Food Biochemistry and Food Processing (2 edition)

BLBS102-c20 BLBS102-Simpson March 21, 2012 13:35 Trim: 276mm X 219mm Printer Name: Yet to Come

372 Part 3: Meat, Poultry and Seafoods

Table 20.3.Band Intensity Ratios of Cross-Linked Chain to Total Monomer Chains in Collagen from the Skin of

Several Sources

Collagens Sources α1/α 2 β/(α 1 +α2) γ/(α 1 +α2)

ASC Calf(a) ND 1.26 0.75

Black drum(a) ND 1.59 1.32

Sheepshead sea bream(a) ND 1.30 0.62

Deep-sea redfish(b) 2.47 1.52 1.10

PSC Black drum(a) ND 0.50 0.23

Sheepshead sea bream(a) ND 0.84 0.51

Deep-sea redfish(b) 2.15 1.03 0.19

Source: (a) Ogawa et al. (2003) and (b) Wang et al. (2007).

ND, not determined.

langbarbel catfish (Zhang et al. 2009), seaweed pipefish (Khan

et al. 2009), deep-sea redfish (Wang et al. 2007), brownstripe

red snapper (Jongjareonrak et al. 2005), ocellate puffer fish

(Nagai et al. 2002a), skate (Hwang et al. 2007), brownbanded

bamboo shark (Kittiphattanabawon et al. 2010a), blacktip shark

(Kittiphattanabawon et al. 2010c), cuttlefish (Nagai et al. 2001),

octopus (Nagai et al. 2002b), scallop (Xuan Ri et al. 2007),

paper nautilus (Nagai and Suzuki 2002), and common minke

whale (Nagai et al. 2008). Skierka and Sadowska (2007) found

that pepsin treatment of Baltic cod skin in acetic acid shortened

the extraction time to 24 hours and the solubility of collagen,

after pepsin digestion increased from 55% to 90%. After ASC

extraction, the residues that represent the cross-linked molecules

are further extracted in the presence of pepsin. The collagen

obtained with pepsin treatment is referred to as “pepsin-soluble

collagen, PSC” (Nagai et al. 2001, Ogawa et al. 2003, Nalinanon

et al. 2007) or “atelocollagen” (Lee et al. 2001, Ikoma et al.

2003). The use of pepsin as the aid of collagen extraction

resulted in the increased yield (see Table 20.4). The yield of ex-

tracted collagen also increased with increasing preswelling time

and pepsin treatment time. From the skin of bigeye snapper (Pri-

acanthus tayenus) subjected to preswelling with 0.5 M acetic

acid and subsequent pepsin hydrolysis, those treated with these

two steps with longer time led to the increase in yield of collagen

extracted (Nalinanon et al. 2007). At the same preswelling time

and hydrolysis time, bigeye snapper pepsin (BSP) exhibited

greater extracting ability than did porcine pepsin. However,

the highest yield (∼65%) for collagen extraction from the

skin of bigeye snapper was found when BSP was added with

a reaction time of 48 hours, regardless of preswelling time

(Nalinanon et al. 2007). Swollen skin, which was pretreated

with acetic acid, possibly had a porous and loose structure

caused by charge repulsion. As a result, the penetration of

pepsin into the skin matrix could be enhanced. Thus, hydrolytic

reaction of pepsin toward collagen was augmented. Miller

(1972) proposed that the mechanism whereby the proteolytic

activity of pepsin alters the solubility properties of cartilage

collagen involves the degradation of the nonhelical region, thus

effectively eliminating a site of intermolecular cross-linking.

Drake et al. (1966) reported that most of intra- and intermolec-

ular cross-links found in collagen occur through the telopeptide

region. Some of the telopeptides of calfskin tropocollagen are

vulnerable to pepsin action, since intramolecular cross-links are

broken on pepsin digestion and fragments comprising a small

fraction of the molecule (approximately 1%) become dialyzable

(Drake et al. 1966). Pepsin treatment for collagen extraction

has the impact on the proportion of compositions. In general,

β-andγ-chains, dimmer, and trimer in PSC are decreased as

compared with those found in ASC. Cleavage of telopeptide

region more likely results in the conversion of cross-links, such

asβ- andγ-chains, to theα-chain, which can be of ease for

extraction. The band intensity ratios ofα1-chain toα2-chain and

cross-linked chain (trimer form,γ, or dimmer form,β)tototal

monomer chain (α 1 +α2) in collagens are shown in Table 20.3.

Nalinanon et al. (2007) reported that higher molecular-weight

(MW) components, includingγ-chain, were found to a greater

extent in ASC extracted from the skin of bigeye snapper

than in PSC. Ogawa et al. (2003) found that the intra- and/or

intermolecular cross-linking of collagens,βandγcomponents,

were richer in ASC than in PSC for collagens from the skin of

black drum and sheepshead sea bream. Similar results were also

reported in collagens extracted from deep-sea redfish (Wang

et al. 2007). Those high-MW components might be degraded

to smaller components, such asβ,α1, orα2, by pepsin action.

Pepsin removes the cross-link-containing telopeptide, and the

concomitantly oneβ-chain is converted to twoα-chains (Nagai

et al. 2001, Wang et al. 2007). Similar changes were also found

in acid-solubilized calfskin tropocollagen when treated with

pepsin. Native calfskin tropocollagen consisted ofα:β:γ at

a ratio of 32:65:3, whereas the components of pepsin-treated

tropocollagen were changed to 72:23:3 (Drake et al. 1966).

Therefore, the yield of collagen extraction was significantly

increased because of the improvement of collagen extractability

by pepsin (Ogawa et al. 2003, Nalinanon et al. 2007, Wang

et al. 2007, Nalinanon et al. 2008, Benjakul et al. 2010).

Generally, commercial pepsin used for collagen extraction

is isolated from porcine stomach. Owing to the limitation of

porcine pepsin mostly associated with the religious constraint,

pepsins from fish origin including bigeye snapper (Nalinanon

et al. 2007), albacore tuna (Nalinanon et al. 2008), and tongol

tuna (Nalinanon et al. 2008, Benjakul et al. 2010) have been

used as the potential aid for collagen extraction from fish skin.