d 5070 263.3 e 10070 319.7 d 405.7 c 597.3401. 7b 15070 Alkali Salt -sol protein 280.0d 248.0e 5070 398.7c 403.0c 10070 484.7555.3 b 15070 I. Mean of four replications. 2. Means within columns having a common superscript 3. Planimeter unit.
Adhes. (PU)3 5.7 e
Cohes.
Gumm. (g) 99.5 d
Chew. (g)
49.2-
Sprin. (070) 31.0d
12.3 c 15.7 b 20.0-
48.547.949.0-
60.0 b 67.970.8-
142.5 c 195.5 b 290.3-
86.8 de 129.7" 206.0-
10.Od 13.0c 20.3-
49.242.451.4-
42.3 c 56.3 bc 59.8 b
137.6c 171.0b 285.3"
72,l e 96.3 d 171.0b
30.8 f
are not significantly different (P :5 0.05).
Effect of squid protein isolates on juiciness of surimi gels
Effect ofsquid protein isolates on texture profile analyses of surimi gels
The final moisture content of pollock surimi gels with various levels of squid tentacle protein isolates after cooking is listed in Table 2a. It is shown that as either squid protein increased, despite the fact that the surimi samples were adjusted to the same moisture level, a reduction of moisture content after cooking was found which would eventually lead to a less juicy product. These results suggest that the water holding capacity of surimi gels depends on the original myofibrillar protein extracted from pollock rather than the combined proteins of pollock and squid. Instead of forming a complicated gel network as predicted, the pollock and squid proteins might gel individually, and interfere with each other in forming a spongy structure which is a system capable of entrapping more liquid. A similar conclusion, based on rigidity and differential scanning calorimetric thermograms, was reported by Burgarella et al. (1985) for a mixture of croaker surimi with egg white or whey protein concentrate.
Results of texture profile analyses of surimi gels are presented in Table 3a. As the squid protein level reached 10070 or higher, samples with added alkali saltsoluble protein had higher fracturability than those with added alkali-soluble protein, indicating that the former were more rubbery and more force would be required for the plunger to penetrate into the samples. Increasing protein levels also increased the hardness of the surimi gels, whereas, no significant difference between the gels prepared from the two different proteins, at the same level, was found except at 15070, where a harder gel was obtained with alkali-soluble protein. The result might be partly due to moisture lost through cooking (Table 2a), and the incorporation of additional squid proteins in the system. It was found that protein extracted with either alkali or alkali salt solution in this study has a similar effect on textural enhancement rather than primarily salt-soluble protein as reported by many researchers. Squid proteins contributed a higher adhesiveness to the surimi gels, whereas, no significant effect on cohesiveness was found. As squid protein increased, the relative concentration of pollock protein decreased; in order to maintain a constant cohesiveness, which is the strength of the internal bonds making up the system (Szczesniak, 1963, 1975), there might be an increase in the strength of the bonds between the pollock protein molecules or that the squid proteins are making some type of contribution to the bonding. Springiness was significantly improved as the level of squid protein increased, and alkali-soluble protein had more impact on the springiness than did alkali salt-soluble protein. The result of an insignificant effect of squid protein on cohesiveness, plus the significant effect on springiness of surimi gels, might suggest there were no interactions between surimi protein and squid protein but rather the proteins gelled individually and formed a dense complex after cooking. Since a major part of the surimi is a low-salt aqueous system, the alkalisoluble protein might disperse better and distribute more uniformly than the alkali salt-soluble protein, thus resulting in a more spongy structure with greater springiness. A higher reading of hardness and spring-
Effect of squid protein isolates on color of surimi gels The color of squid tentacle protein isolates had a significant effect on the color of pollock surimi gels (Table 2a); as the level of squid protein increased, surimi gels became darker and redder. The result was close to the color of the three commercial frankfurters (Table 2b) except the latter were more yellow in color. The color of the squid tentacle protein isolates provided another alternative for coloring the frankfurter analogs besides beet juice concentrate which was used by Buck and Fafard (1985) on red hake surimi. Table 3b. Texture profile analyses of commercial frankfurters. I ,2 Hard. Adhes. (g) (PU)3 Regular 242.7" 252.0" 18.7 b Beef 199.0b 216.3 b 23.7" Chicken 209.7 b 215.7 b 23.3" Sample
Fract. (g)
Cohes. Sprin. (070) 36.8 b 50.4 b 40.9"b 50.8 b 43.2"
61.0"
Gumm. Chew. (g) (g) 92.7" 46.8 b 88.6 b 44.9 b 93.1"
56.9"
I. Mean of four replications. 2. Means within columns having a common superscript are not significantly different (P :5 0.05). 3. Planimeter unit. Can. InSI. Food Sci. Technol. J. Vol. 19. No.4, 1986
Yang and Yang / 161
iness had resulted in higher readings of gumminess and chewiness, and the surimi gels with added alkalisoluble protein were chewier than those with added alkali salt-soluble protein. When the above results were compared with those from commercial franks (Table 3b), a generally higher value, except adhesiveness, was found in the surimi gels with squid proteins added, thus it would provide a frank analog with tougher and chewier texture. However, surimi gels and commercial franks vary in their chemical compositions, especially water (Table 2b) and fat content, and this would complicate an effort to imitate each other. Subsequent study of the fat incorporation on the texture of surimi gels should help with the practical development.
