Food Biochemistry and Food Processing (2 edition)

BLBS102-c20 BLBS102-Simpson March 21, 2012 13:35 Trim: 276mm X 219mm Printer Name: Yet to Come

20 Fish Collagen 381

Table 20.6.Isoelectric Point (pI) of Collagens from Different Sources

Collagens Sources of Collagen Sources of Pepsin Used PI References

ASC Arabesque greenling skin – 6.31 Nalinanon et al. (2010)

Brownbanded bamboo shark skin – 6.21 Kittiphattanabawon et al. (2010a)

Blacktip shark skin – 6.78 Kittiphattanabawon et al. (2010c)

Brownbanded bamboo shark cartilage – 6.53 Kittiphattanabawon et al. (2010b)

Blacktip shark cartilage – 6.96 Kittiphattanabawon et al. (2010b)

PSC Arabesque greenling skin Albacore tuna 6.38 Nalinanon et al. (2010)

Brownbanded bamboo shark skin Porcine 6.56 Kittiphattanabawon et al. (2010a)

Blacktip shark skin Porcine 7.02 Kittiphattanabawon et al. (2010c)

P. tayenusskin Porcine 7.15 Benjakul et al. (2010)

Priacanthus tayenusskin Tongol tuna 7.46 Benjakul et al. (2010)

Priacanthus macracanthusskin Porcine 5.97 Benjakul et al. (2010)

P. macracanthusskin Tongol tuna 6.44 Benjakul et al. (2010)

Brownbanded bamboo shark cartilage Porcine 7.03 Kittiphattanabawon et al. (2010b)

Blacktip shark cartilage Porcine 7.26 Kittiphattanabawon et al. (2010b)

differences in denaturation temperature of collagen from differ-

ent sources might be governed by different contents of imino

acids (proline and hydroxyproline) (Jongjareonrak et al. 2005,

Zhang et al. 2007, Kittiphattanabawon et al. 2010a). The ther-

mal stability of collagen is associated with the restriction of the

secondary structure of the polypeptide chain governed by the

pyrrolidine rings of proline and hydroxyproline and partially by

the hydrogen bonding through the hydroxyl group of hydrox-

yproline (Benjakul et al. 2010).

Zeta (ζ) Potential

Charge of proteins plays a role in properties, especially solubility

as well as interaction with other molecules via ionic interaction.

Collagen from different fish possesses the zero net charge at pH

range of 6.21 to 7.26 (Table 20.6). Generally, the pI of collagen

is determined by amino acid composition. The pH where the

ζ-potential is zero corresponds to the pI of the protein (Ma et al.

2009), in which a net electrical charge of zero at the surface

is obtained. The collagens had a net positive or negative charge

when pH values are below and above their pI, respectively (Nali-

nanon et al. 2010, Kittiphattanabawon et al. 2010a, b, c). At

pI of proteins, hydrophobic–hydrophobic interaction increased,

thereby promoting the precipitation and aggregation of protein

molecules (Jongjareonrak et al. 2005). Nalinanon et al. (2010)

determined theζ-potential of ASC and PSC from arabesque

greenling (Pleurogrammus azonus) at different pHs. Generally,

ζ-potential profiles of both collagens were similar within pH

range tested (Fig. 20.7). The similarity inζ-potential profiles

of ASC and PSC indicated that partial removal of telopeptides

–15.00

–10.00

–5.00

0.00

5.00

10.00

15.00

20.00

25.00

30.00

1 2 3 4 5 6 7 8 9 10 11 12

pH

ζ-Potential (mV)

ASC PSC

Figure 20.7.Zeta (ζ) potential of ASC and PSC from the skin of arabesque greenling at different pHs. Bars represent the standard deviation

from triplicate determinations (Nalinanon et al. 2010).