The influence of dissolved oxygen on the production of difficidin by Bacillus sp.

Difficidin and oxydifficidin are two related antibacterial antibiotics produced by the fermentation of Bacillus subtilis ATCC 39374. Difficidin was much more stable than oxydifficidin under alkaline conditions. Both antibiotics were very unstable at an extremely low pH level (pH ≤ 3.5). In the whole culture broth, most of the antibiotics were found to be bound to the cell mass and appeared to be more stable than the free compounds. The influence of dissolved oxygen tension (DOT) on the fermentation was investigated using a 20-L fermenter coupled with a proportional-integral-derivative (PID) control system to control DOT at a constant level throughout the fermentation by simultaneously varying the air flow rate and agitator speed based on a constant nitrogen gas feed rate. Growth and antibiotics production during the fermentation were studied at different DOT levels. The critical DOT level for the maximum specific growth rate of the culture was found to be lower than 5% air saturation. The difficidin production was significantly affected by DOT in the fermentation broth while the oxydifficidin synthesis appeared to be unaffected. The DOT level of 20% air saturation was critical for difficidin synthesis, below which the volumetric production rates of difficidin were sharply decreased. These results demonstrate the distinct difference between the critical DOT values for difficidin production and specific growth rates. Fermentations with cycling DOT with a periodicity of 1 min were performed to simulate the heterogeneity in DOT of a large scale fermenter. The antibiotics production was not significantly affected by cycling DOT above, below as well as around the critical level for difficidin production. However, an increase in the growth rates when DOT was cycled below and around the critical level caused a marked reduction in the specific production rates of the two antibiotics. In contrast, no effect on growth rates was observed when DOT was cycled above the critical level

A Review on Isolation, Characterization, Modification, and Applications of Proso Millet Starch

Proso millet starch (PMS) as an unconventional and underutilized millet starch is becoming increasingly popular worldwide due to its health-promoting properties. This review summarizes research progress in the isolation, characterization, modification, and applications of PMS. PMS can be isolated from proso millet grains by acidic, alkaline, or enzymatic extraction. PMS exhibits typical A-type polymorphic diffraction patterns and shows polygonal and spherical granular structures with a granule size of 0.3–17 µm. PMS is modified by chemical, physical, and biological methods. The native and modified PMS are analyzed for swelling power, solubility, pasting properties, thermal properties, retrogradation, freeze–thaw stability, and in vitro digestibility. The improved physicochemical, structural, and functional properties and digestibility of modified PMS are discussed in terms of their suitability for specific applications. The potential applications of native and modified PMS in food and nonfood products are presented. Future prospects for research and commercial use of PMS in the food industry are also highlighted

Adsorption of Protein-Coated Lipid Droplets onto Gellan Gum Hydrogel Surfaces

The formation of coatings on hydrogel surfaces due to adsorption of lipid droplets is important in a number of natural and industrial processes, e.g., foods, cosmetics, and pharmaceuticals. The adsorption of cationic protein-coated lipid droplets to the surfaces of anionic hydrogels was examined in this study. An oil-in-water emulsion containing cationic β-lactoglobulin-coated lipid droplets was prepared (d4,3 = 0.3 μm, ζ = +67 mV, pH 3.0). An anionic hydrogel consisting of 1 wt% gellan gum (pH 3.0) was prepared. Emulsions containing different lipid droplet concentrations (0.1–10 wt%) were brought into contact with the hydrogel surfaces for different times (0–24 h). The adsorption of lipid droplets to the hydrogel surfaces could not be explained by a typical adsorption isotherm. We found that the electrical charge on the non-adsorbed lipid droplets became less positive or even became negative in the presence of the hydrogel, and that extensive droplet aggregation occurred, which was attributed to the ability of gellan molecules released from the hydrogels to interact with the lipid droplets. These results may have important consequences for understanding certain industrial and biological processes, as well as for the design of controlled or triggered release systems

Core-Shell Biopolymer Nanoparticles Produced by Electrostatic Deposition of Beet Pectin onto Heat-Denatured Beta-Lactoglobulin Aggregates