Conclusions Squid proteins extracted by either alkali or alkali salt-solution were helpful to both color and texture of pollock surimi gels. Alkali-soluble protein tends to increase the chewiness of the product more effectively than does alkali salt-soluble protein. The latter causes a significant increase in the rubbery property which might not be preferred in frankfurter texture. Hence an alkali-soluble protein isolated from squid tentacles would be an ideal additive in frank analog manufacturing. Further experimentation on the possible interaction mechanisms between surimi protein and squid proteins via physico-chemical study and electron microscopic examination will be presented in the future.
Acknowledgements This study was supported by the Sea Grant Office and University of Maine Agricultural Experiment Station research project Grant No. 1116.
References Ampola, V.G. 1974. Squid-its potential and status as a U.S. food resource. Mar. Fish. Rev. 36(12):28. Anon. 1977. Squid: the untapped seafood. Food Eng. 49(6):119. Anon, 1984. U.S. industry eyes domestic resources. Seafood Bus. Rep. 3(1):30. AOAC. 1980. Official Methods of Analysis. 13th ed. Association of Official Analytical Chemists, Washington, D.C. Bourne, M.C. 1978. Texture profile analysis. Food Techno!. 32(7):62. Buck, E.M. and Fafard, R.D. 1985. Development of a frankfurter analog from red hake surimi. 1. Food Sci. 50(2):321. Burgarella, 1.C., Lanier, T.C. and Hamann, 0.0.1985. Effects of added egg white or whey protein concentrate on thermal transitions in rigidity of croaker surimi. 1. Food Sci. 50(6): 1588. FAO. 1983. Yearbook of Fishery Statistics. Vo!. 52. Food and Agriculture Organization of the United Nations, Rome, Italy. Hasselback, N.H. 1984. The Americanization of surimi. Seafood Bus. Rep. 3(1):26.
162 / Yang and Yang
Holmquist, 1.F., Buck, E.M. and Hultin, H.O. 1984. Properties of Kamaboko made from red hake (Urophycis chuss) fillets, mince, or surimi. 1. Food Sci. 49(1):192. Hunt, S., Grant, M.E. and Liebovich, S.l. 1970. Polymeric collagen isolated from squid (Loligo pealei) connective tissue. Experientia 26(11): 1204. Kahn, L.N., Berk, Z., Pariser, E.R., Goldblith, S.A. and Flink, 1.M. 1974. Squid protein isolate: effect of processing conditions on recovery yields. 1. Food Sci. 39(2):592. Kalikstein, P.H. 1974. The marketability of squid. MIT Sea Grant Report 74:24. Keay, J.N. 1980. Aspects of optimal utilization of the food fish resource through product innovation. In: Advances in Fish Science and Technology. 1.1. Connell (Ed). Fishing News Books, Ltd., Surrey, England. Lee, C.M. 1984. Surimi process technology. Food Techno!. 38(11):69. Lundstrom, R.C. and Racicot, L.D. 1983. Gas chromatographic determination of dimethylamine and trimethylamine in seafoods. lAOAC 66(5): 1158. Matsumoto, 1. 1958. Some aspects on the water-soluble protein of squid protein. Bul!. Tokai Reg. Fish. Res. Lab., No. 20:65. Montecalvo, 1.1r., Constantinides, S.M. and Yang, C.S.T. 1984. Optimization of processing parameters for the properties of flounder frame protein product. 1. Food Sci. 49(1): 172. Otwell, W.S. and Hamann, D.O. 1979a. Textural characterization of squid (Loligo pealei Lesuer): scanning electron microscopy of cooked mantle. 1. Food Sci. 44(5): 1629. Otwell, W.S. and Hamann, D.O. 1979b. Textural characterization of squid (Loligo pealei L.): instrumental and panel evaluations. 1. Food Sci. 44(5): 1636. Rodger, G., Weddle, R.B., Craig, P. and Hastings, R. 1984. Effect of alkaline protease activity on some properties of comminuted squid. 1. Food Sci. 49(1):117. Saffle, R. L. and Galbreath, 1. W. 1964. Quantitative determination of salt-soluble protein in various types of meat. Food Techno!. 18(12):119. Saffle, R.L. 1973. The use of squid in meat emulsion. 1. Food Sci. 38(2):551. SAS. 1982. SAS User's Guide. Statistical Analysis System, SAS Institute Inc., Cary, NC. p 151. Seligsohn, M.R. 1974. Food from the sea: wave of the future? Food Eng. 46(6):57. Slabyj, B.M., Ramsdell, G.E. and True, R.H. 1981. Quality of squid,l/Iex illecebrosus, mantles canned in oi!. Mar. Fish. Rev. 43(6):17. Stanley, D.W. and Hultin, H.O. 1982. Quality factors in cooked North Atlantic squid. Can. Inst. Food Sci. Techno!. 