Stability enhancement of shellac by formation of composite film: Effect of gelatin and plasticizers

The objective of the present study was to reduce the polymerization of shellac by the formation of composite films with gelatin. The 6% w/w of composite film based on shellac and gelatin was prepared by the incorporation of different concentrations of gelatin and was prepared by film casting method. The stability of the composite films was then studied at 40 °C, 75% RH for 180 days in a stability chamber and the physicochemical properties were investigated. The results demonstrated that the higher concentrations of gelatin (30%, 40% and 50%) contributed to slight change in the acid value and the percentage of insoluble solids upon 180 days of storage. These results were due to the protection at the active sites of the shellac, carboxyl and hydroxyl groups, by the electrostatic interaction between the negative charge of shellac and the positive charge of gelatin, resulting in the stabilized shellac. However, the mechanical properties could not withstand the storage time; further investigation was required to improve the stability in terms of mechanical properties of the composite film by the addition of a plasticizer. Two types of plasticizers were used: polyethylene glycol (PEG) and diethyl phthalate (DEP) represented hydrophilic and hydrophobic plasticizers at the concentrations of 5% and 10%, respectively. The addition of both types and concentrations of plasticizers could improve the poor mechanical properties and brittleness of the composite film for a longer storage time. However, only PEG 400 at 5% and 10% w/w acted as a good plasticizer capable of improving the stability of the composite film under the longer periods of storage. Therefore, the attempt to improve the stability in terms of polymerization and mechanical properties of shellac by the formation of the composite film and the addition of the plasticizer could be achieved. The result could be used to develop a new material for the various applications of edible films for coating in food and pharmaceutical industries.     

HPMC、CMC对无麸质面包特性影响的研究

本文采用纯的米粉和红薯淀粉为原料来制作无麸质面包,研究了羟丙基甲基纤维素(HPMC)、羧甲基纤维素(CMC)对无麸质面包的比容、失水率、表皮颜色、硬度和弹性的影响,并从感官上对面包的品质进行了评价。实验结果表明:与空白样相比,添加2%CMC的面包比容增加最多为22%,添加2%CMC面包的黄色指数增加最多为37%,添加1%CMC面包的失水率减小了7%。面包放置24 h、48 h后,含1%CMC的面包硬度变化率减少最多分别为18%、21%,含1%HPMC的面包弹性变化率减少最多分别为18%、19%。     

Improving the physical properties of fish gelatin by high hydrostatic pressure (HHP) and ultrasonication (US)

In this study, it was aimed to improve the physical properties of fish gelatin by using high hydrostatic pressure (HHP) and ultrasonication (US). Gelatin solutions were exposed to different pressures and ultrasonication separately and gelled afterwards. The physicochemical measurements based on gel strength, turbidity and rheology experiments showed that HHP treatment on fish and bovine gelatin stabilized the gelatin network by organising the structure and reducing the free volume. Both processing methods (HHP and US) increased the gel strength significantly (P < 0.05) compared with non-treated samples. Fourier-transform infrared spectroscopy (FTIR) results indicated that conformations of amino acids changed after the treatments. Furthermore, US treatment was shown to destroy the gelatin network, change the gelation mechanism and decreased the degree of aggregation. Both treatments improved the gel characteristics as gel strength, gelling and melting temperatures of the fish gelatin. At the end, the best combination for fish gelatin among HHP and US treatments was found as 400 MPa–10 °C–15 min pressurisation.     

Rheological and thermal effects of galactomannan addition to acorn starch paste

Effect of galactomannans (guar gum and locust bean gum) at different concentrations on rheological and thermal properties of acorn starch pastes was examined. Steady and dynamic shear rheological tests indicated that the magnitudes of consistency index (K), apparent viscosity (η_a,100), Casson yield stress (σ_oc), dynamic moduli (G′, G″), and complex viscosity (η∗) of acorn starch-galactomannan mixtures were much higher than those of the control (0 g/100 g gum concentration), and that these values also increased with an increase in gum concentration. At temperatures ranging from 25 to 70 °C, the effect of temperature on η_a,100 was well described by the Arrhenius equation. In addition, DSC studies showed that the presence of galactomannans resulted in an increase in the transition temperatures (T_o, T_p, and T_c) and a decrease of the gelatinization enthalpy (ΔH). In general, these results suggest that the presence of galactomannans in acorn starch modifies the rheological and thermal properties, but that these modifications are dependent on the gum type and gum concentration.     

