Roles of lipid oxidation and pH on properties and yellow discolouration during storage of film from red tilapia (Oreochromis niloticus) muscle protein

Protein-based films prepared from red tilapia (Oreochromis niloticus) washed and unwashed mince solubilised at pH 3 and 11 were prepared and characterised. Tensile strength (TS) of films from washed mince was greater than that of films prepared from unwashed mince for both pH used (P < 0.05). TS of films prepared at pH 3 was higher than that of films prepared at pH 11 for both of washed and unwashed mince (P < 0.05). Film from washed mince with pH 3 showed the highest TS, while that from unwashed mince with pH 11 had the lowest TS with the highest elongation at break (EAB) (P < 0.05). Films from washed mince had the lower value of thiobarbituric acid reactive substances (TBARS) than did those from unwashed counterpart, regardless of pH used. Nevertheless, TBARS was much higher in films prepared at acidic pH, compared with those prepared at alkaline pH. During storage of 20 days at room temperature, films became yellowish as evidenced by the increases in b^∗ and ΔE^∗-values. Films prepared at pH 11 showed the higher b^∗ and ΔE^∗-values than did those prepared at pH 3, especially for those from unwashed mince. However, films prepared from washed mince at pH 3 showed higher b^∗ and ΔE^∗-values than did those prepared at pH 11 (P < 0.05). Films generally had the increase in TS but the decreases in water vapour permeability (WVP), film solubility and protein solubility after 20 days of storage (P < 0.05). Therefore, lipid oxidation more likely played a role in yellow discolouration of fish muscle protein film, mainly by providing the carbonyl groups involved in Maillard reaction, while pH regulated the rate of reaction.     

Properties of a protein-based film from round scad (Decapterus maruadsi) as affected by muscle types and washing

The effects of muscle types and washing on the properties of a protein-based film from round scad (Decapterus maruadsi) mince were investigated. Washing resulted in an increase in the protein content with a coincidental decrease in the fat content of mince, especially from whole muscle and dark muscle. Among all types of muscle (ordinary, dark and whole muscle), the ordinary muscle rendered the film with the highest tensile strength (TS) (p < 0.05). TS of films from washed mince was greater than that of films prepared from unwashed mince for the same type of muscle used (p < 0.05). Nevertheless, the water vapour permeability (WVP) of films from unwashed mince was higher than that of films prepared from washed mince (p < 0.05). Films from washed mince had higher solubility but lower protein solubility than those from unwashed mince (p < 0.05). Regardless of washing, films from ordinary muscle showed the highest L^∗-value (p < 0.05). However, films prepared from dark muscle were more yellowish than those prepared from other muscles, as evidenced by the greater b^∗-value. Films from round scad mince and washed mince had excellent barrier properties to UV light at the wavelength of 200–280 nm. Generally, films from round scad mince had a lower preventive effect on visible light transmission than had those from unwashed mince. Among films from all muscles, those prepared from dark muscle exhibited the highest barrier to visible light transmission (p < 0.05). Therefore, the properties of films from round scad meat were governed by muscle type as well as by washing.     

Effects of washing with oxidising agents on the gel-forming ability and physicochemical properties of surimi produced from bigeye snapper (Priacanthus tayenus)

The effects of washing with hydrogen peroxide (H₂O₂) and sodium hypochlorite (NaOCl) solutions on the gel-forming ability and physicochemical properties of surimi produced from bigeye snapper (Priacanthus tayenus), stored in ice for up to 14 days, were investigated. Generally, pH and the trichloroacetic acid (TCA)-soluble peptide content of washed mince varied, depending on the type of oxidizing agent and storage time of the fish. With increasing time of storage, the pHs of water- and H₂O₂-washed mince were lower than that of NaOCl-washed mince (P < 0.05). However, no differences in the TCA-soluble peptide contents of the resulting mince washed with any media were observed (P > 0.05). Washing with 20 ppm NaOCl resulted in the highest increase in both the breaking force and the deformation of mince from fish stored in ice for all the times studied (P < 0.05). Natural actomyosin (NAM) extracted from NaOCl-washed mince had higher surface hydrophobicity and disulfide bond (SS) content than that of water-washed mince (P < 0.05). With no effect on Ca²⁺-, Mg²⁺-, or Mg²⁺–Ca²⁺-ATPase activities, NaOCl washing resulted in an increase in Mg²⁺–EGTA-ATPase activity of NAM (P < 0.05). The results suggested that washing mince with the appropriate type and concentration of oxidizing agent can improve the gelling ability of surimi, particularly from low quality fish.     