1. 15(4):277. Suzuki, T. 1981. Fish and Krill Protein: Processing Technology. Applied Science Publishers Ltd., London. Szczesniak, A.S. 1963. Objective measurements of food texture. 1. Food Sci. 28(2):410. Szczesniak, A.S. 1975. General Food Texture profile revisited-Ten years perspective. 1. Texture Stud. 6(1):5. Takahashi, T. 1965. Squid meat and its processing. In: Fish as Food. Vo!. IV. pp. 339-354. G. Borgstrom (Ed.). Academic Press. Inc., N.Y. . Yang, C.S.T., Taranto, M.V. and Cheryan, M. 1983. Optimization of textural and morphological properties of a soygelatin mozzarella cheese analog. 1. Food Proc. Pres. 7(1):41.
Submitted August 2, 1985 Accepted March 5, 1986
J. Ins!. Can. Sci. Techno!. Aliment. Vol. 19, No.4, 1986
RESEARCH
Squid Tentacle Protein: Extraction and Its Effects on the Quality of Atlantic Pollock Surimi Gels Tom C.S. Yang and Angela P.P. Yang Department of Food Science University of Maine 'at Orono 102 Holmes Hall, Orono, Maine 04469
water catfish have been considered as having the highest potential for economic exploitation in surimi type products (Anon., 1984). Atlantic pollock (Pollachius virens) is an underutilized species belonging to the gadoid family which includes cod, haddock, cusk, whiting, and red hake. There is an unexploited abundance of Atlantic pollock; while the estimated potential pollock catch in the Northwest Atlantic fishing area is approximately 75000 tons annually, whereas, in 1981, only 16900 tons were actually harvested (FAa, 1983). A major reason for this underutilization is the limited marketability; as with all gadoids, Atlantic pollock tends to develop an unacceptable rubbery texture during frozen storage (Lundstrom and Racicot, 1983). Although Atlantic pollock is not recommended as either frozen fillet or frozen mince, studies have shown that certain gadoid species can be used to produce surimi and surimi-based products of acceptable quality (Keay, 1980; Holmquist et al., 1984). However, a preliminary study in this laboratory indicated that a surimi made of Atlantic pollock had a weak texture and some texture enhancing ingredients were needed. While surimi products were introduced into the United States in the form of kamaboko, the products, however, are bland and rubbery by American taste standards (Hasselback, 1984). Hence, an ideal surimi for kamaboko or simulated seafoods such as crab, scallop, shrimp, and lobster, which a rubbery texture or high elasticity is essential to characterize shellfish meat, may not be most suitable for such analogs as fabricated frankfurters or patties in which a juicy and chewy texture is desirable. Squid has been used as an important and palatable source of food in the Mediterranean and Oriental countries, whereas, it has been termed as an "untapped" seafood in the U.S., partly because of the negative associations between its name and sea food buyers (Seligsohn, 1974), and its rubbery texture has limited its applicability (Kalikstein, 1974). In addition, the deepwater or shortfin squid (II/ex illecebrosus) har-
Abstract Proteins isolated from tentacles of North Atlantic squid (lIIex illecebrosus) were used to study the effects on selected quality properties of surimi gels prepared from Atlantic pollock (Pollachius virens). The yield of alkali-soluble protein was 70010 and protein concentration of the resulting freeze dried isolate was 79% (dry weight), while the yield of alkali salt-soluble protein was 49% and protein concentration of the isolate was 76% (dry weight). Addition of squid proteins significantly increased texture profiles such as fracturability, hardness, adhesiveness, springiness, gumminess, and chewiness, whereas, cohesiveness remained unchanged. The reddish pigments retained in the squid proteins also made the surimi gels darker and redder. Utilization of proteins isolated from squid tentacles could not only enhance the texture of the surimi gels prepared from Atlantic pollock, but also provide natural color to the finished products which resembled commercial frankfurters.
