Rheological characterization of gel-in-oil-in-gel type structured emulsions

AbstractWe report the fabrication of multiple emulsions where both the enclosed and the external water phases are structured using a combination of two non-gelling biopolymers. Emulsions (with gelled inner water droplets and gelled water continuous phase) were created using a simple ‘one-step’ process where the oil phase (triglyceride oil and polyglycerol polyricinoleate) and the water phase (containing a combination of locust bean gum and carrageenan) were emulsified at an elevated temperature (70 °C) followed by cooling to room temperature. The temperature triggered gelling of the synergistic biopolymer combination led to the formation of structured emulsions on cooling. Flowable to self-standing emulsion gels could be prepared by changing the total concentration of polymers (and the ratios of the individual polymers) as confirmed from low amplitude oscillatory shear rheology and creep recovery measurements. The cryo-scanning electron microscopy images of freeze-fractured emulsion samples revealed the presence of gelled inner water droplets. Further, when subjected to heating and cooling cycles, emulsions displayed reversible rheological changes which could be tuned by simply changing the total polymer concentration and the proportions of individual polymers. Such biopolymer-based structured emulsions with interesting microstructure and rheological properties could find potential applications in bio-related fields like food structuring

Biopolymer-based structuring of liquid oil into soft solids and oleogels using water-continuous emulsions as templates

Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion

Freeze-drying qualities and state diagram of pulp and peel freeze-dried dragon fruits (Hylocereus spp.)

Freeze-drying has been proposed to preserve nutritional values and colour of foodstuff. Moreover, few studies disrobe the influence of freeze-drying on the quality characteristic of tropical fruit, like dragon fruit. In this work, freeze-drying characteristics, vitamin C, betacyanins content, L*, a* and b* colour parameters and state diagram of pulp and peel of white-flesh (Hylocereus undatus) and red-flesh (Hylocereus polyrhizus) dragon fruits were investigated after freeze-drying. The effect of pH level on the colour was monitored due to the pH sensitivity of the red pigment, betacyanins present in dragon fruit. The results show that dragon fruit can be successfully freeze-dried. For nutritional point of view, the retention of vitamin C was high and count up to 71.13% after freeze-drying. Freeze-dried pulp and peel of red-flesh dragon fruit were a potential source of betacyanins particularly the peel. The water solubility of freeze-dried pulp of both dragon fruit types was up to 7 times higher than that of the peel. The visual colour of reconstituted sample unchanged at their natural pH and shows only a small changes between pH 3 and pH 7. All cases of freeze-dried dragon fruits obtained low glass transition temperature that varied between -6.70 and 4.83 °C. However, it can be considered that the freeze-dried dragon fruits can probably be applied for food processing

Physicochemical properties, glass transition state diagram and colour stability of pulp and peel of two dragon fruit varieties (Hylocereus spp.) as affected by freeze-drying

The aim of the current study was to investigate the freeze-dried characteristics: physicochemical properties, colour parameters, total colour change, total betacyanins content and glass transition state diagram, of pulp and peel of white-flesh (Hylocereus undatus) and red-flesh (Hylocereus polyrhizus) dragon fruits. The results show that all dragon fruits can be successfully freeze-dried. For nutritional point of view, the retention of vitamin C counts up to 71.13% after freeze-drying. The water solubility of freeze-dried pulp was significantly different compared to the peel (p<0.05), that was about 7 times higher than that of the peel. Freeze-dried pulp and peel of red-flesh dragon fruit were a potential source of betacyanins content that found up to 360.14 mg/100 g. All freeze-dried dragon fruits obtained low glass transition temperature, varied between -6.70 and 4.83 °C. The visual colour of freeze-dried dragon fruits after rehydration was similar to their original colour. Thus freeze-drying seems to preserve the nutritional and colour properties of dragon fruits after processing. Furthermore, the impact of pH on the colour was also monitored due to the pH sensitivity of the red pigment, betacyanins present in the dragon fruit. The total colour change of all reconstituted freeze-dried gave very small value between pH 3 and pH 7 particularly the peel while the colour seriously changed at out of this pH range. Regarding to the finding results, it can be considered that the freeze-dried pulp of red-flesh dragon fruit can probably be used as a natural colorant due to relatively high in betacyanins, water solubility, vitamin C, and colour stability at low acid condition

Characterization and comparative study on structural and physicochemical properties of buckwheat starch from 12 varieties

