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.     

A predictive model for assessment of decontamination effects of lactic acid and chitosan used in combination on Vibrio parahaemolyticus in shrimps

Vibrio parahaemolyticus is a major causative agent of human gastroenteritis in seafood products including shrimps. Lactic acid and chitosan are natural antimicrobials for food decontamination in the washing process of seafood. In this research, a 4-factor response surface model based on the Box–Behnken experimental design was developed to evaluate the effects of lactic acid (1%, 2%, and 3%, v/v), chitosan (0.4%, 1%, and 1.6%, w/v), rotational rate (90, 110, and 130 rpm) and washing time (10, 20, and 30 min) on reduction of V. parahaemolyticus inoculated in raw shrimps. These treatments achieved 2.2 to 4.3 log₁₀ CFU/g reduction of V. parahaemolyticus in shrimps. Stepwise stratification led to a simplified model that has a satisfactory performance as evidenced by statistical indices (R² = 0.92; p < 0.0001; RMSE = 0.196) and external validation parameters [bias factor (B_f) = 1.01; accuracy factor (A_f) = 1.05]. The model generated an optimum treatment combination (3% lactic acid, 1.6% chitosan, and rotational rate at 110 rpm) that could achieve greatest bacterial reduction of 4.5 log₁₀ CFU/g. Among the four factors, lactic acid and chitosan were the major contributors for bacterial decontamination. Analysis of variances showed a significant interactive inactivation effect (p < 0.05) from combined use of lactic acid and chitosan. The treatments did not have adverse effects on the quality attributes such as color and pH of the shrimps.     

Characterization of antioxidant chitosan film incorporated with Zataria multiflora Boiss essential oil and grape seed extract

Antioxidant chitosan based edible films were developed incorporated with Zataria multiflora Boiss essential oil (ZEO) (5 and 10 g/L) and grape seed extract (GSE) (10 g/L) alone and in combination. The physico-mechanical, wettability, swelling index, color, total phenol and antioxidant characteristics of the films were investigated. Films without any agents were used as control sample. All films, with the exception of 10 g/L GSE + 10 g/L ZEO film, exhibited lower strength and elongation values, and only the addition of 10 g/L ZEO to GSE film improved the water vapor transmission rate of chitosan films. Only GSE containing films had higher swelling index. The incorporation of GSE and ZEO into chitosan film increased the wettability of the surface, total phenol and antioxidant activity. Neat chitosan and ZEO incorporated films had a light yellowish color, whereas GSE + ZEO films were gray.     

A novel active bionanocomposite film incorporating rosemary essential oil and nanoclay into chitosan

Montmorillonite (MMT) nanoclay and rosemary essential oil (REO) were incorporated into chitosan film to improve its physical and mechanical properties as well as antimicrobial and antioxidant behavior. The MMT weight percent relative to chitosan was varied from 1 to 5 and was activated by three REO levels (0.5%, 1%, and 1.5% v/v), and their impact on physical, mechanical, and barrier properties of the chitosan films was investigated. Total phenolic and antimicrobial activity were also evaluated. Microstructure of chitosan/MMT–REO nanocomposites was characterized through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that incorporating MMT and REO into chitosan improves water gain, water vapor permeability, and solubility of the chitosan film by more than 50%. It was also shown that the combined effect of clay and REO improves significantly the tensile strength and elongation of chitosan (p < 0.05). The XRD and FTIR results confirmed that the improvements are related to the MMT exfoliation and good interaction between chitosan and MMT in the presence of REO. Antimicrobial properties of the films also improved by REO incorporation in 1.5% v/v.     

