Effect of water-soluble protein on pressure-induced gelation of Alaska pollack surimi

R. Hayashi and C. Balny (Editors), High Pressure Bioscience and Biotechnology 9 1996 Elsevier Science B.V. All rights reserved.

363

Effect of water-soluble protein on pressure-induced gelation of Alaska pollack surimi Emiko OKAZAKI and Yutaka FUKUDA

National Research Institute of Fisheries Science, 2-12-4, Fukuura, Kanazawa-ku, Yokohama, 236, Japan Abstract SURIMI and WSP was mixed with various ratio and pressurized. The breaking strength of the pressure and heat-induced gel decreased in the WSP and Surimi mixture but remained high in the WSP only. This phenomenon indicated that there was little positive interaction between SURIMI and WSP in the both of pressureinduced gel and heat-induced gel. It was seemed that WSP lowered the strength of pressurized surimi gel because it delayed the polymerization of myofibrillar protein in SURIMI. On the other hand, the pressure-induced gel enhanced smoothness and flexibility, regardless of the amount of WSP contained. These result indicated the possibility that pressurization could be a suitable processing method to give a favorable texture to the surimi-based product containing high quantity of WSP.

1. INTRODUCTION Approximately 20-35% water soluble protein (WSP) is contained in fish meat protein which is believed to impede the gel formation in kamaboko. Generally, in surimi manufacturing, WSP is removed by water-washing process to obtain a higher gel-forming ability. Now, almost 400 million tons of surimi is produced worldwide, so about 50,000 tons of protein is available as surimi, while more than 20,000 tons of WSP are dumped away 1). To dump away this WSP without any use is problematic both from the economical point of view and utilization of marine resources. To utilize this WSP, many trials were done to develop methods to recover WSP and to utilize this as food materials in Japan. Several methods to recover WSP were established 2-4). But, very few methods succeeded practically. It is because the development in the utilization method of recovering WSP is not enough. So, it is necessary to create a WSP which will have functional properties as a food material, and to develop methods of utilizing WSP into food. The nutritive value of WSP is comparable to that of fish muscle protein itself 6). Recently, authors clarified that WSP is texturized to an elastic gel by high pressure, and that the characteristics of pressure-induced gel is different from that of heat-induced gel which is a fragile coagulum 7). Furthermore, denatured WSP, such as recovered protein from washing water in surimi processing can be texturized by pressure if the protein is not extremely denaturedS).

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From the practical point of view, it is logical to utilize WSP in mixed state with surimi since both the proteins are contained in the original fish meat. Therefore, this study aimed to investigate the effect of water soluble protein on pressure-induced gelation of Alaska pollack surimi. 2. T H E P H Y S I C A L P R O P E R T I E S OF T H E P R E S S U R E - A N D H E A T I N D U C E D GELS OF A L A S K A P O L L A C K S U R I M I A N D W S P M I X E D WITH VARIOUS RATIO There are many reports concerning the effect of WSP on the heat-induced gelation of fish meat 9-11). It was said that sarcoplasmic protein have an inhibitory action on the gel strength of heat-induced gel. But, the mechanism of the inhibitory action is not clarified yet. Shimizu et al. reported that sarcoplasmic proteins aggregated with actomyosin during heat denaturation both at low and high ionic strength, t2) The inhibitory effect of WSP in the pressure-induced gel is not clarified yet either. So, attempts were made to know the effect of WSP on the pressureinduced gelation of SURIMI. WSP was added to SURIMI in different ratios and the property of pressure-induced gel was measured. The extraction procedure of WSP on Alaska pollack is shown in Figure 1. The pH of the concentrated WSP was adjusted to 7.0 and the moisture was adjusted to that of surimi's (Alaska pollack surimi, Maruha.Co.,Ltd, SA grade). The WSP extract was added to surimi in different ratios as given in Figure 2., and mixed under vacuum to remove the air. The air free mixture was filled into a polyvinylidene chloride tube, heated at 85~ for 20min, or pressurized at 300MPa for 10 min, cooled at 0~ for about 24 hours and the physical properties were measured by a puncture test using a rheometer.

