Physicochemical properties of pectins from okra (Abelmoschus esculentus (L.) Moench)

Okra pectin obtained by hot buffer extraction (HBSS) consists of an unusual pectic rhamnogalacturonan I structure in which acetyl groups and alpha galactose residues are substituted on rhamnose residues within the backbone. The okra Chelating agent Soluble Solids (CHSS) pectin consists of slightly different structures since relatively more homogalacturonan is present within the macromolecule and the rhamnogalacturonan I segments carry slightly longer side chains. The rheological properties of both okra pectins were examined under various conditions in order to understand the unusual slimy behaviour of okra pectins. The viscosity of the okra HBSS pectin was 5–8 times higher than the viscosity of the okra CHSS pectin. The okra HBSS pectin showed an elastic behaviour (G′ > G″) over a wide range of frequencies (10⁻¹–10 Hz), at a strain of 10%, while okra CHSS and saponified okra HBSS/CHSS pectin showed predominantly viscous responses (G′ < G″) over the same frequency range. The results suggest that the structural variation within the okra pectins greatly affect their rheological behaviour and it is suggested that acetylation of the pectin plays an important role through hydrophobic associations. Dynamic light scattering was used to study the association behaviour of both okra pectins at low concentration (0.001–0.1% w/w). Results showed that the saponified okra pectins did not exhibit a tendency to aggregate in the concentration range studied, whereas both non saponified samples showed a substantial degree of association. These results suggest that the unusual slimy behaviour of the non saponified samples may be related to the tendency of these pectins to associate, driven by hydrophobic interactions.     

Conventional and Microwave-Assisted Extraction of Mucilage from <Emphasis Type="Italic">Opuntia ficus-indica</Emphasis> Cladodes: Physico-Chemical and Rheological Properties

Cactus pear cladodes processing has potential value for mainstream industries and is equally important for marginal rural communities in arid regions. This work is focused on physico-chemical and rheological properties of Opuntia ficus-indica (OFI) peeled cladodes extracted by conventional method “CE” and using microwave-assisted extraction “MAE.” MAE gave the highest yield extraction (8.13 %, w/w) within the lowest extraction time (500 W/7 min) and provided more protein (×1.03) and carbohydrates (×1.51) than CE. The monosaccharides detected by gas chromatography were arabinose, galactose, rhamnose, xylose, and galacturonic acid. The dialyzed mucilage solution characterized by SEC/MALS/VD/DRI (size-exclusion chromatography coupled with online multi-angle light scattering, viscometer detectors, and differential refractive index) revealed fractions with molecular weight (M _w ) ranging from 15.3–15.7?×?10⁶ g mol^?1 for the CE extracts and about 16.7–17.5?×?10⁶ g mol^?1 for the MAE extracts. Dynamic oscillatory testing has been used to study the rheological properties of mucilage solution within the concentration of 0.50–3.00 % (w/v) at 25 °C. The rheological profiles of CE and MAE showed similar behavior. At low frequency and low mucilage concentration (<2.00 %), the viscous component (G") predominated over the elastic component (G'), while for higher frequencies, the behavior is reversed (G'?>?G"). If safely controlled, alternative energies like microwaves could extract soluble polymers with comparable properties to commercial ones, conventionally extracted.     

Extraction of Gelatin from Megrim (Lepidorhombus boscii) Skins with Several Organic Acids

ABSTRACT: Light-colored, dry collagen was obtained and, after dissolving in warm water, turned into soluble gelatin. The type of acid used influenced the gelatin viscoelastic and gelling properties. Acetic- and propionic-acid extracts produced the gelatins with the highest elastic modulus, viscous modulus, melting temperature, and gel strength, especially when skins were previously treated with dilute NaOH. After such treatment, lactic acid was also shown to be suitable for collagen or gelatin extraction. The lowest degree of turbidity was achieved by using citric acid, whereas propionic acid led to the most turbid gelatin. No improvements of rheological properties were observed when acid concentration for extraction was increased above 0.05 M.     

