Fish Bone and Scale as a Potential Source of Halal Gelatin
Fish gelatin is an important alternative gelatin which can be considered as Halal and acceptable by all religions. It is made from fish by-products of which fish skin is the most widely used part. The collagen and gelatin-like property of fish bones and scales coupled with their readily availability make it a potential source for development into gelatin products. This review discusses the potentials for the development and utilization of fish bones and scales in the production of gelatins. It also looks at the raw materials, processes, properties and the improvement of fish gelatins for future commercial use.
November 25, 2010; Accepted: December 02, 2010;
Published: April 04, 2011
Gelatin is a popular collagen derivative primarily used in food, pharmaceutical,
photographic and technical products. In foods, gelatin provides a melts-in-the-mouth
function and to achieve a thermo-reversible gel property. Its clarity, bland
flavor, emulsifying characteristics, stability, texture properties and the ability
to be applied in a wide range of pH, makes it suitable to be used in confectionaries
and dairy products (GMIA, 2001). In addition, it is recommended
for used as a dietetic food, salt reducer, flocculating agent, protein enrichment
and adhesives. In the pharmaceutical industry gelatin is generally used in capsules,
tablets, haemostatic sponge, blood plasma substitutes, suppositories and vitamin
encapsulation (GME, 2010).
Gelatin is obtained from the degradation of collagen, thus collagen-containing
tissues are generally used as sources of gelatin. In mammals, birds and fishes,
the most commonly used source of collagen for gelatin is obtained from body
protein constituents of the skin, tendons, cartilage, bone and connective tissue,
whereas in invertebrates, collagen is an essential constituent of the body wall
(Balian and Bowes, 1977). Porcine and bovine gelatins
are still the most widely used today; therefore the development of alternative
sources of gelatin is one of the issues that have been given much priority.
In addition to the health related issues that, bovine gelatin has a potential
risk of spreading bovine spongiform encephalopathy (BSE), widely known as mad
cow diseases and foot-and-mouth disease (FMD) (Jongjareonrak
et al., 2005), it used is vitally limited by religious concerns.
For instance, Hindus do not consume cow-related product (Karim
and Bhat, 2009). Similarly, Islam considers all pork-related products to
be non Halal and prohibited to be consumed. Thus researches into the used of
some alternative source of gelatins are being pursued. Such researches include
the exploitation of marine and poultry products. It has been established that
fish and fish products in generally can be considered as Halal food as long
as it does not contain toxins and poisons (Huda et al.,
1999). Therefore, the objective of this review is to present the potentials
of using fish bones and scales for gelatins and available technologies to improve
upon the yield of fish gelatins.
RAW MATERIAL OF HALAL GELATIN
Gelatin is a product of rapidly growing market. In 2003, the world market for
gelatin reached 278.300 tons; consisting of 42.4% from pig-skin origin, 29.3%
bovine hides, 27.6% bones and 0.7% from other sources (GEA,
2010). In previous years, (Karim and Bhat, 2009)
reported that the annual world output of gelatin increased to 326.000 tons with
the highest source being pig-skin (46%), followed by bovine hides (29.4%), bones
(23.1%) and other sources (1.5%). In such proportions, existing gelatins do
not meet the demands of the Halal market. As such alternative sources of collagen
for gelatin from other sources other than porcine and bovine have been studied.
They include previous studies on fish skin, bone and fins collagen isolation
by (Nagai and Suzuki, 2000), sea urchin by Robinson
(1997), jellyfish by Nagai et al. (2000)
and bird feet by Lin and Liu (2006).
The production of gelatin from fish waste is a topic that has gain much attention,
especially from fish skin due to its properties and qualities. In addition to
the nature of the fish, that is almost acceptable by all communities, it also
provides a solution to the utilization of huge amounts of fish wastes produced
by the fish industry. For instance Guerard et al.
(2001) reported that, canned fish processing generates solid wastes composed
of muscles after the loins have been taken, fish viscera, gills, flesh dark/dark
muscle, head, bone, and skin, which can be as high as 70% of the original material.
Whereas skin, scale and bone wastes consist of more than 30% of fish processing
(Kittiphattanabawon et al., 2005). As the total
world fisheries reaches about 141.6 million tons (FAO, 2006),
with anticipated increases in subsequent years, its a worth taken effort
to utilize the large quantities of fish waste into useful products such as fish
PROCESSING OF GELATIN
Fish skin, the common source of Halal gelatin: Gelatin can be obtained
in several ways. Johns and Courts (1977) demonstrated
that, the breakage of cross-links and non-covalent bonds of collagen can be
done by direct thermal treatment, use of acidic or alkaline and enzymatic pre-treatments.