Resume Les effets de proteines isolees de tentacules de calmar d' Atlantique Nord (lIIex i/Iecebrosus) furent etudies en rapport avec certaines proprietes qualitatives de gels de surimi prepare a partir de goberge de I' Atlantique (Pollachius virens). Le rendement en proteine soluble al'alcali fut 70% et la concentration proteique de I'isolat Iyophilise correspondant fut 79% (base seche), tandis que Ie rendement en proteine soluble en milieu de sel alcalin fut 49% et la concentration proteique de I'isolat fut 76% (base seche). L'addition de proteines de calmar augmenta significativement les profils de la texture comme la fragilite, la durete, I'adherence, I'e!asticite, I'aptitude a coller et la mastication, tandis que la cohesion ne fut pas affectee. Les pigments rouges presents dans les proteines de calmar contribuerent a rendre les gels de surimi plus fonces et plus rouges. En plus d'accentuer la texture des gels de surimi prepares a partir de goberge de I' Atlantique, les proteines isolees de tentacules de calmar peuvent aussi contribuer ala couleur naturelle des produits finis qui ressemblerent a des saucisses de Francfort de commerce.
Introduction Surimi is a Japanese term for mechanically deboned fish flesh that has been washed with water and mixed with cryoprotectants for a good frozen shelf life and is used as an intermediate product for a variety of fabricated seafoods (Lee, 1984). Fishes such as Alaska pollock, red hake, menhaden, gulf croaker and freshCopyright
0
1986 Canadian Institute of Food Science and Technology
158
vested along the eastern coast of the U.S. and Canada, is considered very leathery (Otwell and Hamann, 1979b). Compared to other marine animals eaten by man, however, squid meat is equal to fish meat in protein content (l6-20OJo) and amino acid composition, and can be considered as an excellent source of protein (Takahashi, 1965). The edible portion, which consists of the mantle, fins, and tentacles, comprises 60 to 80010 of the weight, compared to 20-50% of vertebrate fishes and 20-40% in the commonly eaten shellfish (Ampola, 1974). Unlike most vertebrate fishes, squid contains no remaining bones to concern the processor and the consumer (Anon., 1977). Presently, most studies on squid and its utilization are centered in mantle and fins (Hunt et al., 1970; Saffle, 1973; Kahn et al., 1974; Seligsohn, 1974; Otwell and Hamann, 1979a, b; Slabyj et al., 1981; Stanley and Hultin, 1982; Rodger et al., 1984), few have been on tentacles which also contain a considerable amount of protein. Squid contains a high proportion of both water-soluble protein (Matsumoto, 1958) and saltsoluble protein (Saffle, 1973), and the latter is considered to be helpful in emulsion and texture properties. However, Saffle (l973) found that the squid protein was so soluble in salt solution that most of the squid would go into solution and leave very little material for structure or texture and eventually, an extremely soft and mushy fish sausage product was obtained as the squid was used directly as an emulsifying agent. Similar problems might occur in surimi preparation due to this high proteolytic activity of the squid muscle under normal conditions of surimi preparation (Suzuki, 1981; Rodger et al., 1984). The objective of this study was, therefore, to extract both types of protein from the squid tentacles and examine the effects of these proteins on the quality of Atlantic pollock surimi gels.
Materials and Methods Raw material Fresh (less than 24 h post-harvest) Atlantic pollock fillets were purchased from Stinson Canning Co., Prospect Harbor, ME in February, 1985. The iced fillets were transported to the Department of Food Science, University of Maine, Orono, and processed immediately. Frozen squid tentacles were supplied by National Sea Products Co., Portsmouth, NH. They had been obtained from commercial vessels, frozen and stored at -22°C for 3 mo prior to use. Commercial frankfurters, namely beef, chicken, and regular (contained beef, pork, and chicken meats), were purchased from local stores.
