Food Biochemistry and Food Processing (2 edition)

BLBS102-c21 BLBS102-Simpson March 21, 2012 13:39 Trim: 276mm X 219mm Printer Name: Yet to Come

390 Part 3: Meat, Poultry and Seafoods

Removal of Fat

Raw material with high fat content can be associated with the

negative effect on gelatin. Soaps may be formed during treatment

with alkali prior to gelatin extraction. This soap can contami-

nate the resulting gelatin. Nevertheless, fat removal process was

not included in the pretreatment process for gelatin extraction

from some fish skin with low fat content (Gudmundsson and

Hafsteinsson 1997, Gomez-Guill ́ en et al. 2003, Zhou and Re- ́

genstein 2004Arnesen and Gildberg 2007, Cheow et al. 2007,

Yang et al. 2007, Aewsiri et al. 2008, Nalinanon et al. 2008,

Rahman et al. 2008). A simple defatting can be achieved by

hot water (Waldner 1977). Muyonga et al. (2004) removed fat

in bone of Nile perch (Lates niloticus)bytumblinginwarm

water (35◦C).

Removal of Minerals

Demineralization of the raw material, especially bone or scale,

aims to remove the calcium and other inorganic substances to fa-

cilitate the extraction of collagenous component (Waldner 1977).

The inorganic substances in raw material can be removed by

treatment with dilute hydrochloric acid solution, whereby the

calcium phosphate is dissolved as acid phosphates (Waldner

1977). The fresh bone is commonly treated with hydrochlo-

ric acid solution, in which almost all minerals are completely

removed. Depending on the nature of the material, tempera-

ture, and acid concentration, the demineralization time can be

varied. The acid concentration used is in the range 2–6% HCl

(Waldner 1977). Acid hydrolysis of the protein should be mini-

mized during demineralization. High temperature should also be

avoided since it can enhance the hydrolysis of protein. Bone from

Nile perch (Lates niloticus) was demineralized with 3% HCl at

room temperature prior to extraction using warm water (60◦C)

(Muyonga et al. 2004). Demineralization of tuna fin (Katsu-

wonus pelamis) was carried out at room temperature using

0.6 N HCl (Aewsiri et al. 2008).

Swelling of Pretreated Raw Materials

Prior to gelatin extraction, pretreatment is generally required to

enhance the extraction efficiency. Swelling is important because

it can favor protein unfolding by disruption of noncovalent bond-

ing and predispose the collagen to subsequent extraction and

solubilization (Stainby 1987). Pretreatments can be classified

into two processes and are selectively used on the basis of the

raw materials.

Acid Process Acid hydrolysis is a milder treatment that effec-

tively solubilizes collagens of animals slaughtered at a young age

such as pigs (Foegeding et al. 1996). The pretreatment is aimed

to convert the collagen into a form suitable for extraction. The co-

valent cross-links in the collagen must be disrupted to enable the

release of freeα-chains during the extraction (Johnston-Banks

1990). The process is able to remove other organic substances.

Sulfuric and hydrochloric acids are used, often with the addition

of phosphoric acid to retard color development (Johnston-Banks

1990). Additionally, the acid pretreatment can partially inacti-

vate endogenous proteases involved in degradation. As a result,

the enzymatic breakage of intrachain peptide bonds of collagen

during extraction can be lowered (Zhou and Regenstein 2005).

Nalinanon et al. (2008) reported that gelatin extraction from big-

eye snapper skin using a pepsin-aided process in combination

with a protease inhibitor showed the higher bloom strength than

the gelatin extracted by the conventional process, which had a

substantial degradation of gelatin components.

Moreover, type of acid and concentration affected the yield

and properties of gelatin. The concentration of H+ used in

processing of gelatin from cod skins affected yield and qual-

ity of resulting gelatin (Gudmundsson and Hafsteinsson 1997).

Megrim skin was treated with 0.05 M acetic and 0.05 M propi-

onic acid prior to gelatin extraction using distilled water at 45◦C

for 30 minutes. The gelatin obtained had the highest elastic mod-

ulus, viscous modulus, melting temperature, and gel strength. On

the other hand, gelatin obtained from skin swollen with citric

acid exhibited the lowest turbidity of gelatin solution, whereas

propionic acid led to the most turbid gelatin solution (Gomez- ́

Guill ́en and Montero 2001). Gimenez et al. (2005) reported that

use of lactic acid (25 mM) could be an excellent substitute for

acetic acid for the skin swelling process. The gelatin so obtained

showed similar properties to that prepared by using 50 mM

acetic acid without the negative organoleptic properties. Gelatin

obtained from the acid process is known as type A gelatin.

Alkaline Process Type B gelatins are generally produced by

alkali hydrolysis of bovine materials. This process results in

deamidation as well as degradation, leading to the lowered chain

length (Foegeding et al. 1996). Alkaline pretreatments are nor-

mally applied to bovine hide and ossein. Lime is most commonly

used for this purpose; it is relatively mild and does not cause

significant damage to the raw material by excessive hydrolysis.

However, 8 weeks or more are required for complete treatment.

Lime at concentrations of up to 3% is used in conjunction with

small amounts of calcium chloride or caustic soda. Alkaline

process using caustic soda takes 10–14 days for pretreatment

(Johnston-Bank 1983). Gelatin obtained from the alkaline pro-

cess is known as type B gelatin.

Cho et al. (2004) optimized the extraction condition for pro-

duction of gelatin from shark cartilage using response surface

methodology. Gelatin production has two important steps, (1) al-

kali treatment and (2) hot-water extraction. The alkali treatment

removes noncollagenous protein. Hot-water extraction causes

thermal hydrolysis, leading to the solubilization of gelatin. The

predicted maximum yields of 79.9% for gelatin production

were obtained when alkali treatment using 1.6 N NaOH for

3.16 days and hot-water extraction at 65◦C for 3.4 hours were

implemented.

Acid Process in Conjunction with Pepsin Traditionally, al-

kaline process has been used for gelatin production from raw

material with high degree of cross-linking. These harsh condi-

tions result in random hydrolysis of peptide bonds and decom-

position of some amino acids, leading to a product of variable

quality with a broad molecular weight distribution (Slade and