Physical, chemical, and enzymatic skinning methods to remove the peritoneal membrane from catfish nuggets

To remove peritoneal membrane from catfish nuggets for improving their quality and value, chemical (lye), enzymatic (CLS1®, Proleather FG-G®, and Protease N®), and physical (modified BAADER® 148) skinning methods were studied. The effect of concentration, temperature, and time of skinning methods on percent membrane remaining, color (whiteness), and proximate composition were investigated. Boiling lye (7% NaOH w/v) solution for 15 sec was used to remove peritoneal membrane from catfish nuggets, with 9% membrane remaining and 89% yield. Percent fat of lye-skinned nuggets decreased (p ≤ 0.05) by 62%. Enzyme Proleather FG-F® showed the most promising results amongst the three enzymes at 0.2% (w/v) concentration and 44°C for 15 min immersion time. This resulted in 25% membrane and 103% yield. Whiteness of skinned nuggets from enzymatic (Proleather FG-F®) skinning method increased (p ≤ 0.05) while that from lye skinning method was not different (p > 0.05) from the unskinned nuggets. The optimization of enzymatic (Proleather FG-F ®) skinning method was performed by response surface methodology (RSM). The predicted maximum yield (106%) was obtained at 0.15% concentration at 35°C for 12 min. Membrane remaining (≈30%) could be achieved at 42–44°C for 12 min or longer immersion time, at any enzyme concentration. Amongst all methods, lye skinning was the most effective method in peritoneal membrane removal and fat reduction. Nuggets skinned from enzymatic (Proleather FG-F®) method had lower percent membrane remaining (p ≤ 0.05) than those from the modified BAADER® 148 method, but percent fat and whiteness of skinned nuggets from both methods was not different (p > 0.05). The Proleather FG-F® enzyme at 43°C for 12 min is the recommended treatment to diminish environmental impact and high temperature abuse used with lye.