Effect of precooking and polyphosphate treatment on the quality of microwave cooked catfish fillets

Abstract

In the U.S. market place, there are many examples of precooked poultry products designed to be reheated in a microwave oven and, to a lesser extent, fish products such as tilapia. However, few U.S. catfish products are designed to be microwave cooked or reheated. The first objective of this study was to examine the properties of microwave cooked raw frozen catfish fillets and oven precooked (to 62.8°C) frozen fillets and then reheated by microwave cooking. The second objective was to evaluate changes in properties as a consequence of treatment with a commercial polyphosphate blend (Individually Quick Frozen [IQF]). The sample analysis included weight loss, proximate content, color (CIE L*a*b*), pH, mechanical texture (hardness), and lipid peroxidation (TBARS) measurements. Frozen fillets which contained polyphosphate showed <4% moisture loss after microwave cooking, relative to a 12% moisture loss for fillets without polyphosphate. A large cooking loss of ~40% was observed for precooked fillets after microwave cooking, correlated with a higher percent moisture loss (11% and 13% for fillets with and without polyphosphate, respectively) to comparable samples that were not precooked. For both types of fillets, an increased amount of yellow color was observed for precooked fillets after microwave cooking, relative to comparable fillets that were not precooked. Fillet hardness determined by peak force revealed an overall harder texture (~1.1-1.8 times) for fillets without polyphosphate than fillets with polyphosphate. This study will be used to develop precooked catfish products that can be reheated in a microwave oven.

Keywords: Catfish; microwave; polyphosphate; precooked products; texture.

Figure 1

Correlation between cooking loss and cooking time of three different fillet sizes (fresh samples). The linear regression lines and equations were shown in the plot

Figure 2

Correlation between cooking loss and cooking time of fresh catfish fillets cooked at three different microwave power levels. The linear regression lines and equations were shown in the plot

Figure 3

Comparison of cooking loss for fresh and IQF fillets between various treatments. Bars marked with the same letter designate no significant difference (p ˃ .05) between treatments

Figure 4

Percent weight after cooking treatments and proximate compositions for both fresh and IQF fillets between various treatments. Values were normalized to 100 g for raw (or uncooked) fillets. Weights for the cooked fillets were subsequently calculated by subtracting the cooking loss

Figure 5

Comparison of surface L*a*b* color values for both fresh and IQF catfish fillets between various treatments. Positive a* = degree of redness, positive b* = degree of yellowness, L* = lightness. Different treatments were noted with different colors of balls

Figure 6

Comparison of internal (vertical cross‐section surface) L*a*b* color values for both fresh and IQF catfish fillets between various treatments. Positive a* = degree of redness, positive b* = degree of yellowness, L* = lightness. Different treatments were noted with different colors of balls

Figure 7

Mechanical texture analysis (hardness) of fresh and IQF fillets of various treatments. Results were plotted separately by position of fillet (front, middle, or end). When position of fillet was considered as a random variable, bars marked with the same letter on top, within the same type of fillet, are not significantly different (p ˃ .05). Significant differences between fresh and IQF for the corresponding treatment were noted with an asterisk on the graph of IQF samples

Figure 8

Comparison of TBARS values for fresh and IQF fillets between various treatments. The threshold of MDA concentration that is considered good for consumption was marked with a red dotted line. Bars marked with the same letter designate no significant difference (p ˃ .05) between treatments. Significant differences between fresh and IQF for the corresponding treatment were noted with an asterisk above the bar of IQF samples