Antioxidative activity of chitosans with varying molecular weights

Antioxidant activity of chitosans of different molecular weights (30, 90 and 120 kDa chitosan) in salmon (Salmo salar) was investigated. The progress of oxidation was monitored by employing the 2-thiobarbituric acid-reactive substances (TBARS) and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) scavenging assays. In general, all chitosans exhibited antioxidative activities in salmon. The addition of chitosans to salmon reduced lipid oxidation for seven days of storage. The TBARS values of salmon containing chitosan were significantly lower than those of the control (p < 0.01). At 0.2% (w/v) and 0.5% (w/v) concentrations, the TBARS with chitosan addition was decreased by 75% and 45%, respectively, over 15 days. At 1% concentration, the TBARS value with native chitosan addition was decreased by 32% after 15 days of storage. 90 kDa chitosan showed an increased DPPH free radical-scavenging activity with increasing concentration in the range of 0.2–1% (w/v). The free radical-scavenging activity of the 0.2 mM DPPH solution was saturated by 30 kDa chitosan at a concentration of ?0.7% (w/v), resulting in a strong antioxidant activity of approximately 85%. This was comparable to the DPPH free radical-scavenging activity of BHT.     

Effects of chitosan molecular weight and degree of deacetylation on the properties of gelatine-based films

The effect of chitosan molecular weight (MW) and degree of deacetylation (DD) on the physicochemical properties of gelatine-based films was studied with the goal of improving the films. Determination of the dynamic viscoelastic properties (elastic modulus G′ and viscous modulus G″) of the film-forming solutions revealed that the interactions between gelatine and chitosan were stronger in the blends made with chitosan of higher molecular weights or higher degrees of deacetylation than the blends made with lower molecular weights or degrees of deacetylation. Fish gelatine films modified with chitosan of higher molecular weights or higher degrees of deacetylation had higher tensile strengths (TS, 72.4 MPa for 550 kDa vs. 62.2 MPa for 200 kDa; 63.2 MPa for 93.6% DD vs. 38.0 MPa for 76.5% DD) and higher glass transition temperatures (T_g, 130 °C for 550 kDa vs. 108 °C for 200 kDa; 108 °C for 93.6% DD vs. 103 °C for 76.5% DD). Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD) studies indicated that gelatine and chitosan interactions determined the properties of the film. Thus, combining gelatine and chitosan may be a method for improving the physicochemical properties of gelatine films, especially when using chitosan of higher molecular weights and higher degrees of deacetylation.     

Effect of flaxseed meal on the dynamic mechanical properties of starch-based films

Starch (S)–flaxseed meal (FM) biofilms were prepared from potato and maize starch by incorporating FM up to 15% (dry solid basis) and using glycerol as plasticizer. The dynamic mechanical properties, tensile properties and water vapor permeability (WVP) of these films were measured. The storage modulus of both the starch (control) and starch–FM films decreased as temperature increased. Tan δ increased initially in all the films with increase in temperature until a peak value was reached which allowed the determination of glass transition temperature (T_g). Both tensile strength and Young’s modulus of the starch–FM films increased with increase in the FM content. The WVP of the potato starch–FM films first increased to 2.261 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) when FM content increased to 5% and decreased down to 1.832 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) with further increase in the FM content to 15%. While the WVP values of the cornstarch and corn starch–FM films were not significantly (p > 0.05) different. The incorporation of FM increased the tensile strength, decreased the % elongation at break and increased the T_g.     

Optimisation of freeze drying conditions for purified serine protease from mango (Mangifera indicaCv. Chokanan) peel

This study investigated the possible relationship between the encapsulation variables, namely serine protease content (9–50 mg/ml, X₁), Arabic gum (0.2–10% (w/w), X₂), maltodextrin (2–5% (w/w), X₃) and calcium chloride (1.3–5.5% (w/w), X₄) on the enzymatic properties of encapsulated serine protease. The study demonstrated that Arabic gum, maltodextrin and calcium chloride, as coating agents, protected serine protease from activity loss during freeze-drying. The overall optimum region resulted in a suitable freeze drying condition with a yield of 92% for the encapsulated serine protease, were obtained using 29.5 mg/ml serine protease content, 5.1% (w/w) Arabic gum, 3.5% (w/w) maltodextrin and 3.4% (w/w) calcium chloride. It was found that the interaction effect of Arabic gum and calcium chloride improved the serine protease activity, and Arabic gum was the most effective amongst the examined coating agents. Thus, Arabic gum should be considered as potential protection in freeze drying of serine protease.     