Acidic and alkaline pre-treatment is the most widely used method, and has advantage
over the direct thermal pre-treatment that is carried out under high temperature
(heating and autoclaving), which produces an gel inferior quality.
In recent times, fish skin is the most widely used fish raw material for making
fish gelatin. In previous works, gelatin extraction from fish species have been
carried out using Alaskan pollock skin (Zhou and Regenstein,
2004, 2005), yellow-fin tuna (Cho
et al., 2005), Atlantic cod (Arnesen and Gildberg,
2006), bigeye and brownstripe red Snapper (Jongjareonrak
et al., 2005), Channel catfish skin (Liu et
al., 2008), shark cartilage (Cho et al.,
2004), grass carp skin (Kasankala et al., 2007),
Nile perch skin and bone (Muyonga et al., 2004),
and many more.
Gelatin from acid-treated collagen, known as type A gelatin is the most widely
reported type of gelatin derived from fish skin material.
Karim and Bhat (2009) confirmed that acidic treatment is most suitable method
to be applied for fish skin due to its less covalently cross-linked collagen.
Apart from acidic pre-treatment for Nile perch skin and alkaline pre-treatment
for big eye snapper as reported by Muyonga et al.
(2004) and Benjakul et al. (2009), respectively.
Pre-treatment can be done simultaneously using both acidic and alkaline treatment
as showen by Zhou and Regenstein (2005). Zhou
and Regenstein (2005) found that alkaline and acidic pre-treatments had
positive effect on removing non-collagenous proteins and resulted in high gelatin
yield and gel strength in Alaska Pollock gelatin. Furthermore, they also mentioned
that alkaline treatment followed by acid neutralization provide a neutral or
weak acid extraction medium that makes it possible to produce high gelatin yield.
The removal of non-collagenous materials has been a common preparatory step
in collagen isolation and the extraction of gelatin. Nagai
and Suzuki (2000) performed the removal of non-collagenous proteins with
0.1 N NaOH under 4°C. In fish skin gelatin production, this step is continued
to swelling step using low concentration of either acid or alkali solution.
Previous research carried out by Huda et al. (2004)
indicated that, different concentrations of acetic acid (1, 2, 3 and 4%) during
pre-treatment had no significant effect on sensory evaluation of the produced
gelatin. Contrarily, Yang et al. (2007) mentioned
that acid solution concentration had significant effect on yield of protein
and viscosity of gelatin in their work involving channel catfish.
After pre-treatment process, the gelatin can be extracted with aqueous extraction
and heating (by gentle and mild temperatures) treatment. The extraction can
be performed at a temperature between 50-90°C for 1-6 h before it is separated,
evaporated and usually freeze dried (Wangtueai and Noomhornm,
2009; Zhang et al., 2010). This step distinguishes
between gelatin extractions processes and the isolation of collagen. In collagen
isolation process, collagen is not denatured by heating, but is extracted using
the acid repeatedly and then separated, most commonly by using salting process.
Several fish skin-based gelatin has been reported to have varied bloom value
(gel strength) compared with food grade bovine origin. Benjakul
et al. (2009) reported that gelatin derived from two species of bigeye
snapper fish has bloom strength value of 227.73 and 254.10, which was lower
when compared to gelatin from bovine bones (293.22). Furthermore Gomez-Guillen
et al. (2002) found a bloom value of 350 and 340, for sole and megrim
fish species, respectively. Although bloom values between fish skin gelatins
and other gelatin sources vary, fewer works done on fish skin for producing
gelatin reveals that fish skin is one of potential source of high quality gelatin.
Fish bone and fish scale could also be a potential source of gelatin due to
its similar collagen characteristic to fish skins as reported by Wang
et al. (2008), who showed that collagen composition as isolated from
the skin, scale and bone of deep sea redfish had similar amino acid profile.
Isolation of gelatin from fish bones and scales: There are slight differences
in the process of isolating gelatin from fish skins, bones and scales due to
differences in their characteristics. For bones and scales, demineralized (decalcified)
treatment is a common process employed after removal of non-collagenous material
prior to the acid solution treatment. This process can be carried out by immersion
using compounds such as EDTA until the hard part of bones disappears. In carp
samples, skipjack tuna, Japanese sea bass, ayu, yellow sea bream, chub mackerel,
and bullhead shark, demineralization takes 5 days (Nagai
and Suzuki, 2000a; Duan et al., 2009). Demineralization
has also been achieved using 3% HCl at ambient temperature in Nile perch bones
in approximately 9-12 days until a leached bone (ossein) is formed (Muyonga
et al., 2004). This demineralization period is much longer when compared
to acid treatments on skin samples of the same species which only took 16 h.