Formation and characterization of shellac-hydroxypropyl methylcellulose composite films

Shellac-hydroxypropyl methylcellulose composite films (Sh-HPMC-CFs) were produced and the effects of emulsifier and shellac concentration on the Sh-HPMC-CFs were investigated. Two emulsifiers, stearic acid (SA) and lauric acid (LA), with three ratios of shellac to emulsifier (100:1, 20:1, and 10:1) were tested to select the best ratio of shellac to emulsifier before testing the effect of shellac concentration. When compared to pure HPMC film, the WVP was decreased by 6 and 11% in the Sh-HPMC-CFs containing shellac to LA (ShLA) ratios of 100:1 and 20:1, respectively. However, all the ShSA-HPMC-CFs had higher WVP than the pure HPMC film. In relation to mechanical properties, the ShLA(20:1)-HPMC-CF had the lowest reduction in TS when compared to a pure HPMC film. Therefore, ShLA(20:1) was selected for further characterization. Surface morphology, cross sectional image, thermal stability, WVP, and mechanical properties of the Sh-HPMC-CFs were also measured at varying shellac concentrations (0.1, 0.5, 1.0, and 1.5%). The 0.1 and 0.5% Sh-HPMC-CFs had good distribution of shellac in the film structure while the 1.0 and 1.5% Sh-HPMC-CFs exhibited some agglomeration of shellac. The 0.1 and 0.5% Sh-HPMC-CFs had better moisture barrier than the pure HPMC film. All Sh-HPMC-CFs had better thermal stability than the pure HPMC film and its thermal stability increased as shellac concentration increased.     

Sweetness and texture perceptions in structured gelatin gels with embedded sugar rich domains

Layered and homogeneous gelatin gels with controlled rheological properties were compared for their sensory characteristics, specifically sweetness, hardness, breakdown behaviour and frothing. All gels and layers had a gelatin/water concentration of 5%. The total sugar concentration was 9% in the layered samples and 0, 9, 15 or 22.5% in the homogeneous samples. These concentrations corresponded to the concentrations in the single layers.A seven-layered sample with different sugar concentrations in the layers gave a higher early sweetness intensity than a homogeneous gel with the same mean total sugar concentration. All layered gels were similar in hardness, breakdown behaviour and frothing; for the homogenous samples, sensory hardness was decreased in samples with much sugar. These gels also fell into smaller pieces than the sugarless sample. This study shows that it is possible by controlling the sugar distribution within a sample to produce sweeter gels while the sugar content is maintained.     

The effects of xanthan conformation and sucrose concentration on the rheological properties of acidified sodium caseinate–xanthan gels

Xanthan solution transitions caused by annealing at different temperatures were studied by oscillatory rheology. The rheological behaviour of solutions evaluated at 10 °C showed different irreversible xanthan transitions, depending on the annealing temperature. The effect of xanthan conformation and caseinate, xanthan and sucrose concentrations on the mechanical and stress relaxation properties of acidified dairy gels were also investigated. Xanthan transitions produced different structural characteristics in mixed gels, as observed by their relaxation time and residual stress. The amount of sucrose played an important role in the network formation of gels and on the final elasticity. Intermediate concentrations of sucrose yielded gels that were finer than those obtained with low sucrose content, whereas at high amounts of this co-solute, the gels became more fragile. This quadratic effect of sucrose occurred at lower sucrose contents than in protein–sucrose or polysaccharide–sucrose systems. The mechanical properties at equilibrium were affected only by the strength of the interactions between caseinate and xanthan.     

Effect of hydroxypropylation on physical and rheological properties of sweet potato starch

Sweet potato starches (SPS) were hydroxypropylated to evaluate the effect of molar substitution (MS, 0.042-0.153) on the rheological properties, thermal properties, freeze-thaw stability, paste clarity, and gel strength of hydroxypropylated sweet potato starches (HPSPS). The swelling power and solubility values of HPSPS were higher than those of native sweet potato starch (SPS) and increased with an increase in MS. The transition temperatures (T_o, T_p, and T_c), and enthalpy (ΔH) of gelatinization of HPSPS were lower than those of native SPS, and significantly decreased with an increase in MS.Rheological properties of HPSPS pastes were measured under the conditions of steady and dynamic shear. Their consistency index (K), apparent viscosity (η_a,100), Casson yield stress (σ_oc), complex viscosity (η*), and dynamic moduli (G′ and G″) values decreased with an increase in MS, while their flow behavior index (n) and tan δ (ratio of G″/G′) values increased. The dependence of apparent viscosity on temperature followed the Arrhenius model for all samples. The paste clarity of HPSPS paste was more pronounced with increasing MS of hydroxypropyl groups. The HPSPS gels showed lower gel strength and also better freeze-thaw stability with a significant decrease in syneresis (g/100 g) compared to native SPS.     

