Mechanical properties of mammalian and fish gelatins based on their weight average molecular weight and molecular weight distribution

Acid porcine skin gelatins (type A), lime bone gelatins (type B) and gelatin from different cold water fish species were compared on the basis of low deformation mechanical properties, Bloom value, weight average molecular weight, molecular weight distribution and isoelectric point. The dynamic storage modulus and Bloom value for all types of gelatin increased with increasing weight average molecular weight. Type A and type B gelatins with similar weight average molecular weight exhibited different dynamic storage modulus (G′) and different Bloom values. This is most probably due to a different molecular weight distribution as well as the presence of different hydrolytic fragments. The present study suggests that it may be possible to improve the mechanical properties by removing low molecular weight molecules from a gelatin sample. The Bloom values for gelatin from haddock, saithe and cod were determined to be 200, 150 and 100 g from a linear correlation between G′ and Bloom.     

Effect of clay content, homogenization RPM, pH, and ultrasonication on mechanical and barrier properties of fish gelatin/montmorillonite nanocomposite films

The effect of clay content, homogenization RPM, and pH on the mechanical and barrier properties of fish gelatin/nanoclay composite films was investigated. The addition of 5% nanoclay (w/w) increased the tensile strength from 30.31 ± 2.37 MPa to 40.71 ± 3.30 MPa. The 9 g clay/100 g gelatin film exhibited the largest improvements in oxygen and water barrier properties. Oxygen permeability decreased from 402.8 × 10⁻⁶ ± 0.7 × 10⁻⁶ g m/m² day atm to 114.4 × 10⁻⁶ ± 16.2 × 10⁻⁶ g m/m² day atm and the water vapor permeability decreased from 31.2 × 10⁻³ ± 1.6 × 10⁻³ ng m/m² s Pa to 8.1 × 10⁻³ ± 0.1 × 10⁻³ ng m/m² s Pa. The XRD and TEM observation suggested that the ultrasonication treatment (30 min at 40% output) resulted in exfoliation of the silicates.     

提取温度与提取时间对真鳕鱼骨明胶理化性质的影响

以真鳕鱼骨为原料,对其明胶的理化性质进行了研究。提取温度分别设置为45和70℃,不同提取温度的提取时间分别设置为4和8h。热水抽提后冷冻干燥,得到4种明胶样品,并对其化学组成及理化性质进行研究。结果表明,随着提取温度的升高和提取时间的延长,样品凝胶强度、乳化性和乳化稳定性随之下降,而其浊度和起泡性能则有所上升。红外光谱分析显示,70℃提取制备的明胶样品其酰胺I吸收峰强度要弱于45℃提取的样品,这说明提取温度的升高会导致样品分子结构无序程度的增加。在扫描电镜观察下,高温制备的凝胶结构排列无规则且具有大量孔洞。      

Rheological and sensory properties of fish gelatin gels as influenced by agar from Gracilaria tenuistipitata

Agar extracted from Gracilaria tenuistipitata and commercial agars were incorporated into fish gelatin at various levels (0, 5, 10, 15 and 20% gelatin substitution). G. tenuistipitata agar (GA) had lower failure stress (~16 kPa) than commercial agar (CA) (~20 kPa). However, the former showed higher failure strain (~30%) with lower melting temperature (65.9 °C). The critical linear stress and failure stress of agar/gelatin mixed gels increased with increasing agar levels (P < 0.05). At 15 and 20% of agar used, the mixed gels containing CA exhibited higher failure stress than those with added GA (P < 0.05). Two melting points of agar/gelatin mixed gels were observed, corresponding to the melting temperatures of gelatin and agar gels. Nevertheless, the incorporation of agar lowered the likeness score of gelatin gel. Thus, both GA and CA had the impact on rheological property and the selected sensory characteristics of fish gelatin, depending on the level of substitution.     

Characteristics and functional properties of gelatin from splendid squid (Loligo formosana) skin as affected by extraction temperatures

Gelatin was extracted from the skin of splendid squid (Loligo formosana) at different temperatures (50, 60, 70 and 80 °C) with extraction yield of 8.8%, 21.8%, 28.2%, and 45.3% (dry weight basis) for G50, G60, G70 and G80, respectively. Gelatin from the skin of splendid squid had a high protein content (∼90%) with low moisture (8.63–11.09%), fat (0.22–0.31%) and ash contents (0.17–0.68%). Gelatin extracted at higher temperature (G80) had a relatively higher free amino group content than gelatin extracted at lower temperatures (G50, G60 and G70) (P < 0.05). All gelatins contained α- and β-chains as the predominant components. Amino acid analysis of gelatin revealed the high proline and hydroxyproline contents for G50 and G60. FTIR spectra of obtained gelatins revealed the significant loss of molecular order of the triple-helix. The gel strength of gelatin extracted at lower temperature (G50) was higher than that of gelatins extracted at higher temperatures including G60, G70 and G80, respectively. The net charge of G50, G60, G70 and G80 became zero at pHs of 6.84, 5.94, 5.49, and 4.86, respectively, as determined by zeta potential titration. Gelatin extracted at higher temperature (G80) had the lower L* value but higher a* and b* values, compared with those extracted at lower temperatures (P < 0.05). Emulsion activity index decreased, whilst emulsion stability index, foam expansion and stability increased as the concentration (1–3%) increased (P < 0.05). Those properties were governed by extraction temperatures of gelatin. Thus gelatin can be successfully extracted from splendid squid skin using the appropriate extraction temperature.     

Effects of a cross-linking enzyme on the protein composition,mechanical properties,and microstructure of Chinese-style noodles

Flours, representing the three major classes of Canadian wheat used for the production of noodles, were processed into fresh, Chinese-style, yellow alkaline noodles (YAN) with and without (1 w/w, fwb) the cross-linking enzyme transglutaminase (TG). The flours, YAN-TG and YAN + TG were sequentially extracted to remove albumins and globulins, followed by a series of 50% propanol extractions (±4% DTT) and 50% propanol +4% DTT +1% acetic acid to ensure removal of all extractable gliadin and glutenin components. Reverse-phase (RP) HPLC analyses of all propanol extracts were performed and the change in protein composition and distribution reported. Raw YAN, ±TG, were simultaneously evaluated for their fundamental rheological characteristics using ultrasound and stress relaxation testing. Significant changes in the distribution of protein within the various propanol extracts were observed when the flours were processed into YAN ± TG. The amount of unextractable protein increased by as much as ∼3-fold in YAN + TG, and ∼2-fold in YAN-TG, relative to that present in their respective source flour. Significant differences were observed within and between the YAN variety samples for the longitudinal modulus and the tan delta, when processed ±TG. Significant correlations (p = 0.05) were observed between protein composition, ultrasonic and stress relaxation parameters.