EFFECTS OF DIMENSIONS OF AGAR AND GELATIN GELS ON PALATAL PRESSURE PATTERNS

Eating of agar and gelatin gels in the mouth was studied dynamically in detail. The palatal presures on agar and gelatin gels of various concentrations and dimensions were detected by pressure transducers installed at three locations of the palate. For each of the gels, Pm (the maximum palatal pressure at the initial stage of mastication), P (the mean palatal pressure), W (work), and T (retaining time in the mouth) changed significantly when their concentrations increased. Moreover, gel dimensions also affected Pm, P and W. For a bite-size gel, Pm, P and W increased or remained constant, while for a finer sized gel, Pm, P and W were nearly constant regardless of the increase in rupture strength or gel concentration.     

EFFECTS OF VISCOSITY OF LIQUID FOODS ON PALATAL PRESSURE

The deglutition of non-Newtonian liquids introduced into the mouth was studied dynamically by measuring palatal pressure (P) with pressure transducers set at three locations on the palate. The value of P and the swallowing pressure (S) changed only from 100 to 200 g/cm² over the viscosity range 10⁻² to 10¹ Pa.s. The retaining time (T) and work (W), required for swallowing after the liquid entered the mouth, remained almost constant up to a critical value of 1.0 Pa.s. above which both T and W increased markedly. When the viscosity was low, all of the liquid was swallowed in one deglutition, up to 15 mL volume. Therefore, T was almost constant but S increased with the volume. When the viscosity was high, the liquid was swallowed in several smaller portions. When the volume was high, T increased and S was either constant or it decreased.     

明胶-蔗糖/NaCl体系的LF-NMR弛豫特性及主成分分析

论文主要研究了不同浓度的蔗糖及Na Cl对明胶凝胶体系低场核磁共振(LF-NMR)弛豫特性的影响,并应用主成分分析(PCA)对弛豫特性及其与明胶凝冻强度的相关性进行了分析。结果表明,随蔗糖浓度的增加,明胶-蔗糖凝胶体系的结合水弛豫时间(T21)延长,自由水弛豫时间(T22)和单组份弛豫时间(T2w)缩短,结合水比例(S21%)增大,而自由水比例(S22%)相对减少;而随Na Cl浓度的增加,明胶-Na Cl凝胶体系的T21、T22和T2w均相对延长,S21%和S22%则分别增大和减少。两种凝胶体系之间及其与相应的溶剂之间在PCA得分图上均有明显的区分,且明胶-蔗糖/Na Cl凝胶体系的凝冻强度与其LF-NMR主成分综合得分间存在良好的相关性。研究表明,LF-NMR技术可以有效反映明胶-蔗糖/Na Cl凝胶体系中水分状态及其相应比例的变化,且可反映其凝冻强度的变化,这可为明胶应用于食品生产加工提供一定的指导作用。     

金鲳鱼骨明胶的提取工艺及性质研究

以金鲳鱼骨为原料,以明胶提取率为指标,通过单因素及正交试验探究木瓜蛋白酶酶解提取金鲳鱼骨明胶的最佳工艺,并测定金鲳鱼骨明胶的相关性质。结果表明:提取金鲳鱼骨明胶的最佳工艺条件为酶添加量4.0%、酶解温度45℃、酶解时间1.5 h、酶解pH6.5,明胶提取率达到21.87%。金鲳鱼骨凝胶强度为(154.8±3.8)g,明胶黏度为(2.0±0.43)mPa·s,在450、620 nm波长下的透过率分别为(32±0.12)%、(73±0.49)%,起泡性、起泡稳定性以及乳化性均随着明胶浓度的增加而增强,而乳化稳定性却随着明胶浓度的增加先增强后减弱。紫外光谱、红外光谱分析均显示产品具有明显的明胶特征吸收峰。     

