Improvement of the Characteristics of Steamed Bread by Supplementation of Recombinant alpha-L-arabinofuranosidase Containing xylan-binding domain

Current study investigated the potential to increase the activity of α-L-arabinofuranosidase (TmAra) from Thermotoga marotima on insoluble arabinoxylan (IAX) through fusion to a family 6 xylan-binding domain (CtXBD6) from Clostridium thermocellum. CtXBD6 was fused to the carboxyl terminus of TmAra, and active forms of both TmAra and TmAraCtXBD6 were produced in E. coli and purified to homogeneity for biochemical characterization. TmAraCtXBD6 had similar temperature and pH profiles to TmAra with a decrease in the thermostability and pH stability at pH 7.0–8.2. It exhibited stronger IAX-binding and hydrolytic activity than TmAra. TmAra and TmAraCtXBD6-treated IAX were added to wheat flour to investigate the rheological and textural properties of the finished product. IAX alone had significant increase in dough development time (DDT) and dough stability (DS) and decrease in the softening degree (SD), crumb firmness (CF) and specific volume (SV). On adding TmAra and TmAraCtXBD6 to treat IAX texture, SV and DS improved but decreased DDT, SD, and CF. TmAraCtXBD6 reduced CF and increased SV, and had higher springiness, cohesiveness, and crumb chewiness than TmAra. These results demonstrated that the fusion of CtXBD6 into arabinofuranosidase enables the increase in catalytic performance on insoluble AX substrates, which can be used as more efficient biocatalysts that can improve the quality of AX-rich products.     

Changes in Molecular Characteristics of Cereal Carbohydrates after Processing and Digestion

Different extraction, purification and digestion methods were used to investigate the molecular properties of carbohydrates in arabinoxylan and β-glucan concentrates, dietary fiber (DF) rich breads and ileum content of bread fed pigs. The breads studied were: a low DF wheat bread (WF), whole meal rye bread (GR), rye bread with kernels (RK), wheat bread supplemented with wheat arabinoxylan concentrate (AX) and wheat bread supplemented with oat β-glucan concentrate (BG). The weight average molecular weight (M_w) of extractable carbohydrates in β-glucan concentrate decreased eight-fold after inclusion in the BG bread when exposed to in vitro digestion, while the M_w of purified extractable carbohydrates in AX bread was reduced two-fold, and remained almost unaffected until reaching the terminal ileum of pigs. Similarly, the M_w of purified extractable carbohydrates in GR and RK bread was not significantly changed in the ileum. The AX bread resulted in the highest concentration of dissolved arabinoxylan in the ileum among all the breads that caused a substantial increased in ileal AX viscosity. Nevertheless, for none of the breads, the M_w of extractable carbohydrates was related neither to the bread extract nor ileal viscosity.     

Kinetic analysis of bile salt passage across a dialysis membrane in the presence of cereal soluble dietary fibre polymers

The kinetics of passage of a model bile salt and complete porcine bile across a dialysis membrane, in the presence and absence of two cereal-derived soluble dietary fibre polysaccharides, were studied as a model for passage across the unstirred water layer that lines the small intestine. A first-order kinetic analysis allowed rate coefficients to be derived which quantified the effectiveness of barley mixed linkage β-glucan and wheat arabinoxylan in retarding the transport of bile. For both, a model bile salt and complete porcine bile, rate coefficients decreased with both concentration and viscosity. A combination of viscosity and molecular interaction effects is suggested to control the effect of the two polysaccharides on the transport of bile.     

青稞多糖对玉米淀粉糊化和流变特性的影响

为了研究青稞β-葡聚糖（HBBG）和阿拉伯木聚糖（HBAX）对玉米淀粉（CS）糊化和流变特性的影响,向CS中添加不同质量分数的青稞来源多糖,通过快速黏度仪（RVA）、流变仪、扫描电镜等分析其对CS黏度和表观形貌的影响。结果表明：添加不同质量分数青稞多糖均可降低CS体系的崩解值、延长糊化峰值时间,提高CS的热稳定性;线性链状结构的HBBG通过与淀粉分子交联及自身的聚集作用,增加CS体系黏度、储能模量（G′）和损耗模量（G″）,提高体系的黏弹性;而具有高分支结构的HBAX则通过附着在淀粉颗粒表面,抑制淀粉颗粒膨胀,减少了直链淀粉的渗漏,降低体系峰值黏度、稠度系数K、G和G″等,增强了体系的流动性。     

阿拉伯木聚糖与壳聚糖复凝聚物的制备及表征

研究了不同因素对壳聚糖-阿拉伯木聚糖复凝聚的影响,通过测定平衡相的浊度和复凝聚相收率确定玉米阿拉伯木聚糖（CAX）和壳聚糖（CS）间复合物形成的条件。采用红外光谱、热重分析、扫描电子显微镜和流变学特性对复凝聚物进行表征。研究结果表明,在CAX/CS配比为9:1,体系pH值为4.0,总固形物浓度为3%（m/m）,室温下反应10 min,最大复凝聚相产率达76.04%。红外光谱和热重分析结果表明,CAX/CS复凝聚物是通过CS中的-NH3+和CAX中-COO-之间的相互吸引形成的。用SEM扫描成像显示复凝聚物具有规则且分布均匀的多孔网络结构。CAX/CS复凝聚物粘弹特性取决于发生复凝聚的pH值。在pH值3.5和4.0时,复凝聚物为液体粘弹行为;在pH值5.0时,复凝聚物为固体粘弹性行为。pH值5.0下形成的复凝聚物的G’最高,说明除静电作用外,其他因素也可能对CAX/CS复凝聚物粘弹特性起重要作用。CAX/CS复凝聚物可以作为包封营养素和功能性因子的微囊化壁材。