Buckwheat is an important starch source because of its health benefits. In this study, buckwheat starches isolated from 12 varieties were analyzed based on the morphological, structural and physicochemical properties. The results showed that starch samples from different varieties had high purity with the total starch ranging from 91.29 to 95.11%, while showing significant differences in ash content (0.12-0.25%), protein content (0.26-0.34%) and amylose content (29.55-36.13%), respectively. All samples presented spherical and irregular shapes and typical A-type crystalline structure, but obvious differences in granule size distribution and relative crystallinity (26.37-35.21%) were observed among 12 varieties. Starch samples differed in lamellar structures, showing higher values of thickness of the samples with higher amylose content. In addition, buckwheat starches with higher amylose content showed higher values in light transmittance and rheological properties, while starch samples with lower amylose content obtained higher values in terms of water solubility, swelling power, pasting behaviors and thermal parameters. The principal component analysis and cluster analysis based on starch property parameters indicated that there were significant similarities and differences among 12 varieties, which might be related to the genotypes. This study would provide valuable information for the full use of buckwheat starch in food and non-food industries

Triacylglycerol migration and bloom in filled chocolates: effects of low-temperature storage

This study investigated die effect of storage temperature on triacylglycerol (TAG) migration, visual fat bloom and taste of industrially produced milk chocolates with a hazelnut-based filling. The chocolates were stored for up to 10 months at 18 degrees C, either directly after production or with the inclusion of a variable time at -20 or 4 degrees C immediately after production and prior to further storage at 18 degrees C. TAG migration from the filling through the chocolate shell was quantified by HPLC analysis of chocolate sampled from the chocolates' surface. Both [OOO/SOS] and [LOO/SOS] were used as markers for oil migration. Compared to storage at 18 degrees C only, chilling or freezing of the chocolates for part of the storage time was found to reduce the amount of TAG migration. Effects on diffusion, capillary transport and TAG immobilization during the thermal treatment can be raised as possible reasons for this decrease. Furthermore storage at -20 degrees C decreased oil migration during subsequent storage at 18 degrees C. This suggests a crystallization effect during the storage at -20 degrees C, leading to permanent (micro) structural changes. Although a thermal treatment at 4 degrees C compared to -20 degrees C was less effective in retarding TAG migration, storage at low positive temperatures immediately after production appears already beneficial in the prevention of visual fat bloom. Adverse effects of the thermal treatments on the chocolates' taste were not observed

Combining fat and waxes in hybrid systems for bakery application

Natural waxes have been investigated extensively the latest decade as potential replacers for saturated triglycerides for liquid oil structuring. However, wax-based oleogels are quite shear-sensitive which hampers their functionality in bakery applications and at higher concentrations the risk of a waxy aftertaste is apparent. For this reason, combining hardstock fat with waxes in a hybrid system may lead to partial replacement of saturated fat while maintaining the functionality and texture of the lipid product. In this research, three types of waxes (candellila, carnauba and berry wax) were combined at several concentrations around their respective critical gelling concentration with a palm stearin/rapeseed oil (30/70) mixture into a hybrid system. Hybrid systems were produced under static as dynamic conditions and the physico-chemical properties of these lipid systems was investigated with differential scanning calorimetry (DSC), rheology, polarized light microscopy (PLM) and x-ray diffraction (XRD) to investigate the interaction between the hardstock and the waxes. It was found that addition of waxes induces a faster crystallization of the palm stearin and from the PLM it was observed that the different types of waxes have another impact on the crystal structure of the hybrid system. This leads to a remarkable increase in hardness of the hybrid systems compared to the reference fat system but depending on wax type and applied concentration

Polysaccharide-based oleogels prepared with an emulsion-templated approach

The preparation and characterization of oleogels structured by using a combination of a surface-active and a non-surface-active polysaccharide through an emulsion-templated approach is reported. Specifically, the oleogels were prepared by first formulating a concentrated oil-in-water emulsion, stabilized with a combination of cellulose derivatives and xanthan gum, followed by the selective evaporation of the continuous water phase to drive the network formation, resulting in an oleogel with a unique microstructure and interesting rheological properties, including a high gel strength, G′>4000 Pa, shear sensitivity, good thixotropic recovery, and good thermostability

Impact of thermal treatment on physicochemical, antioxidative and rheological properties of white-flesh and red-flesh dragon fruit (Hylocereus spp.) purees

White-flesh (Hylocereus undatus; WF) and red-flesh (Hylocereus polyrhizus; RF) dragon fruit purees were subjected to a heat treatment for 0 to 60 min at temperatures between 50 and 90 °C. The influence of the different heat treatments on the physicochemical properties, colour, betacyanins content, microbial destruction, antioxidative properties and rheological parameters were investigated. The physicochemical values and antioxidative properties of the unheated RF were significantly higher than that of the unheated WF (p 0.7733) and TCC of RF can be used to predict the betacyanins content (R2 = 0.9442). The antioxidative properties of the heated WF and RF increased with heating treatment. The linear correlation among the antioxidative properties was strong (R2 > 0.8587). WF and RF showed shear thinning behaviour. After heating, the apparent viscosity of WF and RF increased and all cases fitted very well with the power law model (R2 > 0.9988). Thus, the heated dragon fruit purees, particularly the RF, offer possibilities to be applied in foodstuffs due to their interesting physicochemical properties and nutritional attributes after thermal treatment