•It is the first report to prepare alginate gels by freezing-thawing (FT) technique.•Gels could be prepared at pH 4.0 and 3.5, where no gel could be formed without FT.•At pH 3.0, FT treatment increased the storage modulus of gel almost two orders.•The cryogels were softer and demonstrated a melting behavior upon storage.•Solvent crystallization is the driving force in cryogel formation.Adding divalent ions or lowering pH below the pKa values of alginate monomers are common ways in preparing alginate gels. Herein a new way of preparing alginate gels using freeze-thaw technique is described. Solvent crystallization during freezing drove the polymers to associate into certain structures that became the junction zones of hydrogels after thawing. It enabled the preparation of alginate gels at pH 4.0 and 3.5, two pH at which the gel could not be formed previously. At pH 3.0 where alginate gel could be formed initially, applying freeze-thaw treatment increased the gel storage modulus almost 100 times. The formation of hydrogels and the resulting gel properties, such as dynamic moduli and gel syneresis were influenced by the pH values, number of freeze-thaw cycles, alginate concentrations, and ionic strengths. The obtained hydrogels were soft and demonstrated a melting behavior upon storage, which may find novel applications in the biomedical industry.

•Direct application of natural chitin is limited by its poor solubility in water.•Chitin regenerated from phosphoric acid has better dispersibility.•Regenerated chitins can stabilize oil-in-water emulsion at a level of 0.01 g/g oil.•The emulsion stabilization is achieved by Pickering mechanism.•Food applications of chitin are possible without chemical modification.Natural chitin is a highly crystalline biopolymer with poor aqueous solubility. Thus direct application of chitin is rather limited unless chemical modifications are made to improve its solubility in aqueous media. Through a simple dissolution and regeneration process, we have successfully prepared chitin nanofibers with diameters around 50 nm, which form a stable suspension at concentrations higher than 0.50% and a self-supporting gel at concentrations higher than 1.00%. Additionally, these nanofibers can stabilize oil-in-water emulsions with oil fraction more than 0.50 at chitin usage level of 0.01 g/g oil. The droplet sizes of the resulting emulsions decrease with increasing chitin concentrations and decreasing oil fraction. Confocal laser scanning micrographs demonstrate the adsorption of chitin nanofibers on the emulsion droplet surface, which indicates the emulsion stabilization is through a Pickering mechanism. Our findings allow the direct application of chitin in the food industry without chemical modifications.

•Nanostructured celluloses were prepared by a dissolution and regeneration process.•Cold phosphoric acid is used to dissolve the native crystalline celluloses.•Regeneration in water led to the self assembly of nanostructured celluloses.•Cellulose nanofibers or nanospheres can be obtained at varied conditions.This report describes a “green” method for preparing self-assembled nanostructured cellulose through a dissolution and regeneration process. Cold phosphoric acid is used to dissolve cellulose in order to convert crystalline cellulose into its molecular form. Self-assembly of cellulose molecules into nanostructured cellulose is achieved by using water to regenerate cellulose. By controlling the temperature and time of the phosphoric acid treatment between dissolution and regeneration, the degree of polymerization and the degree of substitution of phosphorous for the regenerated celluloses can be tuned. As a result, cellulose nanofibers or nanospheres can be obtained when the treatment temperature is set to 5 or 50 °C, respectively. X-ray analysis shows that the cellulose nanofibers are amorphous and that the cellulose nanospheres are structured similarly to cellulose II with crystallinity indexes between 56 and 73%. Our method offers a “green” process for preparing nanostructured celluloses in high yields.

•Selectivity in ultrasonic release of yeast polysaccharide and protein was studied.•Selectivity at 85 °C was a factor of 9.3 of the one at 25 °C.•The mechanism is speculated to be thermal coagulation of protein within yeast cell.•The finding may be useful in selectively production of yeast fractions.A 20 kHz high-intensity ultrasound was employed for the selective release of polysaccharide and protein from yeast cells. While the release of polysaccharide and protein was affected by most of the processing parameters, the release selectivity, which is the ratio of the amount of polysaccharide released to that of protein, designated as T/P value, was only influenced by sonication time, temperature and ionic strength, among which temperature had the greatest influence. The T/P value at 85 °C was a factor of 9.3 of the one at 25 °C. The underlying mechanism of this selectivity is speculated to be thermal denaturation and aggregation of protein within yeast cells at elevated temperatures leading to the decrease of protein release by ultrasound. This finding may be useful in exploring a novel selective process for producing polysaccharide and protein fractions from yeast biomass.

Native cellulose has a highly crystalline structure stabilized by a strong intra- and intermolecular hydrogen-bond network. It is usually not considered as a good gelling material and emulsion stabilizer due to its insolubility in water. Chemical modification is generally necessary to obtain cellulose derivatives for these applications. In this study, we have shown that, by simply disrupting the hydrogen-bond network of cellulose with phosphoric acid treatment, the regenerated cellulose can be a good gelling material and emulsion stabilizer. Microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analysis have confirmed that the regenerated cellulose is primarily amorphous with low crystallinity in the structure of cellulose II. Stable aqueous suspensions and opaque gels that resist flowing can be obtained with the regenerated cellulose at concentrations higher than 0.6% and 1.6%, respectively. Moreover, it can effectively stabilize oil-in-water emulsions at concentrations less than 1% by a mechanism that combines network and Pickering stabilization.