Optimization of Gelatin Extraction from Silver Carp Skin

ABSTRACT:  Fish skins are a by-product of the fish processing industry that can be successfully processed into gelatin. This study was designed to optimize the extraction process to obtain the highest yield, gel strength, and viscosity for gelatin production from silver carp skin. A fractional factorial design (2 levels, resolution III, 2^9-5) was chosen to screen 9 parameters to determine the most significant ones. Those found to be significant were optimized to determine the maximum value for 3 dependent variables mentioned above. The hydroxyproline content and hydroxyproline/protein ratio of the skin were 1.7% and 6.5%, respectively. The protein content of the skin was 26%. The hydroxyproline content of the gelatin for the sample giving the highest hydroxyproline/protein ratio was 10.9%. This sample was arbitrarily called pure gelatin and the purity of the remaining samples was between 71.8% and 97%. The highest protein and gelatin recovery was 78.1% and 98.8% of the total available, respectively. The latter, gelatin recovery, is proposed to be used instead of protein yield. Four variables were determined as significant in screening and these variables were studied by a central composite rotatable design (4-factor and 5-level with 6 central points) to model the system and response surface methodology was used for optimization. The optimum extraction conditions were 50 °C for the extraction temperature, 0.1 N HCl for the acid concentration, 45 min for the acid pretreatment time, and finally 4 : 1 (v/w) for the water/skin ratio. The predicted responses for these extraction conditions were 630 g gel strength, 6.3 cP viscosity, and 80.8% gelatin recovery. The data suggest that silver carp skin gelatin is similar to those of fish gelatins currently being exploited commercially.     

Optimising conditions for enzymatic extraction of edible gelatin from the cattle bones using response surface methodology

This work was initiated to optimise the factors affecting the enzymatic extraction of edible gelatin from the cattle bones using response surface methodology. A central composite rotatable design was used to evaluate the effects of the enzyme concentration, time of enzymatic treatment and extraction temperature on the yield of extraction, gel strength, apparent viscosity and absorption at 420 nm. The R ² values of regression models for all the response variables were higher than 0.9. Data analysis showed that all the process variables significantly ( P  < 0.01) affected the gel strength and apparent viscosity of extracted gelatin, whereas the effect of extraction temperature on both yield of extraction and absorption at 420 nm was not significant ( P  > 0.05). Graphical optimum conditions for the extraction yield, gel strength, apparent viscosity and absorption at 420 nm were determined as 6.1 ppm, 15.6 h, 70 °C; 9.1 ppm, 11.9 h, 70.3 °C; 7.86 ppm, 14.9 h, 77.5 °C and 2.8 ppm, 10 h, 60 °C, respectively. For all the response variables, the experimental values were very close to the predicted values and were not statistically different ( P  < 0.05).     

2-step optimization of the extraction and subsequent physical properties of channel catfish (Ictalurus punctatus) skin gelatin

ABSTRACT:  To optimize the extraction of gelatin from channel catfish ( Ictalurus punctatus ) skin, a 2-step response surface methodology involving a central composite design was adopted for the extraction process. After screening experiments, concentration of NaOH, alkaline pretreatment time, concentration of acetic acid, and extraction temperature were selected as the independent variables. In the 1st step of the optimization the dependent variables were protein yield (YP), gel strength (GS), and viscosity (V). Seven sets of optimized conditions were selected from the 1st step for the 2nd-step screen. Texture profile analysis and the 3 dependent variables from the 1st step were used as responses in the 2nd-step optimization. After the 2nd-step optimization, the most suitable conditions were 0.20 M NaOH pretreatment for 84 min, followed by a 0.115 M acetic acid extraction at 55 °C. The optimal values obtained from these conditions were YP = 19.2%, GS = 252 g, and V = 3.23 cP. The gelatin obtained also showed relatively good hardness, cohesiveness, springiness, and chewiness. The yield of protein and viscosity can be predicted by a quadratic and a linear model, respectively.     