10:1 (v/w) was used. Ground slurry was then mixed in a beaker for 45 min at 25°C using a magnetic stirrer. The pH was kept constant during extraction by addition of 004 M NaOH or 2M HC!. Following extraction, the slurry was centrifuged at 3,000 x G for 10 min. The supernatant was collected and then protein was precipitated by lowering the pH to 5 with 2M HC!. The precipitate was recovered by centrifugation at 3,000 x G for 10 min, and was subsequently mixed with a minimal volume of distilled water. The pH of the slurry was readjusted to 7 before freeze drying. A 24 h membrane desalination (Fisher Spectrapor 1.8 cm-dia. membrane tubing with 12,000 molecular weight cut-off) was performed on the alkali salt-soluble protein prior to freeze drying. The dried protein (s 2% moisture) was ground through a 40 mesh screen and packaged in air-tight bags and stored at 5°C until used. The extraction was repeated three times.
Surimi preparation The fillets were ground through a 6 mm plate in a Hobart Food Cutter (Model 84141) and washed with six parts of icy water for 30 min with a propeller mixer. The water was decanted after the mince settled. The washing cycle was repeated four times; a 0.1 % NaC! (w/w) solution was used for the last washing to ease the removal of the water. Excess water was removed by a Carver Laboratory press (Model C) at 10,000 psi pressure, and the mince was chopped with 4% sugar, 4% sorbitol, and 0.2% sodium tripolyphosphate (w/w) for 10 min. The process temperature was kept below 10°C at all times. The resulting surimi was packed in 400g portions in polyethylene bags. The bags were placed in waxed freezer boxes and quickly frozen in a blast freezer (-40°C) and stored at -22°C until used.
Surimi gel preparation The frozen surimi was thawed overnight in a 2°C cooler and then was placed in a Hobart Food Cutter and chopped for 2 min with 3% (by weight of surimi) NaC!. The fish paste was kept below 10°C at all times. lo4i(---FIRST biTE
~
~
SECONO BITE
---+
_OOWNSTROKE~~ UPSTROKE ~ ~ OOWNSTROKE---+ ~UPSTROKE-+
H2 ...
Squid protein extraction An optimized extraction method suggested by Kahn et al. (1974) and Saffle and Galbreath (l964) was used with some modifications. Frozen squid tentacles were thawed overnight at 5°C, and were then rinsed and ground with either alkali water or 4% (w/w) salt alkali solution (both were adjusted with OAM NaOH to pH 11) in a Waring blender. A solvent-to-squid ratio of Can. Insl. Food Sci. Techno!. J. Vol. 19, No.4, 1986
-
DISTANCE (CI:1)
Fig. I. Typical Instron texture profile curve for surimi gels. (HI :fracturability; H 2:hardness; AI :area of first downstroke; A 2 :area of second downstroke; A 3 :adhesiveness; A 21Al :cohesiveness; d 2/d l :springiness; hardness x cohesiveness:gumminess;gumminess x springiness:chewiness).
Yang and Yang / 159
Table I. Results of squid tentade protein extraction. I •2 Extraction Protein Yield Concentration (070) (070) Alkali-Soluble Alkali Salt -Soluble
70a
79a
Color measurements
Hunter Color
Lab 57.97 b 14.13 a 12.16a
A Hunter LabScan II Spectrocolorimeter was used to measure the Hunter L, a, and b readings of surimi gel samples prepared the same way as for texture measurement. A sensor with a 1.27 cm aperture was used.
61.89 a 12.ll b 7.35 b
49 b
I. Mean of three replications. 2. Means within columns having a common superscript are not significantly different (P oS 0.05).
Squid protein isolates were added at 5010, 10%, and 15% levels (w/w) with additional water in each batch to maintain the moisture constant. The slurry was then chopped for an additional 3 min. The finished paste was stuffed into aluminum dishes (5 cm-dia., 2.3 cm height) lined with aluminum foil to facilitate gel removal after cooking. The weight of the paste in each dish was kept constant. Dishes, with lids on, were clamped and placed in a preheated oven at 95°e for 40 min. The finished surimi gels were then cooled in an ice bath for 10 min before being removed from the dishes and stored at 2°e until evaluation.
Analytical procedures Moisture was determined by the AOAe method (1980) and nitrogen was determined by the macroKjeldahl method. Extraction yields were computed as follows: g N in total vol of extract x 100070 g N in squid sample
= extraction
yield
Statistical analyses The data were analyzed by the Waller-Duncan Kratio (100) T test using the Statistical Analysis System (SAS, 1982).
