Biomedical Engineering Reference
In-Depth Information
drying, freeze concentration, and freeze texturization [
98
]. Size and location of
ice crystals are major factors in the quality of thawed tissue products. Smaller ice
crystals are preferred in ice cream since large crystals will results in an icy texture.
In freeze drying, ice morphology influences the rate of sublimation and several
morphological characteristics of the freeze-dried matrix as well as the biological
activity of components (e.g., in pharmaceuticals).
Nucleation is the most critical step to control the crystal size distribution during
crystallization [
132
]. The freezing (cooling) rate is usually the parameter used for
controlling the size and size distribution of ice crystals in frozen and partly frozen
systems. Recently, the use of nucleation agents, AFPs, ultrasound, and pressure
freezing methods, known by the generic name of “freezing assisting techniques,”
have been proposed to control nucleation and ice morphology [
133
].
Several potential applications for AFPs have been envisaged in foods [
98
]. In ice
cream manufacture, AFPs have been used to fabricate smaller ice crystals compared
to a control [
134
]. In meat products, ice crystal size are reduced by soaking bovine
and ovine muscle in a aqueous solution up to 1 mg/mL of AFP prior to freezing
at
20
ı
C[
135
]. Preslaughter administration of AFP intravenous injectation to
lambs reduced ice crystal size and drip loss after thawing [
136
]. The gel-forming
functionality of surimi in both chilled and frozen conditions is also preserved by
AFPs. In contrast to conventional cryoprotectants such as sucrose-sorbitol mixtures,
AFPs remarkably preserved Ca
2C
ATPase activity of actiomyosin during storage
and provided better protection [
137
].
Fungal hydrophobin AFPs repressed ice crystal growth during frozen storage,
i.e., ice recrystallization, and modified ice crystal shape in aerated and nonaerated
frozen food products as suggested by Unilever patent [
138
]. Although commercial
AFPs are currently available, they are mainly for research or special uses because
of their high price. Chemical synthesis and genetic engineering may be a solution to
produce cost-effective AFPs, hence the need to promote their applications in frozen
food products [
139
].
2.5
AFPs Synthesis and Mimics
2.5.1
Antifreeze Glycoproteins Synthesis and Mimics
The synthesis of AFGPs as pure glycoforms has been achieved through using
ligation and polymerization strategies, and key structure-activity studies that are
essential to inform the design of functional mimics have been reported [
140
-
142
].
The AFGPs isolated from fish blood plasma range in molecular mass from
approximately 33 kDa (50 repeating units) to 2.6 kDa (four repeating units).
They consist of repeating tripeptide units (Ala-Thr-Ala)
n
with a disaccharide
moiety (Galb1-3GalNAca1-) attached to each threonyl residue [
25
]. Nishimura and
colleagues reported the first synthesis of AFGPs in the form of pure glycoforms in