Effect of pretreatment conditions on physicochemical parameters of carrot juice

Carrot juice obtained by hydraulic press with wooden set-up was subjected to pretreatments (temperature, time and pH) prior to extraction process. Their effects on the most important quality parameters of carrot juice, such as beta-carotene, reducing sugars, pectin, vitamin C, viscosity, pH and acidity were studied. Response surface methodology was employed, where the experiment was carried out according to a central composite rotatable design. The variables ranges used were 61.50–98.50 °C (temperature), 124.55–595.45 s (time) and 2.31–6.69 (pH – concentration of citric acid). The results showed that beta-carotene extraction was significantly increased (52.9%) with these pretreatments in comparison to control samples. All the derived mathematical models for the responses were found to be fit significantly to predict the data. The responses were optimised by numerical method and were found to be 7190 μg per 100 g beta-carotene, 3.41% reducing sugars, 4.96 mg per 100 g vitamin C, 0.59% pectin, 1.64 × 10³ Ns m⁻² viscosity, 5.26 pH and 4.97% acidity at optimum input variables of 75.26 °C (temperature), 349.89 s (time) and 3.2 (pH). The desirability for all the responses was found to be 83.8%.     

Properties of Alaska Pollock Skin Gelatin: A Comparison with Tilapia and Pork Skin Gelatins

ABSTRACT:  The objective of this work was to compare the physiochemical and rheological properties of Alaska pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (∼11%) or pork skin gelatin (∼13%). Most of the protein fractions in AG were α chain, β chain, and other oligomers. The gel strength of AG was 98 gram-force at 10 °C, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil-drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G' was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G' and a minimum in G". G' was found to be a power law function of concentration for all gelatins used: G'= k × Cⁿ. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in a higher melting temperature and a broader melting region for all gelatin gels. For both the AG-pork and AG-tilapia mixed gels, the gel melting temperatures decreased and melting regions narrowed as the AG fraction was increased.     

Reaction of apple pectin with ammonia

Amidated apple pectins were prepared in aqueous and aqueous-alcoholic media, and the factors influencing both ammonolysis and hydrolysis of the ester groups of apple pectin by ammonia were studied.
In aqueous solution, the extent of ammonolysis and hydrolysis was very dependent upon ammonia concentration. In aqueous alcohol, the products were also dependent upon the particular alcohol and its concentration, increasing concentrations suppressing hydrolysis; the overall rate of reaction is much slower than in the absence of alcohol. The product balance between amonolysis and hydrolysis of the ester groups is influenced by the polarity of the medium, and by the concentration of NH⁺₄ and OH⁻.
It was shown that the extents of ammonolysis and hydrolysis of the ester groups are significantly affected by the polarity of the medium and the acid-base equilibrium of the interaction of ammonia with water, i.e. NH₃+H₂O ↔ NH⁺₄+OH⁻. The content of free ester and amidated carboxyl groups in the pectin can be regulated by varying the concentration of ammonia, temperature, reaction time and the polarity of the medium. The rate of enzymic hydrolysis of amidated pectins decreases with increasing amide content. A mechanism for the reaction is proposed.     

Characterization of a thermostable and acidic-tolerable beta-glucanase from aerobic fungi Trichoderma koningii ZJU-T

ABSTRACT:  An extreme thermostable and acidic tolerable β-glucanase was isolated and characterized from aerobic fungi Trichoderma koningii ZJU-T. The optimal reaction temperature and pH for the β-glucanase were 100 °C and pH 2.0, respectively. The β-glucanase showed increased stability at higher temperatures and lower pH values when compared to other β-glucanases. The optimum conditions for the β-glucanase stability were found to be pH 4.0 and 80 °C. Even subjected to 100 °C for 3 h, β-glucanase activity did not show significant reduction. Moreover, K⁺ significantly enhanced β-glucanase activity at the concentration of 1 mM, while EDTA and other metal ions such as Mg²⁺, Mn²⁺, Zn²⁺, Ca²⁺, Fe²⁺, Pb²⁺, and Fe³⁺ inhibited β-glucanase activity. Denaturants, including sodium dodecyl sulfate (SDS) and mercaptoethanol, also inhibited β-glucanase activity at a concentration of 5%. However, in the presence of 7 M urea, residual activity of the β-glucanase still remained 14.5%.     

RELATIONSHIPS AMONG TITRATABLE ACIDITY, pH AND BUFFER COMPOSITION OF TOMATO FRUITS

Relationships among pH, titratable acidity (TA) and buffer composition of tomato fruits were studied using analytical data, from 25 divergent accessions, and from previous work. Citric and malic acids, and phosphate account for about 93% of the TA of tomatoes. An increase in phosphate concentration results in a decrease in [H⁺], whereas an increase in citric and malic acids increases [H⁺] These relationships probably exist because of differences in the origins of phosphate and the two acids. Variation in phosphate concentration can be of practical value in efforts to maintain a safe processing pH in low sugar, low acid varieties because phosphate has a relatively large effect on [H⁺] with a minimal effect on TA.     

