Influence of temperature on the dynamic and steady-shear rheology of pectin dispersions

Impact of thermal treatment on proanthocyanidin-pectin binary complexes: Insights from structural, rheological, antioxidant, and astringent properties

In this study, the effects of thermal treatments on the structural, rheological, water mobility, antioxidant, and astringency properties of proanthocyanidin (PA)-pectin binary complexes were investigated. Thermal treatments (25, 63, or 85 °C) significantly decreased the particle size but increased the molecular weight of PA-pectin complexes, which indicated that heating altered the intermolecular and intramolecular interactions between PA and pectin. The thermal treatments reduced the apparent viscosity of both pectin and PA-pectin complexes, but the presence of proanthocyanidins (PAs) increased the apparent viscosity and water mobility of the PA-pectin complexes. Antioxidant activity analysis showed that the presence of pectin slightly reduced the antioxidant activity of the PAs, but there were no significant changes in the total phenolic content and antioxidant activity after thermal treatment. Finally, we found that pectin reduced the astringency of the PAs by forming PA-pectin complexes. Moreover, the thermal treatments also significantly reduced the astringency of the PA-pectin complexes.

The nonlinear mechanics of highly extensible plant epidermal cell walls

Plant epidermal cell walls maintain the mechanical integrity of plants and restrict organ growth. Mechanical analyses can give insights into wall structure and are inputs for mechanobiology models of plant growth. To better understand the intrinsic mechanics of epidermal cell walls and how they may accommodate large deformations during growth, we analyzed a geometrically simple material, onion epidermal strips consisting of only the outer (periclinal) cell wall, ~7 μm thick. With uniaxial stretching by >40%, the wall showed complex three-phase stress-strain responses while cyclic stretching revealed reversible and irreversible deformations and elastic hysteresis. Stretching at varying strain rates and temperatures indicated the wall behaved more like a network of flexible cellulose fibers capable of sliding than a viscoelastic composite with pectin viscosity. We developed an analytic framework to quantify nonlinear wall mechanics in terms of stiffness, deformation, and energy dissipation, finding that the wall stretches by combined elastic and plastic deformation without compromising its stiffness. We also analyzed mechanical changes in slightly dehydrated walls. Their extension became stiffer and more irreversible, highlighting the influence of water on cellulose stiffness and sliding. This study offers insights into the structure and deformation modes of primary cell walls and presents a framework that is also applicable to tissues and whole organs.

Evaluation of the physicochemical properties of pectin extracted from Musa paradisiaca banana peels at different pH conditions in the formation of nanoparticles

Colombia is one of the major producers and exporters of banana Musa paradisiaca. Its consumption is high then its agro-industrial wastes are important source to extract pectin. In the present study, inorganic acids (nitric acid and hydrochloride acid) and organic acids (citric acid and acetic acid) were evaluated to extract pectin from banana peels at pH 2 and 3, through acid hydrolysis during 1h at the temperature of 85 °C. The extraction yield, degree of esterification (DE) and intrinsic viscosity of the pectin were characterized. Nitric acid (NA) allowed to obtain higher extraction yield (54 ± 10%) and citric acid (CA) allowed to obtain higher DE (76.7 ± 2%). Additionally, the effect of polymer concentration and degree esterification, low degree of esterification (LDE, 33.1%) and high degree of esterification (HDE, 76.7%) were evaluated in the pectin nanoparticles formation. The pectin with HDE formed stable nanoparticles with a particle size of 255 ± 11 nm and the zeta potential value of -45 ± 3 mV, independently of the polymer concentration. Morphology analysis showed aggregated of the pectin nanoparticles.