AGAR AND GELATIN GEL FLAVOR RELEASE

The taste suppression and rupture properties of 0.8-2.0% w/w agar gel and 3.0-6.5% w/w gelatin gel were studied by sensory evaluation and objective measurement. Flavor compound concentrations were determined to equalize the intensity of aspartame sweetness (0.02% w/w for both agar and gelatin gels), sodium chloride saltiness (0.9% w/w for agar gel and 0.2% w/w for gelatin gel), and caffeine bitterness (0.08% w/w for agar gel and 0.07% w/w for gelatin gel) in 1% w/w agar gel and 4.5% w/w gelatin gel. The coefficient of taste intensity = (concentration of flavor compound in the aqueous solution of equiintense taste in gel)/(concentration of flavor compound in gel) was used to compare the difference in gel taste suppression. The coefficient of saltiness intensity of 3.0% w/w gelatin gel exceeded 1.0, and those of other gels were below 1.0. The suppressed variation of the coefficient of saltiness intensity in agar gel was significantly (P<0.01) smaller than that of bitterness depending on agar concentration. No significant differences (P>0.05) in taste suppression between gelatin gels containing the 3 flavor compounds due to changes in gelatin concentration were observed. Rupture energy, which is related to mastication and is a common scale for agar and gelatin gels, was used to evaluate changes in suppression of the coefficient of taste intensities of the 2 gels. The coefficient of bitterness intensity of agar gels was more significantly (P<0.01) suppressed than sweetness and saltiness intensities of gelatin gels. The coefficient of sweetness intensity of gelatin gels was suppressed significantly less than bitterness (P < 0.05) of gelatin gels and sweetness (P < 0.05) and bitterness (P < 0.01) of agar gels.     

Tribo-rheological properties of acid milk gels with different types of gelatin: Effect of concentration

We investigated the effect of low concentrations (0.1 to 1%, wt/wt) of gelatin (types A and B) on the properties of acid milk gels in terms of rheology, tribology, texture, and water-holding capacity to better understand the role of gelatin in yogurt. The 2 types of gelatin showed similar effects on the properties of milk gels, with some minor differences, such as lubrication behavior at low concentrations. During acidification, gelatin at ≤0.4% caused an increase in the gel strength, and at higher concentrations it showed a negative effect. However, during cooling and annealing, we observed a positive effect on gel strength with 0.8 and 1% gelatin. Gelling and melting occurred at 0.8 and 1% concentrations of both types of gelatin. The addition of gelatin tended to decrease the storage modulus of milk gels and increase the apparent viscosity, pseudoplasticity, consistency, and yield stress. The firmness of the gels was decreased by gelatin at medium concentrations, but increased at high concentrations. Gelatin significantly enhanced the water-holding capacity of the gels; we observed no serum at concentrations ≥0.4%. With the addition of gelatin at concentrations ≥0.4%, the particle size of gels was greatly reduced, and their lubrication properties were significantly improved. This study showed that 0.4% was an effective concentration in acid milk gel; above this concentration, the properties of the milk gels were greatly changed. Tribology provided important information for understanding the role of gelatin in milk gels.     

Effect of microbial transglutaminase on gel properties and film characteristics of gelatin from lizardfish (Saurida spp.) scales

The addition of microbial transglutaminase (MTGase) generally increased the gel strength of lizardfish (Saurida spp.) scale gelatin gels (P≤0.05) with an increase in gel strength with the addition of MTGase up to 0.5% (w/v). The texture profile analysis compression tests of lizardfish scale gelatin gel with and without MTGase were studied to determine their effects on gel characteristics. MTGase added to the gels decreased the band intensity of the β- and α-components with increasing concentrations of enzyme. Gel microstructures with various concentration of MTGase showed denser strands in the gels with enzyme compared with the looser stands in non-enzyme-treated gel samples. Films cast from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were transparent and flexible. The lizardfish gelatin films were all slightly yellowish while the bovine gelatin films were clearer. The L value of bovine gelatin films had the highest value (P≤0.05) whereas lizardfish scale gelatin films with and without enzyme were not significantly different (P>0.05) for L, a, and b values and ΔE. The film's mechanical properties included tensile strength (TS) and elongation at break (E) were not significantly different (P > 0.05) for E and the films of lizardfish scale gelatin showed higher TS than the films without enzyme added (P ≤ 0.05). The water vapor permeability of films from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were 21.0 ± 0.17, 26.3 ± 0.79, and 25.8 ± 0.09 g·mm/m(2)·d·kPa, respectively, while the oxygen transmission rate of all 3 types of films were less than 50 cc O(2)/m(2)·d.     

Effects of γ-polyglutamic acid on the gelling properties and non-covalent interactions of fish gelatin

The effects of γ-polyglutamic aid (γ-PGA) on the gelling properties and non-covalent interactions of fish gelatin were investigated. The gel strength and melting temperature of fish gelatin gradually increased, with increasing γ-PGA concentration, although there was no significant change when the γ-PGA concentration was greater than 0.04%. As the concentration of γ-PGA increased, the electrostatic interaction of fish gelatin increased and the hydrophobic interaction between gelatin molecules decreased. The fish gelatin system was comprised of γ-PGA concentrations of 0.04 and 0.06% showing a strong hydrogen bond. When the γ-PGA concentration increased from 0 to 0.04%, more phenolic hydroxyl groups in the tyrosine residue tended to form hydrogen bonds with the protein. However, an additional increase in γ-PGA concentration to 0.1% led to enhanced hydrogen bonding with water molecules. The results of this study showed that hydrogen bonds played an important role in improving the gelling properties of gelatin by γ-PGA.     

