Structural Characteristics of Extracted Collagen from Tilapia (Oreochromis mossambicus) Bone: Effects of Ethylenediaminetetraacetic Acid Solution and Hydrochloric Acid Treatment

Desalting is an important process of bone collagen extraction. In this present study, collagens were prepared from tilapia bone using acetic acid and pepsin. The extracted collagen was partially characterized. Prior to extraction, tilapia bone was desalted by soaking in ethylenediaminetetraacetic acid solution and hydrochloric acid. Thermo-gravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy were performed to analyze the structural characteristics. The extracted protein was classified as collagen by Fourier transform infrared spectroscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and circular dichroism. Results showed that desalination with HCl was fast, but collagen yield was low. No acid-soluble collagen and only 0.5% pepsin-soluble collagen were obtained from HCl-treated fish bone. By comparison, the yields of acid-soluble collagen and pepsin-soluble collagen from ethylenediaminetetraacetic acid-treated fish bone were 3.5 and 6.0%, respectively. These values were observed higher than those from HCl-treated fish bone. In HCl-treated fish bone, the properties of collagen, such as amino acid composition, denaturation temperature, and molecular weight distribution, were different from those of collagen in ethylenediaminetetraacetic acid-treated fish bone. Collagens extracted from ethylenediaminetetraacetic acid-treated fish bone showed more integrated secondary structure. Therefore, ethylenediaminetetraacetic acid can be used more effectively than HCl to extract collagen from tilapia bone.     

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.     

Turkish kefir and kefir grains: microbial enumeration and electron microscobic observation†

Microbial populations in kefir and kefir grains were enumerated by plating. Total lactic acid bacteria, lactoccocci, lactobacilli and yeast populations increased during fermentation and increased slightly during cold storage. Kefir grains had a lactic acid bacteria : yeast ratio of 10 ⁹  : 10 ⁶ . In further studies, kefir grains were observed using scanning electron microscopy (SEM) methods, which indicated yeast colonization on the surface and middle part of the kefir grain. Three types of lactobacilli (short, long and curved) were noted throughout the grain. Lactococci were not observed under SEM; preparation of kefir grains for SEM may have caused removal of lactococci from the grains.     

Enhancement of Functional Properties of Wami Tilapia (Oreochromis urolepis hornorum) Skin Gelatin at Different pH Values

The effects of several agents in two different concentrations and pH values (5.0 and 8.0) on the functional properties of tilapia (Oreochromis urolepis hornorum) skin gelatin were evaluated and compared using a control tilapia skin gelatin and a commercial mammalian gelatin. The addition of the agents (sucrose 4 % and 8 % (w/v), glycerol 5 % and 10 % (v/v), NaCl 0.3 and 0.8 mol/L, MgCl₂ 0.3 and 0.8 mol/L, MgSO₄ 0.3 and 0.8 mol/L, KCl 0.3 and 0.8 mol/L, and transglutaminase 10 and 15 mg/mL) slightly increased the turbidity. There were different ratios of rheological properties depending on the agent, concentration, and pH. The addition of all agents increased the viscosity of the gelatin solution, mainly at pH 5.0. The addition of glycerol (10 % (v/v)) raised viscosity up to 7.45 cP. The setting time was prolonged by incorporating the agents. The gelatin samples with the addition of MgSO4 0.8 mol/L showed higher gel strength than the mammalian gelatin, exhibiting values of 298 and 295g_f at pH 5.0 and 8.0, respectively.     

Physicochemical and Rheological Properties of White-Cheek Shark (Carcharhinus dussumieri) Skin Gelatin

Physicochemical and rheological properties of white-cheek shark (Carcharhinus dussumieri) skin gelatin were determined as a function of either an alkaline-acid or an acid pretreatment. With alkaline-acid pretreatment, the purity of white-cheek shark skin gelatin was increased, with a significantly lower extraction yield, a higher retention of high molecular weight components, and greater preservation of the triple helical structure. Moreover, gelatin from alkaline-acid treated skins showed denser spherical structure, significantly (p < 0.05) different textural properties, better thermostability (T_g = 21°C, T_m = 27.5°C), higher values of both G′ and G″, higher gel strength (330 g), more imino acids (20.3%), and lighter colored gels compared with acid treated white-cheek shark skin gelatin.     