Physicochemical Properties and Antioxidant Activity of Pumpkin Polysaccharide (Cucurbita moschata Duchesne ex Poiret) Modified by Subcritical Water

In this paper, subcritical water (SCW) was applied to modify pumpkin (Cucurbita moschata Duchesne ex Poiret) polysaccharides, and the properties and antioxidant activity of pumpkin polysaccharides were investigated. SCW treatments at varying temperature led to changes in the rheological and emulsifying properties of pumpkin polysaccharides. SCW treatments efficiently degraded pumpkin polysaccharides and changed the molecular weight distribution. Decreases in intrinsic viscosity, viscosity-average molecular weight, and apparent viscosity were also observed, while the activation energy and flow behavior indices increased. The temperature of SCW treatment has a great influence on the linear viscoelastic properties and antioxidant activity of pumpkin polysaccharides. Pumpkin polysaccharides solution treated by SCW at 150 °C exhibited the highest emulsifying activity and antioxidant activity, which was probably due to a broader molecular mass distribution and more reducing ends exposed after treatment. Scanning electron microscopy showed that SCW treatment changed the microstructure of pumpkin polysaccharides, resulting in the exposure of bigger surface area. Our results suggest that SCW treatment is an effective approach to modify pumpkin polysaccharides to achieve improved solution properties and antioxidant activity.

Effect of ultrasonic treatment on rheological and emulsifying properties of sugar beet pectin

The effects of ultrasonic treatment on rheological and emulsifying properties of sugar beet pectin were studied. Results indicated that intrinsic viscosity ([η]) and viscosity average molecular weight ([M v]) decreased with the increased time from 0 to 30 min but increased when the duration prolonged to 45 min. The change of apparent viscosity with shear rate of all pectin solutions could be well described by Sisko model (R 2 ≥ .996) and the infinite-rate viscosity (η ∞) and the consistency coefficient (k s) values decreased after ultrasonic treatment. Ultrasonic treatment could have an effect on dynamic moduli and activation energy of sugar beet pectin solutions. Particle size of pectin emulsions decreased and absolute zeta potential increased with increased time from 0 to 20 min. Excessive ultrasonic duration (30 and 45 min) could result in the aggregation of oil droplets in pectin emulsion and decrease in emulsifying stability. It could be concluded that ultrasonic treatment could affect the rheological and emulsifying properties of sugar beet pectin. The results have important implications for understanding the ultrasonic modification of sugar beet pectin.

Pectin from Husk Tomato (Physalis ixocarpa Brot.): Rheological behavior at different extraction conditions

A rheological study was carried out to evaluate formulations of test dispersions and gels of high methoxyl pectins (HTHMP) obtained at different conditions from husk tomato waste (Physalis ixocarpa Brot.). The effect of extraction agent (hydrochloric acid or citric acid), blanching time (10 or 15min) and extraction time (15, 20 or 25min) on the rheology of the tested samples was evaluated. Flow behavior and activation energy were evaluated on the test dispersions, while (E_a) frequency sweeps, temperature sweep, creep-recovery test and penetration test were performed on the gels. HTHMP dispersions showed shear thinning flow behavior, while showing a good fit to Cross model. Extraction agent, blanching time and extraction time did not have effect on Cross parameters (η_z, η∞, C, and m). E_a decreased as blanching time and extraction time increased. Frequency sweeps revealed high dependence on frequency for both G' and G", while temperature sweeps (25- 95°C) showed thermostable husk tomato pectin gels. Hydrocloric acid (HCl) extracted pectin gels showed stronger structure than citric acid (CA) gels.

Rheological and microstructural properties of porcine gastric digesta and diets containing pectin or mango powder

Hydrated polysaccharides and their assemblies are known to modulate gastric emptying rate due to their capacity to change the structural and rheological properties of gastric contents (digesta). In the present study, we investigated the rheological and microstructural properties of gastric digesta from pigs fed with diets incorporating mango powder or pectin, and compared results with those from hydrated diets of the same water content, in order to investigate the origins for rheological changes in the pig stomach. All of the hydrated diets and gastric digesta were particle-dominated suspensions, generally showing weak gel or more solid-like behavior with the storage modulus (G') always greater than loss modulus (G") under small deformation oscillatory measurements, and with small deformation viscosity greater than steady shear viscosity (i.e. non-Cox-Merz superposition). Although significant rheological differences were observed between the hydrated diets, rheological parameters for gastric digesta were similar for all diets, indicative of a rheological homeostasis in the pig stomach. Whilst the addition of gastric mucin (20mg/mL) to control and mango diets altered the rheology to match the gastric digesta rheology, the effect of mucin on the pectin-containing diet was negligible. The viscous effect of pectin also hindered the action of alpha amylase as observed from relatively less damaged starch granules in pectin digesta compared to mango and control digesta. Based on the experimental findings that the rheology of gastric digesta differs from hydrated diets of the same water content, the current study revealed composition-dependent complex behavior of gastric digesta in vivo, suggesting that the rheology of food products or ingredients may not necessarily reflect the rheological effect when ingested.

