Extraction methods and some physical properties of mesquite (Prosopis chilensis (Mol) Stuntz) seed gum

To evaluate the potential use of mesquite (Prosopis chilensis (Mol) Stuntz) seed gum, the behaviour of the gum was studied using two extraction methods (alkaline and acid), different pH values, two concentrations (0.2 and 0.4% w/v) and different temperatures. The capacity of the gum to stabilise food foams was also evaluated. The alkaline extraction yield (24.9%) was higher than the acid extraction yield (17.7%). Owing molecular to hydrolysis caused by the acid, acid extraction resulted in a lower protein content. Gum from acid extraction had a higher viscosity than that from alkaline extraction at all temperatures investigated (10, 20, 30, 40, 50 and 60 °C). There were no significant differences between the viscosities of mucilage dispersions at the different values of pH studied (3.0, 4.0 and 5.0). The addition of extracted mesquite gum (obtained by either method and at either concentration studied) to egg white foam provided a higher stability and decreased the liquid drainage and collapse of the foam. Copyright © 2004 Society of Chemical Industry     

海藻酸钠和黄原胶糊料粘弹性行为的研究

通过稳态剪切和小幅振荡剪切应力扫描试验,研究了海藻酸钠和黄原胶糊料的粘弹性能.结果表明:与海藻酸钠相比,黄原胶在低用量、低剪切速率下就具有高粘度,表现出显著的假塑型流体"剪切变稀"特征.海藻酸钠以粘性效应为主,表现出较多的类液态特征,而黄原胶以弹性效应为主,表现出较多的类固态特征.随着剪切应力的增加,海藻酸钠的粘弹性能比较稳定,损耗模量始终大于储能模量,损耗角大于45°,主要表现出粘性行为;黄原胶的粘弹性能经历了由高弹性向粘性转变的突变区,在突变之前其储能模量大于损耗模量,损耗角小于45°,表现出很显著的弹性行为.     

魔芋胶和玉米淀粉混合物黏弹特性的研究

目的 研究魔芋胶对玉米淀粉黏弹特性的影响。方法 以玉米淀粉为原料, 加入不同比例的魔芋胶, 采用动态流变仪来研究魔芋胶玉米淀粉糊化混合物的黏弹特性。结果 Power-Low模型能够有效地表征魔芋胶玉米淀粉糊化混合物的流变性能。魔芋胶玉米淀粉糊化混合物为假塑性流体, 与单独的玉米淀粉糊相比, 随着魔芋胶的添加量增大, 糊化混合物黏稠性增大, 假塑性增强。随着频率的增大, G?和G?均增大, 损失正切值tan δ＜1, 说明魔芋胶的加入使得糊化混合物具有优越的黏弹性。结论 当魔芋胶/玉米淀粉质量比为0.4:0.8时, 糊化混合物弹性最小, 黏性最大, 糊化混合具有更好的协同增稠作用, 即糊化混合物流体流动特征显著。     

Dynamic viscoelastic study on the gelation of basil seed gum

Oscillatory measurements were used to investigate the effect of temperature and concentration on the viscoelastic and gelling properties of basil seed gum (BSG). Linear viscoelastic region was determined by strain sweep and it was found in 0.5% strain. Storage modulus (G′) was greater than loss modulus (G″) in all concentrations and they increased by improving BSG concentration. Yield stress value was determined by stress sweep and it increased from 1.40 to 7.47 Pa when BSG concentration increased from 1% to 3%. Frequency sweep showed BSG solution was a typical weak gel, and complex viscosity (η*) had linear correlation with frequency. The effect of temperature on gel forming was investigated during heating (20–90 °C) and cooling (90–20 °C) phases. BSG was characterised as a thermo‐reversible gel and did not have thermal hysteresis. Gelling temperature was raised as BSG concentration was increased. Exhibiting special rheological properties of BSG makes it as a proper synergistic gel, which can be applied in real food systems such as dairy desserts.     

Impact of xanthan gum,sucrose and fructose on the viscoelastic properties of agarose hydrogels

Mixed carbohydrate systems are of special interest for the food and non-food industry as they offer a versatile range of unique and novel functional properties. However, intense research is required to understand the complex processes occurring in such systems on a molecular level and to be able to modify them aim-oriented. In food, characteristic properties are based on the physicochemical functions of the biopolymers added. Thus, small deformation tests and moisture analysis have been applied to study the impact of xanthan gum and two types of sugar on the viscoelastic properties, the sol–gel transition and the water holding capacity of 1% agarose hydrogels. Agarose gels are very elastic, turbid and prone to synaeresis, which impinges on their mouth feeling. Additions of xanthan gum revealed less elastic gels with an unaffected water holding capacity. Progressive addition of two different types of up to 40% of sugar yield an increase of the elasticity of agarose gels, whereby sugar concentrations of 60% partially result in a structural breakdown and thus a significant lower network structure but better water holding. In ternary systems, the effect of the sugar concentration and sugar type used is diminished by xanthan gum. The gelation mechanism of agarose gels with a distinct amount of co-solutes is presumably mainly affected by the water shortage evolved from the competition for it of all solutes present.     