葡聚糖水溶液流变性研究

本实验研究了葡聚糖水溶液的流变性能,选取了五种不同分子量的葡聚糖,分别考查了分子量、溶液浓度、溶液温度等因素对葡聚糖水溶液流变性的影响。结果显示,多数葡聚糖水溶液表现出牛顿流体的特性,而当葡聚糖分子量为531000,溶液浓度为30%时,溶液则表现出假塑性流体的性质,黏度随着剪切速率的提高而降低。当葡聚糖浓度较低时(≤1%),水溶液均表现出一种特殊的流变性,即黏度随着剪切速率增加先降低后升高,本研究对出现这一现象的原因进行了分析。     

Effects of ultrasound and infrared assisted conductive hydro-drying,freeze-drying and oven drying on physicochemical properties of okra slices

Okra (Abelmoschus esculentus) is a nutritious vegetable but it is highly perishable and drying is one of the best methods for its preservation. Ultrasound and infrared assisted conductive hydro-drying (UIACHD) is a new patented drying method that can dry food materials with high quality and high energy efficiency. In this study, okra slices were dried using UIACHD with different settings and also by freeze-drying and oven drying. The UIACHD drying curves, moisture content, color, vitamin C content, hydrocolloids rheology and microstructure of the dried okra sample as affected by drying method were investigated. Drying curves showed that the application of ultrasound and infrared could increase the drying rate. In terms of quality parameters, UIACHD performed significantly better than oven drying and the quality of the products was comparable to freeze-drying. Flow and oscillation rheology tests showed that UIACHD drying could result in okra hydrocolloids with higher apparent viscosity and the application of ultrasound and infrared has preserved the rheological properties of the okra hydrocolloids. The microstructure of the dried okra slices was also well preserved by UIACHD. This study showed that UIACHD is a suitable drying method for maintaining the physicochemical quality of dried okra.Industrial relevanceDried okra can be used as a nutritious and functional ingredient in the formulation of different products such as soups, sauces and other culinary products. This study shows that ultrasound and infrared assisted conductive hydro-drying can be a suitable method for the production of high quality dried okra with well-retained color, nutritional value and rheological properties.     

Physico-chemical and film forming properties of giant squid (Dosidicus gigas) gelatin

Giant squid (Dosidicus gigas) inner and outer tunics were subjected to hydrolysis with pepsin prior to gelatin extraction (G1 gelatin) by a mild-acid procedure. Furthermore, a second gelatin extraction (G2 gelatin) was done using the collagenous residues that remained from the first extraction. Pepsin allows the collagen solubilisation and the extraction yield to increase by yielding extracts high in α-chains. G1 exhibited good gel forming ability but G2 showed poor viscoelastic behaviour and low gel strength, in agreement with the results for the molecular weight distribution, which showed a considerably higher content of low molecular weight components. In spite of these differences, both G1 and G2 showed good filmogenic ability and similar properties were found including the absence of colour, opacity, low water vapour permeability and high puncture deformation. Nevertheless, films made from G1 had a higher puncture force than films made from G2 as a result of the different molecular weight distribution.     

不同大麦品种来源β-葡聚糖流变学特性

优化大麦β-葡聚糖提取工艺,在提取料水比1∶10,提取液pH=7,提取温度60℃,提取时间4h条件下,可得纯度为96.89%、分子量为1×106大麦β-葡聚糖;利用凝胶过滤色谱法测定5种不同大麦品种来源β-葡聚糖分子特征参数,并使用静态和动态粘弹性测定法研究其流变学特性。结果表明,所得大麦β-葡聚糖分子量在不同大麦品种间差异较大,在0.6×106～1.8×106之间;在浓度0.8%及以上时,江苏啤麦β-葡聚糖具有明显假塑性流体特征;与其它品种相比,1.0%浓度江苏饲麦β-葡聚糖溶液零剪切粘度最低,说明β-葡聚糖分子量越高,分布范围越窄,零剪切粘度越高;浓度为2.0%江苏啤麦具有显著弹性特征,在5个品种中表现出最高增稠能力。     

Fractionation by gel exclusion HPLC of proteins from acidic and alkaline extractions of Phaseolus beans

The proteins extracted from Phaseolus vulgaris (white kidney, navy) beans and P. lunatus (baby lima, large lima) beans by sodium hydroxide (NaOH) solution and citric acid (CA) solutions were fractionated by gel exclusion high-pressure liquid chromatography. The isoelectric amorphous proteins from the NaOH extraction and bipyramidal crystalline and spheroidal proteins from the CA extractions were also fractionated. Both the NaOH and the CA extracts of the beans contained 8–10 fractions. The proteins isolated from the extracts of the P. vulgaris beans were comprised predominantly of a relatively large molecular weight fraction, regardless of the microstructure of the protein precipitate; several of the fractions which were relatively major components of the extracts were not found in the precipitates obtained from the extracts. The differences in behaviour between the extracts and protein isolates of the different beans might be related to genetic variations.     

