Use of lactic acid for extraction of fish skin gelatin

The ability of lactic acid compared to acetic acid for Dover sole (Solea vulgaris) skin swelling and the subsequent gelatin extraction was examined. The resultant gelatins were evaluated in terms of extraction yield, amino acid composition, molecular weight distribution, gel strength, viscoelastic properties, ability to refold into triple helical structures, and aggregation phenomena. Lactic acid (25 mM) proved to be an excellent substitute for acetic acid during the skin swelling process, as the gelatin preparation thus obtained presented quite similar properties to that prepared by using 50 mM acetic acid without the negative organoleptic properties of this acid. However, the application of 50 mM lactic acid gave rise to a highly hydrolysed gelatin, with lower folding ability, gel strength and viscoelastic properties than those obtained using 25 mM lactic acid or 50 mM acetic acid.