Furthermore, Wangtueai and Noomhornm (2009) employed
a low alkaline concentration(0.1-0.9%) at 30°C for 1-5 h to process lizardfish
scales, whereas Arafah et al. (2008) used 4-6%
HCl in 24-48 h demineralization period for snakehead fish bone. In addition
to the demineralization process, raw materials from both porcine and bovine
bones undergo a process of defatting (GEA, 2010). In fish
bones, this process is done by using butyl alcohol, hexane or a detergent (Duan
et al., 2009; Nagai and Suzuki, 2000a; Wang
et al., 2008). Not only different in demineralization (Duan
et al., 2009) used different condition to perform acid treatment
at carp fish. For the skin and scale, 0.1 M NaOH in 1:8 (w/v) sample/alkali
solution was used under stirred for 6 h, while for bone the ratio was set into
An alternative approach to substitute acidic or alkaline pre-treatment by using
enzymes in the production of gelatin from grass carp has been demonstrated by
Zhang et al. (2010). In their work they use protease
enzymes (after the removal of non-collagenous part by NaCl and demineralization
using HCl) at a neutral pH and 20-40°C for 1-12 h. This produced a good
quality gelatin with gel strength of 172-219 g. Several methods for gelatin
and collagen isolation from fish bones and scales are presented in Table
CHEMICAL PROPERTIES OF BONE AND SCALES GELATIN
Table 2 summarizes the amino acid composition of bone and
scale based gelatins. In general, the amino acid composition of both fish scale
and bone is almost similar to fish skin-based gelatin, and showed slight differences
with commercial gelatin. With the exception of gelatin from pigskin origin,
all other gelatins do not contain aspargine and glutamine. In addition, amino
acid composition of fish scales and bone varied, particularly in cysteine content.
Amino acids from pigskin gelatin and bone gelatins (Nile perch bone, commercial
bones) do not contain cysteine. Gelatin from fishs bone and scale, in
general have higher of imino acids (proline) content than the fish skin gelatin
and almost the same with commercial gelatin from pigskin and bone. Muyonga
et al. (2004) mentioned that the higher content of imino acid in
Nile perch contributed to better gelling properties in their gelatin.
However, the content of hydroxyproline in fish skin gelatin is higher when
compared with fish bone and scale gelatin as well as from commercial gelatin.
For the content of glycine, which is the most common component in collagen,
fish-based gelatin had lower quantities compared to those from mammalian sources
(Wangtueai and Noomhornm, 2009; Zhang
et al., 2010; Liu et al., 2008; Muyonga
et al., 2004; Kasankala et al., 2007;
Ledward, 2000), although Zhang et
al. (2010) found a very high content of glycine in grass carp scale.
Arnesen and Gildberg (2002) mentioned that the lower
concentration of hydroxyproline in fish compared to bovine and porcine accounts
for the low gel strength in fish based gelatins. Nonetheless,
Intarasirisawat et al. (2007) reported that heat-stable indigenous
proteases were responsible for the degradation of gelatin molecules especially
α and β-chains during extraction at elevated temperature; the results
of this is low bloom value of gelatin.
Muyonga et al. (2004) compared gelatin extracted
from young and adult bones of Nile perch and found that gelatin extracted from
young bones had higher concentration of low molecular weight fraction compared
to gelatins from old bones. Recent study carried out by Zhang
et al. (2010) using grass carp scales and enzymatic treatment revealed
that the lower the amino acids content of gelatin, the higher the α-chain
PHYSICAL PROPERTIES OF FISH BONE AND SCALES GELATIN
The physical properties of fish bones and scales based gelatins are summarized
in Table 3. The yield of gelatin extraction have been reported
to range from 0.98-3.9% for bones and 9.1-10.9% for bovine gelatin was 322±4.56
(Wangtueai and Noomhornm, 2009).
|| Procedures employed to isolate fish bones and scale gelatin/collagen
||Amino acids composition of several gelatins from fish bones
and scales (/100 residues)
This study also mentioned that, the optimum conditions for gelatin extraction
by alkaline pre-treatment was achieved using NaOH solution at a concentration
of 0.51%, 78°C for 3.10 h treatment time and 3.02 h extraction time. Cheow
et al. (2007) reported that gelatin from sin croaker and shortfin
scad had low gel strength (of 124.94 and 176.92 g, respectively) compared to
bovine gelatin 239.98 g (9.76±0.12 mg 100 g).
|| Physical properties of several gelatins from fish bones and
scales (/100 residues)
Lower bloom value might be the biggest problem for gelatin from fish origin,
although some works have indicated that fish skin had higher gel strength than
bovine and porcine gelatin (Arnesen and Gildberg, 2002;
Cho et al., 2005).