Adding enzymatically modified gelatin to enhance the rehydration abilities and mechanical properties of bacterial cellulose

Bacterial cellulose (BC) possesses excellent water holding capacity. However, increased crystallization causes a decrease in the rehydration ability of dried BC. Due to its excellent hydrophilic properties, we used gelatin and its enzymatically modified form (EMG) to prepare BC nano-composites in an attempt to enhance the rehydration abilities properties of BC. The polar peptide fraction was increased by extended hydrolysis of fish gelatin in Alcalase. Peptides smaller than 10 kDa were obtained by hydrolysis at 50 °C for 20 min. Protein contents of composites prepared by immersing BC in 5% gelatin (Gelatin/BC) or EMG (EMG/BC) solution were 81% and 92%, respectively, both of which then formed high gelatin/BC composites (HGBC). The protein content of EMG/BC was higher than that of Gelatin/BC, as compared with low gelatin/BC composites (LGBC) that were formed by immersion in a corresponding 0.5% solution. Among both HGBC and LGBC composites, EMG/BC exhibited the best rehydration abilities. Freeze-dried EMG/BC also exhibited the fastest rehydration rate and the best ability to restore wet-type composites. Composite microstructures revealed that BC was enveloped by gelatin when non-polar EMG (NPEMG) and polar EMG (PEMG) entered the BC network and adsorbed onto cellulose ribbons. The microstructure of EMG/BC contained both PEMG/BC and NPEMG/BC structures. Gelatin hydrolysates, penetrating BC networks and forming stable composites, improved the rehydration ability of dried BC. The polar functional groups of gelatin and its hydrolysates represent the key factors contributing to the hydrophilic nature of composites.     

Nano-biomaterials application: Morphology and physical properties of bacterial cellulose/gelatin composites via crosslinking

Nano-scale bacterial cellulose (BC) provides a fine structural network; therefore, this study investigated alkaline treated BC/gelatin composites (ATBC/G) crosslinked with transglutaminase (ATBC/G/T), genipin (ATBC/G/G), or EDC (ATBC/G/E), to improve the mechanical strength and hydrophilic property of BC composites. The ATBC/G composites displayed increased gelatin content, moduli, and hardness with increased gelatin concentrations in the immersion solution. EDC most effectively improved the mechanical properties of ATBC/G composites. Gelatin entering ATBC network, fills the empty spaces and connects to the 3D structure of ATBC. The ATBC/G/E composites maintain a network structure under 10% gelatin concentrations because gelatin tightly attaches to the ATBC surface. The ATBC/G composite exhibited analogical crystal morphology of ATBC, however, increased gelatin concentrations in addition to the EDC treatment decreased crystallinity in the composites. The FTIR spectrograph of the ATBC/G composites revealed the OH groups of the composites tended to increase. Therefore, gelatin crosslinking disrupted the crystallization formed from the hydrogen bonds between cellulose molecules. Crosslinking can also enhance the rehydration ratio.     

Rheological and functional properties of gelatin from the skin of Bigeye snapper (Priacanthus hamrur) fish: Influence of gelatin on the gel-forming ability of fish mince

The rheological and functional properties of gelatin from the skin of bigeye snapper (Priacanthus hamrur) fish were assessed. The protein content of dried gelatin was 94.6% and moisture content was 4.2%. The amino acid profile of gelatin revealed high proportion of glycine and imino acids. The bloom strength of solidified gelatin was 108 g. The average molecular weight of fish skin gelatin was 282 kDa as determined by gel filtration technique. The emulsion capacity (EC) of gelatin at a concentration of 0.05% (w/v) was 1.91 ml oil/mg protein and with increase in concentration, the EC values decreased. The gelling and melting temperatures of gelatin were 10 and 16.8 °C, respectively as obtained by small deformation measurements. The flow behavior of gelatin solution as a function of concentration and temperature revealed non-Newtonian behavior with pseudoplastic phenomenon. The Casson and Herschel–Bulkley models were suitable to study the flow behavior. The yield stress was maximum at 10 °C with the concentration of 30 mg/ml. Thermal gelation behavior of threadfin bream (Nemipterus japonicus) mince in presence of different concentration of gelatin was assessed. Gelatin at a concentration of 0.5% yielded higher storage modulus (G′) value than control. Frequency sweep of heat set gel with gelatin revealed strong network formation.     