Properties and Stability of Protein-based Films from Red Tilapia (Oreochromis niloticus) Protein Isolate Incorporated with Antioxidant during Storage

Film from fish protein isolate (FPI) from red tilapia (Oreochromis niloticus) muscle prepared at pH 3 and incorporated with 100 ppm Trolox (FPIT film) was prepared and characterized in comparison with film prepared from unwashed mince film (UWM film) during storage of 40 days at room temperature (28–32°C). FPIT film had higher tensile strength (TS) and elongation at break (EAB) but lower water vapor permeability (WVP) than UWM film (p?<?0.05). During the storage, FPIT film had much lower thiobarbituric acid reactive substances value than UWM film. Furthermore, FPIT was more transparent and had no yellow discoloration, as evidenced by no change in b* and ΔE* values during the storage of 40 days. Both UWM and FPIT films were stabilized mainly by hydrogen bond, followed by hydrophobic interaction, disulfide bond, and nondisulfide covalent bond. Fourier transforms infrared spectra indicated that FPIT film contained the lower amount of lipids with the lower amplitude of amide B band, compared with UWM film. Higher degradation temperature (Td) was observed in FPIT film, indicating a greater protein–protein interaction in film matrix. FPIT film had smoother surface and cross-section than UWM film. After 40 days of storage, both films had the increase in TS and Td but lower EAB, WVP, and protein solubility. This was more pronounced in UWM film and was associated with the formation of nondisulfide covalent bond in the film network, most likely mediated by the interaction between protein and lipid oxidation products via Maillard reaction. Thus, film from FPI incorporated with antioxidant had the improved mechanical and physical properties without yellow discoloration.     

The effect of myofibrillar/sarcoplasmic protein ratios on the properties of round scad muscle protein based film

The effect of the ratios of myofibrillar protein (MP) to sarcoplasmic protein (SP) from round scad (Decapterus maruadsi) muscle on the properties of the resulting films was investigated. Tensile strength (TS) of films decreased with increasing SP content (p < 0.05). Films prepared from MP/SP ratio of 10:0 (w/w) exhibited the highest TS (p < 0.05). Elongation at break (EAB) of films prepared with SP content greater than 30% had the decreased EAB (p < 0.05). Water vapor permeability (WVP) of films increased when SP content increased up to 20% and decreased with increasing SP content up to 30% (p < 0.05). Solubility of films decreased but protein solubility increased with increasing SP contents (p < 0.05). The a*-value and ΔE* of film increased with increasing SP content. Films with all MP/SP ratios exhibited the negligible transmission to the light in UV range. Therefore, it is suggested that the type and ratio of proteins in fish muscle, both SP and MP, influenced the properties of film from round scad muscle. Results suggested that the removal of sarcoplasmic protein from fish muscle by thorough washing was an effective means to improve the mechanical properties as well as color of the fish muscle protein-based film.     

Effects of plasticizers on the properties of edible films from skin gelatin of bigeye snapper and brownstripe red snapper

The effects of type and concentration of plasticizers on the mechanical properties (tensile strength, TS and elongation at break, EAB), water vapor permeability, light transmission, transparency and color of fish skin gelatin edible films from bigeye snapper (Priacanthus marcracanthus) and brownstripe red snapper (Lutjanus vitta) were investigated. At the same plasticizer concentration, fish skin gelatin films from both species plasticized with glycerol (Gly) showed the greatest EAB (P<0.05), whereas ethylene glycol (EG) plasticized films showed the highest TS (P<0.05). Films prepared from brownstripe red snapper skin gelatin exhibited slightly greater TS than those of bigeye snapper skin gelatin (P<0.05) when Gly and sorbitol (Sor) were used. EG, polyethylene glycol 200 (PEG 200) and polyethylene glycol 400 (PEG 400) affected the mechanical properties of both films differently. Films generally became more transparent and EAB, water vapor permeability (WVP), as well as light transmission of films increased, but TS and yellowness decreased with increasing plasticizer concentrations.     

