Effect of four viscous soluble dietary fibers on the physicochemical, structural properties, and in vitro digestibility of rice starch: A comparison study.

The effect of carboxymethyl cellulose (CMC), high-methoxyl pectin (HMP), konjac glucomannan (KGM), and xanthan gum (XG) on the physicochemical, structural properties, and digestibility of rice starch were investigated and compared. The four viscous soluble dietary fibers (VSDFs) increased the viscosity, storage modulus and loss modulus while decreased the pasting temperature and gelatinization enthalpy. Moreover, XG produced the lowest peak viscosity and dynamic modulus compared with the other VSDFs. Furthermore, the degree of short-range ordered structure of starch with KGM increased from 0.8448 to 0.8716; and the relative crystallinity of starch with XG increased by 12%. An ordered and reunited network structure was observed in SEM. In addition, VSDF inhibited the digestibility of rice starch and significantly increased the resistant starch content. This study compared the effect of four VSDFs on the physicochemical, structural and digestion properties of rice starch to fully understand and develop their application to starchy foods.

Preparation of konjac glucomannan/casein blending gels optimized by response surface methodology and assessment of the effects of high-pressure processing on their gel properties and structure.

BACKGROUND: In order to improve the compatibility of polysaccharide-protein mixtures and enhance their performance, a response surface methodology was used to optimize the preparation conditions of konjac glucomannan/casein blend gel. Moreover, the effects of high-pressure processing (HPP) on the gel properties and structure were also investigated. RESULTS: The optimal preparation parameters were a temperature of 60 °C, a total concentration 40 g kg-1 , and a dietary alkali concentration 5 g kg-1 . Under these conditions, the experimental value of hardness was 38.7 g, which was close to the predicted value. HPP increased gel hardness by 161-223% and led to a more compact structure at 200-600 MPa/10 min, while a hardness increase of ∼120% and damaged structure were observed at 600 MPa/30 min. Fourier transform infrared spectroscopy showed that noncovalent interactions are likely the most important factor in the modification of gel hardness; indeed, hydrogen bonding interactions in the gels are enhanced when subjected to HPP, but are weakened at 600 MPa/30 min. COUCLUSION: Protein-polysaccharide complexes with excellent properties could be obtained through this method, with broad application prospects in the food industry. © 2018 Society of Chemical Industry.

Structures of D-glyceraldehyde-3-phosphate dehydrogenase complexed with coenzyme analogues.

Crystal structures of GAPDH from Palinurus versicolor complexed with two coenzyme analogues, SNAD(+) and ADP-ribose, were determined by molecular replacement and refined at medium resolution to acceptable crystallographic factors and reasonable stereochemistry. ADP-ribose in the ADP-ribose-GAPDH complex adopts a rather extended conformation. The interactions between ADP-ribose and GAPDH are extensive and in a fashion dissimilar to the coenzyme NAD(+). This accounts for the strong inhibiting ability of ADP-ribose. The conformational changes induced by ADP-ribose binding are quite different to those induced by NAD(+) binding. This presumably explains the non-cooperative behaviour of the ADP-ribose binding. Unexpectedly, the SNAD(+)-GAPDH complex reveals pairwise asymmetry. The asymmetry is significant, including the SNAD(+) molecule, active-site structure and domain motion induced by the coenzyme analogue. In the yellow or red subunits [nomenclature of subunits is as in Buehner et al. (1974). J. Mol. Biol. 90, 25-49], SNAD(+) binds similarly, as does NAD(+) in holo-GAPDH. While, in the green or blue subunit, the SNAD(+) binds in a non-productive manner, resulting in a disordered thionicotinamide ring and rearranged active-site residues. The conformation seen in the yellow and red subunits of SNAD(+)-GAPDH is likely to represent the functional state of the enzyme complex in solution and thus accounts for the substrate activity of SNAD(+). A novel type of domain motion is observed for the binding of the coenzyme analogues to GAPDH. The possible conformational transitions involved in the coenzyme binding and the important role of the nicotinamide group are discussed.