Microstructure and rheology of phase-separated gels of gelatin + oxidized starch

We report on small-deformation rheology and confocal microscopy at 24 °C of high-sugar gel samples based on an aqueous mixture of gelatin + oxidized (non-gelling) starch exhibiting thermodynamic incompatibility. Using a standard protocol involving the heating of previously rapidly quenched samples at a fixed holding temperature (24–60 °C) for a fixed time (from 20 s to 30 min), gel samples of different storage modulus and degrees of spinodal-type phase separation were systematically generated. The developing time-dependent modulus of the gelatin gel was found to be sensitive to the extent of gelatin crosslinking as influenced by the nature of the thermal processing conditions. Under identical processing conditions, a gradual increase in starch content gave gels of lower elastic modulus and increased degree of microscopic phase separation. Taken all together, our results indicate that the gel rheology is determined by a subtle combination of overall system composition and temperature/time processing history. We conclude that the mechanical properties of this mixed biopolymer system are not directly deducible from the extent of phase separation observed microscopically without detailed additional information concerning sample preparation and treatment conditions.     

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.     

Conformational ordering and gelation of gelatin in mixtures with soluble polysaccharides

Previous studies have shown that conformationally disordered, soluble biopolymers cause large enhancements in self-association of calcium pectinate, thermally denatured whey protein and gelling maltodextrin under conditions where the pre-gel solutions remained as a single phase. The purpose of the present work was to screen for similar enhancements in gel strength and rate of conformational ordering of gelatin on incorporation of soluble, disordered polysaccharides. Type B gelatin was used at a fixed concentration of 5.0 wt%, at a pH well above its isoelectric point of ∼4.5. Mixtures were prepared at 45 °C, where the gelatin is in the disordered coil form. Gel strength was characterised as Young's modulus (E), derived from the initial slope of compression curves for gels formed by holding for 16 h at 5 °C. Rate of conformational ordering of gelatin (triple-helix formation) was monitored by changes in optical rotation during and after rapid quenching from 45 to 5 °C. The polysaccharides studied were carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), guar gum, gum arabic, dextran and inulin, all of which were used in compression testing. Combinations of gelatin with HPMC and guar gum became immediately turbid on mixing and could not, therefore, be included in the samples characterised by optical rotation. The other mixtures remained homogeneous (i.e. single-phase) on holding at 45 °C. The results obtained were entirely negative. Incorporation of the soluble polysaccharides caused no significant changes in Young's modulus, and optical rotation values remained within ∼10% of those for gelatin alone. It is suggested that the enthalpic advantage of segregation is sufficient to overcome the small reduction in entropy from association of conformationally immobile subunits in gelation of calcium pectinate, whey protein and maltodextrin, but not sufficient to overcome the much greater loss of entropy from conversion of flexible gelatin coils to rigid triple helices.     

Characterization of fish gelatin from surimi processing wastes: Thermal analysis and effect of transglutaminase on gel properties

Fish gelatin extraction from wastes of fish Herring species (Tenualosa ilisha) was carried out by a series of pretreatment with 0.2 M Ca(OH)₂ followed by 0.1 M citric acid and final water extraction at 50 °C for 3 h. The resulting fish gelatin preparation was evaluated for its dynamic viscoelastic properties, gelling and melting temperatures and gel strength. The gelling and melting temperatures of gelatin samples (at 6.67%, w/v) were obtained from differential scanning calorimetry and rheological studies. The melting temperature of extracted fish gelatin (EFG) obtained ranged from 16.2 to 16.7 °C compared to that of commercial fish gelatin gel (CFG), from 23.7 to 25.6 °C and halal bovine gelatin (HBG), from 26.5 to 28.7 °C. On the other hand, gelling temperatures of EFG, CFG and HBG ranged from 5.1 to 5.2 °C, 11.9 to 17.46 °C, and 12.6 to 19.33 °C, respectively. EFG gave gels with a considerably lower G′ values than CFG and HBG. The bloom strength of EFG gels at 6.67% (w/v) was 69.03 g which was much lower than HBG (336.2 g) and CFG (435.9 g). Enzyme transglutaminase was added in the amounts of 0.5, 1.0, 3.0 and 5.0 mg/g gelatin to modify the gel properties of the extracted fish gelatin. The modified EFG gels obtained had higher gel strengths of 101.1 g and 90.56 g with added transglutaminase of 1.0 and 3.0 mg/g, respectively. However with addition of 5.0 mg/g enzyme the gel strength increased only up to 75.06 g. SDS-PAGE of extracted gelatin gel showed protein band intensities for α1-chains and 53 kDa but in gels added with higher concentration of transglutaminase, these protein band intensities seemed to disappear.     