Technical Approach to Simplify the Purification Method and Characterization of Microbial Transglutaminase Produced from Streptoverticillium ladakanum

In order to fast and economically purify MTGase from Streptoverticillium ladakanum , a stepwise elution method was developed and compared with linear gradient elution method. MTGase was purified to electrophoretical homogeneity by using CM Sepharose CL-6B and Blue Sepharose Fast Flow chromatographies by linear gradient or stepwise methods. The recovery of MTGase by linear gradient and stepwise methods were 68.4% and 81.0%, respectively. The optimal temperature and pH were 40 °C and 5.5, respectively. It was stable at pH 5.0 to 7.0 and had a rate constant (KD) of 6.21 °o 10^-5 min^-1 for thermal inactivation at 45 °C. The purified MTGase was activated by K⁺ Na⁺, Ca²⁺, Mn²⁺, and Mg²⁺, not affected by Fe³⁺, EDTA, but inhibited by Cu²⁺, Zn²⁺, Hg²⁺, Ni²⁺, Co²⁺, Cd²⁺, PCMB, NEM, IAA, and PMSF. A simple stepwise method was developed for the purification of MTGase from S. ladakanum.     

Rheological behaviour of acorn starch dispersions: effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics ( n  = 0.23–0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25–70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient ( R ² = 0.97–0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol⁻¹. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η_a,100) in the temperature range of 25–70 °C. Magnitudes of storage ( G' ) and loss ( G ") moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G ' were higher than those of G " over most of the frequency range (0.63–62.8 rad s⁻¹). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox–Merz superposition rule.     

Effect of batch extraction conditions on yield of soluble solids from rooibos tea

Extraction of soluble solids from rooibos tea (Aspalathus linearis) was investigated by single stage batch extraction. The effect of extraction temperature, extract: tea mass ratio and flow rate of water on extract concentration and yield of soluble solids was determined. Extract concentration and yield increased linearly with increase in temperature from 23 to 90°C.
Increasing the mass ratio from 5:1 to 10:1 decreased extract concentration, but increased yield. Both extract concentration and yield decreased with an increase in flow rate from 0.1 to 0.2 m³/hr. The water-soluble solid content of rooibos tea leaf was 21.74%, 75.1% of which was extracted at 90°C, mass ratio 10:1 and flow rate 0.1 m³/hr.     

Purification and Characterization of Escherichia coli Sulfite Reductase and its Application in Surimi Processing

ABSTRACT: The NADPH-sulfite reductase from Escherichia coli was purified to electrophoretic homogeneity by ammonium sulfate fractionation, and DEAE Sephacel and Sephacryl S-300 HR chromatography. The recovery and molecular weight were 31.7% and 119000, while the optimal pH and temperature for the activity were 7.7 and 25°C, respectively. It was strongly inhibited by PCMB, KCN, Hg²⁺, Fe²⁺, Fe³⁺, Ca²⁺, Co²⁺, and Cu²⁺, moderately by NEM, PMSF, IAA, Cd²⁺, Zn²⁺, Mn²⁺, and Ba²⁺. Addition of purified reductase significantly increased the reactive SH and gel strength of surimi prepared from frozen mackerel. The data suggest the high potential of microbial NADPH-sulfite reductase in surimi processing using frozen fish or denatured muscle proteins as raw materials. Keywords: Escherichia coli , sulfite reductase, mackerel, purification, characterization     

Influence of sodium and calcium ions on rheological behaviour of wheat glutenins extracted in alkaline ethanol solution

Wheat glutenins were extracted in alkaline aqueous solution containing 50% (v/v) ethanol and 0.025  m NaOH from the gluten residue after extraction using 70% (v/v) aqueous ethanol. Rheological behaviours of the solutions were investigated as a function of protein concentration and ion strength. Sodium (Na⁺) and calcium (Ca²⁺) ions have different influences on the rheological behaviour of the glutenin solution of 48 mg mL⁻¹. While addition of Na⁺ results in Newtonian fluids with a reduction in apparent viscosity in comparison with the salt-free solution, addition of Ca²⁺ leads to the formation of a viscoelastic network with enhanced shear-thinning. The solutions containing 0.2  m and 0.4  m Ca²⁺ exhibit yielding at low strain rates. The solution containing 0.6  m Ca²⁺ behaves as a pseudoplastic fluid with the appearance of two Newtonian plateaus at low and high strain-rate limits.     