The purpose of this study was to produce and characterize core-shell biopolymer particles based on electrostatic deposition of an anionic polysaccharide (beet pectin) onto amphoteric protein aggregates (heat-denatured beta-lactoglobulin [beta-lg]). Initially, the optimum conditions for forming stable protein particles were established by thermal treatment (80 degrees C for 15 min) of 0.5 wt% beta-lg solutions at different pH values (3 to 7). After heating, stable submicron-sized (d=100 to 300 nm) protein aggregates could be formed in the pH range from 5.6 to 6. Core-shell biopolymer particles were formed by mixing a suspension of protein aggregates (formed by heating at pH 5.8) with a beet pectin solution at pH 7 and then adjusting the pH to values where the beet pectin is adsorbed (\u3c pH 6). The impact of pH (3 to 7) and salt concentration (0 to 250 mM NaCl) on the properties of the core-shell biopolymer particles formed was then established. The biopolymer particles were stable to aggregation from pH 4 to 6, but aggregated at lower pH values because they had a relatively small -potential. The biopolymer particles remained intact and stable to aggregation up to 250 mM NaCl at pH 4, indicating that they had good salt stability. The core-shell biopolymer particles prepared in this study may be useful for encapsulation and delivery of bioactive food components or as substitutes for lipid droplets

Influence of Degree of Polymerization of Low-Molecular-Weight Chitosan Oligosaccharides on the α-Glucosidase Inhibition

Chitosan oligosaccharide (COS) is a bioactive compound derived from marine by-products. COS consumption has been demonstrated to lower the risk of diabetes. However, there are limited data on the inhibitory effect of low-molecular-weight COSs with different degrees of polymerization (DP) on α-glucosidase. This study investigates the α-glucosidase inhibitory activity of two low-molecular-weight COSs, i.e., S-TU-COS with DP2–4 and L-TU-COS with DP2–5, both of which have different molecular weight distributions. The inhibition constants of the inhibitors binding to free enzymes (Ki) and an enzyme–substrate complex (Kii) were investigated to elucidate the inhibitory mechanism of COSs with different chain lengths. The kinetic inhibition model of S-TU-COS showed non-completive inhibition results which are close to the uncompetitive inhibition results with Ki and Kii values of 3.34 mM and 2.94 mM, respectively. In contrast, L-TU-COS showed uncompetitive inhibition with a Kii value of 5.84 mM. With this behavior, the IC50 values of S-TU-COS and L-TU-COS decreased from 12.54 to 11.84 mM and 20.42 to 17.75 mM, respectively, with an increasing substrate concentration from 0.075 to 0.3 mM. This suggests that S-TU-COS is a more potent inhibitor, and the different DP of COS may cause significantly different inhibition (p < 0.05) on the α-glucosidase activity. This research may provide new insights into the production of a COS with a suitable profile for antidiabetic activity

Astaxanthin-Loaded Pickering Emulsions Stabilized by Nanofibrillated Cellulose: Impact on Emulsion Characteristics, Digestion Behavior, and Bioaccessibility

Astaxanthin (AX) is one of the major bioactives that has been found to have strong antioxidant properties. However, AX tends to degrade due to its highly unsaturated structure. To overcome this problem, a Pickering O/W emulsion using nanofibrillated cellulose (NFC) as an emulsifier was investigated. NFC was used because it is renewable, biodegradable, and nontoxic. The 10 wt% O/W emulsions with 0.05 wt% AX were prepared with different concentrations of NFC (0.3–0.7 wt%). After 30 days of storage, droplet size, ζ-potential values, viscosity, encapsulation efficiency (EE), and color were determined. The results show that more stable emulsions are formed with increasing NFC concentrations, which can be attributed to the formulation of the NFC network in the aqueous phase. Notably, the stability of the 0.7 wt% NFC-stabilized emulsion was high, indicating that NFC can improve the emulsion’s stability. Moreover, it was found that fat digestibility and AX bioaccessibility decreased with increasing NFC concentrations, which was due to the limitation of lipase accessibility. In contrast, the stability of AX increased with increasing NFC concentrations, which was due to the formation of an NFC layer that acted as a barrier and prevented the degradation of AX during in vitro digestion. Therefore, high concentrations of NFC are useful for functional foods delivering satiety instead of oil-soluble bioactives