Characteristics of the gelatin extracted from Channel Catfish (Ictalurus Punctatus) head bones

Three gelatins were prepared from channel catfish head bones by hot water after the head was pretreated with alkali protease, quickly desalted by 0.4 mol/L HCl and soaked in 9 g/L Ca(OH)₂. The extraction conditions of gelatins were 5 °C, pH 4.0, 4 h, 82 °C, pH 2.5, 2 h and 90 °C, pH 3.0, 3 h, respectively. The studies showed there were many differences between these gelatins. The first head bone gelatin contained high content of imino residues and more high molecular weight proportions of β and γ components. Gel strengths of the second and third gelatins were 209 ± 7 g and 117 ± 5 g, lower than that of the first head bone gelatin (282 ± 11 g). Furthermore, the first head bone gelatin achieved the highest gelling and melting points. The first head bone gelatin showed strong ability of clarification when it was used to clarify apple juice. At the same time, the nutritional components of apple juice changed a little except Vitamin C.     

Small heat shock proteins and toughness in intermediate pHu beef

Bull M. longissimus dorsi (n = 94) categorised into high (n = 28), intermediate (n = 14) and low (n = 52) ultimate pH (pH_u) were aged at − 1.5 °C for 28 days. Shear force was higher and more variable (p < 0.05) in intermediate pH_u samples during ageing. Titin, filamin and desmin degradation was also less extensive in intermediate pH_u samples compared to the other two pH categories. The extent of the decline of HSP20, HSP27 and αβ-crystallin concentrations during post mortem ageing was pH_u related such that high pH_u meat maintained the highest concentration of small heat shock proteins followed by intermediate and low pH_u meat. μ-Calpain autolysis was slowest in intermediate pH_u and cathepsin B activities remained consistently low during ageing in this group (p < 0.05). Meat toughness in the intermediate pH_u group may be attributed to the combination of a larger pool of sHSP with a sub-optimal cathepsin B activity and intermediary μ-calpain activities.     

Characterization of polyphenol oxidase from butter lettuce (Lactuca sativa var. capitata L.)

Polyphenol oxidase (PPO) was isolated from butter lettuce (Lactuca sativa var. capitata L.) grown in Poland and its biochemical characteristic were studied. PPO from butter lettuce showed a higher affinity to 4-methylcatechol than to catechol. The K_M and V_max values were: 3.20 ± 0.01 mM and 4081 ± 8 U/ml min⁻¹ for catechol and 1.00 ± 0.09 mM and 5405 ± 3 U/ml min⁻¹ for 4-methylcatechol. The optimum pHs of the enzyme were found to be 5.5 using catechol and 6.8 using 4-methylcatechol as substrate. The enzyme had a temperature optimum of 35 °C. The enzyme was relatively stable at 30 °C and 40 °C. The times required for 50% inactivation of activity at 50 °C, 60 °C and 70 °C were found to be about 30, 20 and 5 min, respectively. Inhibitors used for investigation in this study were placed in relative order of inhibition: p-hydroxybenzoic acid > glutathione ≈ ascorbic acid > l-cysteine > EDTA > citric acid. The enzyme eluted in the chromatographic separations was analyzed electrophoretically under denaturating conditions. The analysis revealed a single band on the SDS–PAGE which corresponded to a molecular weight of 60 kDa.     