Characteristics of Gelatin from Giant Grouper (Epinephelus Lanceolatus) Skin

Gelatin extraction from the skin of giant grouper (Epinephelus lanceolatus) was conducted by acid process with a yield of 20.27 g/100 g wet skin sample. The characteristics of extracted gelatin from giant grouper was investigated in this study, and further compared to that from commercial tilapia. Results showed that when compared to commercial tilapia, giant grouper had lower levels of bloom strength and foam formation ability, but greater values of viscosity, foam stability, and lightness (L*) on gelatin skin. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis analysis revealed three high-bands intensities of major protein components of giant grouper skin gelatin, representing α1-chain, α2-chain, and β-components, and was similar to that of standard calf skin collagen type I. Compared to giant grouper, commercial tilapia contained extra proteins with molecular weight less than 70 kDa on the sodium dodecyl sulphate-polyacrylamide gel electrophoresis of both skin gelatins.     

Effects of microwave frying and different flour types addition on the microstructure of batter coatings

In this study, the influences of microwave frying and various flour types on microstructure of batter coatings were investigated. Control batter formulation contained only wheat and corn flour. To determine the effects of different flour types, 30% of the corn and wheat flour mix was replaced with chickpea, rice or soy flours. Frying was performed in microwave oven at 365 W (70%) power level for 1.5 min after bringing the oil temperature to 180 ± 1 °C. Samples were also fried in a conventional fryer at 180 °C for 1.5 and 5.0 min for comparison. Microwave fried samples had higher specific bulk volume and porosity values and also smoother inner surface as compared to conventionally fried samples. Porosity values of different batter formulations were in the range of 0.425–0.484 in 1.5 min microwave fried chicken samples and 0.348–0.392 in 5.0 min conventionally fried ones. Microwave fried samples had comparable or lower hardness values than the conventionally fried ones depending on the flour type used in batter formulation. Microstructure of fried batter was different for different batter formulations. Microwave fried control and chickpea flour containing batter provided formation of larger gas cells on the outer surface. Soy flour containing batter resulted in smallest size gas cells for both frying methods.     

Effects of Pretreatment on Properties of Gelatin from Perch (Lates Niloticus) Skin

Fish gelatins obtained from perch fish skin pretreated with various solutions containing acetic acid, sodium hydroxide (NaOH) and sodium chloride (NaCl) were successfully characterized for their nanostructure pattern using field emission scanning electron microscopy. Each pretreatment transformed collagen to gelatin with fibril, zigzag cracks, straight rods, and cross-linked rods nanostructure patterns. Pretreatment solutions also affect the gel yield, gel strength, amino acid profile, and functional groups in perch gelatin as analyzed by Fourier transform infrared spectroscopy. Samples pretreated with NaCl, NaOH, and acetic acid solution showed the highest gel yield (22.84%) and gel strength (179.84 g). Fourier transform infrared spectra for perch gelatins also revealed weak C–N amide II and III bond stretches as well as weak C=O bond stretch.     

Functional Properties of Grass Carp (Ctenopharyngodon Idella), Nile Perch (Lates Niloticus) and Nile Tilapia (Oreochromis Niloticus) Skin Hydrolysates

The influence of using an endo-peptidase (alcalase) on the functional properties of hydrolysis products from Nile perch, Grass carp, and Nile tilapia skin was studied. Reaction conditions were controlled at pH 8.25, 60°C, and the enzyme was added on the basis of standard activity units at an enzyme to substrate ratio of 1.7 g/100 g protein. The reaction was allowed to proceed for 85 min and enzyme was inactivated by heat. The soluble protein fractions were recovered and lyophilized. All freeze-dried fish skin hydrolysates powders had a light yellow color and contained up to 90% protein. Nitrogen solubility varied from 95.93 to 98.72% and was not significantly different at 5% probability level. The water and oil holding capacities of the skin hydrolysates were good in the range of 2.8 to 3.2 mL/g and 3.4 to 3.8 mL/g, respectively. Emulsification capacity varied from 11.3 to 21 mL/0.5 g with Nile perch skin hydrolysate having the highest score while Nile tilapia skin hydrolysate was the lowest. Grass carp skin hydrolysate was not able to form stable foam, unlike the Nile perch and Nile tilapia skin hydrolysate. Alcalase treated freshwater fish skin exhibited satisfactory functional properties hence may play an important role as an ingredient in the food and pharmaceutical industry.     

The microstructure of almond (Prunus dulcis (Mill.) D.A.Webb cv. ‘Nonpareil’) cotyledon

Microstructure of almond (Prunus dulcis (Mill.) D.A. Webb cv. ‘Nonpareil’) cotyledon was observed with light, scanning and transmission electron microscopy. The objective of this study was to characterise almond cotyledon surfaces as well as to describe internal and subcellular organisation. The testa has an outer epidermis, which consists of relatively large thin-walled cells, which range from 100 to 300 μm in width. The major portion of the testa consists of approximately 14-20 layers of flattened parenchymal cells with the total thickness of the layers ranging from 80 to 120 μm. The remainder of the testa was comprised of a small amount of vascular tissue. The embryo consisted primarily of parenchymal tissue with relatively thin cell walls (1-3 μm in thickness) and a small amount of provascular tissue. Protein bodies up to 12 μm in width and spaces once occupied by lipid bodies up to 3 μm in width were present in all cells of the embryo.     