The chemical composition and some physical properties of a water-soluble gum from Prosopis africana seeds

A water‐soluble gum was extracted from the endocarp capsule of the seed coat of Prosopis africana. The gum yield varied substantially with the method of dehulling. Maximum yield was obtained after boiling in 0.1 m Na₂CO₃ for 4 h. The effects of two different gum concentrations on the rheological properties of gum solutions were examined. The gum formed viscous solutions at low concentrations and exhibited stable viscosity in the pH range 6.0–8.0. Chemical analyses showed that the purified gum had a composition of 2.4% fat, 1.04% protein, 21.5% crude fibre and a gelation concentration of at least 10%. Galactose and mannose were the major polysaccharides identified. Large reductions in viscosity were observed with the addition of various concentrations of Na⁺ salts. The activation energies of flow for 2 and 3% gum solutions were in the range of 19.2–22.8 kJ mol^?1 and were characteristic of systems with little intra‐ and intermolecular interactions.     

NaCl浓度对蔗糖酯黄原胶乳浊液稳定性的影响

研究NaCl浓度对蔗糖酯-黄原胶溶液的水力学直径DH、ζ-电势和界面张力及乳浊液的粒径d4,3、ζ-电势、粘度和稳定性的影响。在此基础上,探讨蔗糖酯-黄原胶相互作用与乳浊液稳定性之间的联系。结果表明:随着NaCl浓度增加,由于静电屏蔽作用,蔗糖酯-黄原胶溶液的DH值、ζ-电势和界面张力均增大,导致乳浊液ζ-电势和d4,3也逐渐增大。NaCl浓度达到0.1mol/L时,由于蔗糖酯-黄原胶疏水作用增强,形成蔗糖酯-黄原胶复合物,提高液滴的空间位阻作用,使得复合乳浊液稳定性高于蔗糖酯乳浊液稳定性。      

Chia (Salvia hispanica L.) seed mucilage as a fat replacer in yogurts: Effect on their nutritional,technological, and sensory properties

Growing consumer demand for healthy and nutritious products has motivated scientists and food manufacturers to design novel dairy products with higher fiber levels and lower fat content that are free of chemical additives. Chia seed mucilage (CSM) is a healthy natural gel extensively used as a dietary source of soluble fiber, a bulking agent, and a fat replacer in a large variety of foods. In this study, we evaluated the effect of CSM on the nutritional, technological, and sensory properties of skimmed yogurts. The addition of 7.5% CSM to a yogurt formula lowered the degree of syneresis of the resulting yogurt during storage compared with full-fat yogurts. The nutritive value of the enriched yogurts improved due to higher levels of dietary fiber compared with full-fat and skimmed yogurts. Moreover, rheological measurements revealed greater consistency, firmness, and viscosity, as well as the formation of a highly structured network and better resistance to stress in yogurts containing 7.5% CSM. The sensory acceptance of the yogurts enriched with 7.5% CSM was similar to the reference samples in acidity, creaminess, and viscosity terms. These results confirm the feasibility of using CSM as a fat replacer to design novel skimmed yogurts.     

Influence of guar gum addition on physicochemical,microbial, rheological and sensory properties of stirred yoghurt

This study investigated the effects of adding guar gum (0, 0.6 and 0.8 g/100 mL) on the physicochemical, microbial, rheological and sensory properties of stirred yoghurt. Incorporation of guar gum into the yoghurt significantly affected the pH and colour, but did not significantly influence the lactic acid bacteria counts. The magnitudes of apparent viscosity (η_a,100), consistency index (K), yield stress (σ_oc), storage modulus (G′) and loss modulus (G″) for yoghurt samples containing guar gum (0.6–0.8 g/100 mL) were significantly greater than those for the control (without guar gum), indicating that guar gum can improve the steady and dynamic shear rheological properties of yoghurt.     