单宁酸和芦丁对马哈鱼鱼皮明胶凝胶性质的影响

为提高鱼皮明胶的凝胶性能,探究了不同质量分数单宁酸、芦丁及二者的氧化态(0％、2％、4％、6％和8％)对马哈鱼鱼皮明胶凝胶强度、色差、微观结构、T2弛豫性质、十二烷基硫酸钠聚丙烯酰胺凝胶电泳(sodium dodecyl sulfate polyacrylamide gel electrophoresis,SDS-PA...     

Effect of pH, water activity and gel micro-structure, including oxygen profiles and rheological characterization, on the growth kinetics of Salmonella Typhimurium

In this study, the growth of Salmonella Typhimurium in Tryptic Soy Broth was examined at different pH (4.50-5.50), water activity a(w) (0.970-0.992) and gelatin concentration (0%, 1% and 5% ) at 20 degrees C. Experiments in TSB with 0% gelatin were carried out in shaken erlenmeyers, in the weak 1% gelatin media in petri plates and in the firm 5% gelatin media in gel cassettes. A quantification of gel strength was performed by rheological measurements and the influence of oxygen supply on the growth of S. Typhimurium was investigated. pH, as well as a(w) as well as gelatin concentration had an influence on the growth rate. Both in broth and in gelatinized media, lowering pH or water activity caused a decrease of growth rate. In media with 1% gelatin a reduction of growth rate and maximal cell density was observed compared to broth at all conditions. However, the effects of decreasing pH and a(w) were less pronounced. A further increase in gelatin concentration to 5% gelatin caused a small or no additional drop of growth rate. The final oxygen concentration dropped from 5.5 ppm in stirred broth to anoxic values in petri plates, also when 0% and 5% gelatin media were tested in this recipient. Probably, not stirring the medium, which leads to anoxic conditions, has a more pronounced effect on the growth rate of S. Typhimurium then medium solidness. Finally, growth data were fitted with the primary model of Baranyi and Roberts [Baranyi, J. and Roberts, T. A., 1994. A dynamic approach to predicting bacterial growth in food. International Journal of Food Microbiology 23, 277-294]. An additional factor was introduced into the secondary model of Ross et al. [Ross, T. and Ratkowsky, D. A. and Mellefont, L. A. and McMeekin, T. A., 2003. Modelling the effects of temperature, water activity, pH and lactic acid concentration on the growth rate of Escherichia coli. International Journal of Food Microbiology 82, 33-43.] to incorporate the effect of gelatin concentration, next to the effect of pH and a(w). A two step and a global regression procedure were applied. Both procedures were able to fit the data well, but the global regression procedure led to smaller standard errors on the parameters.     

Effects of acid concentration and the UHP pretreatment on the gelatinisation of collagen and the properties of extracted gelatins

An ultra‐high‐pressure (UHP) transmission medium with HCl was applied as a pretreatment to extract gelatin. The effects of the acid concentration (0–1% (w/v)) on the gelatinisation of collagen and the properties of gelatin were investigated. An increase in the acid concentration decreased the thermostability of collagen and increased the yield of gelatin (from 64% increased to 80%). The content of the subunit components in the pretreated collagen and the gelatin declined slightly as the acid concentration was increased, resulted in slight decrease (P > 0.05) in the gel strength (from 435 g decreased to 408 g). The analysis of Fourier transform infrared spectroscopy (FTIR) spectra showed that the triple‐helical structure, secondary structures of the collagen and covalent cross‐linking in the collagenous fibres were damaged gradually as the acid concentration was increased. The scanning electron microscopy (SEM) images showed that the smooth surface of collagen was partly disrupted with microvoids after UHP/1% HCl pretreatment, which may be related to the damage on the covalent cross‐linking.     

