Comparative Evaluation of Hydrochloric and Acetic Acid Pretreatments for Chicken-Skin Gelatin and Its Application in Edible Films

Abstract

Chicken skin is a collagen-rich poultry by-product with potential for gelatin production and biodegradable edible films. This preliminary comparative study evaluated gelatin obtained from broiler chicken skin pretreated with 4% hydrochloric acid (HCl) or 3% acetic acid (CH₃COOH) and its application in edible films. Gelatin yield was calculated as the mass of dried gelatin relative to the initial wet weight of chicken skin. The gelatin was characterized using Fourier-transform infrared (FTIR) spectroscopy, and edible films were prepared using 2% gelatin, 1% carboxymethyl cellulose (CMC), and 1 mL glycerol. Based on an initial wet chicken-skin weight of 1,000 g per treatment, the recorded gelatin yields were 5.4% for HCl and 5.6% for CH₃COOH. Both gelatin samples exhibited characteristic Amide A, I, II, and III absorption bands. The HCl-derived film had a thickness of 0.098 ± 0.002 mm and a tensile strength of 29.59 ± 0.34 MPa, whereas the CH₃COOH-derived film had a thickness of 0.104 ± 0.002 mm and a tensile strength of 25.00 ± 0.17 MPa. Both films were transparent, with the HCl-derived film described as slightly rigid and the CH₃COOH-derived film as slightly elastic. However, each acid pretreatment was applied to only one gelatin-extraction batch, and the acid type was confounded with acid concentration. Therefore, the observed differences are descriptive and cannot establish the superiority of either acid treatment. Further studies using independently replicated extractions and standardized treatment conditions are needed to confirm these preliminary findings.