Influence of exopolysaccharides on the structure,texture, stability and sensory properties of yoghurt and related products

The impact of microbial exopolysaccharides (EPS) from lactic acid bacteria (LAB) on dairy products such as yoghurt, cheese, or milk based desserts has been extensively described in recent years. It is well known that EPS influence viscosity, syneresis, firmness, as well as sensory properties. The rheological properties of milk products may depend on several factors, such as EPS location (capsular, free), EPS structure (molecular mass, side chains, stiffness, charge), EPS concentration, and the interaction of EPS with other product compounds (proteins, minerals, or bacteria). This review summarises literature concerning the structural and rheological characterisation, localisation and specific application of several EPS from LAB, and intends to critically evaluate different methods and conclusions reported in research. The main focus is on the behaviour and effect of EPS, either produced in situ or added as stabiliser, on acid milk gels.     

Effect of soapwort extract on physical and sensory properties of sponge cakes and rheological properties of sponge cake batters

Soapwort extract yields relatively stable, soap-like foam in aqueous solution because of its saponin content. The objective of this study was to utilise the advantage of the high foam forming capacity of soapwort extract in the production of sponge cakes. Egg white proteins were partially replaced with soapwort extract in the sponge cake formulation. The effects of soapwort extract addition on the rheological and physical properties of cake batters and on the physical and sensory properties of sponge cakes were determined. Replacing egg white proteins with soapwort extract, up to 75% by weight, did not have any significant influence on the specific gravity of batters (p > 0.05). Addition of soapwort extract into the cake mixture did not influence the flow behaviour indices (n) of cake batters nor the consistency indices (K) of cake batters. In general, replacing egg white proteins with soapwort extracts (up to 75% by weight) did not alter physical properties of sponge cakes. Replacing egg white proteins with soapwort extract had no unfavourable influence on the sensory properties of sponge cakes. Indeed, sponge cakes formulated with soapwort extract (by replacing egg white proteins by 50% and 75% on weight basis) received significantly higher chewiness scores than did control cakes (p < 0.05). This study showed that egg white proteins could be partially replaced with soapwort extract in the formulation of sponge cakes.     

Gelling properties of kefiran, a food-grade polysaccharide obtained from kefir grain

The physicochemical and gelling properties of kefiran, a water-soluble glucogalactan with probed health-promoting properties, were investigated. Gel permeation chromatograms revealed a single distribution of molecular weight corresponding to 10⁷ Da. Intrinsic viscosity of kefiran determined using Huggins extrapolations was 6.0 dl/g and using Kramer approximations was 5.95 dl/g.Kefiran has a Newtonian behaviour in diluted solutions, which becomes pseudoplastic at higher concentrations. Rheological behaviour of the solution before and after freeze drying was evaluated by small deformation oscillatory rheological measurements. The mechanical spectrum of solution corresponded to an entangled network behaviour. After freeze–thaw treatment of the solution, a rheological behaviour transition from a liquid-like system to a gel was observed. The storage modulus (G′) in cryogels was 35 times higher than the value obtained for the solution. Rheological characteristics of the cryogel were influenced by kefiran concentration. As the polymer concentration increased, higher number of interactions was evident for the increment in both moduli (G′ and G″). The behaviour of kefiran cryogels about 37 °C determines its ability to melt at mouth temperature. These results suggest that kefiran cryogels could be an interesting alternative for its application in food formulations.     

Innovative processing technology in agar recovery: Combination of subcritical water extraction and moderate electric fields

Emerging processing technologies are gaining importance due to ecological benefits and high extraction efficiency. Agarophytes are seaweeds highly recognized for their agar content. This work aimed at evaluating the potential of combining subcritical water extraction and moderate electric fields (MEF) for agar extraction. Different temperature and time binomials were applied, keeping the same severity factor, under subcritical water conditions with and without MEF. The influence in the agar extraction yields, its composition and technological properties was evaluated. Moderate electric fields proved to be a valuable tool in agar recovery, particularly for G. sesquipedale, improving agar's extraction yield up to 40% at 140 °C in the presence of MEF. Applied treatments and extraction technologies did not affect gelling ability, rheological behaviour, structure, and molecular weight distribution of the obtained agars. Therefore, the feasibility of alternative processing technologies was demonstrated, with gains in efficiency and processing time.     