Steady shear flow behavior of gum extracted from Ocimum basilicum L. seed: Effect of concentration and temperature

Steady shear flow behavior of basil seed gum (BSG) was investigated between 0.5% and 2% (wt/wt) concentration and temperatures of 5-85 °C. BSG showed shear thinning behavior at all concentrations and temperatures. The Herschel-Bulkley model was employed to characterize flow behavior of BSG solutions at 0.1-1000 s⁻¹ shear rate. The pseudoplasticity of BSG increased markedly with concentration. Flow behavior of 1% BSG indicated a higher viscosity of this gum at low shear rates compared to xanthan, konjac and guar gum at similar concentration. The activation energy of BSG quantified using an Arrhenius equation increased from 4.9 × 10³ to 8.0 × 10³ J mol⁻¹ as concentration changed from 0.5% to 2% wt/wt. This indicated a heat-resistant nature of BSG. Increasing the apparent viscosity of BSG as temperature increase from 60 °C showed a sol-gel behavior of BSG based on dynamic oscillatory measurements. The static yield stress was obvious between shear rates 0.001-0.1 s⁻¹ (9.98 Pa for 1% BSG at 20 °C). The existence of the yield stress, high viscosity at low shear rates and pseudoplastic behavior of BSG make it a good stabilizer in some food formulations such as mayonnaise and salad dressing.     

瓜尔胶和黄原胶对马铃薯淀粉糊化特性影响的比较研究

将马铃薯淀粉分别与瓜尔胶和黄原胶以一定的比例复配,探讨两种胶体对马铃薯淀粉黏度、热稳定性、凝沉性、冻融稳定性和质构特性等糊化特性的影响。结果表明:瓜尔胶提高了淀粉糊的黏度和冻融稳定性,降低了淀粉糊的热稳定性、凝沉性、硬度、黏附性、胶黏性和咀嚼性;而黄原胶增加了淀粉糊的热稳定性和冻融稳定性,但降低了糊的黏度、凝沉性、硬度、黏附性、胶黏性和咀嚼性;且随着两种胶体含量的不同淀粉糊化特性也不同。      

Influence of gluten on the viscoelastic properties of starch pastes and gels

Viscoelastic properties of dispersions (60–300 g kg⁻¹) of gluten (G) and wheat starch (S) blends (0 < G/S < 0·20) and wheat flour have been studied during heating and cooling. In both cases, the moduli followed power law relationships with concentration. The temperature at which the transient network development began, caused by granule–granule interactions, decreased as the concentration increased and increased with an increase in the proportion of gluten. Moreover, gluten weakened the strength of both starch pastes and gels, as shown by the lower values of the moduli. The viscoelastic behaviour of flour samples reflected the role played by internal lipids. A structural model is proposed in order to explain the influence of gluten on the rheological behaviour of starch pastes and gels. © 1998 Society of Chemical Industry.     

Effect of heating temperature,pH, concentration and starch/whey protein ratio on the viscoelastic properties of corn starch/whey protein mixed gels

The viscoelastic properties of corn starch (CS) gels were more dependent on heating temperature, while the properties of whey protein isolate (WPI) gels were more dependent on pH. Thus heating temperature (75, 85, 95 °C) and pH (5, 7, 9) were varied to obtain a series of mixed gels with interesting viscoelastic properties. WPI gels showed extensive stress relaxation (SR) indicative of a highly transient network structure, while CS gels relaxed very little in 2000 s. Based on SR results, it appeared that CS/WPI mixed gels with 25 and 50% CS formed compatible network structures at 15% total solids only at pH 9. This supposition was supported by SEM microstructures obtained for dehydrated gels and a synergistic increase in the large‐strain fracture stress for these gels. Some synergy was also found for mixed gels at 30% total solids at pH 9, while at pH 7 the mixed gels seemed to contain separate additive WPI and CS networks unlike the case for pH 7 at 15% total solids. In both cases (15 and 30% total solids) the degree of elasticity of the mixed gels decreased as the WPI content increased. Mixed gels (CS:WPI = 0.5) at pH 9 showed increased fracture stress and fracture strain relative to the same gels at pH 7. This suggests that a unique chemical compatibility exists at pH 9 and results in gels that combine the elasticity of CS and the internal stress dissipation of WPI. © 2001 Society of Chemical Industry     

The effect of pectin concentration on viscoelastic and sensory properties of processed cheese

The effect of pectin addition on viscoelastic properties of model processed cheeses with 40% w/w dry matter and 50% w/w fat in dry matter after 42 days of storage at temperature 6 ± 2 °C has been investigated using dynamic oscillation rheometry (plate–plate geometry; frequency range 0.1–50.0 Hz; temperature 20 °C). The role of pectin concentration (0.2%, 0.4%, 0.6% and 0.8% w/w) has been studied. Also, the sensory evaluation of samples has been made to assess cheese appearance, rigidity, spreadability and flavour. All samples with the pectin addition were more rigid and less spreadable compared with processed cheeses without pectin. With the increasing concentration of pectin the storage ( G ') and loss ( G ") moduli rose at the whole tested frequency range (0.1–50.0 Hz). Growing pectin content resulted in the decrease in loss tangent (the nature of gel was changed to more elastic material). The dependence of processed cheese rigidity on pectin concentration (in range 0–0.8% w/w) was not linear. The appearance and flavour were not worse by pectin addition.