Packaging-specific influence of chitosan on color stability and lipid oxidation in refrigerated ground beef

We examined the influence of chitosan on lipid oxidation and color stability of ground beef stored in different modified atmosphere packaging (MAP) systems. Ground beef patties with chitosan (1%) or without chitosan (control) were packaged either in high-oxygen MAP (HIOX; 80% O₂ + 20% CO₂), carbon monoxide MAP (CO; 0.4% CO + 19.6% CO₂ + 80% N₂), vacuum (VP), or aerobic packaging (PVC) and stored at 1 °C. Chitosan increased (P < 0.05) redness of patties stored in PVC and CO, whereas it had no effect (P > 0.05) in HIOX. Chitosan patties demonstrated lower (P < 0.05) lipid oxidation than controls in all packaging. Control patties in PVC and HIOX exhibited greater (P < 0.05) lipid oxidation than those in VP and CO, whereas chitosan patties in different packaging systems were not different (P > 0.05) from each other. Our findings suggested that antioxidant effects of chitosan on ground beef are packaging-specific.     

Physical properties of edible emulsified films based on pistachio globulin protein and fatty acids

Novel edible composite films were prepared from pistachio globulin protein (PGP), saturated fatty acids, and an emulsifier using the emulsification technique. The water vapor permeability (WVP) of the emulsified films was reduced by approximately 37–43% by fatty acid addition. The effect of fatty acid on the oxygen permeability (OP) of PGP films was indirectly determined as the oil peroxide value. The OPs of the emulsified films were lower than those of a PGP film without fatty acid, but the differences were not significant (P < 0.05). The mechanical properties of PGP films were also affected by fatty acid addition; the ultimate tensile strength (UTS) was diminished, and elongation at breaking (E) decreased considerably (35–70%). Furthermore, the incorporation of fatty acid increased the opacity of the films. Finally, differential scanning calorimetry showed that the glass transition temperature (T_g) of the PGP film was ∼127 °C and was not considerably affected by fatty acid addition.     

Effect of phenolic compounds on the properties of porcine plasma protein-based film

Properties of porcine plasma protein-based film incorporated with tannic acid, caffeic acid and ferulic acid at different concentrations (1–3% (w/w) of protein content) were studied. Film-forming solution (FFS) containing 3% protein (w/v) and 70% glycerol (w/w of protein content) was preheated at 70 °C for 30 min and adjusted pH to 10 followed by the addition of phenols and film casting. Tensile strength (TS) of resulting film increased by 123.3, 194.3 and 19.5% and elongation at break (EAB) increased by 71.1, 86.3 and 10.2%, respectively, compared with the control film, when tannic acid, caffeic acid and ferulic acid at a level of 3% was added. The use of all phenolic compounds slightly increased water vapor permeability (WVP) of resulting films (p < 0.05). The increases in a^∗- and b^∗-values of films were observed as the higher concentrations of tannic acid and caffeic acid were used. This was associated with the lowered transparency of resulting films. FFS containing 3% caffeic acid with prior oxygenation, especially with pH 10, yielded the film with increased TS but lowered EAB (p < 0.05). Oxygenation of FFS was associated with the lower L^∗-value and higher a^∗-value of resulting films. Therefore, phenolic compounds could be used as natural cross-linkers which affected the properties of porcine plasma protein-based film differently.     

Manufacture and characterization of gelatin films derived from beef,pork and fish sources using twin screw extrusion

Gelatin films derived from beef, pork and fish sources were manufactured by twin-screw, co-rotating extrusion. The effect of extrusion processing parameters, namely; screw speed (100–400 rpm) and temperature (90, 90, 90, 90 °C and 90, 120, 90, 90 °C) on the mechanical and barrier properties of gelatin films were studied. Increasing screw speed up to 300 rpm improved (P < 0.05) tensile strength (TS) and reduced (non-significantly) water vapour permeability (WVP) values for all manufactured gelatin films. However, the WVP of various gelatin film types was reduced (P < 0.05) when a screw speed of 400 rpm was employed. Increasing the speed of extrusion promoted (P < 0.05) increased solubility of films in water. Manufacture of films using a higher temperature profile resulted in films possessing higher puncture strengths (PS), increased water barrier properties with higher water solubility.     