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Figure 2. Preparation of SURIMI + WSP gel by heating or pressurization

365 Figure 3. shows the breaking strength, breaking strain, and water-holding capacity of the pressure and heat-induced gel of WSP added surimi. The breaking strength and the breaking strain of heat-induced gel of W S P - s u r i m i mixture d e creased with an increase in WSP content. The gel containing more than 20% of WSP was very brittle, fragile gel. This result was almost the same as with the reports mentioned above 9-11). In the pressure-induced gel, the breaking strength of W S P surimi mixture decreased with the WSP content but remained high in the WSP only. Namely, the WSP itself formed an elastic gel by pressure, but WSP did not make the gel strength of the pressure-induced gel higher when it was mixed with surimi. On the other hand, the pressure-induced gel enhanced the breaking strain such as smoothness and flexibility, regardless of the amount of WSP. Even in the mixture containing more than 50% of WSP, the pressure-induced gel kept a high flexibility. This phenomenon was in contrast with the h e a t - i n d u c e d gel whose texture was lacking in flexibility.

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Figure 3. Physical measurement of pressure- and heat- induced gel from SURIMI + WSP mixture. Physical measurement was accomplished with a penetration test using spherical plunger (diameter: 5mm) by rheometer, the specimen was shaped cylindrical state (height, 25mm; diameter, 23mm). The speed of the stage on which the sample piece was placed was set at lmm/sec. The breaking strain is expressed as the distance of plunger movement from the top to the point where the maximum gel strength was obtained. Water holding capacity was measured as follows: The specimen was placed between a couple of two sheets of filter paper and pressed at 10kg/cm2 for 20 sec. The water content after pressing was measured. These results showed that there was slight positive interaction between surimi and WSP in both the pressure and h e a t - i n d u c e d gel from the viewpoint of gel strength, but WSP did not adversely affect the breaking strain and the total texture of the pressure-induced gel more than that in the heat-induced gel. Shoji et al. 13) reported that the breaking strength of pressure-induced gel of salted ground surimi increased remarkably during storage, and in the case of storage at 5~ the maximum gel strength was obtained after more than 120 hrs of storage periods. In this experiment, the physical properties were measured at only 24hrs after pressurization~ so if the storage was carried out much longer, a higher breaking

366

strength than the one shown in Figure 4. would have been obtained. So, nextly, the change in the physical properties of pressure-induced gel containing 25% WSP during storage for 120 hours was examined.

3. T H E C H A N G E IN P H Y S I C A L P R O P E R T I E S OF P R E S S U R E - I N D U C E D G E L OF SURIMI WITH OR W I T H O U T W S P Three kinds of surimi containing natural WSP or denatured WSP gel were prepared, the contents of myofibrillar protein were adjusted equally among the preparations. Each surimi preparation was mixed with 2.5% NaC1 and kneaded to a pasty state after which they were filled into polyvinylidene chloride tubes, pressurized, and stored at 5~ for a specified time (Figure 4.). The change in the physical property was measured by puncture test by rheometer. ' Surimi Protein I

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Figure 4. Preparation of pressure-induced gel from SURIMI + 25% WSP. (A),(B),(C) was adjusted to have the same myofibrillar protein content. (B) included 25% of natural WSP against the amount of SURIMI protein. (C) included 25% of denatured WSP against the amount of SURIMI protein. Denatured WSP was obtained by heating at 90~ for 30 rain. The content of other components except moisture was adjusted to be the same among each sample.

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Figure 5. Physical property change of pressure-induced gel of SURIMI + WSP during storage after pressurization.

367 Figure 5. shows the changes in the physical properties of pressure-induced gel during storage at low temperature after pressurization. The gel strength of (B) at the beginning of the storage was lower than (A) although the gel contained high amount of protein. This would be reflected the inhibitory effect of WSP on gelation. The gel strength of (C) was a little higher than (A), because of the lower water content. It was seemed that the denatured WSP had no inhibitory effect. However, after 120 hours of storing, the gel strength of (B) became very similar to (A) or (C). It can be said that WSP disturbed the pressure-induced gelation of surimi, but the effect was only a delaying one since the maximum gel strength was achieved after a period of storing. On the other hand, there was no difference in the breaking strain which reflects the flexibility between (A), (B) and (C).