氯化钠添加量对鱼皮明胶凝胶性能和结构的影响

以罗非鱼鱼皮为原料制备鱼皮明胶,通过单轴压缩实验、差示扫描量热实验(DSC)和红外光谱法(FT-IR)探讨了不同氯化钠添加量(0、0.5%、1.0%、1.5%、2.0%、3.0%,w/v)对不同浓度鱼胶凝胶样品(2%、4%、6.67%,w/v)的真实应力、杨氏模量、热焓值和结构的影响。结果表明,随着鱼胶浓度增加其真实应力和杨氏模量显著增加,表明鱼胶的凝胶强度和硬度显著增加,添加氯化钠后,鱼胶体系的凝胶强度和硬度随氯化钠添加量的增加呈现显著下降趋势,当氯化钠添加量达到3%时,鱼胶凝胶强度和硬度的值最小。差式扫描量热量热分析结果表明,随着氯化钠浓度的增加,热焓值下降,鱼胶的凝胶网络交联程度变弱。傅里叶变换红外光谱分析结果表明,随着氯化钠添加量增加,酰胺Ⅰ带吸收峰逐渐向低波数方向移动,氢键形成受到抑制,鱼胶凝胶强度降降低。研究表明氯化钠的存在破坏了鱼胶凝胶样品的空间结构,降低了鱼胶的凝胶性能。     

Effects of concentration on nanostructural images and physical properties of gelatin from channel catfish skins

Physical properties are crucial to gelatin utilization and the physical properties are determined by structure. Therefore, it is important to investigate the nanostructure and physical properties of gelatin over the full range of concentrations which are widely applied in research and industry. Nanostructure of gelatin can be investigated by atomic force microscopy (AFM). However, it is hard to obtain reliable AFM images of gelatin with high concentrations (1–6.67%). In this study, methods for imaging gelatin with high concentration were explored and developed, which mainly included six steps. Then the relationships among concentration, nanostructure and physical property of gelatin extracted from channel catfish skins (Ictalurus punctatus) were studied. The high-resolution AFM images show fibril structure in gelatins with concentrations from 1% to 6.67%. However, in low concentrations (<1%), most nanostructures of gelatin were spherical aggregates and fibril structure only existed occasionally. Correspondingly, there were no significant differences of gel strength, texture profile and viscosity among several groups of gelatin when the concentration was lower than 1%, in contrast, these properties changed dramatically when the concentration was greater than 1%. It indicates that there must be some close relationships among concentration, nanostructure and physical property of gelatin. The illustration of nanoscale transition would help us understand the macroscale changes of physical properties.     

Skin gelatin from bigeye snapper and brownstripe red snapper: Chemical compositions and effect of microbial transglutaminase on gel properties

Fish skin gelatin was extracted from the skin of bigeye snapper (Priacanthus macracanthus) and brownstripe red snapper (Lutjanus vitta) with yields of 6.5% and 9.4% on the basis of wet weight, respectively. Both skin gelatins having high protein but low fat content contained high hydroxyproline content (75.0 and 71.5 mg/g gelatin powder). The bloom strength of gelatin gel from brownstripe red snapper skin gelatin (218.6 g) was greater than that of bigeye snapper skin gelatin (105.7 g) (P<0.05). The addition of microbial transglutaminase (MTGase) at concentrations up to 0.005% and 0.01% (w/v) increased the bloom strength of gelatin gel from bigeye snapper and brownstripe red snapper, respectively (P<0.05). However, the bloom strength of skin gelatin gel from both fish species decreased with further increase in MTGase concentration. SDS-PAGE of gelatin gel added with MTGase showed the decrease in band intensity of protein components, especially, β- and γ- components, suggesting the cross-linking of these components induced by MTGase. Microstructure studies revealed that denser and finer structure was observed with the addition of MTGase.     

Effect of microbial transglutaminase on the functional properties of megrim (Lepidorhombus boscii) skin gelatin

This paper examines the effect of a microbial transglutaminase (TGase) on the gelling and viscoelastic properties of a gelatin from megrim (Lepidorhombus boscii) skins. Although TGase extended the setting time of fish gelatin, it was found that melting temperature, gel strength and viscosity in solution at 60 °C were considerably increased by the covalent cross‐linking action of the enzyme, as observed by SDS‐PAGE and SEM. Increasing concentrations of TGase increased the elasticity and cohesiveness of gelatin gels but reduced gel strength and hardness. Partial inactivation of the enzyme was achieved thermally without negatively affecting the properties of the gelatin; whether or not gelatin is thermoreversible depends essentially on the degree of enzyme inactivation. © 2001 Society of Chemical Industry     

Visco‐Elastic and Flow Properties of Gelatin from the Bone of Freshwater Fish (Cirrhinus mrigala)

The average yield of gelatin from the bone of freshwater fish (Cirrhinus mrigala) was 6.13%. The fluorescence spectra revealed maximum emission at 303 nm indicating the exposure of chromophores to bulk solvent. The amino acid profile of gelatin revealed a higher proportion of glycine and imino acids. The bloom strength of gelled gelatin was 159.8 g. The average molecular weight of fish bone gelatin was 281 kDa as determined by gel filtration technique. The dynamic oscillatory test of gelatin solution as a function of time and temperature revealed gelling and melting temperatures of 8.0 °C and 17.0 °C, respectively. The flow behavior of gelatin solution as a function of concentrations and temperatures revealed non‐Newtonian behavior with pseudo‐plastic phenomenon. The Herschel–Bulkley and Casson models were found suitable to study the flow behavior. The emulsion capacity (EC) of gelatin was inversely proportional to its concentration.     