Physico-chemical properties of whey protein isolate films containing oregano oil and their antimicrobial action against spoilage flora of fresh beef

Antimicrobial films were prepared by incorporating different levels of oregano oil (0.5%, 1.0%, and 1.5% w/w in the film forming solution) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were not affected by the addition of oregano oil at any of the concentrations used. A reduction of the glass transition temperature (∼10–20 °C), as determined by dynamic mechanical thermal analysis (DMTA), was caused by addition of oil into the protein matrix. A decrease of Young modulus (E) and maximum tensile strength (σ_max) accompanied with an increase in elongation at break (%EB) was observed with increasing oil concentration up to a level of 1.0% (w/w). Wrapping of beef cuts with the antimicrobial films resulted in smaller changes in total color difference (ΔΕ) and saturation difference (Δ_chroma) during refrigeration (5 °C, 12 days). The maximum specific growth rate (μ_max) of total flora (total viable count, TVC) and pseudomonads were significantly reduced (P < 0.05) by a factor of two with the use of antimicrobial films (1.5% w/w oil in the film forming solution), while the growth of lactic acid bacteria was completely inhibited. These results pointed to the effectiveness of oregano oil containing whey protein films to increase the shelf life of fresh beef.     

Physical properties of a composite film containing sunflower seed meal protein and its application in packaging smoked duck meat

Sunflower seed meal protein (SP) films were prepared using various plasticizers, cross-linking agents, Cloisite Na⁺ or red algae, and their physical properties, such as tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) were determined. The TS, E, and WVP of the SP film containing sucrose and fructose (2:1) as a plasticizer and cinnamaldehyde as a cross-linking agent were 3.05 MPa, 34.42%, and 2.25 × 10⁻⁹ g m/m² s Pa, respectively. The incorporation of Cloisite Na⁺ improved the physical properties of the SP film. The TS of the SP/Cloisite Na⁺ composite film containing 3% Cloisite Na⁺ increased by 2.19 MPa, and the WVP of the composite film decreased by 0.52 × 10⁻⁹ g m/m² s Pa compared to the SP film. The incorporation of red algae also improved the TS of the SP film. The TS of the SP composite film containing 1.2% red algae increased by 3.82 MPa compared to the SP film. In addition, an SP/red algae composite film containing grapefruit seed extract (GSE) was prepared and used in food packaging. After 12 days of storage, the population of Listeria monocytogenes inoculated on smoked duck meats packed with the SP/red algae composite film containing 1.2% GSE decreased by 1.31 log CFU/g compared to the control packaging. Therefore, these results suggest that SP composite films can be prepared by the addition of red algae to the SP film–forming solution and that the SP/red algae composite film containing GSE can be used as an antimicrobial food packaging material.     

Characteristics of submicron emulsions prepared by ultra-high pressure homogenisation: Effect of chilled or frozen storage