Results and Discussion
Extraction of squid tentacle proteins Texture profile analyses Texture was measured according to Yang et al. (1983) and Bourne (1978) with some modifications. An Instron Universal Testing machine (Model 1000) was used and a plunger with a diameter of 5 mm was attached to the moving crosshead. The speed of the crosshead was set at 20 mm/min in both the upward and downward directions. The recording chart speed was set at 20 mm/min. The sample was obtained by using a cork borer with a 20 mm inside diameter, shaped with a sharp knife to a 20 mm height. The penetration of the plunger into the sample was set for 16 mm (80% deformation). A full scale load range of 1000 g was used and two consecutive bites were taken. Seven parameters, i.e., fracturability, hardness, adhesiveness, cohesiveness, springiness, gumminess, and chewiness, were obtained from the resulting curve (Figure I). The measurements were conducted at 25 ± loe, and four replications were made. Table 2a. Moisture content and color of squid-pollock surimi gels. 1.2
Sample Control Alkali-soluble protein 5070 10070 15070 Alkali salt-soluble protein 5070 10070 15070
Hunter Color
Moisture (070)
L
78.45 a
76.60"
75.42 b 73.57 c 71.5l d
59.66 c 53.84 d 49.76 f
9.27 d 11.90b 13.56a
1O.44c 1O.69 b 10.62c
76.22 b 73.91" 70.75 d
60.83 b 52.7ge 49.96 f
8.65 e 11.l3 c 13.16a
8.44d 7.18 e 7.3ge
a
b
The extraction yield, protein concentration, and the Hunter color of both alkali-soluble and alkali saltsoluble proteins of squid tentacles are listed in Table I. Alkali-soluble protein had a significantly higher yield than the alkali salt-soluble protein, while both yields were lower than that of squid mantles reported by Kahn et al. (1974). A greater proportion of nonprotein materials (such as mouth beak, eyes, suckers, and cartilage) existing in the tentacle part might explain this lack of agreement. In surimi processing, a pH ranging from 6 to 7 is suggested for strong gel texture (Lee, 1984). This pH, however, is not the optimum condition for squid protein extraction (Kahn et al., 1974). Using a squid protein isolate obtained from a separate extraction at higher pH, followed b~ isoelectric precipitation would seem to be more practIcal than the direct incorporation of squid meat during the surimi processing. The protein concentration of both alkali- and alkali salt-soluble proteins was similar to that of protein isolated from fish frame (Montecalvo et al., 1984). Alkali-soluble protein was significantly darker, redder, and yellower than alkali salt-soluble protein, and both would provide a reddish-pink color which resembled the color of red meat products such as frankfurters (to be discussed later)'.
11.99a Table 2b. Moisture content and color of commercial frankfurters.1.2 Sample
I. Mean of four replications 2. Means within columns having a common superscript are not significantly different (P oS 0.05).
160/ Yang and Yang
Regular Beef Chicken'
Moisture (070) 53.8 b 54.3 b 56.2a
Hunter Color
Lab 1O.45c 14.35 b 15.46a 15.44 a /3.81 b 13.58 c
58.84 a 54.62 b 50.73 c
I. Mean of four replications . 2. Means within columns having a common superscript are not sIgnificantly different (P oS 0.05). J. Inst. Can. Sci. Technol. Aliment. Vol. 19. No.4. 1986
Table 3a. Texture profile analyses of squid-pollock surimi gels. J.2 Fract. (g)
Sample
Hard. (g) 202.0e
190.0f Control Alkali-sol protein 299.7 d 5070 263.3 e 10070 319.7 d 405.7 c 597.3401. 7b 15070 Alkali Salt -sol protein 280.0d 248.0e 5070 398.7c 403.0c 10070 484.7555.3 b 15070 I. Mean of four replications. 2. Means within columns having a common superscript 3. Planimeter unit.
Adhes. (PU)3 5.7 e
Cohes.
Gumm. (g) 99.5 d
Chew. (g)
49.2-
Sprin. (070) 31.0d
12.3 c 15.7 b 20.0-
48.547.949.0-
60.0 b 67.970.8-
142.5 c 195.5 b 290.3-
86.8 de 129.7" 206.0-
10.Od 13.0c 20.3-
49.242.451.4-
42.3 c 56.3 bc 59.8 b
137.6c 171.0b 285.3"
72,l e 96.3 d 171.0b
30.8 f
are not significantly different (P :5 0.05).