Particle size effects in colloidal gelatin particle suspensions

This paper describes the effects of simple shear flow on the formation and properties of colloidal gelatin particle suspensions. Microscopy and light scattering show that simple shear flow of a phase-separating gelatin-dextran mixture gave smaller particles with a narrower size distribution. Upon gelation due to a temperature decrease, the viscosity of the gelatin increased, which altered the coalescence and break-up behaviour of the particles formed. The small particles obtained by a high shear during processing aggregated into larger particle clusters, once particle solidified upon gelation. The particle size can be predicted using correlation with droplet break-up and coalescence considering the properties before gelation. The sizes of the clusters can be predicted with the coalescence behaviour using the properties after gelation. Clusters originating from small particles resist more deformation, resulting in pronounced rheological effects (e.g. increase viscosity, increased strain softening point).     

Effect of heating temperature and sodium chloride concentration on ultrastructure and texture of gels made from giant squid (Dosidicus gigas) with addition of starch,l-carrageenan and egg white

This paper seeks to compare the ultrastructure of gels made from frozen muscle of giant squid (Dosidicus gigas) at various temperatures with a number of different rheological parameters, with reference to a variety of added ingredients (non-muscle proteins and hydrocolloids) and to NaCl concentration. Interesting data on gel rheological properties were found where formulae containedl-carrageenan, starch and egg white, with a low salt concentration (1.5%). This seems to be because carrageenan forms an independent network which supports the principal structure formed by the fish protein; starch is incorporated into the network and retains water; and egg white forms a supplementary network which helps to improve rheological properties.     

An approach for the enhancement of the mechanical properties and film coating efficiency of shellac by the formation of composite films based on shellac and gelatin

The purpose of this study was to enhance the mechanical properties and film coating efficiency of shellac by the formation of composite films with different concentrations of gelatin. The composite films were prepared by the casting method and their mechanical and physicochemical properties were investigated. The results demonstrated that the puncture strength and percentage elongation of the composite film increased from 3.61 to 15.58 MPa and from 3.80% to 32.47% as the gelatin concentration increased to 50% w/w, respectively, indicating the enhancement of the strength and flexibility of the shellac film. The efficiency of the composite film over two model substrates, i.e., hydrophilic and hydrophobic substrates, respectively, was also studied. The work of adhesion and spreading coefficient of the composite film increased from 66.42 to 83.53 mN/m and from −8.14 to −3.07 mN/m for the hydrophilic substrate, indicating the improvement of the coating efficiency whereas the hydrophobic substrate showed the opposite trend with the increase in gelatin concentration. Therefore, the formation of the composite film not only improved the mechanical properties of shellac but also enhanced the efficiency of film coating by the modification of different concentrations of hydrocolloid polymer to suit with the type of coating substrate. Hence the knowledge of composite film could make beneficial contributions to the various applications in film coating for the food and pharmaceutical industries.     

Effect of polymer ratio and calcium concentration on gelation properties of gellan/gelatin mixed gels

Gelation properties of gellan/gelatin mixed solutions were studied using dynamic viscoelastic testing at eight different ratios of gellan (1.6–0.2% w/v) to gelatin (0–1.4% w/v) and seven different calcium levels (0–30 mM). The gelation temperature and gelation rate of the mixed gels were significantly affected by the ratio of gellan to gelatin as well as concentration of calcium. Addition of calcium at low levels resulted in an increase in gelation temperature and gelation rate compared to gels with no added calcium. Further increases in calcium increased the gelation temperature, but caused a decrease in gelation rate of the mixed gels. In addition, the presence of gelatin generally had a negative influence on gelation rate, especially at high proportions and when the solution had a high gelling temperature, probably by physically hindering the growth and development of gellan crosslinks. It appeared that in the presence of calcium, gellan formed the continuous gel matrix, with gelatin present as a discontinuous phase. Gellan/gelatin mixtures can form gels over a wide temperature range by varying the ratio of the two polymers as well as the calcium concentration.     

