Farm raised fresh Channel Catfish fillets were purchased from a local supermarket and were first diced (approximately 3x3x2 cm), and assigned to one of 4 treatment groups which were: 1) non-tumbled, no egg white added; 2) tumbled, no egg white added; 3) non-tumbled, egg white added; and 4) tumbled, egg white added. A proper amount of ingredients [2% salt, 1% egg white powder from Ballas Egg Products Co. (Zanesville, OH.), 1% sucrose, 0.5% white pepper, 0.1% garlic, 0.25% sodium tripolyphosphate, 0.01% nitrite and 0.01% natural lemon flavor] were placed on the product. An intermittent tumbling procedure (40 min rest, 20 min work) was used for 12 hours at 6oC on tumbled batches. Non-tumble batches were stored for the same time in the same place. Additionally, fish tissue (zero time) was used as a second control (fresh) and contained only two percent salt.
Gel strength of raw fish muscle was measured using the Instron Universal Testing Machine as described by Lee and Chung (1989) and Chung and Lee (1990) with slight modification. Approximately 120 g of batter from ground fish was prepared before and after treatment by using a kitchen blender (Model 5900 with 500 ml capacity, Oster) attached to a Waring Blender motor (Model 700A, Waring Products Co.). The gels were prepared from 60 g of ground fish plus 60 grams ice water containing 2.0% NaCl (for fresh zero time samples only, the others also had the regular treatment ingredients), and they were heated at 85 oC for 20 minutes in a water bath (Model 82, Precision Scientific Co. Chicago, IL). The gel samples were then chilled immediately in ice water and stored in a refrigerator (4 ± 2oC) for 24 hours. The gel hardness was measured after the temperature of the samples was equilibrated to room temperature for 15 to 20 min. Gel slices approximately 1.0 cm (± 1 mm) in length and preweighed (in quintuplicate) were used to measure gel hardness using a 6 mm diameter probe on the Instron (Instron Co. Model 1000, Canton, Maine). The compression (75%) test with a 5 kg/50 Newton weight beam was utilized with a crosshead and chart speed of 50 and 20 mm/min respectively, without lubricating the samples. The test consisted of two compression cycles (two bite) and the results were used to calculate the texture profile parameters such as cohesiveness, springiness, gumminess and chewiness. The gel strength (hardness) was expressed as Newton/g sample.
Additionally, expressible moisture measurements were conducted as described by Lee and Chung (1989) and Ockerman (1985).
Texture Profile Analyses (TPA) other than gel strength such as, cohesiveness, springiness, gumminess, and chewiness were measured and/or calculated from gel strength results as explained by Bourne (1978) and Harper (1991). In this experiment, again the quadrupilcate peak areas from the gel strength evaluation were determined by using a planimeter (KE 62 000, Keuffel and Esser Co., Cleveland OH).
The panelists with an average of four years test experience were given approximately 5x5x10 mm slices and were asked to score them for degree of firmness on a 9 point scale (1: very soft; 5: medium; 9: very firm). The samples were scored on the basis of intensity of resistance to breaking by hand and/or mastication (Lee and Chung, 1989).
Fresh (zero time) controls were evaluated immediately after the fish samples reached the lab, while the four treatment groups were sampled immediately after the tumbling process. That is, the experiment consisted of a 1+ (2 x 2) factorial block design (fresh, tumbling, and egg white) with five replications. The individual fish batches are considered as a block. Difference in treatment means and correlations were determined using SAS (SAS, 1985). Duncan's multiple range test was used for multiple comparisons of means. Additionally, if no interaction term was detected, tumbling and egg white treatment data were combined where appropriate, and another statistical analysis was performed on the processing treatments to see the influence of these factors (tumbling and egg white). In this analysis, data from the zero time tissue (fresh) was not included and the data from the selected parameters were pooled for each treatment.