Protein interactions with cyanidin‐3‐glucoside and its influence on α‐amylase activity

BACKGROUND: Recent studies indicate that the bioavailability of anthocyanins is extremely low. One of the possible reasons could be their binding to proteins. Therefore, the binding affinity of cyanidin‐3‐glucoside (Cy3glc) to HSA and α‐amylase was investigated by the quenching of protein tryptophan fluorescence. From data obtained, the binding constants and the free Gibbs energy were calculated. The changes in conformation of the proteins tested were studied with circular dichroism and the influence of binding on α‐amylase activity determined. RESULTS: Cy3glc quenched the tryptophan fluorescence and upon ligand binding a change in protein structure was observed related to the corresponding decrease in the α‐amylase activity. The association constants of 25 to 77 × 10³ L mol^?1 were calculated for different proteins, indicating weak interactions of non‐covalent nature. Competitive binding with HSA in the presence of 8‐anilino‐1‐naphthalene sulfonic acid suggest involvement of hydrophobic interactions, in the case of HSA the possible site being subdomain IIA. CONCLUSION: The strongest affinity of Cy3glc for HSA being at pH 7 underlines its potential in transport and distribution of the phenolic compounds in organisms. An influence on salivary amylase activity is possible when drinking berry juices with high anthocyanins content. Copyright © 2008 Society of Chemical Industry     

具有菲环骨架的高分子载体固定淀粉酶交联聚集体

用80%异丙醇溶液将淀粉酶沉淀聚集,随后用戊二醛交联制备交联淀粉酶聚集体(cross-linked amylase aggregates,CLEAs-A),最后将CLEAs-A共价固定在具有大孔的菲环骨架的载体上,制备固定化CLEAs-A。探讨各种优化条件,研究固定化CLEAs-A的酶学性质,结果显示固定化酶的热稳定性和储存稳定性明显提高,重复反应7批次后,相对活性仍保留63.29%。此外,扫描电子显微镜和孔径测量展现了固定化CLEAs-A的表面和孔径结构。此法可作为一种通用方法,制备出工业生产中所需要的具有高生物催化性能的固定化酶。     

海洋低温淀粉酶菌株的筛选、鉴定及酶学性质研究

以大连黄海海泥和海水为样品,采用稀释涂布平板透明圈法初筛、摇瓶发酵复筛,得到一株淀粉酶高产菌ZXS-5,测得酶活为6.25 U/mL。通过形态学、生理生化及16S rDNA序列鉴定,菌株ZXS-5为荧光假单胞菌（Pseudomonas fluorescens）。该酶的最适作用温度为25 ℃,酶的热稳定性相对较差;最适作用pH值为8.0,属于碱性酶,该酶在酸性条件下稳定性较差;Ba2+、Cu2+、乙二胺四乙酸（EDTA）对该酶抑制性较强,Fe2+、Zn2+、Mn2+对该酶的活性影响不明显,Mg2+、Na+对该酶激活作用较弱,Ca2+对该酶激活作用较强。     

压榨型鲜湿米粉条凝胶质构特性及食用品质影响因素

以压榨型鲜湿米粉条凝胶品质影响因素为研究对象,主要探讨了大米粉基本理化指标、快速黏度分析(rapid visco analyze,RVA)糊化特性、大米淀粉结晶特性对压榨型鲜湿米粉条的食用品质及其凝胶质构特性的影响。研究表明大米粉直链淀粉的质量分数与米粉条的感官得分、质构特性指标(除黏附性、弹性外)呈显著或极显著正相关(P0.05,P0.01),大米粉支链淀粉质量分数与米粉条感官得分、质构特性指标(除黏附性、弹性外)呈显著或极显著负相关(P0.05,P0.01);大米粉粗蛋白(除与恢复性呈显著正相关外)、粗脂肪质量分数与米粉条凝胶特性和食用品质相关性不显著(P0.05);X射线衍射、傅里叶变换红外光谱2种方法分析得到的结晶度RX和RI均与米粉条的凝胶特性指标和食用品质感官得分均无显著相关性(P0.05)。RVA糊化特性参数中的峰值黏度、最低黏度和最终黏度与米粉条的感官得分、质构特性指标(除黏附性、弹性外)呈显著或极显著正相关性(P0.05,P0.01);衰减值虽与感官得分、凝胶质构特性指标(除与黏附性显著负相关外)均呈一定的负相关性,但均不显著(P0.05);而回生值则与米粉条感官得分、凝胶质构特性指标的硬度、胶着性、咀嚼性、恢复性均呈极显著正相关(P0.01)。由此可见,直链淀粉、支链淀粉质量分数及RVA糊化特性参数可用来预测压榨型鲜湿米粉条的食用品质关键性指标。     

Physicochemical Properties of Rice Steeped in Hot or Warm Water

Prolonged steeping of rice grains in hot or warm water was examined to study the gelatinization process of rice starch. Rice treated at 75°C for 8–18 hr showed the same type “V” X-ray diffraction pattern as that of cooked rice. Rice treated at 50–60°C for 24–72 hr showed a strengthened type “A” pattern. The gelatinization degree of the 75°C treated rice determined by the β-amylase-pullulanase method and Brabender amylography was as high as that of cooked rice. The value of the 50–60°C treated rice was lower than that of raw rice. The gelatinization temperature of rice varied with the two types of treatment.     