Polyphenol oxidase activity,phenolic acid composition and browning in cashew apple (Anacardium occidentale, L.) after processing

This study describes the extraction and characterisation of cashew apple polyphenol oxidase (PPO) and the effect of wounding on cashew apple phenolic acid composition, PPO activity and fruit browning. Purification factor was 59 at 95% (NH₄)₂SO₄ saturation. For PPO activity, the optimal substrate was catechol and the optimum pH was 6.5. PPO K_m and V_max values were 18.8 mM and 13.6 U min⁻¹ ml⁻¹, respectively. Ascorbic acid, citric acid, sodium sulphite and sodium metabisulphite decreased PPO activity, while sodium chloride increased PPO activity. Wounding at 2 °C and 27 °C for 24 h increased PPO activity but storage at 40 °C reduced PPO activity. Gallic acid, protocatechuic acid and cinnamic acid (free and conjugate) were identified in cashew apple juice. Cutting and subsequent storage at 40 °C hydrolysed cinnamic acid. 5-Hydroxymethylfurfural content in cashew apple juice increased after injury and storage at higher temperatures, indicating non-enzymatic browning.     

Preparation and characterisation of gelatins from the skins of sin croaker (Johnius dussumieri) and shortfin scad (Decapterus macrosoma)

Gelatins were prepared from the skins of the tropical fish, sin croaker (Johnius dussumeiri) and shortfin scad (Decapterus macrosoma). Visual appearance, colour, pH, bloom strength, viscoelasticity, melting point and amino acid profiles of the fish gelatins were evaluated. Shortfin scad gelatin had higher melting and gelling temperatures than those of sin croaker gelatin. The bloom strengths of gelatins from sin croaker and from shortfin scad were 125 and 177 g, respectively, compared to 240 g for commercial bovine gelatin. The pH values were significantly different between the solutions of the two fish gelatins. The elastic modulus (G′) of the fish gelatin gels increased by more than 10-fold and the viscous modulus (G″) of fish gelatin solution increased sixfold after holding at 5 °C for 2 h. These viscoelastic properties of bovine gelatin only increased by less than twice.     

Segregative interactions and competitive binding of Ca in gelling mixtures of whey protein isolate with Naκ-carrageenan

Gelling mixtures of Na⁺κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0 wt% and carrageenan concentration was varied in the range 0.05–3.0 wt%. Ca²⁺ cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl₂. The concentration of CaCl₂ used in most of the experiments was 8 mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45 °C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1 °C/min) and holding at 5 °C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80 °C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5 °C, to give composite networks with both components gelled; and (iv) re-heating to 80 °C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5 °C, before and after thermal gelation of WPI.     

An unusual manifestation of phase separation in mixtures of disordered gelatin with konjac glucomannan

The behaviour of konjac glucomannan (KGM) and the galactomannans locust bean gum (LBG), guar gum and fenugreek gum at a concentration of 0.2 wt% in mixtures with type B gelatin in the solution state at 40 °C was examined by visual inspection. At gelatin concentrations of ∼2 wt% and above, the mixtures with LBG and guar gum formed cloud-like flocs, attributed to association of unsubstituted “smooth” regions of the mannan backbone in response to segregative interactions with gelatin. Fenugreek gum, which has no such smooth regions, did not form flocs, but gave a dispersion of small, gel-like particles. Mixtures of gelatin with KGM showed the unusual, striking phenomenon of forming a single gel-like lump which remained suspended in the surrounding liquid, neither rising nor sinking. The single lumps formed by mixtures of 0.2 wt% KGM with 5.0 wt% gelatin were studied in detail. The gelatin content, as determined by macro-Kjedahl analysis and comparison of the area of differential scanning calorimetry (DSC) cooling and heating peaks with calibration curves for gelatin alone, was ∼1.35 wt%. Rheological characterisation by low-amplitude oscillatory measurements and creep-recovery experiments showed that, despite its gel-like appearance, the lump had the properties typical of a solution of densely entangled polysaccharide coils, including close Cox–Merz superposition of steady-shear viscosity (η) and complex dynamic viscosity (η*). The concentration of KGM, determined by comparison of the maximum value of η* in the Newtonian region at low frequency with calibration curves for KGM alone, was 3.4 wt%. The composition of the surrounding liquid was obtained by calculations of mass balance, giving values of 5.20 wt% gelatin and 0.024 wt% KGM. The “p-factor” determined as the ratio of water to gelatin in the solution divided by the ratio of water to KGM in the lump was 0.65, well within the range found for other biopolymer mixtures. It is concluded that the gelatin–KGM mixtures show normal liquid–liquid phase separation, but that the phases have exactly the same density, preventing resolution into two liquid layers, and that enthalpically unfavourable interactions are instead minimised by one of the phases assuming spherical geometry.     

