Effect of Polyphosphate Treatment on the Quality of Baked or Microwaved Catfish Fillets.

Frozen fish fillets designed to be baked in the home oven have been one of the major ways fish are consumed in the US.  Examples include frozen salmon, tilapia, pollock, and cod with different types of pre-treatment such as precooked, marinated, or breaded and par-fried products.  However, frozen catfish fillets are a relatively small portion of the baked and/or microwaved market.

The first objective of this study was to compare the properties of raw frozen catfish fillets baked in a convection oven or cooked in a microwave.  The second objective was to evaluate changes in properties as a consequence of treatment with a commercial polyphosphate blend (IQF).  

Both fresh and IQF catfish samples were purchased from a commercial Mississippi catfish processor and stored frozen.  Fillets (5-7 oz) were trimmed and cut vertically into three pieces, each weighing approximately 50 g.  For each treatment, six fillet pieces were used.  Sample analysis included weight loss, proximate content, color (CIE L*a*b*), pH, mechanical texture (hardness), and lipid peroxidation (TBARS) measurements.

Significantly greater moisture retention properties were observed for IQF samples, regardless of cooking treatment, relative to the comparable fresh samples, which did not contain polyphosphate.  A large cooking loss of ~30% correlated to a reduced moisture content was observed for microwaved samples, with 9.4% moisture loss relative to 4.5% for baked fresh samples.  All fresh fillets had a significantly greater amount of red and yellow color, on both surface and cross-section surface, relative to the comparable IQF samples.  All cooked fresh fillets were significantly harder (1.2-1.8 times) than IQF fillets, with microwaved samples showing greater hardness than baked samples.

This study will be used to develop frozen catfish products that can be cooked in a home oven or microwave oven.