Mixed gels of gelatin and whey proteins, formed by combining temperature and high pressure

Mixed and pure gels of gelatin and whey protein concentrate (WPC) were formed by using temperature and high pressure simultaneously. Combining these gel formation methods enables the two polymer networks to set at the same time. The microstructure of the gels was studied by means of light microscopy and transmission electron microscopy, and the rheological properties by means of dynamic oscillatory measurements and tensile tests. The pH values investigated were 5.4, 6.8 and 7.5. The isoelectric point of the WPC is around pH 5.2 and that of gelatin between pH 7.5 and 9. At pH 5.4, the mixed gel formed a phase-separated system, with a gelatin continuous network and spherical inclusions of the WPC. The storage modulus (G) of the mixed gel was similar to that of a pure gelatin gel. At pH6.8, the mixed gel formed a phase-separated system, composed of an aggregated network and a phase with fine strands. The aggregated network proved to be made up of both gelatin and WPC, and the fine strands were formed of gelatin. The mixed gel at pH 6.8 showed a high G compared with the pure gels, which decreased significantly when the gelatin phase melted. At pH 7.5 the mixed gel was composed of one single aggregated network, in which gelatin and WPC were homogeneously distributed. It was impossible to distinguish the gelatin from the WPC in the mixed network. The mixed gel at pH 7.5 showed a significantly higher G than the pure gels. As the gelatin phase was melted out for the mixed gel, a large decrease in G was observed. The pure gelatin gels, formed by a temperature decrease under high pressure, proved to be pH-dependent, showing an increase in aggregation as the pH increased from 5.4 to 7.5. A fine-stranded, transparent gelatin gel was formed at pH 5.4, while an aggregated, opaque gel was formed at pH 7.5. The stress at fracture for the gelatin gels decreased as the aggregation, and consequently the pore size, increased.     

Gelation behaviour of fish skin gelatin in the presence of methanol-water and ethanol-water solvent system

The aim of this study was to investigate the different concentrations of methanol and ethanol (5%-40%, v/v) on the gel, rheological and structural properties of fish skin gelatin (FG). The results showed that lower contents of both methanol and ethanol (5%-15%, v/v) increased gel strength, hardness and chewiness of FG gels. Rheological results showed that the viscosity of methanol-water-induced FG increased from 0.32 to 5.20 Pa·s with increased concentration of methanol, whereas an opposite trend was found for the ethanol-water-induced ones. Compared with ethanol-water-indued FG gels, methanol-water-induced gels present lower gelation times, and higher gel properties, because of the formation of more hydrogen bonds during gelation. Lower contents of methanol significantly unfold gelatin with the increase in β-sheets. Finally, the mechanism of methanol- and ethanol-induced FG gelation was updated. This research can serve as a guide for semi-solid food which contains alcohol and medicinal products.     

Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

SENSORY AND MECHANICAL ATTRIBUTES OF GEL TEXTURE

Eighteen experienced judges evaluated the texture of gels varying in gelatin concentration (22-45 g/L) in terms of firmness by oral and manual shear and compression, cohesiveness, and extent of breakdown in the mouth. Manual compression and biting with the front teeth discriminated well across gel concentrations. All sensory measures except extent of breakdown increased with gelatin concentration. Instron (IUTM) measurements showed that increasing gelatin concentration resulted in an increase in maximum force and force/deformation, but had little effect on deformation at yield and rupture or in elasticity and cohesiveness. Results from mechanical measurements varied with the type of force applied (compression, shear or puncture), the loading rate (50 or 200 mm/min), and the extent of deformation attained (40–90%). The highest discrimination across gel concentrations was achieved with shear force at a rate of 200 mm/min and at greater deformations. Sensory responses correlated most highly with the following IUTM measurements: (1) Compression forces at yield and at deformations of 70 and 85% at the higher crosshead speed; (2) Compression forces below the yield point at the lower crosshead speed; and (3) Shear forces measured at maximum deformation (90%) at 200 mm/min.