干燥方式对秋葵多糖结构特征和抗氧化性的影响

秋葵中富含黏性多糖类成分.本文研究干燥方式对秋葵多糖结构特征和抗氧化性能的影响.将秋葵原料分别用热风干燥、自然干燥和真空冷冻干燥处理,用水提醇沉法制备获得水溶性多糖,然后对其基本理化性质、单糖组成、红外光谱、黏度和抗氧化性进行比较分析.结果显示:3种多糖主要由I型鼠李糖半乳糖醛酸(RG-I)果胶组成,具有不同的线性程度...     

Characterisation of soy extract processed under different drying methods and extraction conditions

Soybean extract (SE), enriched in soy soluble polysaccharide (SSPS), was evaluated in three different conditions varying in extraction temperature and drying process: SE‐A ?80 °C, freeze‐dried, SE‐B ?80 °C, spray‐dried, SE‐C ?95 °C, spray‐dried. Spray‐dried SE presented lower moisture content, smaller and more uniform particles. In addition, zeta potential showed the same negative surface charge for all extracts showing the prevailing behaviour of SSPS. Moreover, all biopolymers were composed of three main molecular weight (Mw) fractions, but the Mw distribution was different between the three ingredients, reflecting their rheological behaviour in aqueous solution. Higher mean Mw led to enhanced apparent viscosity observed in neutral and acid pH for SE‐A, followed by ‐B and ‐C, respectively. The inverse behaviour was observed for intrinsic viscosity at neutral pH. However, SE‐C showed lower intrinsic viscosity at acid pH, which was attributed to protein–polysaccharide interaction presents in the solution.     

Preparation and Aqueous Properties of Starch‐grafted Polyacrylamide Copolymers

In the present work, starch‐grafted polyacrylamide copolymers were prepared and their rheological properties, either in water or in water‐based muds, were investigated. The advantages in using starches as substrates to prepare additives which are suited for improving stability and the rheological properties of water‐based muds, lie in their low cost, and their lower biodegradability than native starches. Thus, various copolymer series were prepared by free‐radically grafting acrylamide (AM) onto starch using ceric ammonium sulphate (CAS) as initiator. It is shown that the intrinsic viscosity and the molecular weight of the grafted starches are controlled by the initiator and monomer concentrations. Furthermore, to predict the behaviour of the samples under oil‐well conditions, the aqueous solution properties of the copolymers such as water solubility, viscosity, shear rate, were determined as function of temperature, salt concentration and type, and aging time. The knowledge of these properties is a prerequisite for the use of the copolymers in drilling fluids. The data indicate that starch‐grafted polyacrylamide copolymers as compared to the non‐modified starch, behave as shear‐thinning, are salt resistant, and their rheological properties are stable with time. The grafted starches as prepared above were also added to water‐based mud and the rheological properties of the resulting muds were determined under oil‐well conditions. Grafted starches, having high AM contents, are more efficient in decreasing the filtrate volume, and increasing the plastic viscosity of the muds, when compared to PAC‐L, a modified cellulosic polymer used in the filtration control of most water‐based muds. Such improvements in the rheological properties of the muds were found to result from the behaviour and/or properties of the grafted starches in water.     

Phase behaviour of oat β-glucan/sodium caseinate mixtures varying in molecular weight

The isothermal phase behaviour at 5 °C of mixtures of sodium caseinate and oat β-glucan isolates varying in molecular weight (MW) was investigated by means of phase diagram construction, rheometry, fluorescence microscopy and electrophoresis. Phase diagrams indicated that the compatibility of the β-glucan/sodium caseinate system increases as β-glucan MW decreases. Images of mixtures taken at various biopolymer concentrations revealed phase separated domains. Results also revealed that at the state of thermodynamic equilibrium, lower MW samples yielded considerable viscosity in the mixture. At equivalent hydrodynamic volume of β-glucan in the mixtures, samples varying in molecular weight exhibited similar flow behaviour. A deviation dependent on the protein concentration was observed for the high MW sample in the concentrated regime due to the size of β-glucan aggregates formed. Results demonstrate that by controlling the structural features of β-glucan in mixtures with sodium caseinate, informed manipulation of rheological properties in these systems can be achieved.     