Characterization of gelation time and texture of gelatin and gelatin–polysaccharide mixed gels

The effects of cooling rate, holding temperature, pH and polysaccharide concentration on gelation characteristics of gelatin and gelatin–polysaccharide mixtures were investigated using a mechanical rheometer which monitored the evolution of G′ and G″. At low holding temperatures of 0 and 4 °C, elastic gelatin gels were formed whereas a higher holding temperature of 10 °C produced less elastic gels. At slow cooling rates of 1 and 2 °C/min, gelling was observed during the cooling phase in which the temperature was decreased from room temperature to the holding temperature. On the other hand, at higher cooling rates of 4 and 8 °C/min, no gelation was observed during the cooling phase. Good gelling behavior similar to that of commercial Strawberry Jell-O^® Gelatin Dessert was observed for mixtures of 1.5 and 15 g sucrose in 100 ml 0.01 M citrate buffer containing 0.0029–0.0066 g low-acyl gellan. Also, these mixed gels were stronger than Strawberry Jell-O^® Gelatin Desserts as evidenced by higher G′ and gel strength values. At a very low gellan content of 0.0029 g, increasing pH from 4.2 to 4.4 led to a decrease in the temperature at the onset of gelation, G′ at the end of cooling, holding and melting as well as an increase in gel strength. The gelation time was found to decrease to about 40 min for gelatin/sucrose dispersions in the presence of 0.0029 g gellan at pH 4.2 whereas the corresponding time at pH 4.4 was higher (79 min). In general, the gelation time of gelatin/sucrose dispersions decreased by a factor of 2 to 3 in the presence of low-acyl gellan. The addition of low-acyl gellan resulted in an increase in the gelation rate constant from 157.4 to 291 Pa. There was an optimum low-acyl gellan content for minimum gelation time, this optimum being pH dependent. Addition of guar gum also led to a decrease in gelation time to 73 min with a corresponding increase in the gelation rate constant to 211 Pa/min though these values were not sensitive to guar gum content in the range of 0.008–0.05 g. The melting temperature of gelatin/sucrose/gellan as well as gelatin/sucrose/guar mixtures did not differ significantly from that of pure gelatin or Strawberry Jell-O^® Gelatin Desserts. At pH 4.2, the melting rate constant was highest at a low-acyl gellan content of 0.0029 g whereas the rate constant was insensitive to low-acyl gellan content at pH 4.4. Addition of guar did not seem to affect the melting temperature or the melting rate constant.     

Gelation, oxygen permeability, and mechanical properties of mammalian and fish gelatin films

The objective of this study was to evaluate the gelation, thermal, mechanical, and oxygen permeability properties of different mammalian, warm- and cold-water fish gelatin solutions and films. Mammalian gelatin solutions had the highest gel set temperatures, followed by warm-water fish and then cold-water fish gelatin solutions. These differences were related to concentrations of imino acids present in each gelatin, with mammalian gelatin having the highest and cold-water fish gelatin having the lowest concentrations. Mammalian and warm-water fish gelatin films contained helical structures, whereas cold-water fish gelatin films were amorphous. This was due to the films being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian and warm-water fish gelatin solutions and well above the gelation temperature of cold-water fish gelatin solutions. Tensile strength, percent elongation, and puncture deformation were highest in mammalian gelatin films, followed by warm-water fish gelatin film and then by cold-water fish gelatin films. Oxygen permeability values of cold-water fish gelatin films were significantly lower than those for mammalian gelatin films. These differences were most likely due to higher moisture sorption in mammalian gelatin films, leading to higher oxygen diffusivity.     

Physicochemical and textural properties of heat-induced pea protein isolate gels

Chemical and thermal properties of pea protein isolates (laboratory prepared or native; PPIn and commercial; PPIc) and textural properties of heat-set gels obtained from pea protein isolates were compared with homologous soy protein isolates (laboratory prepared, or native; SPIn and commercial; SPIc). The protein banding pattern resulting from electrophoresis separation confirmed the presence of predominant storage proteins of pea and soy seeds in the respective protein products. PPIc and SPIc had lower nitrogen solubility than their native counterparts, likely due to their denaturated state which was further confirmed by the absence of distinct endotherms in these commercial materials compared to the laboratory prepared ones. Addition of NaCl at 1.0–2.0% (w/w) to PPIn and SPIn slurries increased thermal transition temperatures for both proteins.     

High pressure calorimetry at sub-zero temperature: evaluation of the latent heat and frozen water ratio of gelatin gels

An isothermal differential high-pressure calorimeter was specifically designed and described in this study. After calibration, the apparatus was validated by measuring the latent heat of ice melting. A good agreement was observed between the experimental results and literature data. The latent heat of gelatin gels at two different dry matter contents (2 and 10% w/w) was measured at sub-zero temperatures and high pressure. The main result showed that the latent heat values were influenced by both the melting temperature and the dry matter content. A decrease of the latent heat of melting of the gels with increasing melting pressure (decreasing of the melting temperature) probably indicated a modification in the ratio of frozenable water in these gels under pressure.