Properties and antioxidant activity of fish skin gelatin film incorporated with citrus essential oils

Properties of protein-based film from fish skin gelatin incorporated with different citrus essential oils, including bergamot, kaffir lime, lemon and lime (50% based on protein) in the presence of 20% and 30% glycerol were investigated. Films containing 20% glycerol had higher tensile strength (TS) but lower elongation at break (EAB), compared with those prepared with 30% glycerol, regardless of essential oils incorporated (p < 0.05). Films incorporated with essential oils, especially from lime, at both glycerol levels showed the lower TS but higher EAB than the control films (without incorporated essential oil) (p < 0.05). Water vapour permeability (WVP) of films containing essential oils was lower than that of control films for both glycerol levels (p < 0.05). Films with essential oils had varying ΔE^* (total colour difference), where the highest value was observed in that added with bergamot essential oil (p < 0.05). Higher glycerol content increased EAB and WVP but decreased TS of films. Fourier transforms infrared (FTIR) spectra indicated that films added with essential oils exhibited higher hydrophobicity with higher amplitude at wavenumber of 2874–2926 cm⁻¹ and 1731–1742 cm⁻¹ than control film. Film incorporated with essential oils exhibited slightly lower thermal degradation resistance, compared to the control film. Varying effect of essential oil on thermal degradation temperature and weight loss was noticeable, but all films prepared using 20% glycerol had higher thermal degradation temperature with lower weight loss, compared with those containing 30% glycerol. Films added with all types of essential oils had rough cross-section, compared with control films, irrespective of glycerol levels. However, smooth surface was observed in all film samples. Film incorporated with lemon essential oil showed the highest ABTS radical scavenging activity and ferric reducing antioxidant power (FRAP) (p < 0.05), while the other films had lower activity. Thus, the incorporation of different essential oils and glycerol levels directly affected the properties of gelatin-based film from fish skin.     

Chemical and sensory quality changes of fish fingers,made from mirror carp (Cyprinus carpio L., 1758), during frozen storage (−18 °C)

The effects of frozen storage at −18 °C on the chemical and sensory qualities of fish fingers produced from unwashed and washed mirror carp (Cyprinus carpio) mince were investigated. The amounts of moisture, crude protein, lipid, crude ash, ω3 polyunsaturated fatty acids (PUFA ω3), and ω6 polyunsaturated fatty acids (PUFA ω6) in fish fingers produced from unwashed mince (UWF) were found to be 68.50%, 15.5%, 6.00%, 2.20% 2.31%, and 55.2%, respectively, while they were found to be 70.23%, 10.8%, 2.14%, 1.80%, 2.28%, and 54.6%, respectively, in carp fingers produced from washed mince (WF). The thiobarbituric acid value (TBA, mg malonaldehyde/kg) was found to be significantly higher in mince of WF than in mince of UWF and increased significantly during frozen storage in both the mince of UWF and WF (p < 0.05). A significant decrease in pH was obtained throughout the washing treatment (p < 0.05). There were no significant differences of pH in either the mince of UWF or WF between the beginning and end of the storage periods (p > 0.05), whereas a sharp increase was observed in the fourth month in both groups. The protein solubilities of the mince of both UWF and WF decreased significantly throughout the storage periods (p < 0.05). Sensory parameters of colour, odour, flavour, and general acceptability for both groups decreased during the frozen storage period (p < 0.05) but were still within acceptable limits. It was also concluded that mirror carp was a good source for fish fingers and that product could be stored for five months in a frozen state without undesirable changes of sensory and chemical qualities.     

