Research and Reviews: Meat, Special Circular 172-99, Some Physicochemical Changes in Catfish Muscle as Influenced by Egg White and Tumbling

H. W. Ockerman¹ and H. Yetim
The Ohio State University Department of Animal Sciences

Abstract

Egg white (1%) and intermittent tumbling (20 minutes work and 40 minutes rest) (12 hours at 6°C) positively influenced the physiochemical properties of fish muscle tissue when compared with non-treated tissue. Salt-soluble protein extraction allowed the production of a fish log out of fish pieces. With these treatments, little proteolysis and a satisfactory flavor were noted and maintained during extended refrigerated storage.

Introduction

There have been a number of research projects in the fishery area investigating the effects of protein hydrolysis on the functionality of muscle foods, i.e., emulsion, gelling, and binding properties. For example, the quality of a cooked meat gel (kamaboko) is highly related to its elasticity, and if a poor elastic gel is produced, it often loses its commercial value due to the proteolysis taking place during cooking (Makinodan et al., 1985; Boye and Lanier, 1988). Unlike terrestrial animal tissue, fish muscle has remarkably high indigenous proteases which immediately start to break down the proteins after the fish are harvested and during processing or improper handling, storage, and cooking (Aksnes, 1989; Morrissey et al., 1993). These proteases are active either at low or high temperatures and are responsible for flakiness, non-adhesive attributes, and weak gel-forming ability of fish muscle. Non-fish proteins or binders were incorporated to produce surimi-type fish products to improve gelling and binding properties. But little is known about the relationships between the physicochemical properties of non-fish protein and the textural properties of restructured fish products (Aksnes, 1989; Chung and Lee, 1990; and Yu, 1992). However, the literature on surimi and protein functionality contains many reports (Babbitt and Reppond, 1988; Hastings et al., 1990; and Chan et al., 1992). The limitations for the use of various fish species for surimi production are usually due to higher proteolytic activity and the degradation of the proteins, resulting in a poor product. This problem has been illustrated for many fish species (1.2). It is reported that the incorporation of protease inhibitors such as egg white, wheat or potato starch, plasma hydrolysate, whey proteins, and soy protein isolate would be necessary to prevent proteolysis and maintain gel-forming ability of surimi products. (Aksnes, 1989; Lee, 1986).

The tumbling technique, which has been widely used in the red-meat industry, is a physical operation in which meat pieces are subjected to physical forces to improve quality characteristics by accelerating the curing process. It relies on gravitational impact and abrasion against other meat pieces to disrupt muscle fibers and extract the myofibrilar proteins that are necessary for binding meat sections together. Subsequently, molding or placing the meat fragments into a casing and cooking will produce the final tumbled and reformed meat product (Yetim, 1993; Yetim and Ockerman, 1995). To satisfy the growing demand for processed seafood products (Chung and Lee, 1990), new types of restructured fish products should be considered since there is currently very limited choice of these types of products. There is also minimal information on the indigenous proteases and construction elements of restructured fish products and their cooking responses, and there has been no study regarding tumbling of fish muscle for reforming purposes.

The objectives of this research were to evaluate physicochemical changes of fish muscle during processing, to monitor the activity of indigenous proteases (in situ), to observe the effects of a non-fish protein incorporation and a tumbling technique on the water-holding properties and texture of fish muscle.

Materials and Methods

Fresh channel catfish fillets were first diced (approximately 3 x 3 x 2 cm), and subjected to the following: 1) nontumbled, no egg white added (control); 2) tumbled, no egg white added; 3) nontumbled, egg white added; and 4) tumbled, egg white added. The ingredients (2% salt, 1% egg white powder [in egg-white batches], 1% sucrose, 0.5% white pepper, 0.1% garlic, 0.25% sodium tripolyphosphate, 0.01% nitrite, and 0.01% natural lemon flavor) were added into the product on a fish weight basis, and the intermittent tumbling (20 minutes work, 40 minutes rest) was done for 12 hours at 6°C on the tumbling batches while storing the nontumble batches in the same place for the same time.

Degree of proteolysis was determined as described by Aksnes (1988) with a slight modification. The trichloroacetic acid (TCA) soluble nitrogen concentration was expressed as a percentage of the original nitrogen in the sample and was considered as degree of proteolysis.

The EPH values of the protein samples from the myofibrilar fraction of the fish muscle were measured by a heptane binding method based on the reports by Mohammadzadeh-k et al. (1969) and Mangino et al. (1985) using a Hewlet-Packard 5890A (Starrod Avendale, Pa.) gas chromatograph (GC) equipped with a hydrogen-flame ionization detector. A standard curve was prepared using an undecane, n-heptane, and nonane solutions to compute the effective protein hydrophobicity values which were fully described by Yetim (1993).