Effects of Alkaline and Acid Pretreatments on Alaska Pollock Skin Gelatin Extraction

Pretreatments with different alkalis and acids at different concentrations were used to determine their effects on gelatin extraction from Alaska pollock skin. The alkaline pretreatments with the OH concentrations lower than 0.5 mol/L removed noncollagenous proteins without significant loss of skin collagen. The acid pretreatments caused loss of collagen, even using a weak acid with a low H concentration at a low temperature. The presence of proteases might cause degradation of gelatin extract, but the pretreatments with NaOH or Ca(OH)₂ at 0.1 mol/L OH concentration, or acetic acid at 0.05 mol/L H concentration could significantly decrease the degradation by proteases. The combination of an alkaline pretreatment followed by an acid pretreatment not only removed the noncollagenous proteins, but also provided the proper pH condition for extraction, during which some cross‐linkages could be further destroyed but with less breakage of polypeptide chains.     

The Green Oat Story: Possible Mechanisms of Green Color Formation in Oat Products during Cooking

ABSTRACT:  Consumers occasionally report greenish colors generated in their oat products when cooking in tap water. Here we have investigated pH and ferrous (Fe²⁺) ion as possible mechanisms for this color change. Steel-cut oat groats can turn brown-green color when cooked in alkaline conditions (pHs 9 to 12). Extraction of this color with methanol, and high-pressure liquid chromatography indicated a direct association of this color with the phenolic acid or avenanthramide content of the oat. The presence of 50 mM NaHCO₃ in water will cause oat/water mixtures to turn alkaline when cooked as CO₂ is driven off, generating OH⁻ ion. Although tap water rarely, if ever, contains so much bicarbonate, bicarbonate is used as a leavening agent in baking applications. Industrial interests using baking soda or alkaline conditions during oat processing should be aware of possible off color generation. We have also found that as little as 10 ppm Fe²⁺ will turn oat products gray-green when cooked. The aleurone stained darker than the starchy endosperm. Other divalent cations, such as Ca²⁺ or Mg²⁺ had no effect on cooked oat color. As much as 50 ppm Fe²⁺ may be found in freshly pumped well water, but Fe²⁺ reacts quickly with oxygen and precipitates as Fe(OH)₃. Thus, some freshly pumped well water may turn oats green when cooked, but if the water is left under atmospheric conditions for several hours, no discoloration will appear in the cooked oats.     

Rheology of Stirred Yogurt as Affected by Added Milk Fat, Protein and Hydrocolloids

The rheological characterization of stirred yogurt with added milk fat, Na caseinate (or micellar casein) and gelatin (4 Bloom strengths), starch or a xanthan gum/LBG 50:50 mixture was carried out. Dynamic and shear values were measured at 8°C and syneresis at 4°C. Consistency (k* and k) and syneresis were more frequently influenced by the composition variables than the power law factors n* and n and the critical strain γ_c. The k* ranged from 15.8 to 576 Pa sn*, n* from 0.038 to 0.220, γ^c from 1.6 to 49.0 10^-3, k from 0.37 to 32.47 Pa sⁿ, n from 0.005 to 0.587, and syneresis from 0.0 to 49.2%.     

Extraction of ginger rhizome: kinetic studies with supercritical carbon dioxide

The rates of extraction of [6]-gingerol from ground dried Jamaican ginger rhizomes were determined in supercritical carbon dioxide over the pressure range 128–197 bar (1850–2850 psi) and the temperature range 50–65°C. The CO₂ densities varied from 0.415 to 0.775 g cm⁻³. First-order plots showed two approximately linear sections with an initial intercept. The first linear section corresponded to a relatively fast initial extraction stage while the last 20% or so of the gingerol was extracted in the much slower subsequent stage. Reducing the ginger particle size by a factor of 3 increased the rate constant of the fast stage nine-fold. Despite the low viscosity of the supercritical fluid, the rate constants of the fast stage were much smaller than in extractions with organic solvents. Only when the CO₂ density was increased to 0.775 g cm⁻³ did the rate constant of the fast stage rise to a value comparable with, but still smaller than, those in organic solvents of similar density. The rate constants of the later slow extraction stage were also somewhat smaller than the corresponding values in organic solvents at 30°C.     