Effect of Kiam (Cotylelobium lanceolatum Craib) Wood Extract on the Haemoglobin-Mediated Lipid Oxidation of Washed Asian Sea Bass Mince

Introduction

Effect of ethanolic kiam wood extract (EKWE; 12 0.05% and 0.1%, w/w) on the retardation of haemoglobin-mediated lipid oxidation of washed Asian sea bass mince added without and with menhaden oil stored in ice up to 10 days was investigated.

Results and discussion

Samples containing haemoglobin had the highest peroxide value (PV) within the first 8 days and possessed the greater amount of thiobarbituric acid-reactive substances (TBARS), compared to those added with no haemoglobin (P?<?0.05), regardless of 5% menhaden oil addition. Incorporation of 5% (v/w) menhaden oil to the washed mince had no impact on the formation of PV and TBARS, compared with oil-free samples during the storage (P?>?0.05). With addition of EKWE, lipid oxidation in washed mince added with haemoglobin and menhaden oil was retarded, especially when the higher level (0.1%; w/w) was used, as evidenced by lowered PV and TBARS. Formation of volatile lipid oxidation compounds was retarded in the sample containing oil and haemoglobin and treated with 0.1% EKWE, compared with that without the addition of EKWE after 10 days of storage in ice (P?<?0.05).

Conclusion

Sensory analysis revealed that samples containing haemoglobin without and with oil added had the highest intensity of fishy odour, compared to those treated with EKWE (0.05% and 0.1%) and the control sample (washed mince; P?<?0.05). Thus, EKWE, especially at a level of 0.1%, could serve as a potential natural antioxidant in prevention of lipid oxidation and retardation of development of fishy odour and volatile lipid oxidation compounds in washed mince during iced storage.     

Round scad protein-based film: Storage stability and its effectiveness for shelf-life extension of dried fish powder

Storage stability of different round scad (Decapterus maruadsi) protein-based films including (1) control film without palm oil and chitosan, (2) film with 25% palm oil (glycerol substitution) and (3) film with 25% palm oil and 40% chitosan (protein substitution) was investigated. During storage (54% relative humidity, 28-30 °C), tensile strength (TS) of the films without and with 25% palm oil or 25% palm oil in combination with 40% chitosan increased continuously, while elongation at break (EAB) decreased markedly when storage time increased up to 8 weeks (p < 0.05). No changes in water barrier properties were observed throughout the storage time up to 4 weeks (p > 0.05). Film solubility slightly increased but protein solubility decreased continuously during storage (p < 0.05). All films became darker and more yellowish as storage time increased. When round scad muscle protein-based films were used to cover dried fish powder, the samples covered with the film containing 25% palm oil and 40% chitosan showed lower thiobarbituric acid reactive substances (TBARS) and yellowness than other samples during the extended storage up to 21 days (p < 0.05). No differences in moisture content of all samples covered with different films were noticeable (p > 0.05), except those covered with HDPE, which had the lowest moisture content. Thus, round scad protein-based film incorporated with palm oil and chitosan could be a promising packaging material to prevent lipid oxidation in oil enriched foods.     

Comparison of the properties of multi-composite fish gelatin films with that of mammalian gelatin films

Four types of films viz. gelatin, gelatin–MMT, gelatin–chitosan and gelatin–MMT–chitosan prepared from redsnapper and grouper bone gelatin were compared with the mammalian gelatin films, for their mechanical and barrier properties. Grouper gelatin films had higher tensile strength (TS) and Young’s modulus (YM), but lower elongation at break (EAB) than redsnapper films. Incorporation of MMT and chitosan improved the TS (p < 0.05) of the films. Water solubilities were lower (p < 0.05) in films incorporated with chitosan compared to simple gelatin film. Protein solubilities were lower in gelatin–MMT films, irrespective of the type of solvent used. The water vapour transmission rates (WVTR) of fish and mammalian gelatin films were similar, but addition of MMT had reduced WVTR (p < 0.05). SEM micrographs depicted smoother surface for gelatin–MMT and gelatin–MMT–chitosan films. Thus, composite fish gelatin films made with MMT and chitosan could be the good natural biodegradable films due to their better mechanical and barrier properties.     

