Food Biochemistry and Food Processing (2 edition)

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21 Fish Gelatin 389

bonds and is partially reversible in agreement with the gelling

properties of gelatin (Bigi et al. 1998). Gelatin has been widely

applied in the food industry as ingredients to improve the elas-

ticity, consistency, and stability of foods. It can be used for

medical and pharmaceutical purposes such as encapsulation,

production of hard and soft capsules, wound dressing, adsor-

bent pads, and edible film formation. Furthermore, it can be

applied for biomaterial-based packaging and photographic in-

dustries (Jongjareonrak et al. 2006c).

PRODUCTION OF GELATIN

Production of gelatin can be divided into three main steps, (1)

pretreatment, (2) extraction, and (3) drying (Fig. 21.1). All pro-

cesses used for gelatin extraction have direct impact on the yield

and properties of gelatin obtained. The process has been opti-

mized for different sources of raw materials (Cho et al. 2004,

Zhou and Regenstein 2004, Cho et al. 2005, Yang et al. 2007).

Pretreatment of Raw Material

Removal of Noncollagenous Protein

Prior to gelatin extraction from raw material, the pretreatment is

practically implemented to increase purity of gelatin extracted.

Alkaline solution has been used to remove considerable amounts

of noncollagenous materials (Johns and Courts 1977, Zhou and

Regenstein 2005) and break some interchain cross-links. Also,

the process is able to inactivate proteases involved in degrada-

tion of collagen (Regenstein and Zhou 2007b). During alkaline

pretreatment, the type of alkali does not make a significant dif-

Raw materials

↓

Noncollagenous protein removal process

↓

Fat removal process (optional)

↓

Demineralization process (optional)

↓

Swelling process

↓

Extraction with distilled water

↓

Filtration

↓

Clarification (optional)

↓

Drying

↓

Gelatin powder

Figure 21.1.Scheme for gelatin extraction.

ference, but the concentration of alkali is critical (Zhou and

Regenstein 2005). Yoshimura et al. (2000) reported that alkali

attacks predominantly the telopeptide region of the collagen

molecule during pretreatment. Thus, some collagen can be sol-

ubilized by an alkali solution. Long time and high concentration

of alkaline pretreatment decreased the yield of gelatin from skin

of channel catfish (Yang et al. 2007). The concentration of al-

kali, time, and temperature used for pretreatment varied with

raw materials (Table 21.1).

Table 21.1.Pretreatment Conditions for the Extraction of Gelatin from Different Fishes

Conditions

Raw Materials

Alkaline

Type/Concentration

Temperature

(◦C)

Time

(min)

Alkaline Changing

(times) References

Brownbanded bamboo

shark and blacktip

shark

0.1 M NaOH 15–20 40 3 Kittiphattanabawon

et al. (2010)

Atlantic salmon skin 0.04 N NaOH 8 30 2 Arnesen and Gildberg

(2007)

Cod skin 0.2%(w/v) NaOH NMa 40 3 Gudmundsson and

Hafsteinsson (1997)

Sin croaker skin and

shortfin scad skin

0.2%(w/v) NaOH NM 40 3 Cheow et al. (2007)

Yellowfin tuna skin 0.1 N NaOH 20 40 3 Rahman et al. (2008)

Megrim skin 0.2 N NaOH 5 30 3 Montero and

Gomez-Guillen

(2000)

Black tilapia and red

tilapia skin

0.2%(w/v) NaOH 15–27 40 3 Jamilah and Harvinder

(2002)

Shark cartilage 1.6 N NaOH 8 3.14 days 1 Cho et al. (2004)

aNM: not mentioned.