Chemical and biophysical properties of gelatins extracted from the skin of octopus (Octopus vulgaris)

Gelatins from alkali-pre-treated skin of Octopus (Octopus vulgaris) were extracted with different concentrations of pepsin at pH 2.0. The resulting octopus skin gelatins OSG0, OSG5, OSG10 and OSG15, extracted, respectively, without enzyme treatment or with 5, 10 and 15 U of pepsin/g alkaline treated skin were evaluated for gel strength, textural parameters, thermal and gelling properties. The yield of gelatin extracted without enzymatic pretreatment was only 3.21% and the addition of pepsin (15 U/g) increased the yield of gelatin extraction to 7.78%. Molecular weight distribution of gelatins indicates that OSG10 and OSG15 contain peptides with molecular weights less than 10 kDa (>40%). In addition, Fourier transform infrared (FTIR) spectra of extracted gelatins were slightly different, indicating that the triple helical structure of gelatins was affected by pepsin treatment. Compared to OSG0, pepsin gelatins exhibited lower gel strength, hardness, adhesiveness, transition, gelling and melting temperatures and all of the values decreased with increasing enzyme concentration. In addition foam expansion (FE) was affected by enzyme treatment, and the values decreased as pepsin increased. However, the emulsifying activity index (EAI) values of all gelatins were the same. Further, FE and EAI increased with increasing concentrations (1–3%, w/v). The results showed that octopus skin can be a good source for gelatin. •Pepsin treatment of skin of octopus increased the yield of gelatin extraction.•Pepsin treatment decreases α and β-bands intensity of resulted gelatin.•Enzymatic pretreatment leads to the apparition of peptides with low molecular weight.•FTIR and X-ray show that high pepsin levels causes the loss of gelatin structure.•Control gelatin showed the highest gel strength, gelling and melting point.