2,3-Dihydroxybenzoic Acid Decarboxylase from Fusarium oxysporum: Crystal Structures and Substrate Recognition Mechanism.

A 2,3-dihydroxybenzoic acid decarboxylase from Fusarium oxysporum (2,3-DHBD_Fo) has a relatively high catalytic efficiency for the decarboxylation of 2,3-dihydroxybenzoic acid (DHBA) and carboxylation of catechol, thus it has a different substrate spectrum from other benzoic acid decarboxylases. We have determined the structures of 2,3-DHBD_Fo in its apo form and complexes with catechol or 2,5-dihydroxybenzoic acid at 1.55, 1.97, and 2.45 Šresolution, respectively. The crystal structures of 2,3-DHBD_Fo show that the enzyme exists as a homotetramer, and each active center has a Zn2+ ion coordinated by E8, H167, D291 and three water molecules. This is different from 2,6-DHBD from Rhizobium sporomusa, in which the Zn2+ ion is also coordinated with H10. Surprisingly, mutation of A10 of 2,3-DHBD_Fo to His resulted in almost complete loss of the enzyme activity. Enzyme-substrate docking and site-directed mutation studies indicate that residue R233Δ interacts with the 3-hydroxy group of 2,3-DHBA, and plays an important role in substrate recognition for this enzyme, thus revealing the molecular basis 2,3-dihydroxybenzoic acid decarboxylase.

Alkali-Induced Protein Structural, Foaming, and Air-Water Interfacial Property Changes and Quantitative Proteomic Analysis of Buckwheat Sourdough Liquor.

In this study, the protein structural, foaming, and air-water interfacial properties in dough liquor (DL) ultracentrifugated from buckwheat sourdough with different concentrations of an alkali (1.0-2.5% of sodium bicarbonate) were investigated. Results showed that the alkali led to the cross-linking of protein disulfide bonds through the oxidation of free sulfhydryl groups in DL. The alterations in protein secondary and tertiary structures revealed that the alkali caused the proteins in DL to fold, decreased the hydrophobicity, and led to a less flexible but compact structure. The alkali accelerated the diffusion of proteins and decreased the surface tension of DL. In addition, the alkali notably improved the foam stability by up to 34.08% at 2.5% concentration, mainly by increasing the net charge, reducing the bubble size, and strengthening the viscoelasticity of interfacial protein films. Quantitative proteomic analysis showed that histones and puroindolines of wheat and 13S globulin of buckwheat were closely related to the changes in the alkali-induced foaming properties. This study sheds light on the mechanism of alkali-induced improvement in gas cell stabilization and the buckwheat sourdough steamed bread quality from the aspect of the liquid lamella.

Insights into heat-induced molecular-level interactions between wheat and common buckwheat proteins.

This study investigated the heat-induced interactions between wheat and buckwheat proteins by heating wheat proteins, buckwheat albumin, globulin, and mixtures of wheat flour with buckwheat albumin/globulin at 50, 65, 80, 95, and 100 °C. The results showed that the cross-linking reactions of wheat glutenin with buckwheat albumin and globulin initiated at 80 and 95 °C, respectively. Buckwheat albumin decreased the extractability of α-gliadin by 35 % at 95 °C and 5.9 % at 100 °C. The linkage of buckwheat globulin to wheat glutelin prevented part of the wheat gliadin from linking to glutelin, resulting in the extractability of α- and γ-gliadin increased by 8.6 % and 11 % at 95 °C, respectively. The chemical forces results indicated that interactions between wheat and buckwheat proteins were primarily driven by disulfide bonds and hydrophobic interactions. This study provides a theoretical basis for better regulating the wheat-buckwheat protein network to improve the quality of buckwheat-enriched products.

Effect of characteristics of different wheat flours on the quality of fermented hollow noodles.

Hollow noodles, also known as Kongxin noodles in China, are traditionally hand-made noodles produced by spontaneous fermentation. It is easy to cook, nutrient-rich, and delicious. However, it is difficult to realize industrial production by spontaneous fermentation due to its complexity. More recently, new techniques have emerged for producing such noodles industrially using commercial yeasts. However, there are no reports on how to choose the raw materials for making fermented hollow noodles. Therefore, the suitability of eleven local varieties of wheat flour was determined by evaluating their physicochemical, rheological properties, and pasting properties. Flour and dough properties of wheat flour were also correlated with the quality characteristics of hollow noodles. The correlation coefficient data indicated that the color score was negatively correlated with ash content and positively correlated with starch content. Different from ordinary dried noodles, a negative correlation was observed between cooking time (CT) and protein content. Water absorption (NWA) of hollow noodles was negatively affected by extensograph properties. Water absorption of flour (FWA) and extensibility (E) were found to be highly correlated to hollow rate (Hol-R), indicating that these two indexes could predict the fermentation status of hollow noodles. Results showed that wheat flours with higher swelling index of glutenin (SIG), FWA, E, and pasting temperature (PT) had better dough fermentation power and stability and thus were beneficial to the production of high-quality hollow noodles. This study provides a simple method for the industrial production of hollow noodles and provides a basis for the selection of raw materials for their production.

Effects of salt and kansui on rheological, chemical and structural properties of noodle dough during repeated sheeting process.

Effects of different levels of salt (1-2%, fwb) and kansui (0.5-1%) on the rheological, chemical and structural characteristics of noodle dough developed by repeated sheeting were studied. The rupture stress was increased by salt and kansui. The rupture elongation was increased by salt while reduced by kansui. The rupture stress and elongation increased to a maximum at 3 or 4 sheeting passes then decreased. The larger polymeric glutenin (LPP) increased while glutenin macropolymer (GMP) and free SH contents declined with the increased sheeting passes except for the dough contained 1% kansui at which these indicators remained constant. The ß-sheet was increased while the ß-turn was decreased by salt and kansui. The results showed the LPP disaggregated from GMP through physical disentanglement and experienced a reaggregation process with the SS bonds participate in, but the addition of kansui especially at 1% concentration could inhibit the disaggregation of GMP through protein cross-linking.

Effect of heat-moisture treatment on the structure and physicochemical properties of ball mill damaged starches from different botanical sources.

The morphology, structure and physicochemical properties of ball milling (BM) damaged starches from mung bean, potato, corn and waxy corn were investigated before and after heat-moisture treatment (HMT) (100 °C, for 12 h at a moisture content of 25%). The results showed that the damaged starch (DS) content of BM modified starches was decreased by 4.49%, 10.68%, 17.11% and 22.98% after HMT for mung bean, potato, corn and waxy corn starch, respectively. The solubility and swelling power were significantly decreased, and the modified effect was depended on the type of starch, among which waxy corn starch exhibited the maximum reduction. Different degrees of aggregation and fusion of granules were found in starches modified with BM-HMT, and the extent of fusion was related to amylose content and crystalline pattern. The crystallinity of BM modified starches was increased by 6.3%, 5.9%, 17.9% and 22.4% after HMT for mung bean, potato, corn and waxy corn starch, respectively. The dual physical modification had various effects on the starches from different botanical sources, the increase in crystallinity and peak temperature (Tp) were related to the DS and amylose content, and the changes in gelatinization temperature range (Tc-To) were related to the crystalline pattern of starches.