**5.2 Temperature control**

interaction [58]. Hence the per cent elongation values of the film blends were very

Not all collagen extraction methods result in a collagen product that will be suitable for film preparation. Hence, to develop a collagen film with desired properties, it is necessary to investigate the various processes to prepare acid/alkaline/ enzyme/acid-enzyme collagen that could easily be used as a raw material for extruded or casting of collagen-based films. O'Sullivan [6] reported that

hydrochloric acid solubilisation extraction method of collagen is not favourable for the fabrication of edible films. However, acetic acid solubilisation with further processing gave a suitable collagen product as a raw material for the fabrication of

Every bovine collagen extraction procedure is restricted to the following four

• Cutting the de-haired hide section into approximately 1 cm x 1 cm pieces.

• Extraction temperature: For bovine tissue, the extraction procedure can be carried out at room temperature, as collagen denaturation temperature for bovine is 39°C. However, it is preferable to extract collagen at a temperature

• Solubilisation: acid solubilisation, acid and enzyme solubilisation, or modified

Prior to collagen extraction, the sample is chopped to increase the extraction surface area and to speed up the extraction process. However, the temperature of the sample needs to be monitored, as high temperatures will unravel the tropocollagen making it soluble in solution, resulting in gelatine (denatured collagen). This greatly reduces the value of the protein, thus if native collagen is desired, any heating or denaturation of collagen should be avoided at every step of the process. Bovine collagen extraction is mostly carried out at temperatures of approximately

Collagen from juvenile sources (e.g. new-born calves or chicken embryos) will readily swell and dissolve in a low concentration of acetic acid solution and can be recovered by precipitating out the collagen by adding 1 to 5 M NaCl. However different types of collagen from different tissues will precipitate at different NaCl

The older the animal/tissue sample, the greater the amount of lysinehydroxylysine covalent cross-links that form between tropocollagen units. These cross-links typically form between the unwound part of a tropocollagen strand and another part of another tropocollagen unit, improving structural strength and chemical resistance of collagen, making the sample largely insoluble in acetic acid. The amount of cross-linking depends on the type of tissue (i.e. tendons are highly crosslinked to give strength) and age of the tissue (i.e. mature sources, such as bull-hides have high cross-linking in comparison to younger sources such as calf-hides) [60].

**5. Methods used to extract collagen from bovine hides**

• De-hairing, cleaning and storage of the hide section off-cutting.

**5.1 General extraction procedure requirements**

of 4°C to prevent contamination.

4°C to prevent bacterial contamination [9].

concentrations [59].

**218**

methods combining acids and enzymes.

low (0.30–5.10%) [57].

*Biotechnological Applications of Biomass*

edible film fabrication.

variable conditions:

To prevent collagen denaturation and contamination, majority of the researchers carry out the collagen extraction process at approximately 4°C. Contamination occurs due to thermal denaturation or microbial degradation (**Table 3**).
