Carboxylated chitosan improved the stability of phycocyanin under acidified conditions.

Phycocyanin, a natural blue colorant, derived from Spirulina platensis, is now widely used in the food industry. However, its main drawbacks are loss of color and denature of structure in an acidic environment. In this study, carboxylated chitosan (0.1 %-1 % w/v) was chosen as an additive in acid-denatured phycocyanin for preserving phycocyanin's blue color and natural structure. Zeta-potential and particle size revealed that the carboxylated chitosan with high negative charge adsorbed on phycocyanin and provided stronger electrostatic repulsion to overcome the protein aggregation. Ultraviolet-visible absorption spectrum and fluorescence spectroscopy showed that the carboxylated chitosan recovered the microenvironment of tetrapyrrole chromophores and ß-subunits, which led the secondary structure changed and the trimers depolymerized into the monomers changed by the acidic environment. Furthermore, Fourier transform infrared spectroscopy revealed highly negatively charged carboxylated chitosan with the groups (NH2, COOH and OH) could restored the microenvironment of tetrapyrrole chromophores and ß-subunits of phycocyanin, and interact with phycocyanin through hydrogen bonding, NH bonding, ionic bonding and van der Waals, which led to a change in secondary structure and depolymerization of trimers into monomers. Our study demonstrated the carboxylated chitosan played a beneficial role in recovering the structure of acid-denatured phycocyanin and its blue color.

Investigation of the interactions between food plant carbohydrates and titanium dioxide nanoparticles.

Titanium dioxide (TiO2) is commonly used as food whitening in candies, chocolates, and cakes with high carbohydrate contents. The potential interaction between the food carbohydrate and food grade TiO2 nanoparticle was little known. Therefore, we explored the interaction between TiO2 nanoparticles and seven common carbohydrates, including monosaccharides, disaccharides, and polysaccharides. The result showed that all the carbohydrates tested interacted with the surfaces of the TiO2 nanoparticles and formed biocoronas. TEM and SEM images provided information about the morphology formation of biocoronas. The surface potential and size of the TiO2 nanoparticles altered after interacting with the carbohydrates. FTIR spectroscopy and QCM-D findings showed insights into the molecular origin and nature interaction between TiO2 and carbohydrates. The results illustrated that TiO2 nanoparticles can interact with carbohydrates, enter the body as a food additive, and interact with food matrix for a series of reactions. Compared with monosaccharides or disaccharides, food polysaccharides have stronger adsorption on the surface of nanoparticles. This is a preliminary judgment for the subsequent in vitro simulated digestion. Our result could be useful for understanding and controlling the behavior of nanoparticles in food and the human gut.

Identification and characterization of antioxidant and immune-stimulatory polysaccharides in flaxseed hull.

Flaxseeds are widely consumed for their desirable sensory attributes and health benefits. We focused on enhancing the sustainability and economic potential of flaxseeds by characterizing functional attributes of polysaccharides isolated from flaxseed hull residues. In particular, antioxidant and immune-stimulatory polysaccharides were isolated and purified from flaxseed hull. Infrared spectroscopy was used to identify the key functional groups. The polysaccharides were composed of mannose, rhamnose, galactose, glucose, galactose, xylose, arabinose, and fucose. In vitro studies showed certain flaxseed hull polysaccharide fractions exhibited strong antioxidant activities, increased nitric oxide levels, and enhanced the production of cytokines (TNF-α and IL-6). In the presence of 200 µg/mL of one of these fractions, the levels of p-ERK, p-JNK, and p-p38 increased significantly by 1.8-, 9.0-, and 6.7-fold. These polysaccharide fractions may exhibit their immune-regulatory properties partly by modulating the MAPK pathway. The flaxseed hull polysaccharides identified have potential application as natural antioxidants and immune-enhancing nutraceuticals.

Influence of gene regulation on rice quality: Impact of storage temperature and humidity on flavor profile.

Effects of high temperature-high humidity (HT-HH) storage on the flavor profile of rice were investigated. Volatile compounds such as aldehydes, ketones, and furans increased when rice was stored under HT-HH conditions, leading to a pronounced deterioration in rice quality. Correspondingly, the fatty acid content of the rice significantly increased during storage. Lipid oxidation was also accelerated under HT-HH conditions leading to the formation of peroxides. However, catalase activity was reduced under these conditions promoting the accumulation of peroxides. For the first time, insights into the genetic mechanisms responsible for these changes were obtained using RNA-sequencing to establish the flavor metabolic pathways in rice. Under HT-HH conditions, gene expression of lipase increased while that of catalase decreased, leading to faster hydrolysis and oxidation of the rice lipids. As a result, a series of lipid degradation products was formed (such as fatty acids, aldehydes, and ketones) that decreased the rice flavor quality.