Figure 6. The change in SDS-polyacrylamide gel electrophoretic pattarn of pressure-induced gel of SURIMI + WSP during storage after pressurization. To know the change of subunit compositions of myofibrillar protein, each specimen was solubilized in the SDS-Urea medium containing 2% SDS, 8M Urea, 2% Mercaproethanol, and applied to SDS-polyacrylamide gel electrophoresis. In each gel, Myosin heavy chain (HC) decreased corresponding with the increase of the gel strength. This suggested the formation of high molecular weight components of HC. In the gel of SURIMI only, the rate of decrease of HC was the same as that in SURIMI + denatured WSP, but in the gel containing natural WSP, the rate was lower than the former two. These changes were parallel to the change in gel strength. Addition of WSP seemed to delay the gelation of surimi by high pressure. This phenomenon was confirmed by SDS-Polyacrylamide gel electrophoresis, Figure 6. It is concluded that though WSP seemed to impede pressure-induced gelation of surimi, subjecting high pressure to the WSP and Surimi mixture gave a favorable texture in the surimi-based product.

368 4. REFERENCES

1 E. Okazaki and M. Sakamoto. An Inquiry as to the Actual Conditions of Wastewater Treatment at Plants for Processing Alaska Pollack Frozen-Surimi. Bull. Natl. Res. Fish. Sci., No 4, 57-68 (1992). 2 F. Nishioka and Y. Shimizu. Recovery of Proteins from Washings of Minced Fish Meat by pH-Shifting Method. Bulletin of the Japanese Society of Scientific Fisheries, 49 (5,) 795-800 (1983). 3 Y. Miyata. Concentration of Protein from the Wash Water of Red Meat Fish by Ultrafiltration Membrane. Bulletin of the Japanese Society of Scientific Fisheries, 50 (4), 659-663 (1984). 4 H. Niki, T. Kato, E. Deya, and S. Igarashi. Recovery of Protein from Effluent of Fish Meat in Producing Surimi and Utilization of Recovered Protein. Bulletin of Japanese Society of Scientific Fisheries, 51 (6), 959-964 (1985). 5 H. Hasegawa, H. Watanabe, and R. Takai. Methods of Recovery of Fish Muscle Water-soluble Protein by Electrocoagulation. Bulletin of Japanese Society of Scientific Fisheries, 48 (1), 65-68 (1982). 6 E. Okazaki. A Study on the Recovery and Utilization of Sarcoplasmic Protein of Fish Meat Discharged during the Leaching Process of Surimi Processing. Bull. Natl. Res. Inst. Fish. Sci., No.6, 79-160 (1994). 7 E. Okazaki and K. Nakamura. Factors Influencing Texturization of Sarcoplasmic Protein of Fish by High Pressure Treatment. Nippon Suisan Gakkaishi, 58, 2197-2206 (1992). 8 E. Okazaki. Pressure-induced texturization of water-soluble protein denatured by heating, pH-shifting and organic solvent treatments. High Pressure Bioscience, San-ei-shuppan, Kyoto, 296-303 (1994). 9 M. Okada. Effect of Washing on the Jelly Forming Ability of Fish Meat. Bulletin of the Japanese Society of Scientific Fisheries, 30 (3) 255-261 (1964). 10 A. Hashimoto, N. Katoh, H. Nozaki, and K. Arai. Inhibiting Effect of Various Factors in Muscle of Pacific Mackerel on Gel Forming Ability. Bulletin of the Japanese Society of Scientific Fisheries., 51 (3), 425-432 (1985). 11 T. Nakagawa, F. Nakayama, H. Ozaki, S. Watabe, and K. Hashimoto. Effect of Glycolytic Enzymes on the Gel-forming Ability of Fish Muscle. Nippon Suisan Gakkaishi, 55 (6) 1045-1050 (1989). 12 Y. Shimizu and F. Nishioka. Interactions between Horse Mackerel Actomyosin and Sarcoplasmic Proteins during Heat Coagulation. Nippon Suisan Gakkaishi, 40,231-234 (1974). 13 T. Shoji, H. Saeki, A. Wakameda, M. Nakamura, and M. Nonaka. Effect of Storage Temperature on Changes in Gel Strength and Myofibrillar Protein of Pressure-induced Gel of Walleye Pollack Surimi. Nippon Suisan Gakkaishi, 58, 329-336 (1992).