天冬多糖理化性质和流变学特性研究

以野生天冬块根为原料,通过水提醇沉法得到天冬多糖(asparagi radix polysaccharide,ARP),研究其理化性质和流变学特性。结果表明,ARP中总糖含量为(93.75±1.68)%,总糖醛酸含量为(26.99±0.97)%,酯化度为(38.2±0.14)%,重均分子量为730 kDa。ARP由鼠李糖(Rha)、阿拉伯糖(Ara)、半乳糖(Gal)、葡萄糖(Glc)、木糖(Xyl)、甘露糖(Man)6种单糖和半乳糖醛酸(GalA)、葡萄糖醛酸(GlcA)2种糖醛酸组成,物质的量比是0.27∶1.39∶4.42∶12.66∶1∶0.50∶4.83∶0.29。扫描电镜和原子力显微镜观察发现ARP构象为球形聚集状,表面结构紧致平滑。X-衍射结果表明ARP结晶度低。热学特性结果显示ARP具有较高的热稳定性。流变学结果表明,温度、质量浓度、盐离子(Na⁺和Ca²⁺)的种类和浓度对ARP的黏度和剪切应力均有影响,且作用方式不同。ARP溶液的黏度随着剪切速率的增加呈现下降趋势,出现剪切稀化现象,表明ARP溶液属于非牛顿流体。研究结果为天冬多糖在食品和医药等领域的开发利用提供理论依据。     

黄秋葵全粉对小麦面团流变学特性的影响

为了探究黄秋葵全粉对小麦面团流变学特性的影响,采用Mixolab混合实验仪、吹泡仪、流变发酵仪以及旋转流变仪等技术手段研究了混合粉（黄秋葵全粉添加量为0、1%、3%、5%、7%、9%）面团的热机械学特性、吹泡特性、流变发酵特性以及动态流变学特性。结果表明,随黄秋葵全粉添加量的增加,混合粉湿面筋含量降低,减少幅度达79.96%;面团的吸水率由63.30%增加到65.90%,形成时间和稳定时间先下降后上升,蛋白质弱化度增强;面团的蒸煮稳定性没有发生变化,但糊化峰值粘度下降,回生值减小;面团的韧性、延展性以及发酵性能下降,最大发酵高度Hm值下降了39.80%。此外,面团的储能模量G'和损耗模量G'均显著增加（P<0.05）,且G'增加占主导地位。综上所述,黄秋葵全粉的添加显著改变了小麦面团的流变学特性,且各添加量下混合粉面团的流变学特性指标有差异。研究结果为黄秋葵复合面制品的开发提供了理论依据。     

Effect of γ-polyglutamate on the rheological properties and microstructure of tofu

The effects of γ-polyglutamates with different concentrations (0.1%, 0.15%, 0.2%) and molecular weights (high, medium, low) addition on the rheological properties, microstructure, and syneresis of tofu were studied. The addition of γ-polyglutamate increased the gelation time, and decreased the storage modulus (G′) and the loss modulus (G″) of tofu. The molecular weight and concentration of γ-polyglutamate effectively changed the rheological properties of tofu. The network of tofu without γ-polyglutamate addition was constructed by fine strands in a dense arrangement as seen by using scanning electron microscope. However, the addition of γ-polyglutamate reduced the thickness of the strands in tofu network. Tofu syneresis was also reduced by the addition of γ-polyglutamate. Increase the concentration of γ-polyglutamate significantly decreased the syneresis of tofu. This trend was more evident on the tofu with high molecular weight γ-polyglutamate.     

RHEOLOGICAL AND INTERFACIAL BEHAVIOUR OF SOME WHEAT PROTEIN FRACTIONS 1

Gluten from the wheat variety Monopol was fractionated by successive extractions with dilute HCl (0.625–1.5 mM). The first two fractions, obtained at the highest pH values, contained a high proportion of low molecular weight proteins, they spread quickly at the air/water interface and when added to a wheat flour dough they increased the phase angle of the dough. The three following fractions contained a high proportion of high molecular weight proteins, they spread very slowly at the air/water interface and they caused the wheat flour dough to become stiffer (the storage modulus increased) and more elastic (the phase angle δ decreased). The last fractions obtained in amounts enough for investigation were in between the other fractions in the molecular weight distribution and interfacial behaviour, and they hardly affected the rheological properties of the dough.