Sweetpotato α- and β-Amylases: Characterization and Kinetic Studies with Endogenous Inhibitors

Sweetpotato α- and β-amylases were characterized to assist optimization of direct hydrolysis of starch by endogenous amylases. In kinetic studies purified starch was substrate, and ascorbate, oxalate, phenolics, phytate and sweetpotato extracts were assayed for inhibitory activity. α-Amylase had optimum pH between 5.8 and 6.4 and was stable from pH 5.0 to 9.0. Optimum activity occurred at 71.5°, but it was inactivated by heat in the absence of Ca²⁺ at > 63°. The Km for soluble starch was 2.08 mg/mL. The molecular weight was 45000 daltons. α-Amylase activity was reduced up to 70% by 0.2 mM K-ascorbate and moderately by Na-oxalate and Na-phytate. β-Amylase had optimum pH between 5.3 and 5.8, and was stable from pH 4.0 to 8.0. Its maximum activity was at 53° and it was inactivated at 60°. Km for soluble starch was 3.71 mg/mL. At 0.08 mM, K-ascorbate strongly inhibited β-amylase activity.     

Starch digestibility of foods: a nutritional perspective

Dietary starch varies greatly in digestibility and its effects on the utilization of other nutrients. The variation appears to be due to differences in starch components and their crystallinity. Processing treatments, storage conditions, chemical modification, and genetic breeding influence the digestibility of starch. Cereal starches are generally more digestible than root/tuber and legume starches. Although cooking often significantly improves the digestibility of poor and intermediately digestible starches, some foods such as bananas with starches of these types are consumed uncooked. The efficient digestion of starch is especially important to specific groups of people such as infants under 6 months of age. Ruminants must also be provided with highly digestible starch to assure maximum production efficiency. Poor digestibility of starch may have negative effects on the utilization of protein and minerals but is likely to have positive effects on the availability of certain vitamins. Decreases in the rate of starch digestion may have therapeutic application. Most clinical studies have reported that starch blockers do not elicit a significant decrease in the digestion of starch in humans. Much remains to be learned, clarified, and understood about starch digestion and its effects on diabetes and weight control.     

SCREENING OF BARLEY VARIETIES FOR ALPHA-AMYLASE CONTENT

Abrasion of barley induces accelerated water uptake and malt production and a higher hot water extract is obtained. These improvements are largely due to an increased rate of germination and faster α-amylase production. If a barley that behaved as though it were naturally abraded were available it could be of advantage economically. A world collection of barley varieties has been screened for α-amylase content using abraded and unabraded Proctor as controls. Field grown barley and varieties grown under controlled conditions in a glasshouse have been compared. The environmental effect on field-grown material seems to be consistent for all varieties and does not appear to affect which part of the α-amylase distribution curve that variety occupies. Of the 1362 varieties examined, some 13% exceeded the α-amylase activity of abraded Proctor, but only about 1% were two-row husked varieties. There is the possibility that some of these two-row husked barleys might be suitable for introducing the genetic factor for high α-amylase into a high-yielding, disease-resistant barley.     

Phospholipid Hydrolysate and Antistaling Amylase Effects on Retrogradation of Starch in Bread

Effects of phospholipid hydrolysate and antistaling amylase on starch retrogradation in bread and wheat flour were investigated by differential scanning calorimetry (DSC). Phospholipid hydrolysate containing more than 90% lysophospholipid was obtained using phospholipase A₂ and was effective in forming amylose-lipid complexes. Both wheat flour and bread containing phospholipid hydrolysate were retrograded to a lesser degree when stored at room temperature. The retrogradation rate for bread with antistaling amylase was low. We postulated that antistaling amylase broke links in amylose and amylopectin, thereby promoting the formation of amylopectin-lipid complexes. The combined effect of phospholipid hydrolysate and antistaling amylase was greater than their individual effects.     

淀粉酶的性质和分类

淀粉酶是能催化淀粉水解转化的一群酶的总称.在食品工业和淀粉糖工业中被广泛利用,国内外对淀粉酶的研究已取得很大的进展.本文着重对淀粉酶的性质和分类进行综述.根据水解淀粉分子的糖苷键的类型,提出将淀粉酶分成三类,即仅作用于1,4-α-D一葡糖苷键的淀粉酶:仅用作于1,6-α-D-葡糖苷键的淀粉酶;作用于1,4-α-D-葡糖苷键又作用于1,6——α—D-葡糖苷键的淀粉酶.