Expressible moisture was determined by quantifying the amount of water expressed on three layers of filter paper (Whatman #1) upon compression by the Instron testing machine (Model 1000, Instron Co., Canton, Maine) as described by Lee and Chung (Lee and Chung, 1989). It was reported in percentage of total moisture. The total gel moisture content of the sample was determined by the oven method (Ockerman, 1985).

Total nitrogen was determined by kjeldahl procedure, and a pH meter (Radiometer, PHM 22 Copenhagen, Denmark) was used for pH measurements as described by Ockerman (1985).

Fresh (zero time) control and the four treatment groups were sampled after the tumbling process. The experiment consisted of a 1 + (2 x 2) factorial block design (fresh, tumbling, and egg white) with five replications. Differences and comparisons of treatment means and correlation were determined using the SAS program (SAS, 1985).

Results and Discussion

The changes in proteolysis, effective protein hydrophobicity (EPH), and expressible moisture (EM) values due to tumbling and egg-white incorporation are shown in Figures 1, 2, and 3. There were significant (P < 0.05) differences between fresh and processed samples in terms of proteolysis, EPH, and EM. The tumbling did not make a significant difference; another statistical analysis was conducted by combining the related observations, where appropriate. The effects of either tumbling or egg-white addition on raw fish were observed. The results can be seen in detail in Table 1. The data presented in this table are the mean values of the selected parameters from pooled data of each treatment in which fresh (zero-time) observations are not included. Egg white had a significantly lowered proteolysis and EM while yielding higher EPH as compared to no-egg white added control groups. On the other hand, tumbling did not affect the degree of proteolysis, but it significantly decreased EM and EPH values of the fish proteins.

Figure1. Changes in the proteolysis (% Trichloroacetic acid-soluble nitrogen) with tumbling and egg white in fresh or processed fish muscle. Fresh: Zero Time Condition, CNT: Control-Non Tumble, CT: Control-Tumble, ENT: Egg White-Non Tumble, ET:Egg White-Tumble. ^a,b Means with the same letters are not significantly different (P > 0.05).

Figure2. Changes in the degree of (EPH) effective protein hydrophobicity (mg heptane/g protein) of proteins with tumbling and egg white in fresh or processed fish muscle. Fresh: Zero Time Condition, CNT: Control-Non Tumble, CT: Control-Tumble, ENT: Egg White-Non Tumble, ET:Egg White-Tumble. ^a,b Means with the same letters are not significantly different (P > 0.05).

Figure3. Changes in the amount (%) of expressible moisture with tumbling and egg white in fresh or processed fish muscle. Fresh: Zero Time Condition, CNT: Control-Non Tumble, CT: Control-Tumble, ENT: Egg White-Non Tumble, ET:Egg White-Tumble. ^a,b Means with the same letters are not significantly different (P > 0.05).

A slight but significant proteolysis took place in the control group during processing compared to the zero-time (fresh) analysis. Egg-white-added- and-tumbled products had slightly lower proteolysis value, but it was not significant. However, it can be stated that egg white plus tumbling action may have prevented further proteolysis in the fish product (Figure 1). Additionally, as can be seen in Table 1, egg-white-added samples had lower proteolysis compared to the no-egg-white-containing samples. However, tumbling did not significantly affect the rate of proteolysis though it showed a lower proteolysis value (Table 1). There are many reports that support this finding that egg white either prevents or reduces the proteolysis in fish muscle although no study was found with tumbling (Chung and Lee, 1990; Haga et al., 1980; Hamann et al., 1990). In general, all the treatments showed a fairly low proteolysis, which may have been affected by the salt content used in this experiment.

Inhibition of the proteolytic activity with high percentage of NaCl in fish muscle was reported by Noda et al. (1982). Also, it was determined that endogenous proteolytic enzymes were susceptible to NaCl (Fik et al., 1985). They reported that the inhibitory effect of NaCl on fish enzymes increased with increasing NaCl concentration, but this effect decreased with increasing hydrolysis time.

Table 1. The Influence of Egg White (EW) on Proteolysis, Effective Protein Hydrophobicity (EPH), and Expressible Moisture (EM) of Processed Fish Muscle.
Parameter¹	No-EW Added	± SE6	EW Added	±SE
Proteolysis³	0.258^a	0.004	0.250^b	0.003
EPH⁴	77.295^b	2.277	89.920^a	1.734
EM⁵	4.260^a	0.219	3.896^b	0.207
Parameter²	Non-Tumble	± SE	Tumble	± SE
Proteolysis³	0.256	0.003	0.251	0.004
EPH⁴	88.915^a	2.114	78.300^b	2.657
EM⁵	4.332^a	0.208	3.733^b	0.209
¹ Tumbling data were combined. ²Egg-white data were combined. ³% Trichloroacetic acid soluble nitrogen. ⁴Effective protein hydrophobicity by heptane binding (mg heptane/g protein). ⁵% Expressible moisture in muscle gel. ⁶SE = Standard Error. ^a,bMeans with the same superscript letters in a row are not signicantly different (P > 0.05).