Retrogradation properties of high amylose rice flour and rice starch by physical modification

A new physical modification applied to prevent the retrogradation of rice flour and rice starch was investigated. This study examined the retrogradation properties of treated rice flour or rice starch paste by three stirring or heating-stirring, or without. The results proved that the retrogradations of rice flour and rice starch were both not substantially affected by three stirring modifications. However, three heating-stirring treatments had a marked effect on retarding the retrogradation of rice flour, but did not affect that of isolated rice starch. In the differential scanning calorimetry (DSC) analysis, modified rice flour by three heating-stirring exhibited the lowest retrogradation enthalpy (3.04 J/g dry matter) as compared to the control RF (5.93 J/g dry matter) and by three stirring (5.08 J/g dry matter). Meantime, it had almost the least recrystallization of retrogradation by X-ray diffraction (XRD). It was also found through scanning electron microscopy (SEM) that the granule structure of this modified rice flour had a more honeycomb-like structure and the lowest crystallinity as compared to the others.     

罗非鱼肉蛋白酶解液的抗氧化活性

采用胰蛋白酶、复合蛋白酶、风味蛋白酶、木瓜蛋白酶、菠萝蛋白酶、罗非鱼胃蛋白酶和罗非鱼肠蛋白酶分别酶解罗非鱼肉蛋白,研究并比较不同酶对罗非鱼肉蛋白的酶解效果及产物的抗氧化特性。结果表明:7种酶的酶解液都显示了一定的抗氧化性,其中木瓜蛋白酶酶解液水解度(DH)最高,为20.85%,对DPPH自由基、O2-.清除率均最佳,分别为75.74%、34.35%;罗非鱼胃蛋白酶酶解液的DH为17.03%,对.OH清除率和还原力均最高,分别为60.51%、0.653。整体的抗氧化性能显示:罗非鱼胃蛋白酶和木瓜蛋白酶酶解罗非鱼肉蛋白得到的酶解液的抗氧化活性优于其他酶。     

Effect of Drying on Rheological,Thermal, and Structural Properties of Desert Truffles (Terfezia Claveryi) Powder Dispersions

The effect of drying methods (freeze-drying and tray-drying) on the rheological, thermal and functional properties of truffle flour dispersion was studied. Sieve analysis showed the number of finest particles in the freeze-drying samples were significantly higher than the tray-drying samples whereas no significant difference was observed in the particle size distribution through laser diffraction measurement. The freeze-drying sample had significantly higher water holding capacity, sediment volume fractions, and superior instrumental color values than the tray-drying sample. Upon thermal scanning, two distinct starch-lipid complex melting transitions for the freeze-drying and one for the tray-drying sample were detected. Contrary to differential scanning calorimetric measurement, the oscillatory shear measurement successfully detected a distinct gelatinization temperature for the freeze-drying sample between 64 and 67.6°C. The mechanical rigidity of the dispersion was significantly influenced by the drying method and the freeze-drying sample exhibited the higher mechanical strength over the tray-drying sample throughout the frequency range (0.1 to 10 Hz). Viscoelasticity of the dispersion was estimated by a power-type relationship correlating the elastic modulus and frequency. Various shapes of truffle particles including rod, round, oval, and irregular were observed through the scanning electron microscope. This study provided in-depth knowledge on structural/rheological properties of truffle powder produced by two drying processes.     

Characteristics of Different Types of Starch in Starch Noodles and Their Effect on Eating Quality

Several commercial starch noodles made from legume, tuber, geshu (kudzu and sweet potato) and fernery starches were used to study the characteristics of starch in starch noodles and their effect on eating quality of starch noodles. Scanning electron microscopy observation found that the special inner structure of starch noodles was composed of some broken starch granules and some gel-like substances. Tuber and legume starches had the highest and lowest solubility, swelling power, swelling factor, setback, breakdown, peak viscosity, and final viscosity, respectively. Legume and tuber starches had the highest and lowest gelatinization temperature, respectively. Tuber and geshu starches had the highest amylose leaching rate, while legume starches owned the lowest value (p < 0.05). Tuber starches had the highest conclusion temperature of gelatinization (151.12~158.86°C). Fernery starches had the lowest value of retrogradation enthalpy (967.33 J/g dry starch). Legume starch noodles had the lowest broken rate (0.00~1.67%), swelling ratio (332.64~343.57%), and cooking loss (2.40~2.74%), and the highest hardness (87.47~93.29 g/mm2), shear deformation (0.49~0.52), and elasticity (0.58~0.62), However, tuber and fernery starch noodles did the opposite, tuber and legume starch noodles had the highest and lowest cohesiveness, respectively. All the above cooking and starch properties test results of starch noodles demonstrated that, compared with others, legume starch noodles are relatively well in eating quality. The correlation analysis showed that the cooking and physical quality of starch noodles could be perfected significantly by improving the swelling and pasting properties for starch of starch noodles, while thermal properties had no obvious influence on them.     