Effects of partial hydrolysis and plasticizer content on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin with different degree of hydrolysis (DH: 0.40, 0.80 and 1.20%) added with glycerol as plasticizer at various levels (10, 15 and 20%, based on protein) were investigated. Films prepared from gelatin with all DH had the lower tensile strength (TS) and elongation at break (EAB) but higher water vapor permeability (WVP), compared with the control film (without hydrolysis) (p < 0.05). At the same glycerol content, both TS and EAB decreased, while WVP increased (p < 0.05) with increasing %DH. At the same DH, TS generally decreased as glycerol content increased (p < 0.05), however glycerol content had no effect on EAB when gelatins with 0.80 and 1.20% DH were used (p > 0.05). DH and glycerol content had no marked impact on color and the difference in color (ΔE^∗) of resulting films. Electrophoretic study revealed that degradation of gelatin and their corresponding films was more pronounced with increased %DH, resulting in the lower mechanical properties of films. Based on FTIR spectra, with the increasing %DH as well as glycerol content, higher amplitudes for amide-A and amide-B peaks were observed, compared with film from gelatin without hydrolysis (control film) due to the increased –NH₂ group caused by hydrolysis and the lower interaction of –NH₂ group in the presence of higher glycerol. Thermo-gravimetric analysis indicated that film prepared from gelatin with 1.20% DH exhibited the higher heat susceptibility and weight loss in the temperature range of 50–600 °C, compared with control film. Thus, both chain length of gelatin and glycerol content directly affected the properties of cuttlefish skin gelatin films.     

Retardation of myoglobin and haemoglobin-mediated lipid oxidation in washed bighead carp by phenolic compounds

Antioxidative activities of phenolic compounds (caffeic acid, gallic acid and tannic acid; 200 ppm) in washed mince (pH 6), with added myoglobin (Mb) and haemoglobin (Hb), from bighead carp (Hypophthalmichthys nobilis), during 9 days of iced storage, were studied. Tannic acid exhibited the preventive effect on discolouration of washed mince containing Mb or Hb during storage (P < 0.05). High peroxide value (PV) was found and large amount of, thiobarbituric acid-reactive substances (TBARS) and hexanal were formed in washed mince containing haem proteins, especially Hb. As determined by apo Streptococcal haem-associated protein, Hb had the lower haem affinity than Mb. Phenolic compounds, especially caffeic acid and gallic acid, could lower lipid oxidation induced by Mb or Hb throughout storage (P < 0.05). Prevention of haem release, as well as inhibition of lipid oxidation induced by haem proteins with selected phenolic compounds, should be an alternative means in lowering discolouration and lipid oxidation in fish muscle.     

Starch-gelatin edible films: Water vapor permeability and mechanical properties as affected by plasticizers

Physical and mechanical properties of edible films based on blends of sago starch and fish gelatin plasticized with glycerol or sorbitol (25%, w/w) were investigated. Film forming solutions of different ratios of sago starch to fish gelatin (1:0, 2:1, 3:1, 4:1, and 5:1) were used and cast at room temperature. Amylose content of sago starch was between 32 and 34% and the protein content of the fish gelatin was found to be 81.3%. The findings of this study showed that the addition of fish gelatin in starch solutions has a significant effect (p < 0.05), resulting in films with lower tensile strength (TS) and higher water vapor permeability (WVP). On the other hand, increasing protein content (from 10.9% to 21.6%) in film samples plasticized with sorbitol showed significantly lower (p < 0.05) TS but no trend was observed in % elongation-at-break (EAB) and no differences in WVP. However, TS decreased with higher protein content in the samples when either plasticizers were used in general, but no significance differences was observed among the samples (p < 0.05) with glycerol with exception to film with high protein content (21.6%) only and no trend was observed in % EAB among samples as well. Significant difference (p < 0.05) was observed in TS and viscosity between different formulations with sorbitol. The morphology study of the sago starch/fish gelatin films showed smoother surfaces with decreasing protein in the samples with either plasticizer. DSC scans showed that plasticizers and protein content incorporated with sago starch films reduced the glass transition temperature (T_g) and melting temperature (T_m) and the melting enthalpy (ΔH_m). In this study, observation of a single T_g is an indication of the compatibility of the sago starch and fish gelatin polymers to form films at the concentration levels used.     