Model O/W pre-emulsions at an initial temperature of 24 °C and pH 6.3, and containing (w/w) 4.3% whey proteins plus 15, 30 or 45% peanut oil were processed using a ∼15 L/h homogeniser with a high pressure (HP) valve immediately followed by cooling heat exchangers. The effect of ultra-high pressure homogenisation (UHPH) between 100 and 300 MPa (P₁) or of recycling (1–3 homogenisation passes) at 200 MPa was investigated on the droplet size distribution, size indices and viscosity. Fluid temperatures were measured at the inlet (T₁) and outlet (T₂) of the HP-valve, and after immediate cooling downstream of the HP-valve (T₃) as they varied throughout UHPH. Short-life heating phenomena and mechanical energy involved in droplet processing were clearly influenced by emulsion composition. Oil droplet diameters decreased when (P₁) increased from 100 to 300 MPa leading to submicron droplets at ≥200 MPa. Monomodal distributions with droplets well below 0.3 μm were obtained after recycling at 200 MPa for the three oil contents, with a peak at 138 nm (distribution in volume) or 60–70 nm (in number frequency). The emulsion behaviour varied from fluid (and quite Newtonian) to thick (and shear thinning) depending on the droplet size reduction and the oil volume fraction. Emulsions displayed an excellent stability vs. creaming and coalescence after 9 d storage at 5 °C. Freezing followed by 13 d storage at −24 °C then thawing, induced an increase in particle sizes depending both on the oil volume fraction and (P₁). After UHPH at 200–225 MPa (±recycling), the freezing/thawing process maintained most of oil droplet size below 1 μm at 15% (w/w) oil, and induced mainly oil droplet aggregation through SDS-labile interactions at higher oil contents.     

Effect of pretreatment on lipid oxidation and fishy odour development in protein hydrolysates from the muscle of Indian mackerel

Impact of different pretreatments on chemical compositions of Indian mackerel mince was studied. Mince prepared using washing/membrane removal/alkaline solubilisation process (W–MR–Al) contained the lowest remaining myoglobin and haem iron content and also showed the lowest total lipid and phospholipid contents. When mince and W–MR–Al were hydrolysed using Alcalase for up to 120 min, a higher degree of hydrolysis (DH) was found in W–MR–Al after 30 min of hydrolysis. Furthermore, hydrolysate from W–MR–Al had lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and non-haem iron content throughout hydrolysis period (P < 0.05). When hydrolysate powder produced from mince and W–MR–Al (0–0.3% w/v) were fortified in milk, the former resulted in the lower likeness score (P < 0.05) at all levels used. The addition of the latter, for up to 0.2%, had no effect on likeness of all attributes, compared with milk without fortification (P > 0.05). Therefore, the appropriate pretreatment of mince yielded hydrolysate with lower fishy odour.     

The antimicrobial activity of microencapsulated thymol and carvacrol

The aim of the present study was to determine the antimicrobial (AM) properties of plastic flexible films with a coating of microcapsules containing carvacrol and thymol as natural AM agents. Microencapsulation of these agents enables their controlled release and leads to the destruction (or growth inhibition) of a broad spectrum of microorganisms such as, Escherichia coli O157:H7, Staphylococcus aureus, Listeria innocua, Saccharomyces cerevisiae and Aspergillus niger. It was found that the studied AM agents are strong inhibitors to the growth of mycelium, but they were not effective against spore germination of mold. Thymol (T) and carvacrol (C) showed a significant AM activity against the studied microorganisms, with minimal inhibitory concentrations (MIC) of 125-250 ppm and 75-375 ppm for thymol and carvacrol respectively. The synergistic effect of combinations of thymol and carvacrol was also studied and it was found that the highest synergism was achieved at a concentration of 50% T and 50% C. The release of the AM agents was carried out at 4 °C during 28 days. The concentration of the microencapsulated AM agents showed a range of zones of inhibition of 4.3-11.3 mm for the microorganisms at 10% of thymol and 10% of carvacrol. At these concentrations the release of the AM agents (within 48 h) was greater than required for the most resistant microorganism (E .coli O157:H7), as reflected by the relatively large zone of inhibition. The results of the present study confirm the suitability of using microencapsulated thymol and carvacrol incorporated in polymer films for AM food packaging.     