Cell wall invertase immobilisation within gelatin gel

Yeast cell wall invertase (CWI) was immobilised within 10% gelatin hydrogel. The result of entrapment was the complete immobilisation of all the added CWI. The activity of immobilised biocatalyst was 93 ± 3 U/g, with activity yield of 30%. The optimum pH was in range of 4.5–5.0 for free and immobilised biocatalyst. The optimum temperature was 60 °C for both free and gelatin immobilised CWI. Immobilised CWI was more stable than free CWI above optimum activity temperatures. The K_m of free and immobilised CWI was 35.10 ± 2.99 mM and 71.45 ± 3.23 mM, respectively. The V_max values were estimated as 8.23 ± 0.24 mM/min and 0.121 ± 0.002 mM/min, respectively. Immobilised CWI was tested in a batch reactor using 50% sucrose (w/v). After 70 consecutive cycles gelatin immobilised CWI retained 75% of its original activity.     

Effect of beef ultimate pH and large structural protein changes with aging on meat tenderness

This study investigated the effect of ultimate pH (pH_u) in beef on the degradation of large structural proteins during refrigerated storage using SDS-PAGE. M. longissimus dorsi from bull carcasses were selected and classified into three groups: low pH_u (≤ 5.79), intermediate pH_u (5.80–6.19) and high pH_u (≥ 6.2) muscles. Samples were then stored at − 1.5 °C for 1, 2, 7, 14, 21 and 28 days. Meat tenderness was measured at each aging time. Depending on meat pH_u, different protein patterns and degradation rates of structural proteins were found. Rapid changes of large structural proteins took place within 48 h post mortem. Besides titin and nebulin, degradation of filamin was clearly revealed. Two more large protein bands corresponding to myosin family members also exhibited fast decline with storage time. It suggested that the fast degradation of these proteins is a key factor in the improvement of meat tenderness.     

Pineapple fruit bromelain affinity to different protein substrates

Optimal pH and temperature conditions for proteolytic activity of pineapple fruit bromelain were determined using five different substrates: azocasein and azoalbumin (pH 3–10 at 20–70 °C), casein and sodium caseinate (pH 2–10 at 20–70 °C), and haemoglobin (pH 2–6.5 at 30–60 °C). Fruit bromelain has shown optimum activity at pH 7.5 for azoalbumin and at 6.5 for azocasein, all at 55 °C. Fruit bromelain activity determined with casein and sodium caseinate has shown optimum activity at 59 °C, while the optimum pH was 7.7 for casein and 6.5 for sodium caseinate. Optimum hydrolysis conditions of fruit bromelain towards haemoglobin showed a sharp peak at an acidic pH 2.9 at 37 °C. The lowest results of K_m and the highest results of V_max/K_m were found for azocasein and azoalbumin. These substrates are highly recommended for fruit bromelain activity determination.     

Improvement of heating uniformity in packaged acidified vegetables pasteurized with a 915 MHz continuous microwave system

