Effects of modified atmosphere packaging on the postharvest quality of mulberry leaf vegetable.

Fresh mulberry leaf vegetable is nutritive and becoming popular. However, available preservation technologies are deficient. In present work, the effects of two kinds of modified atmosphere packaging on postharvest quality of fresh mulberry leaf vegetable stored at 4 °C were evaluated. The respiration rate of samples in the modified polyethylene packages (MP20) was 12.88-22.65% lower than that in normal polyethylene packaging (CK). The content of total soluble solids, soluble protein, and total polyphenol in MP20 was less changed than that in CK, and the vitamin C retention was higher as well. Moreover, the lignin content in MP20 was lower than that in CK during storage (19.79% vs 13.38% at day 8), and that was significantly positively related to the polyphenol oxidase and peroxidase activities inhibition. Taken together, a packaging with moderate gas permeability (MP20) is suitable for nutrition maintenance and lignification inhibition of fresh mulberry leaf vegetable during cold storage.

Nanocomplexation between thymol and soy protein isolate and its improvements on stability and antibacterial properties of thymol.

The complexation of thymol with soy protein isolate (SPI) at various mixing mass ratios, as well as some physicochemical characteristics, stability and antibacterial properties of the resultant complexes, was evaluated. The loading capacity of thymol in complexes formed at a mixing mass ratio of 2.5:12 was 10.36%, and the particles were spherical with a z-average diameter less than 110 nm. Fluorescence spectroscopy results indicated the SPI-thymol nanocomplexes were formed mainly through hydrophobic interactions. Upon nanocomplexation, the solubility, sustained release, thermal stability and antibacterial activity of thymol were greatly improved. Moreover, the encapsulation efficiency and solubility of thymol in complexes were improved with the increasing mixing mass ratio, while the stability and antibacterial activity of thymol were not significantly different among all the complexes. These findings suggest that SPI could be used as a nanocarrier for improving solubility and stability of thymol.

Soy Soluble Polysaccharide as a Nanocarrier for Curcumin.

The complexation between soy soluble polysaccharide (SSPS) and curcumin at pH 7.0 and 4.0, as well as some physicochemical characteristics of the resultant complexes, was investigated. The encapsulation efficiency and loading amount of curcumin in the complexes at pH 4.0 reached 67.3% and 4.49 µg/mg SSPS, respectively. Ethanol-induced denaturation and structural unfolding of the protein fraction in SSPS was essential for complex formation. The complexation with curcumin resulted in aggregation of SSPS and the subsequent formation of compacted nanoparticles with curcumin as the core. The complexation greatly improved the heat stability and in vitro bioaccessibility of curcumin. In general, the encapsulation efficiency, heat stability, and bioaccessibility of curcumin in the complexes at pH 4.0 were better than those at pH 7.0. The findings are of importance for the development of food grade nanovehicles for enhanced water solubility, stability, and bioaccessibility of hydrophobic bioactives.

Core-Shell Soy Protein-Soy Polysaccharide Complex (Nano)particles as Carriers for Improved Stability and Sustained Release of Curcumin.

Using soy protein isolate (SPI) and soy-soluble polysaccharides (SSPS) as polymer matrixes, this study reported a novel process to fabricate unique core-shell complex (nano)particles to perform as carriers for curcumin (a typical poorly soluble bioactive). In the process, curcumin-SPI nanocomplexes were first formed at pH 7.0 and then coated by SSPS. At this pH, the core-shell complex was formed in a way the SPI nanoparticles might be incorporated into the interior of SSPS molecules without distinctly affecting the size and morphology of particles. The core-shell structure was distinctly changed by adjusting pH from 7.0 to 4.0. At pH 4.0, SSPS was strongly bound to the surface of highly aggregated SPI nanoparticles, and as a consequence, much larger complexes were formed. The bioaccessibility of curcumin in the SPI-curcumin complexes was unaffected by the SSPS coating. However, the core-shell complex formation greatly improved the thermal stability and controlled release properties of encapsulated curcumin. The improvement was much better at pH 4.0 than that at pH 7.0. All of the freeze-dried core-shell complex preparations exhibited good redispersion behavior. The findings provide a simple approach to fabricate food-grade delivery systems for improved water dispersion, heat stability, and even controlled release of poorly soluble bioactives.

Nanocomplexation between curcumin and soy protein isolate: influence on curcumin stability/bioaccessibility and in vitro protein digestibility.

The complexation of nanoparticles in unheated and heated (at 75-95°) soy protein isolate (SPI) with curcumin and the effects on curcumin stability/bioaccessibility and in vitro protein digestibility were investigated. The nanoparticles did not display noticeable changes in size and morphology upon nanocomplexation with curcumin, except their surface hydrophobicity. The encapsulation efficiency of curcumin progressively decreased with increasing initial curcumin concentration in the dispersion, while the load amount linearly increased. The solubility of curcumin in water was enhanced by the complexation above 98000-fold (vs free curcumin in water). The formation of the nanocomplexes considerably improved the storage stability of curcumin. In vitro simulated digestion experiments indicated that the complexation also improved the bioaccessibility of curcumin; the bioaccessibility was greatly impaired by hydrolysis-induced protein aggregation. Addtionally, the nanocomplexation significantly improved the in vitro protein digestibility of both unheated and heated SPI.

Nanocomplexation of soy protein isolate with curcumin: Influence of ultrasonic treatment.

Soy protein isolate (SPI) can act as effective nanocarriers for water-insoluble curcumin, however, the maximal capacity of this protein to load curcumin and molecular mechanism for the formation of the nanocomplexes are still little known. This work investigated the formation and properties of SPI-curcumin nanocomplexes formed at a low concentration of 0.05% (w/v), as well as the influence of a high intensity ultrasonic treatment on the nanocomplexation. Most of the particles in non- or ultrasonic-treated SPIs were present in nanoparticle form with z-average sizes of about 50-52nm. The load amount (LA) of curcumin in the non-treated nanocomplexes reached 103.9µg/mg SPI. The ultrasonic treatment of the protein solution further significantly increased the LA, while the LA was considerably decreased by the treatment after the nanocomplexation. The complexation with curcumin significantly increased the particle size and ζ-potential of both non- and ultrasonic-treated SPIs, but led to a considerable reduction in surface hydrophobicity, with the greater changes observed for ultrasonic-treated SPI. The nanocomplexation with SPIs remarkably improved the storage stability of curcumin, with much better improvement observed for the ultrasonic-treated SPI. Both the number and nature of hydrophobic sites are important for the nanoparticles in SPI to exhibit high capacity to load curcumin molecules. This study confirmed that SPI exhibited a high capacity to load water-insoluble curcumin, and an ultrasonic pretreatment could further improve its encapsulation efficiency and stability of curcumin.