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

21 Fish Gelatin 401

The mixtures of fish gelatin andκ-carrageenan had the gels

with varying degree of turbidity, depending on the concentration

of polymers, pH, ionic strength, and the nature of the added salt

(Haug et al. 2004). The highest gel strength was found when

20 mM KCl and 20 mM NaCl were added into the mixtures

of 1% (w/v)κ-carrageenan with 2% and 5% (w/v) fish gelatin,

respectively. However, these mixtures exhibited more turbid gel

thanκ-carrageenan or fish gelatin alone since the system un-

dergoes associative phase separation promoted by the release of

counterions (Piculell et al. 1995). Complexes of fish gelatin and

κ-carrageenan at 60◦C were probably stabilized by electrostatic

interactions and the solutions were highly turbid, and at 4◦Cthe

strongest gel was obtained (Haug et al. 2004).

Liu et al. (2007a) determined the hardness of gelatin/pectin

mixed gels with different ratios. The addition of pectin resulted

in the increased gel hardness. The strong interactions between

two polymers in the mixed solution resulted in a synergistic

effect. At the same gelatin content, the lower pectin content

added to the system resulted in a harder gel. The excess pectin

content formed the repulsive forces in the junction zones, which

might reduce the formation of linkages between the aggregated

helices, leading to weakened gel structures (Liu et al. 2007a).

Oxidation process

Free radical-mediated protein modification affects protein func-

tionalities. Protein oxidation can lead to the formation of several

different kinds of protein cross-links (Stadtman 1998). For ex-

ample, abstraction of H atoms from protein by radical could

result in the reaction with one another to form –C–C– pro-

tein cross-linked products. The oxidation of protein sulfhydryl

groups can lead to disulfide –S–S– cross-linked proteins. Ad-

ditionally, the carbonyl groups obtained by the direct oxidation

of amino acid side chains of one protein may react with the

lysine amino groups of another protein to form Schiff-based

cross-linked products.

Fenton reaction, involving a mixture of ferrous ion (Fe^2 +)and

H 2 O 2 , generates hydroxyl radicals (HO•) at room temperature

(Walling 1975, Fenton 1984) as shown in equation below:

Fe^2 ++H 2 O 2 →Fe^3 ++HO•+OH−

H 2 O 2 is largely used in oxidation process. Its oxidizing prop-

erties are not only due to the presence of an active oxygen atom

in the molecule, but also to its ability to participate in radi-

cal reactions, with the homolysis of the O–O bond, leading to

the formation of the HO•radical (Chedeville et al. 2005). HO•

radical can oxidize organic compounds in solution (Namkung

et al. 2008).

Aewsiri et al. (2009a) reported that uses of H 2 O 2 for bleach-

ing of cuttlefish skin prior to gelatin extraction could improve

the bloom strength of gelatin gel. H 2 O 2 might induce the ox-

idation of protein with the concomitant formation of carbonyl

groups. Those carbonyl groups might undergo Schiff base for-

mation with the amino groups, in which the protein cross-links

were most likely formed (Stadtman 1997). Moreover, OH•can

abstract H atoms from amino acid residues to form carbon-

centered radical derivatives, which can react with one another

to form C–C protein cross-linked products (Stadtman 1997).

The larger protein aggregates were mostly associated with the

improved bloom strength.

Additionally, free radical in protein could be generated by

irradiation, such as UV-irradiation and gamma-irradiation. Irra-

diation makes protein oxidized, followed by the generation of

free radical, resulting in either cross-linking (protein aggrega-

tion) or degradation of protein. Bhat and Karim (2009) reported

that gelatin treated with UV-irradiation for 60 minutes prior

to preparing the gel showed higher gel strength than the gelatin

treated with UV-irradiation for 30 minutes as well as that without

any UV-irradiation, respectively. Bessho et al. (2007) reported

that insolubility due to cross-linking of the gelatin hydrogels

was induced at doses above 8 kGy gamma-irradiation. Hydro-

carbon groups (alkyl or a phenyl group of the side chains) are

the cross-linking sites of gelatin hydrogels.

APPLICATIONS OF GELATIN

Gelatin has been used widely in many sections of the food indus-

try. The major uses cover jellies, confectionery, meat products,

and chilled dairy products. It can be used in the pharmaceutical

industry, especially for hard and soft capsule manufacture and in

the photographic industry, which uses the unique combination

of gelling agent and surface activity to suspend particles of sil-

ver chloride or light-sensitive dyes (Kragh 1977, Fiszman et al.

1999, Soper 1999, Choi and Regenstein 2000, Park et al. 2007,

Zhou and Regenstein 2007, Cheng et al. 2008, Binsi et al. 2009).

Due to the drawbacks of fish gelatin—that it does not gel

at room temperature and requires temperature below 8–10◦C

for setting, it can also be used in other applications that do not

require a high bloom value such as for prevention of syneresis

and modification of food texture. Fiszman et al. (1999) studied

the effect of the addition of gelatin on the microstructure of acid

milk gels and yogurt and on their rheological properties. The

addition of 1.5% gelatin developed fairly firm and deformable

gels with almost total absence of syneresis. Dynamic rheology

showed that the yogurts with added gelatin exhibited more solid-

like behavior than the ones prepared without it.

Gelatins from tuna or tilapia skin (warm-water fish) have

a melting point of 25–27◦C (Choi and Regenstein 2000) and

have a bloom value of 200–250 g. These gelatins more closely

resemble bovine or pig gelatin, which melts at 32–35◦C. Fish

gelatin with lower gel melting temperatures had a better release

of aroma and offered a stronger flavor (Choi and Regenstein

2000). By increasing the concentration of gelatin or by using

gelatin mixtures, desserts made from fish gelatins would be

more similar to desserts made from high bloom pork skin gelatin

(Zhou and Regenstein 2007).

Cheng et al. (2008) observed that combinations of fish gelatin

with pectin have been used to make a low-fat spread. A de-

crease in the fish gelatin to pectin ratio (3:0, 2:1, 1:1, and 1:2)

resulted in an increase in bulk density, firmness, compressibility,

adhesiveness, elasticity, and meltability. On the other hand, use

of gelatin/sodium alginate blends to form casings could lower

water losses and lipid oxidation during chilled storage as com-

pared to pectin casing (Liu et al. 2007b). Recently, Binsi et al.