The physicochemical characteristics and hydrophobicity of high amylose starch–glycerol films in the presence of three natural waxes

The film forming behaviour and hydrophobicity of high amylose (HA) starch in the presence of three different natural waxes (beeswax, candelilla wax and carnauba wax) were studied in the presence and absence of Tween-80. The HA starch:glycerol (G) ratio was maintained at 80:20 (on dry solid basis) and the concentration of wax was varied from 5% and 10% (w/w). The melted wax samples were homogenized with HAG dispersion with or without Tween-80 and the films were prepared by solution casting. The hydrophobicity and water-barrier properties in these films were determined by using contact angle (CA), water vapour permeability (K_w) tests, and water sorption isotherm at 0.529 RH and 20 °C. The K_w values of the HAG films decreased significantly (p < 0.05) with the addition of 5% concentration of these waxes. Then the addition of Tween-80 to the HAG + wax films increased the K_w values significantly (p < 0.05). The presence of these waxes in the presence and absence of Tween-80 resulted into different sorption isotherms and the water adsorptivity and moisture diffusion coefficient values were also affected. The presence of Tween-80 increased the CA in HAG + carnauba wax films while the CA was found to decrease in the case of other two waxes. The highest hydrophobicity was observed in HAG + carnauba wax + Tween-80 films in which the CA was >80.0° both at 5% and 10% (w/w) wax concentration. These higher CA values in HAG + carnauba wax + Tween-80 films were found to be related to the higher surface roughness in these films.     

Effects of hydrogen peroxide and Fenton’s reagent on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Properties of film from cuttlefish (Sepia pharaonis) ventral skin gelatin without and with partial hydrolysis (1.2% degree of hydrolysis), as influenced by H₂O₂ and Fenton’s reagent at different levels, were investigated. Films treated with H₂O₂ (0.01–0.04 M) and Fenton’s reagent [H₂O₂ (0.01–0.04 M) + FeSO₄ (0.001–0.004 M)] had higher tensile strengths (TS) but similar or lower elongations at break (EAB), compared with the control film (p < 0.05). Slight differences in water vapour permeability (WVP) were observed for all films. Films treated with Fenton’s reagent had a lower L^∗-value but higher a^∗-, b^∗- and ΔE^∗-values, while films treated with H₂O₂ had lower b^∗-values (p < 0.05), than had the control film. Cross-linking was pronounced in films treated with H₂O₂ or Fenton’s reagent and was associated with increased heat stability. Films treated with Fenton’s reagent had the lowest solubility in water (p < 0.05). However, fragmentation more likely took place when Fenton’s reagent (at a higher level) was used. Generally, similar results were noticeable between films from gelatin with and without partial hydrolysis. Thus, H₂O₂ and Fenton’s reagent directly affected the properties of film from cuttlefish skin gelatin, regardless of hydrolysis.     

Layer-by-Layer Technique to Developing Functional Nanolaminate Films with Antifungal Activity

The layer-by-layer (LbL) deposition method was used to build up alternating layers (five) of different polyelectrolyte solutions (alginate, zein-carvacrol nanocapsules, chitosan and chitosan-carvacrol emulsions) on an aminolysed/charged polyethylene terephthalate (A/C PET) film. These nanolaminated films were characterised by contact angle measurements and through the determination of water vapour (WVTR) and oxygen (O₂TR) transmission rates. The effect of active nanolaminated films against the Alternaria sp. and Rhizopus stolonifer was also evaluated. This procedure allowed developing optically transparent nanolaminated films with tuneable water vapour and gas properties and antifungal activity. The water and oxygen transmission rate values for the multilayer films were lower than those previously reported for the neat alginate or chitosan films. The presence of carvacrol and zein nanocapsules significantly decreased the water transmission rate (up to 40 %) of the nanolaminated films. However, the O₂TR behaved differently and was only improved (up to 45 %) when carvacrol was encapsulated, i.e. nanolaminated films prepared by alternating alginate with nanocapsules of zein-carvacrol layers showed better oxygen barrier properties than those prepared as an emulsion of chitosan and carvacrol. These films containing zein-carvacrol nanocapsules also showed the highest antifungal activity (～30 %), which did not significantly differ from those obtained with the highest amount of carvacrol, probably due to the controlled release of the active agent (carvacrol) from the zein-carvacrol nanocapsules. Thus, this work shows that nanolaminated films prepared with alternating layers of alginate and zein-carvacrol nanocapsules can be considered to improve the shelf-life of foodstuffs.