Properties of biodegradable blend films based on fish myofibrillar protein and polyvinyl alcohol as influenced by blend composition and pH level

Effects of the ratios of fish myofibrillar protein (FMP) from bigeye snapper (Priacanthus tayenus) to polyvinyl alcohol (PVA) (FMP:PVA; 10:0, 8:2, 6:4, 5:5, 4:6, 2:8, 0:10) and pH levels (3 and 11) on the properties of resulting films were investigated. Both tensile strength (TS) and elongation at break (EAB) of films increased with increasing PVA content (p < 0.05). When PVA was incorporated up to 40%, films prepared at pH 11 had the higher TS than did those prepared at pH 3 (p < 0.05). However, as PVA content was greater than 40%, films prepared at pH 3 exhibited the higher TS than did those prepared at pH 11 (p < 0.05). Water vapor permeability (WVP) of the films prepared at pH 3 increased when PVA content increased up to 40% and decreased with further increases in PVA content (p < 0.05). PVA films had the higher TS, EAB and WVP than did FMP films and FMP/PVA blend films prepared at both pHs. Films exhibited the increased L∗ and a∗ values but decreased b∗ value with increasing PVA content at both pHs. Films prepared at pH 11 showed higher b∗ value than did those prepared at pH 3 when PVA content was greater than 40% (p < 0.05). FMP/PVA blend films exhibited the negligible transmission to the UV light. At pH 3, light transmission of the films increased as PVA content increased (p < 0.05). At all FMP/PVA ratios, films prepared at pH 11 were less transparent than those prepared at pH 3 (p < 0.05). Therefore, blend composition and pH level influenced the properties of FMP/PVA blend films.     

Structure-modifying alkaline and acidic pH-shifting processes promote film formation of soy proteins

The effect of pH-shifting, a process that induces the molten globule state in proteins, on the film-forming potential of soy protein isolate (SPI) at different temperatures was investigated. Partial unfolding at pH 1.5 or 12, followed by refolding at pH 7.0, was performed to alter the protein structure. Glycerin-plasticised films were prepared from pH-treated SPI at ambient temperature (20 °C), or by heating at 50, 60, 70, or 80 °C (30 min). Tensile strength (TS), elongation at break (EAB), water vapour permeability (WVP), protein solubility (pH 3–7), and non-participating proteins of films were analysed, and the film microstructures were examined. The pH₁₂-treated SPI spontaneously formed a transparent, slightly yellowish film at 20 °C, which had the greatest EAB, while pH_1.5-treated and native SPIs required preheating at 50 and 70 °C, respectively, to form a film. Heating generally decreased solubility and WVP but increased TS. Films formed from both pH₁₂- and pH_1.5-treated SPIs were more elastic (up to 2-fold greater in EAB, P < 0.05) than the film formed from untreated SPI despite slightly reduced TS and WVP. Electrophoresis revealed disulphide bonds between A and B subunits of glycinin being a dominant force in pH₁₂- and pH_1.5-treated SPI films, while noncovalent forces were abundant in untreated SPI films. The pH₁₂-treated SPI film consisted of more interactive protein strands than other SPI films, which seemed to explain its superior elastic properties.     

The effects of pretreatments on antioxidative activities of protein hydrolysate from the muscle of brownstripe red snapper (Lutjanus vitta)