Partial Characterization of Tamarind (Tamarindus indica L.) Kernel Starch Oxidized at Different Levels of Sodium Hypochlorite

The effects of different levels of sodium hypochlorite (1–4 g/100 g dry solids active chlorine) on the physicochemical, pasting, and structural properties of tamarind kernel starches were investigated. The isolated starch had low traces of non-starch components, such as protein, fat, and ash, indicating its purity. Both the carboxyl and carbonyl contents in the oxidized starches increased significantly with the increase in chlorine concentration. The introduction of carboxyl and carbonyl groups resulted in significantly lower amylose content. The swelling power of oxidized starches was significantly lower than native starch and the solubility values increased when the chlorine concentration increased at all the measured temperatures. The percentage of light transmittance increased progressively after oxidation. Pasting properties showed that in treatments at high active chlorine concentrations, the peak viscosity decreased more drastically than in treatments at low chlorine concentration, indicating a greater degradation of starch. The morphology of the starches was not altered after oxidation. After oxidative treatment no change in the X-ray diffraction pattern was observed but intensity of the peaks increased. Therefore, tamarind kernel being underutilized raw material, has a great potential as a non-conventional source of starch and desirable properties of this starch can be enhanced by oxidation for applications in food industry.     

几种淀粉的相对分子质量分布、微晶结构及形貌的研究

以小麦、马铃薯、甘薯、玉米、芋头为原料提取淀粉。采用碘兰值法、凝胶色谱、X衍射和扫描电镜,研究淀粉组成及淀粉级分的特性、淀粉的晶体特性和微观形态,为淀粉类食品的深加工提供理论基础。研究表明,芋头淀粉的碘兰值最小,其他4种淀粉碘兰值相差不大。玉米淀粉为高直链淀粉,小麦淀粉的3个级分较明显。马铃薯淀粉表现为B型X衍射图谱的特征,甘薯淀粉表现为C型X衍射图谱的特征,而小麦淀粉、玉米淀粉和芋头淀粉表现为A型X衍射图谱的特征,马铃薯淀粉的结晶度最小,玉米淀粉的结晶度最大、微晶尺寸最小,甘薯淀粉的微晶尺寸最大。     

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.     

不同制备方法桑叶蛋白功能性质的比较

以广东桑大10为原料,采用水提法制备叶蛋白浓缩液,用加热法、酸沉法、酸热法、盐析法沉淀叶蛋白,分别得到蛋白样品RC、SC、SR、LC。对所得样品进行功能性质测定,与大豆分离蛋白对比,得出不同样品的功能特点。结果表明,异亮氨酸、赖氨酸分别为桑叶粉的第一、第二限制性氨基酸。不同沉淀方法对叶蛋白的功能性质有显著影响:LC的溶解性、起泡性、乳化性、吸油性最好,均优于SC、SR及RC;SR的持水性优于SC及RC,但乳化性、起泡性较差;RC、LC的胶凝性最好。与SPI相比,4个样品的吸油性均优于SPI,持水性、胶凝性则显著低于SPI(p0.05);LC的乳化稳定性(68.57%)及SC的起泡性(40%)最好,显著优于SPI(54.86%、37.67%),RC与SPI相当,SR最差,显著低于SPI(p0.05)。LC电镜扫描结果显示其具有典型的蜂巢结构。     

Changes in wheat and potato starches induced by gamma irradiation: A comparative macro and microscopic study

Wheat and potato starches were treated by gamma irradiation (0, 3, 5, 10, 20, 35, and 50 kGy). Apparent amylose content, gelatinization maximum consistency, swelling power, viscosity, and textural parameters decreased in potato and wheat starch pastes as irradiation dose increased. Nevertheless, the decrease of apparent amylose content and swelling power was greater in potato starch than in wheat one. High gamma irradiation doses made potato starch granules more sensitive to shear. On the other hand, no modification in the granule shape was observed by scanning electron microscopy. However, through heat-treatment, starch granules destroyed as irradiation dose increased. Consequently, the effect of irradiation on granular structure appeared to be greater in potato starch than in wheat starch.