A comparison of the activation energy of viscous flow for hen egg-white lysozyme obtained on the basis of different models of viscosity for glass-forming liquids

The paper presents the results of viscosity determinations on aqueous solutions of hen egg-white lysozyme at a wide range of concentrations and at temperatures ranging from 5°C to 55°C. On the basis of these measurements and different models of viscosity for glass-forming liquids, the activation energy of viscous flow for solutions and the studied protein, at different temperatures, was calculated. The analysis of the results obtained shows that the activation energy monotonically decreases with increasing temperature both for solutions and the studied protein. The numerical values of the activation energy for lysozyme, calculated on the basis of discussed models, are very similar in the range of temperatures from 5°C to 35°C.

Polissacarídeos extraídos da gabiroba (Campomanesia xanthocarpa Berg): propriedades químicas e perfil reológico

A Campomanesia xanthocarpa Berg (Myrtaceae) é uma frutífera nativa brasileira, com ampla distribuição natural na região Sul. Embora apresente frutificação abundante, produza frutos com características sensoriais e nutricionais atrativas, esses não são coletados e se perdem nos campos. Neste trabalho, a polpa do fruto sem semente (1500 g) foi triturada em etanol / água na proporção de 1:4 (v/v), refluxada por 15 minutos em temperatura de ebulição. O resíduo obtido foi submetido a extrações sequenciais. As extrações foram otimizadas utilizando um planejamento fatorial 2², tendo como variáveis a concentração do ácido cítrico (0,5 e 5%) e a temperatura (50 e 100 ºC). Os polissacarídeos provenientes de diferentes extrações foram caracterizados quanto à composição química e perfil reológico. Os altos teores de ácidos urônicos, arabinose e galactose detectados em todas as frações, indicam que estas são constituídas por polissacarídeos pécticos. Os polissacarídeos extraídos da polpa da gabiroba apresentaram um comportamento pseudoplástico. Todas as frações apresentaram como característica resistência frente às variações de temperatura. Quando submetidas a ciclos de aquecimento e posterior resfriamento estes géis retornam à sua estrutura original.

Definition of the rheological glass transition temperature in association with the concept of iso-free-volume

Small deformation dynamic oscillation was used to develop an index of physical significance for the rationalisation of the mechanical properties of high co-solute/biopolymer systems during vitrification. The index is based on the combined framework of Williams-Landel-Ferry equation with the free volume theory and is called the 'rheological glass transition temperature, T(g)' thus differentiating it from the empirical calorimetric T(g) used in thermal analysis. The rheological T(g) is located at the conjunction of two distinct molecular processes, namely: free-volume effects in the glass transition region and the predictions of the reaction-rate theory in the glassy state. The method of reduced variables was used to shift the mechanical spectra of shear moduli to composite curves. The temperature dependence of shift factors for all materials was identical provided that they were normalised at suitably different reference temperatures, which reflect iso-free-volume states. The treatment makes free volume the overriding parameter governing the mechanical relaxation times during vitrification of high co-solute/biopolymer systems regardless of physicochemical characteristics. We believe that potential applications resulting from this fundamental work are numerous for the food and pharmaceutical industries.

Viscosity of bovine serum albumin aqueous solutions as a function of temperature and concentration

This paper presents the results of viscosity determinations on aqueous solutions of bovine serum albumin (BSA) at a wide range of concentrations and at temperatures ranging from 5 degrees C to 45 degrees C. On the basis of these measurements a general formula connecting the relative viscosity eta r with temperature T and concentration c of the dissolved proteins was established: [formula: see text] The quantities alpha, beta, B, D and delta E are described in the text below. A simple substantiation of the formula was also given. This relation gives immediately the Mooney approximation and allows the prediction of the values of the parameter S and a self-crowding factor K in this approximation. By applying an asymptotic form of the formula such rheological quantities as the intrinsic viscosity and Huggins coefficient were calculated.