High bloom value (gel strength) of some gelatin derived from fish bone is one
of the advantages fish bone gelatin has over gelatin produce from fish skin. Zhou
and Regenstein (2005) reported that Alaska pollock gelatin from fish skin
have a bloom value of 98 g. Furthermore, a bloom value of 108 g for salmon and
71 g for cod (Arnesen and Gildberg, 2007), 124.9 g for
Sin croaker (Cheow et al., 2007), 128.1 g for red
tilapia skins (Jamilah and Harvinder, 2002), 56 g for
Bigeye snapper and 135.5 g for bigeye pepsin (Nanilamon et
al., 2008) and 105.7 for Brownstripe red snapper Jongjareonrak
et al. (2005) have been reported. These values differ significantly
with gelatin from porcine and bovine origin. Nonetheless fish products have a
high potential to be used for gelatin. GEA (2010) showed
that, gelatin is applied in various sectors in the industry based on different
bloom grades (50-300) according to user needs.
Gelatins of fish bone and scales origin also have lower setting and melting
point which has been reported to range from 13.3-19 and 20.7-26.9, respectively;
as well as the viscosity (28.2 and 30.0) compared with gelatins of bovines and
commercial fish origin, which ranges from 22.5-25.3 and 26.3-31.6, respectively
as well as the viscosity (40.0 and 46.0 mSt), yet the isoionic point of fish
bone ad scale gelatin are stable at 7.0-7.2 (Muyonga et
al., 2004; Liu et al., 2008).
IMPROVEMENT OF FISH ORIGIN GELATIN
The low yields of gelatin obtained from fish by-products compared to gelatin
from other sources are issues of concern. A number of studies have been carried
out to address this challenge. For instance, Gudmunsson
and Hafsteinsson (1997) mentioned that the quality of gelatin can be controlled
to the desired standard by manipulating pre-treatment and processing conditions.
The same researchers also reported that, a treatment combination of citric acid,
low concentration of sulfuric acid and sodium hydroxide resulted in a higher
yield (14%) compared to 11% when a high concentration of citric acid (>1%)
and sulfuric acid, and NaOH (>2%) were used. Arafah et
al. (2008) also showed that, a higher concentration of acid, together
with increased extraction temperature did lower the gelatin yield of mackerel
fish skin. Zhang et al. (2010) used enzymatic treatment
for grass carp scales and concluded that, gelatin from grass carp scales can
be made into good quality gelatin which will have high gel viscoelastic property
at lower temperature and good quality gel strength (276±12 g) compared
to commercial porcine gelatin. Aewsiri et al. (2009)
reported that fish products can be subjected to bleaching to enhance the quality
of the gelatin. Thus in their study, they employed H2O2
as a bleaching agent in gelatin production from cuttlefish, and found higher
yield, brighter color and effective increase in gel strength. Fernandez-Diaz
et al. (2003) mentioned that gelatin extracted from lower temperature
storage fish skin had higher gel strength compared to samples that stored at
higher temperature. Bhat and Karim (2009) also observed
that UV irradiation increased the gel strength of fish gelatin.
Production of gelatin from fish bones and scales are important alternative source for fish skin gelatin. Although the resulting yield from fish bone and scales gelatin is lower than that obtained from fish skin, the quality of gelatin produced is not inferior when compared. Nonetheless several studies have indicated that gelatins produced from fish bones and scales have acceptable gel strength (bloom value). Weak gel strength and low melting point, makes gelatin derived from fish unable to be used completely to replace the role bovine and porcine gelatin plays. With the development of research, various solutions such as enzyme-aided processes, combination of acid-alkali solutions and gelatin bleaching processes have been found to improve the quality of gelatin from fish bone and scales.
Preparation of gelatin from fish by-products is a way of utilizing the huge waste created by the fish industry into useful products. It also has the advantage of being accepted with ease as Halal and Kosher food.
The first author is grateful to the Institute of Postgraduate Studies, Universti Sains Malaysia for the opportunity given him to pursue a Ph.D programme through USM Fellowship Scheme. Both authors are also grateful for the support given by the Universti Sains Malaysia for running research in the area of fish processing technology.
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