In this experiment, 1.0% egg white reduced the proteolytic activity during processing (Table 1 and Figure 1), although there was a relatively small amount of proteolysis. However, Haga et al. (1980) reported that the use of 3.0% dried egg white reduced the proteolysis and would improve the gel strength of surimi made from Pacific whiting. Likewise, Chung and Lee (1990) observed the superiority of 3.0% egg white to improve the textural and functional properties of whiting surimi over equal levels of some other protein concentrates. At 2.0% addition of egg-white proteins, gel strength of the fish muscle was significantly increased, and it was also postulated that using a protease inhibitor would be necessary to improve textural quality of some fish products (24).

There were very significant alterations in the EPH caused by the treatments compared to fresh fish. The EPH was significantly increased with egg white compared to fresh or the other control group. However, EPH was significantly reduced by the tumbling process, which included either tumbling alone or tumbling plus egg-white treatment (Table 1 and Figure 2). This result was interesting because the influence of tumbling on EPH was in the negative direction compared to the egg-white treatment, which was a positive influence. Li-Chan et al. (1987) reported that unheated cod-fish muscle samples had the highest protein hydrophobicity, but showed relatively low gel strength compared to other species. It has been postulated that increased hydrophobicity is generally related to the amount of exposed hydrophobic groups of the proteins in the food systems (LeBlane and LeBlane, 1992). Also, there was a significant positive correlation between pH and EPH. Increasing the pH of the product yielded more protein hydrophobicity, which is thought to be related to a number of other functional properties of food proteins (LeBlane and LeBlane, 1992; Kato and Hakai, 1980).

As shown in Figure 3, a significantly low EM was observed in the egg-white-added-plus- tumbled treatment when compared to fresh and control groups, but there were no significant differences between the control and other treatments for EM. That is, egg white did not significantly reduce expressible moisture although the percent value was lower. However, pooled data in Table 1 showed that EM was lowered with either egg white or tumbling, although the only significance was found with tumbling plus egg white with unpooled data (Figure 3). Similar results for EM were also reported by Chung and Lee (1990); however, the compressive force of the surimi gel samples was significantly increased with egg-white addition. A negative significant correlation was noted between pH and EM; this result would be expected because of the relation between the isoelectric pH of muscle proteins and water-holding capacity (Ockerman, 1983).

Conclusions

Results indicate that either the separate or the combination of egg-white addition and tumbling significantly altered physicochemical properties of fish-muscle tissue studied in this experiment. Egg-white incorporation increased effective protein hydrophobicity and decreased proteolysis and expressible moisture. Tumbling, on the other hand, decreased proteolysis, EM, and EPH as compared to the nontumbled control groups. Egg white plus tumbling had also a reducing effect on proteolysis and EM in the processed fish muscle. In general, all treatments resulted in a fairly low proteolysis which may be due to the salt content which has reportedly caused a reducing effect on proteolytic activity in fish muscle. The tumbling action and egg-white addition significantly influenced effective hydrophobicity. It is interesting that the influence of tumbling on EPH was in the negative direction, while egg white showed the reverse outcome. Also, increasing the pH of the product increased protein hydrophobicity, which will affect the protein functionality. A significant positive correlation (0.79) occurred between pH and EPH while a significant negative correlation (-0.59) was noted between pH and EM. Therefore, it might be suggested that tumbling and egg-white addition may be utilized to increase the functional properties of fish proteins during processing.

References

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Morrissey, M. T., Wu, J. W., Lin, D. and An, H. 1993. Effect of food grade protease inhibitors on autolysis and gel strength of surimi. 1993-IFT Ann. Mt. Tech. Prog. Abst. 346, pp 89, July 10—14, Chicago, IL.

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Ockerman, H. W. 1983. Chemistry of Meat Tissue. Department of Animal Sciences, The Ohio State University, Columbus, Ohio.

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Yetim, H. 1993. Biochemical and Structural Alterations of Restructured Fish Muscle as Influenced by Egg White, Tumbling, and Storage Time. Dissertation. Department of Animal Sciences, The Ohio State University, Columbus, Ohio.

¹ For more information, contact at: The Ohio State University 15 Animal Science, 2029 Fyffe Road, Columbus, OH 43210, (614) 292-4317, Fax (614) 292-2929; email:ockerman.2@osu.edu

Research and Reviews: Meat

Special Circular 172-99