| Gelatin from chum salmon(Oncorhynchus keta)skin(GCSS)was extracted using water method at 40 ?,50 ?,60 ?,70 ?,80 ? and 90 ? in this research.The yield of GCSS increased from 26.1%to 43.5%as temperature increased from 40 to 90 ?(p<0.05).The amino acid composition was determined by high performance liquid chromatography(HPLC).Glycine was dominant amino acid(>30%)followed by alanine and proline(>10%)in obtained gelatin.Total imino acids content was 111?121 residue/1000 residue,and its content declined as temperature increased(p<0.05).The protein pattern was determined by SDS-PAGE electrophoresis.GCSS40,50 and 60 exhibited strong ?-,?1-and ?2-chain while the three sharply faded in GCSS70,80 and 90,forming low molecular weight fragments.The functional group information of gelatin was determined by FTIR.Amide A,? and ? were shifted to higher wavenumber in GCSS70,80 and 90 compared with that of GCSS40,50 and 60.X-ray diffraction analysis showed lower intensity of peak at 7° in GCSS80 and 90(<46%)than in other GCSS(>54%).The color of gelatin was measured by a colorimeter.a*,b*and ?E*value increased as temperature increased(p<0.05).The gel strength of gelatin was measured by a texture analyzer.Gel strength of GCSS declined from 87.7 to 4.97 g as temperature increased from 40 to 80 ?(p<0.05)and that of GSCC90 was too low to be measured.Emulsion activity and stability decreased as temperature increased(p<0.05).Foam expansion and stability of GCSS40,50 and 60 were lower than those of GCSS70,80 and 90(p<0.05).GCSS had a good yield,fair emulsifying and foaming capability but poor gel properties.Extraction temperature greatly affected the yield,composition and functionality of GCSS.The temperature should be lower than 50 ? for GCSS extraction.Subsequently,gel strength enhancement of GCSS with different concentration of oxidized tannic acid,chlorogenic acid and caffeic acid was investigated.The results showed that gel strength of samples added with oxidized polyphenols was higher than that of control group(p<0.05),but the degree of enhancement was different.Among them,oxidized tannic acid was the best(p<0.05),and the gel strength of the samples increased significantly with the increase of its concentration(p<0.05).L*value of gelatin added with oxidized tannic acid were higher than that of control group(p<0.05),a*and b*values had no significant difference to control group(p<0.05).a*and b*value of gelatin gel with oxidized chlorogenic acid and caffeic acid increased and its L*value decreased;these two oxidized polyphenols made gelatin gel darker.GCSS gel had three strong high molecular weight bands(one band>116.0 kDa,two bands loacked in 66.4?97.2 kDa)and two low molecular weight bands(loacked in 44.3?66.4 kDa and 29.0?44.3 kDa,respectively).Commercial gelatin had only two high molecular weight bands(>116.0 kDa).Amide I were shifted to higher wavenumber in the gel with oxidized polyphenols;meanwhile Amide A shifted to lower wavenumber in the gel with oxidized tannic acid,indicating that the number of hydrogen bonds increased.Scanning electron microscopy(SEM)analysis showed that the voids of gelatin gel added with oxidized polyphenols was smaller and distributed uniformlly;the voids of gelatin gels added with oxidized tannic acid were the smallest and even distributed.The results showed that oxidized tannic acid had the best effect of enhancing gel strength of GCSS,and no negative effect on color properties were observed.Moreover,the research aimed to explore the application of GCSS,expecially its film-forming abilities.Extraction temperature and glycerol content are two common factors affecting gelatin film properties.By using chum salmon skin,this research prepared the gelatin edible film and investigated the effects of gelatin extraction temperature(40 ?,50 ?,60 ?,70?,80 ?,90 ?)and glycerol applying content(1.0%,1.1%,1.2%,1.5%,2.0%)on film thickness,mechanical properties,colour properties,optical properties,microstructure and infrared information.Films prepared from gelatin extracted from above temperatures were marked as F40,F50,F60,F70,F80 and F90,respectively.The thickness of the gelatin film was measured by a thickness gauge.It is shown that film using gelatin from middle extraction temperature(F40,F50,F60)showed higher thickness than film made from high extraction temperature(F70,F80,F90)with the addition of glycerol at 1.0%,1.2%and 1.5%(p<0.05).For F40,addition of 1.0%,1.1%,1.2%glycerol provided higher thickness than 1.5%and 2.0%did(p<0.05).The mechanical properties of gelatin were determined by texture analyzer.Mechanical analysis results show that middle temperature film had stronger tensile strength(TS)than high temperature film(p<0.05)and most high TS were found in F50 and F60,which can reached to 30?40 Mpa.With addition of 1.5%to 2.0%glycerol,elongation at break(EAB)of film increased as temperature increased(p<0.05),up to 350%.TS of F50,F70 and F80 declined as the increasing use of glycerol content(p<0.05).a*and b*value of film rose as the increase of extraction temperature(p<0.05)and glycerol exhibited slightly influence to colour properties of F50 and F60.Water vapour permeability(WVP)showed increase coinciding with the increase of extraction temperature and glycerol content(p<0.05).Transmission of film under 200 nm and 280 nm was 0.00%while that under 350?800 nm was 46.53%?74.57%.Transmission of F60 was much lower than that in F40 and F50(p<0.05).ATR-FTIR infrared spectrometer analysis found that the gelatin films exhibited the classic absorption regions of gelatin,which included amide-?,?,? band and amide A,B band.Among them,amide A transferred to lower wavelength as temperature climbed and its amplitude increased with increase of glycerol content.SEM was used to investigate the microstructure of gelatin film.No distinct crack or gaps were found in surface and cross section of film.All the above results indicate that extraction temperature mattered to the mechanical functionality,WVP and colour properties.However,glycerol content only showed influences to the two former.It is noticed that there may be some interactive effects between gelatin extraction temperature and glycerol content on film,since not always the same response model towards these two factors were observed.Thus,chum salmon skin gelatin edible film with good property can be prepared by optimizing the gelatin extraction temperature and glycerol applying content.Further research focusing on sophisticated additives effect for properties improvement of gelatin film should be continued. |
PDF Full Text Request