Continuous microwave processing to produce shelf-stable acidified vegetables with moderate to high salt contents poses challenges in pasteurization due to reduced microwave penetration depths and non-uniform heating. Cups of sweetpotato, red bell pepper, and broccoli acidified to pH 3.8 with citric acid solution containing 0-1% NaCl were placed on a conveyor belt and passed through a microwave tunnel operating at 915 MHz and 4 kW with a 4 min residence time. The time-temperature profiles of vegetable pieces at 5 locations in the package were measured using fiber optic temperature sensors. Addition of 1% NaCl to the cover solution lowered microwave penetration into vegetable pieces and decreased the mean temperature in cups of acidified vegetables from 84 to 73 °C. Soaking blanched vegetables for 24 h in a solution with NaCl and citric acid prior to processing improved microwave heating. Heating was non-uniform in all packages with a cold spot of approximately 60 °C at a point in the container farthest from the incident microwaves. More uniform heating was achieved by implementation of a two-stage rotation apparatus to rotate vegetable cups 180° during processing. Rotating the cups resulted in more uniform heating and a temperature of 77 °C at the cold spot. This is above the industrial standard of 74 °C for in-pack pasteurization of acidified vegetables. The effective treatment involved blanching, soaking for 24 h in a NaCl and citric acid solution, and 180° rotation. This work has contributed to a better understanding of the influence of salt addition and distribution during dielectric heating of acidified vegetables using a 915 MHz continuous microwave system.     

Elaboration of a probiotic oblea from whey fermented using Lactobacillus acidophilus or Bifidobacterium infantis

A novel probiotic product was developed, which was formulated as an oblea (wafer-type dehydrated traditional Mexican dessert) using goat sweet whey fermented with Bifidobacterium infantis or Lactobacillus acidophilus. To obtain the probiotic oblea, the fermented whey was formulated with prebiotic carbohydrates (inulin and resistant starch) and gelatin, and the preparation was poured onto a polytetrafluoroethylene-coated nonstick baking pan, dried in a convection oven, and finally dehydrated at a low relative humidity and room temperature (23 ± 2°C). The amounts of prebiotic carbohydrates and gelatin to be used in the formulation were determined by a factorial experimental design. An untrained sensory panel evaluated 3 quality characteristics (film formation, homogeneity, and smoothness) in the final product. Three different drying temperatures were tested, namely, 40, 55, and 70°C. Bacterial survival at each temperature was determined by viable plate-counting. The best formulation, based on the quality characteristics tested, consisted of 58.33% (vol/vol) of fermented whey, 8.33% (vol/vol) of 6% (wt/vol) resistant starch dispersion, 16.66% (vol/vol) of 15% (wt/vol) inulin solution, and 16.66% (vol/vol) of a 10% (wt/vol) gelatin solution. Drying at 55 ± 2°C for 2.66 ± 0.22 h allowed for concentrations of probiotic bacteria above 9 log₁₀ cfu/g, which is above the minimum concentration required in a probiotic product.     

Effect of heat treatment of film-forming solution on the properties of film from cuttlefish (Sepia pharaonis) skin gelatin

Effects of heat treatment at different temperatures (40–90 °C) of film-forming solution (FFS) containing 3% gelatin from cuttlefish (Sepia pharaonis) ventral skin and 25% glycerol (based on protein) on properties and molecular characteristics of resulting films were investigated. The film prepared from FFS heated at 60 and 70 °C showed the highest tensile strength (TS) with the highest melting transition temperature (T_max) (p < 0.05). Nevertheless, film from FFS heated at 90 °C had the highest elongation at break (EAB) with the highest glass transition temperature (T_g) (p < 0.05). With increasing heating temperatures, water vapor permeability (WVP) of films decreased (p < 0.05), but no differences in L*-value and transparency value were observed (p > 0.05). Based on FTIR spectra, the lower formation of hydrogen bonding was found in film prepared from FFS with heat treatment. Electrophoretic study revealed that degradation of gelatin was more pronounced in FFS and resulting film when heat treatment was conducted at temperature above 70 °C. Thus, heat treatment of FFS directly affected the properties of resulting films.     

Raman spectroscopic analysis and rheological measurements on natural actomyosin from haddock (Melanogrammus aeglefinus) during refrigerated (4 °C) and frozen (−10 °C) storage in the presence of trimethylamine-N-oxide demethylase from kidney of lizardfish (Saurida tumbil)

