Markedly compressible behaviors of gellan hydrogels in a constrained geometry at ultraslow strain rates

The fracture behaviors of gellan hydrogels under compression remarkably depend on the strain rate as well as the boundary conditions for lateral expansion. In the geometry with no constraint for lateral expansion (conventional uniaxial compression), the gels rupture at relatively small strains independently of the compression rates. In contrast, when the gels are compressed extremely slowly (at a strain rate of ca. 10⁻⁵ s⁻¹) in the geometry prohibiting the lateral expansion at their top and bottom surfaces, they are remarkably compressible down to 2% of the initial height without macroscopic fracture and they are accompanied by a large amount of water release. In such markedly compressed gels, many microscopic cracks are formed around the central layer, where strain concentration occurs due to the nonuniform deformation arising from the constrained geometry. In the highly compressible case, the formation of macroscopic cracks is prevented by the localization of microscopic cracks as well as the enhancement in mechanical toughness by a significant increase in polymer concentration due to water release.     

Effects of cononsolvency on gelation of poly(vinyl alcohol) in mixed solvents of dimethyl sulfoxide and water

We studied the rates of gelation and phase separation of poly(vinyl alcohol) (PVA) solutions in mixtures of dimethyl sulfoxide (DMSO) and water at 25 °C and found that both the rates show a maximum at a volume fraction of DMSO φ_DMSO=0.60 while gelation was not observed either in pure DMSO or pure water, suggesting that water-DMSO is a cononsolvent system for PVA. On the basis of the data by Cowie [Can J Chem 36 (1961) 2240] we concluded that the 1:2 stable complex between one DMSO molecule and two water molecules is the main cause of this cononsolvency.     

Enzymatic modifications of pea protein and its application in protein-cassava and corn starch gels

The interactions between starch and proteins during processing influence pasting and rheological properties of starch and produce modifications on starch gel structure. Enzymatic modifications have been proposed for overcoming the limitations of using proteins as food ingredients. This work aimed to study the impact of native and enzymatically modified pea proteins on the properties of protein-starch (from cassava or corn) gels. Pea protein isolate (PPI) was incubated with endopeptidase (AL) or microbial transglutaminase (TG). Pasting profile, rheological behaviour and water retention capacity of protein-starch gels were analyzed. Protein (native and enzymatically modified) incorporation increased the viscosity of both corn and cassava starches during gel preparation. However, the hydrolyzed protein reduced drastically the increment of viscosity of protein-starch gels. The addition of PPI led to corn starch network that shifted from an elastic-like nature to a more viscous-like, whereas the opposite effect was observed in cassava gel network. TG- and AL-treated proteins led to a decrease of both G′ and G″ moduli of protein-starch gels, and AL-treated proteins showed the highest decrease on these parameters. Hydrolyzed proteins also favoured the syneresis of the protein-corn starch gel, whereas crosslinked proteins tended to reduce it. Enzymatic modifications of pea proteins affected significantly pasting and rheological properties of protein-starch gels.     

Sweetness and texture perceptions in structured gelatin gels with embedded sugar rich domains

Layered and homogeneous gelatin gels with controlled rheological properties were compared for their sensory characteristics, specifically sweetness, hardness, breakdown behaviour and frothing. All gels and layers had a gelatin/water concentration of 5%. The total sugar concentration was 9% in the layered samples and 0, 9, 15 or 22.5% in the homogeneous samples. These concentrations corresponded to the concentrations in the single layers.A seven-layered sample with different sugar concentrations in the layers gave a higher early sweetness intensity than a homogeneous gel with the same mean total sugar concentration. All layered gels were similar in hardness, breakdown behaviour and frothing; for the homogenous samples, sensory hardness was decreased in samples with much sugar. These gels also fell into smaller pieces than the sugarless sample. This study shows that it is possible by controlling the sugar distribution within a sample to produce sweeter gels while the sugar content is maintained.     

Microalgae biomass interaction in biopolymer gelled systems

Microalgae are an enormous biological resource, representing one of the most promising sources for the development of new food products and applications. Pea protein/κ-carrageenan/starch gels, interesting vegetarian alternatives to dairy desserts, served as model systems to study the addition of microalgal biomass, its effect, and subsequent rheological behaviour. Spirulina and Haematococcus gels presented a markedly different rheological behaviour compared to the control mixed biopolymer gelled system. The present goal is to clarify how these microalgae affect the gelation and interact with each biopolymer present in the complex mixed gel system. Hence, the aim of the present work is to study the effect of Spirulina and Haematococcus microalgal biomass addition on the rheological behaviour of pea protein, κ-carrageenan and starch simple gels, as well as in pea protein/κ-carrageenan and pea protein/starch systems. The gelation process was monitored in-situ through dynamic oscillatory measurements (temperature, time and frequency sweep tests) for a 24 h maturation period, and rheological results were supported with fluorescence optical microscopy observations. The addition of Spirulina and Haematococcus to biopolymer gelled systems induced significant changes in the gels’ rheological behaviour and microstructure. In general, it was observed that the gelling mechanism is ruled by the biopolymers, while microalgae seem to be embedded in the gel network acting as active particle fillers. The addition of Haematococcus resulted in more structured gels in comparison to the control and Spirulina systems. In the case of κ-carrageenan gels, both microalgae induced a large increase in the rheological parameters, which should be related to the high ionic content of microalgal biomass. Spirulina addition on starch systems promoted a decrease in the gels’ rheological parameters. This should be related to the starch gelatinization process, probably by competing for water binding zones during the granules’ hydration process.     

Gel mechanical properties of milk whey protein–dextran conjugates obtained by Maillard reaction

The effect of Maillard reaction on the mechanical properties of whey protein isolate (WPI) heat-induced gels was evaluated. WPI and dextran (15–25 kDa) conjugates were obtained by controlled dry heating during storage at 60 °C and 63% relative humidity for 2, 5 and 9 days. Changes in browning intensity and content of free amino groups were used to estimate the Maillard reaction. A decrease in free amino groups of WPI was observed when increasing polysaccharide concentration and reaction time. An increase in both a* and b* CIE Lab colour parameters indicated the development of a reddish-brown colour, typical of the Maillard reaction. Uniaxial compression and stress relaxation tests were performed to measure the mechanical properties of mixed and conjugate gels. Maillard reaction significantly modified the mechanical properties of WPI/DX gels, and even prevented fracture when conjugate gels were subjected to 80% deformation in uniaxial compression test.     

间苯二酚在聚合物凝胶堵水技术中的应用

间苯二酚作为聚丙烯酰胺的优良交联剂已成功应用于油田聚合物凝胶堵水技术。本文综述了将间苯二酚应用于近井地带小剂量堵水作业、地层深部大剂量堵水作业以及地层内就地交联聚合物弱凝胶驱替作业的室内研究和现场应用成果。     

HPAM／柠檬酸铝胶态分散凝胶形成条件研究

采用一种简化的实验程序测定胶态分散凝胶（ＣＤＧ）的转变压，用测得的转变压值作为评价参数，考察由ＨＰＡＭ、柠檬酸铝、硫脲、氯化钾组成的ＣＤＧ的形成条件及相对强度。所考察的形成条件包括ＨＰＡＭ的来源和浓度，柠檬酸铝和氯化钾的浓度，ｐＨ值，绝大部分实验工作在４０℃和ｐＨ＝７．０的条件下进行，用一组实验考察了温度的影响（７０℃和４０℃）。