abcdMeans with the same letters are not significantly different (P > 0.05) for each bar class (Instron or panel).
Gel Strength
The results of the Texture Profile Analysis of the fish muscle are shown in Figures 1 and 2. Gel strength (GS) was significantly increased by egg white addition and the tumbling process when compared to thecontrol. This might be related to lower degree of proteolysis which was reported by Ockerman and Yetim (1999) and/or supporting protein network in the system (Yetim, 1993). Moreover, egg white plus tumbling further increased the GS of the fish proteins. All of these results from the Instron were confirmed by the panel evaluation of gel firmness (Figure 1).
|
| Figure 1. Changes in gel strength (Newton/g sample)
and gel firmness [from panel evaluation with a 1 (soft) to 9
(firm) scale] measured after tumbling and egg white
incorporation into catfish. Fresh: Zero Time, CNT: Control
Non-Tumbled, CT: Control Tumbled, ENT: Egg White Non-Tumbled,
ET: Egg White Tumbled. abcdMeans with the same letters are not significantly different (P > 0.05) for each bar class (Instron or panel). |
There are many reports of the relationship between non-fish protein addition and GS (Haga et al., 1980; Lanier et al., 1981; Kim et al., 1987; Chung and Lee, 1990; Reppond and Babbit, 1993). Some researcher found an almost linear negative relationship between the degree of proteolysis and gel hardness in fish protein gels (Montejano et al., 1983; Reppond and Babbit, 1993). In this experiment, egg white positively affected the gel strength of the fish muscle gels by either preventing proteolysis or by supporting the protein network in the gel. It has been reported that some of the globular food proteins such as soy proteins, egg white, potato protein, whey proteins, wheat proteins and blood proteins contain specific protease inhibitors. For example, Lin and Lanier (1980) reported that the activity of alkaline proteases in fish muscle were inhibited by an egg white protein (ovomucoid). It is also documented, that including a protease inhibitor into a minced fish product, increased gel hardness to twice the level when compared to the control group (Lanier et al., 1981). Ueno et al. (1984) demonstrated textural improvements due to reduced proteolytic activity in surimi from Alaska pollack and sardine by incorporating blood plasma and/or lactalbumin. Additionally, Hamann et al. (1990) used dried plasma hydrolysate and egg white solids in surimi produced from Atlantic menhaden which retarded proteolytic activity that remained even after the washing steps of the surimi process. It is also reported that 1.0% egg white significantly reduced the proteolytic activity during processing though there was a relatively small amount of proteolysis (Ockerman and Yetim, 1999). Moreover, Haga et al. (1980) reported that the use of 3.0% dried egg white can reduce proteolysis and would improve the gel strength of surimi made from Pacific whiting. Likewise, Lee et al. (1990) observed that 3.0% egg white improved 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 two different fish muscle was significantly increased. It was also postulated that using a protease inhibitor would be necessary to improve the textural quality of fish products (Reppond and Babbit, 1993).