Changes in viscoelasticity and structure of haddock natural actomyosin (NAM) treated with partially purified trimethylamine-N-oxide demethylase (TMAOase) in the presence of cofactors (FeCl₂, ascorbate and cysteine), after refrigerated storage (4 °C) for 15 days or after frozen storage (−10 °C) for eight weeks, were elucidated using FT-Raman spectroscopy and dynamic viscoelastic measurement. Greater increases in the final storage modulus (G′) and loss modulus (G″), reflecting protein aggregation, were observed in the simulated NAM systems, containing NAM, trimethylamine oxide (TMAO) and cofactors, stored at −10 °C, compared to those stored at 4 °C, particularly in the system with a higher concentration of TMAOase (p < 0.05). Raman spectroscopy revealed that amide I and amide III bands of NAM were affected by TMAOase added as well as by storage temperature. The decrease in the CH₂ bending region near 1450 cm⁻¹, in the presence of TMAOase upon storage, suggested an increase in hydrophobic interactions of aliphatic residues. Changes in a doublet near 830 and 850 cm⁻¹ indicated an involvement of tyrosine residues as hydrogen bond donors in the system containing TMAOase after storage at both temperatures. The systems stored at −10 °C generally showed greater structural alteration than those kept at 4 °C, especially in the presence of 15 units of TMAOase/g. Therefore, TMAOase played an important role in the structural alteration and aggregation of haddock muscle proteins, mainly by the induction of formaldehyde formation.     

Microstructure & rheology of mixed colloidal dispersions: Influence of pH-induced droplet aggregation on starch granule–fat droplet mixtures

The creation of high quality reduced-fat food products is challenging because the removal of fat adversely affects quality attributes, such as appearance, texture, and flavor. This study investigated the impact of pH-induced droplet aggregation on the properties of model food systems consisting of fat droplets and starch granules. Oil-in-water emulsions (2 wt.% oil) containing whey-protein coated lipid droplets aggregated extensively when heated (90 °C, 5 min) at pH values around their isoelectric point (pH 5) but not at lower (pH 3.5) or higher (pH 7) values, which was attributed to changes in electrostatic repulsion. The physicochemical properties of mixed lipid droplet–starch dispersions (2 wt.% oil, 4 wt.% starch) prepared under similar conditions (pH 3.5, 5, and 7; 90 °C for 5 min) were also measured. At pH 5, extensive lipid droplet aggregation was observed in mixed systems, which led to a large increase in their yield stress and apparent viscosity when compared to mixed systems at pH 3.5 and 7. These results show that the rheological properties of mixed fat droplet–starch granule suspensions can be modulated by controlling the electrostatic interactions between the fat droplets so as to change their flocculation state. This study has important implications for fabricating high quality reduced-fat products with desirable sensory attributes.     

Indigenous proteases in the skin of unicorn leatherjacket (Alutherus monoceros) and their influence on characteristic and functional properties of gelatin

Indigenous proteases in the skin of unicorn leatherjacket (Alutherus monoceros) were characterised using autolytic study. Maximised autolysis was found at pH 7 and 50 °C. Autolysis was markedly inhibited by 0.04 mM soybean trypsin inhibitor (SBTI), suggesting that heat activated serine protease was predominant in the skin. The impact of indigenous proteases on the properties of gelatin extracted from unicorn leatherjacket skin was investigated. Gelatin was extracted from unicorn leatherjacket skin using distilled water at 50 °C for 12 h in the presence and absence of 0.04 mM SBTI. In the presence of SBTI, the degradation was markedly inhibited, but a lower gelatin extraction yield was obtained (P < 0.05). Extracted gelatins contained α₁ and α₂ chains as the predominant components with some degradation peptides. FTIR spectra indicated a greater loss of molecular order of the triple helix and a higher degradation was found in gelatin extracted in the absence of 0.04 mM SBTI. The net charge of gelatin samples extracted with and without 0.04 mM SBTI became zero at pHs of 8.45 and 7.31, respectively, as determined by ζ-potential titration. Higher gel strength (320.68 ± 3.02 g) was obtained in gelatin extracted with SBTI, compared with that of gelatin extracted without SBTI (288.63 ± 1.44 g). High emulsifying activity index but lower emulsifying stability index was observed in the former. Therefore, heat-activated serine protease was involved in the degradation of gelatin molecules, thereby affecting the yield, proteinaceous components and properties of gelatin from unicorn leatherjacket skin.