Yield,viscosity, and gel strength of wami tilapia (Oreochromis urolepis hornorum) skin gelatin: Optimization of the extraction process

A factorial design and response surface methodology were used to optimize the extraction process of tilapia skin gelatin (Oreochromis urolepis hornorum). The concentrations of NaOH (0.15%–0.35%) and H₂SO₄ (0.15%–0.35%), the extraction temperature (40°C–60°C), and the extraction time (3–15 h) were independent variables. Response variables were yield (%), viscosity (mPa·s), and gel strength (g). The NaOH (%) and H₂SO₄ (%) concentrations had significant influences (p<0.05) on viscosity and gel strength, while the extraction temperature (°C) and the extraction time (h) showed significant influences (p<0.05) on all dependent variables. Increasing the temperature and extraction time provided higher yields with a reduction in the gelatin viscosity and gel strength. Tilapia fish skin can be used as a source for production of gelatin.     

Retaining Green Pigments on Thermally Processed Peels-on Green Pears

ABSTRACT: The interest in developing peels-on thermally processed (canned) green pears has prompted the investigation of retaining green pigments during thermal processes. Use of zinc ions as a processing aid for the retention of green pigment and surface pretreatment to remove waxy layer and a part of the top cuticle layer of the peels for enhancing reactions of zinc ions with chlorophylls in peel tissues were studied. Whole pears or pear chunks were subjected to zinc treatment during presoaking in 5200 ppm Zn²⁺ solutions for 60 min or blanching at 94 °C for 6, 12, and 18 min in a 1300, 2600, or 5200 ppm Zn²⁺ solution for identifying the most appropriate procedures for retaining green peel pigments. Pears were then thermally processed in glass jars at 94 °C for 20 min after commercial canning. Canned pears were subjected to an accelerated shelf life test in rooms set at 10 °C, 21 °C, and 38 °C under fluorescent light. CIELAB L *, a *, and b * color values of pear samples were monitored during storage up to 35 wk. Results showed that surface pretreatment is essential for ensuring the reactions of zinc ions with green pigments, thus retaining green pigment during thermal treatment. Blanching pears in zinc solution containing about 1300 ppm Zn²⁺ was effective in obtaining attractive green-colored canned pears. Hue angle and - a * (greenness) values of canned pears were significantly ( P < 0.05) associated with blanching time and zinc concentration in blanching solutions, and remained stable over 19 wk of storage under intensive illumination at all 3 temperatures. The technology used zinc ions as a processing aid, thus significantly minimizing the zinc content in the final processed pears.     

Osmotic Dehydration of Tomato in Sucrose Solutions: Fick's Law Classical Modeling

ABSTRACT:  Osmotic dehydration of tomato was modeled by the classical Fick's law including shrinkage, convective resistance at the interface and the presence of water bulk flow. Tomato slices having 8 mm thickness were osmotically dehydrated in sucrose solutions at 50, 60, and 70 °Brix and at 35, 45, and 55 °C. Other experiments were done in a 70 °Brix sucrose solution at 35 °C with tomato slices of 4, 6, and 8 mm thickness and at different motion levels (velocities 0, 0.053, and 0.107 m/s). Tomato weight, water content, and °Brix of the products were measured as a function of processing time (20, 40, 80, 160, and 320 min). Results showed that temperature, concentration, thickness, and solution movement significantly influenced water loss and sucrose gain during the osmotic dehydration of tomato. The model predicted the modifications of soluble solid content and water content as a function of time in close agreement with the experimental data. Experimental Sherwood number correlations for sucrose and water were determined as Sh _s = 1.3 Re ^0.5 Sc _s^0.15 and Sh _w = 0.11 Re ^0.5 Sc _w^0.5, respectively. The effective diffusion coefficients of water (4.97 10⁻¹¹– 2.10 10⁻¹⁰ m²/s) and sucrose (3.18 10⁻¹¹– 1.69 10⁻¹⁰ m²/s) depended only on temperature through an Arrhenius-type relationship.