Different pretreatments of mince from brownstripe red snapper (Lutjanus vitta) including 1) washing; 2) membrane separation; 3) washing followed by membrane separation and 4) membrane separation followed by washing were conducted prior to hydrolysis. Among the resulting minces, that subjected to membrane separation with subsequent washing (MS/W) contained the lowest remaining myoglobin content, phospholipid content, heme iron and non-heme iron contents (p < 0.05) and showed the lowest TBARS values throughout 9 days of storage at 4 °C in the presence and absence of 0.15 mol L⁻¹ cupric acetate (p < 0.05). When hydrolysates from 1) mince, 2) MS/W and 3) protein isolate from MS/W (PI) with different degree of hydrolysis (DH) (20, 30 and 40%) were prepared using proteases from pyloric caeca of brownstripe red snapper, antioxidative activities determined by DPPH, ABTS radical scavenging activities, ferric reducing antioxidant power and metal chelating activity varied with hydrolysates and DH. Antioxidative activities increased with increasing DH up to 40% (p < 0.05). At all DH tested, hydrolysate prepared from MS/W exhibited the highest antioxidative activities determined by all assays, compared to those from mince and PI (p < 0.05). Hydrolysate from MS/W with 40% DH had the molecular weight lower than 6.5 kDa as determined by SDS-PAGE. In liposome oxidation system, the addition of hydrolysate from MS/W resulted in the lower TBARS, compared with the control throughout the incubation period of 48 h at room temperature (25-28 °C). Therefore, fish mince with membrane separation followed by washing was the most appropriate source for production of hydrolysate possessing antioxidative activity with the lowered amount of lipids and pro-oxidants.     

Edible films made from membrane processed soy protein concentrates

Edible films were prepared from membrane processed soy protein concentrate (MSC) at various film forming solution pHs, and their mechanical, barrier, and physical properties were compared with soy protein isolate (SPI) films. As the film solution pH increased from 7 to 10, the resulted MSC films were more transparent, yellowish, and had lower oxygen permeabilities. However, tensile strength (TS), modulus of elasticity (ME) and water vapor permeabilities of MSC films were not affected by film solution pHs. The values of MSC films prepared at pH 7 were not significantly (P>0.05) different from those of SPI films prepared at alkaline solutions (pH 8-10). The uniform TS and ME values of MSC film over the wide film solution pH ranges were attributed to the higher solubility of MSC at pH 7. For the films formed at neutral film solutions (pH 7.0), MSC films showed significantly (P<0.05) higher elongation value, film solubility, and transparency compared to SPI films.     

Effect of plasticizer content on the functional properties of extruded gelatin-based composite films

Beef gelatin, in combination with varying levels of glycerol, was used to manufacture films by extrusion. A twin-screw co-rotating extruder was employed to produce the films and the mechanical and barrier properties of the films were investigated. Increasing the plasticizer content increased (P < 0.05) elongation at break (EAB) values but decreased (P < 0.05) tensile strength (TS) values. Oxygen permeability (OP) values for gelatin-based composite films increased (P < 0.05) as the concentration of glycerol increased. Additionally, the solubility of films in water and seal strength increased as glycerol content increased. FTIR results indicated that increasing glycerol concentration increased and displaced the peak situated around 1032 cm⁻¹, which corresponded to glycerol. Gelatin-based composite films with a concentration of 0.2% glycerol possessed the lowest water vapor permeability (WVP) and OP values. From the data generated in this study, it is clear that the use of a plasticizing agent in film formulations should be carefully considered because of the negative effects that the plasticizing agent could have on extruded film barrier properties.     

Influences of degree of hydrolysis and molecular weight of poly(vinyl alcohol) (PVA) on properties of fish myofibrillar protein/PVA blend films

Biodegradable blend films based on fish myofibrillar protein (FMP) and poly(vinyl alcohol) (PVA) were prepared and characterized. PVA with different degrees of hydrolysis (DH) and molecular weights (MW) had the impact on properties of FMP/PVA (1:1, w/w) blend film. The blend films with higher MW of PVA were more tensile resistant, as indicated by the greater tensile strength (TS) and elongation at break (EAB), while the films with PVA of lower DH were more flexible. The blend film with PVA-BP26 (DH: 86–98% mol; MW: 124,000–130,000 g/mol) exhibited the greatest tensile performance and the lowest water vapor permeability (p < 0.05), compared with other films. SEM and FTIR results revealed that FMP and PVA were compatible and their intermolecular interaction was enhanced, providing the blend film with desirable properties. Therefore, incorporation of PVA with appropriated DH and MW could improve the properties of the FMP-based film.