Effect of squid protein isolates on juiciness of surimi gels
Effect ofsquid protein isolates on texture profile analyses of surimi gels
The final moisture content of pollock surimi gels with various levels of squid tentacle protein isolates after cooking is listed in Table 2a. It is shown that as either squid protein increased, despite the fact that the surimi samples were adjusted to the same moisture level, a reduction of moisture content after cooking was found which would eventually lead to a less juicy product. These results suggest that the water holding capacity of surimi gels depends on the original myofibrillar protein extracted from pollock rather than the combined proteins of pollock and squid. Instead of forming a complicated gel network as predicted, the pollock and squid proteins might gel individually, and interfere with each other in forming a spongy structure which is a system capable of entrapping more liquid. A similar conclusion, based on rigidity and differential scanning calorimetric thermograms, was reported by Burgarella et al. (1985) for a mixture of croaker surimi with egg white or whey protein concentrate.
Results of texture profile analyses of surimi gels are presented in Table 3a. As the squid protein level reached 10070 or higher, samples with added alkali saltsoluble protein had higher fracturability than those with added alkali-soluble protein, indicating that the former were more rubbery and more force would be required for the plunger to penetrate into the samples. Increasing protein levels also increased the hardness of the surimi gels, whereas, no significant difference between the gels prepared from the two different proteins, at the same level, was found except at 15070, where a harder gel was obtained with alkali-soluble protein. The result might be partly due to moisture lost through cooking (Table 2a), and the incorporation of additional squid proteins in the system. It was found that protein extracted with either alkali or alkali salt solution in this study has a similar effect on textural enhancement rather than primarily salt-soluble protein as reported by many researchers. Squid proteins contributed a higher adhesiveness to the surimi gels, whereas, no significant effect on cohesiveness was found. As squid protein increased, the relative concentration of pollock protein decreased; in order to maintain a constant cohesiveness, which is the strength of the internal bonds making up the system (Szczesniak, 1963, 1975), there might be an increase in the strength of the bonds between the pollock protein molecules or that the squid proteins are making some type of contribution to the bonding. Springiness was significantly improved as the level of squid protein increased, and alkali-soluble protein had more impact on the springiness than did alkali salt-soluble protein. The result of an insignificant effect of squid protein on cohesiveness, plus the significant effect on springiness of surimi gels, might suggest there were no interactions between surimi protein and squid protein but rather the proteins gelled individually and formed a dense complex after cooking. Since a major part of the surimi is a low-salt aqueous system, the alkalisoluble protein might disperse better and distribute more uniformly than the alkali salt-soluble protein, thus resulting in a more spongy structure with greater springiness. A higher reading of hardness and spring-
Effect of squid protein isolates on color of surimi gels The color of squid tentacle protein isolates had a significant effect on the color of pollock surimi gels (Table 2a); as the level of squid protein increased, surimi gels became darker and redder. The result was close to the color of the three commercial frankfurters (Table 2b) except the latter were more yellow in color. The color of the squid tentacle protein isolates provided another alternative for coloring the frankfurter analogs besides beet juice concentrate which was used by Buck and Fafard (1985) on red hake surimi. Table 3b. Texture profile analyses of commercial frankfurters. I ,2 Hard. Adhes. (g) (PU)3 Regular 242.7" 252.0" 18.7 b Beef 199.0b 216.3 b 23.7" Chicken 209.7 b 215.7 b 23.3" Sample
Fract. (g)
Cohes. Sprin. (070) 36.8 b 50.4 b 40.9"b 50.8 b 43.2"
61.0"
Gumm. Chew. (g) (g) 92.7" 46.8 b 88.6 b 44.9 b 93.1"
56.9"
I. Mean of four replications. 2. Means within columns having a common superscript are not significantly different (P :5 0.05). 3. Planimeter unit. Can. InSI. Food Sci. Technol. J. Vol. 19. No.4, 1986
Yang and Yang / 161
iness had resulted in higher readings of gumminess and chewiness, and the surimi gels with added alkalisoluble protein were chewier than those with added alkali salt-soluble protein. When the above results were compared with those from commercial franks (Table 3b), a generally higher value, except adhesiveness, was found in the surimi gels with squid proteins added, thus it would provide a frank analog with tougher and chewier texture. However, surimi gels and commercial franks vary in their chemical compositions, especially water (Table 2b) and fat content, and this would complicate an effort to imitate each other. Subsequent study of the fat incorporation on the texture of surimi gels should help with the practical development.
Conclusions Squid proteins extracted by either alkali or alkali salt-solution were helpful to both color and texture of pollock surimi gels. Alkali-soluble protein tends to increase the chewiness of the product more effectively than does alkali salt-soluble protein. The latter causes a significant increase in the rubbery property which might not be preferred in frankfurter texture. Hence an alkali-soluble protein isolated from squid tentacles would be an ideal additive in frank analog manufacturing. Further experimentation on the possible interaction mechanisms between surimi protein and squid proteins via physico-chemical study and electron microscopic examination will be presented in the future.
Acknowledgements This study was supported by the Sea Grant Office and University of Maine Agricultural Experiment Station research project Grant No. 1116.
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162 / Yang and Yang
Holmquist, 1.F., Buck, E.M. and Hultin, H.O. 1984. Properties of Kamaboko made from red hake (Urophycis chuss) fillets, mince, or surimi. 1. Food Sci. 49(1):192. Hunt, S., Grant, M.E. and Liebovich, S.l. 1970. Polymeric collagen isolated from squid (Loligo pealei) connective tissue. Experientia 26(11): 1204. Kahn, L.N., Berk, Z., Pariser, E.R., Goldblith, S.A. and Flink, 1.M. 1974. Squid protein isolate: effect of processing conditions on recovery yields. 1. Food Sci. 39(2):592. Kalikstein, P.H. 1974. The marketability of squid. MIT Sea Grant Report 74:24. Keay, J.N. 1980. Aspects of optimal utilization of the food fish resource through product innovation. In: Advances in Fish Science and Technology. 1.1. Connell (Ed). Fishing News Books, Ltd., Surrey, England. Lee, C.M. 1984. Surimi process technology. Food Techno!. 38(11):69. Lundstrom, R.C. and Racicot, L.D. 1983. Gas chromatographic determination of dimethylamine and trimethylamine in seafoods. lAOAC 66(5): 1158. Matsumoto, 1. 1958. Some aspects on the water-soluble protein of squid protein. Bul!. Tokai Reg. Fish. Res. Lab., No. 20:65. Montecalvo, 1.1r., Constantinides, S.M. and Yang, C.S.T. 1984. Optimization of processing parameters for the properties of flounder frame protein product. 1. Food Sci. 49(1): 172. Otwell, W.S. and Hamann, D.O. 1979a. Textural characterization of squid (Loligo pealei Lesuer): scanning electron microscopy of cooked mantle. 1. Food Sci. 44(5): 1629. Otwell, W.S. and Hamann, D.O. 1979b. Textural characterization of squid (Loligo pealei L.): instrumental and panel evaluations. 1. Food Sci. 44(5): 1636. Rodger, G., Weddle, R.B., Craig, P. and Hastings, R. 1984. Effect of alkaline protease activity on some properties of comminuted squid. 1. Food Sci. 49(1):117. Saffle, R. L. and Galbreath, 1. W. 1964. Quantitative determination of salt-soluble protein in various types of meat. Food Techno!. 18(12):119. Saffle, R.L. 1973. The use of squid in meat emulsion. 1. Food Sci. 38(2):551. SAS. 1982. SAS User's Guide. Statistical Analysis System, SAS Institute Inc., Cary, NC. p 151. Seligsohn, M.R. 1974. Food from the sea: wave of the future? Food Eng. 46(6):57. Slabyj, B.M., Ramsdell, G.E. and True, R.H. 1981. Quality of squid,l/Iex illecebrosus, mantles canned in oi!. Mar. Fish. Rev. 43(6):17. Stanley, D.W. and Hultin, H.O. 1982. Quality factors in cooked North Atlantic squid. Can. Inst. Food Sci. Techno!. 1. 15(4):277. Suzuki, T. 1981. Fish and Krill Protein: Processing Technology. Applied Science Publishers Ltd., London. Szczesniak, A.S. 1963. Objective measurements of food texture. 1. Food Sci. 28(2):410. Szczesniak, A.S. 1975. General Food Texture profile revisited-Ten years perspective. 1. Texture Stud. 6(1):5. Takahashi, T. 1965. Squid meat and its processing. In: Fish as Food. Vo!. IV. pp. 339-354. G. Borgstrom (Ed.). Academic Press. Inc., N.Y. . Yang, C.S.T., Taranto, M.V. and Cheryan, M. 1983. Optimization of textural and morphological properties of a soygelatin mozzarella cheese analog. 1. Food Proc. Pres. 7(1):41.
Submitted August 2, 1985 Accepted March 5, 1986
J. Ins!. Can. Sci. Techno!. Aliment. Vol. 19, No.4, 1986