顶空固相微萃取—气相色谱法测定木糖发酵液中乙醇

建立了顶空固相微萃取(HS-SPME)和气相色谱(GC)联用测定木糖发酵液中乙醇的方法。针对目标组分详细研究了萃取头的种类、萃取时间、萃取温度、pH值、离子强度及解吸条件对HS-SPME的影响。GC载气(高纯氮气)流速为4.0mL/min,色谱柱为DB-ALC2毛细管柱(30m×0.53mm,2μm),柱温:40℃;在优化的条件下,以叔丁醇为内标物,内标法-校准曲线法定量,测定乙醇的线性范围为50～300μg/L;检出限(3倍噪声)为4.19μg/L,相对标准偏差小于6%;回收率为91.01%～97.90%。该方法用于木糖发酵液中乙醇的测定,结果令人满意。     

低浓度乙酸预处理玉米芯的工艺研究

以脱除木质素,降解半纤维素为木糖,提高纤维素酶解得率为目的,研究了低浓度乙酸预处理玉米芯的效果,考察了乙酸质量分数、预处理温度和时间对预处理的影响。研究结果表明:质量分数5%乙酸预处理玉米芯可以脱除大部分的半纤维素和少部分木质素,预处理后的玉米芯具有较好的水解效果。低浓度乙酸预处理玉米芯最优条件为:预处理温度160℃,保温时间60 min,乙酸质量分数5%,固液比1∶8(g∶mL)。在此条件下,玉米芯固体渣回收率为53.75%,固体渣中纤维素保留率93.17%,半纤维素脱除率87.36%,木质素脱除率25.04%,预处理液中木糖质量浓度15.56 g/L。预处理后的玉米芯固体经72 h酶解,酶解得率为92.69%。     

Variability and cluster analysis of arabinoxylan content and its molecular profile in crossed wheat lines

Non-starch polysaccharides (NSP) in cereals, after starch and gluten proteins, determine the technological and nutritional properties of flour, dough and end product. From NSPs, the arabinoxylans are the most important components studied in wheat nowadays. The novelty of our study is the investigation of the variability and clustering ability of the wheat lines based on different quantitative and qualitative traits of arabinoxylans. The quantitative properties, the total and the water-extractable arabinoxylan content of wheat flours were measured separately by gas chromatography. The qualitative property referring to the structure of the molecule was the molecular weight distribution measured by size exclusion liquid chromatography. According to the results the variability of arabinoxylan properties in the breeding lines varied between wider ranges then the values measured for the parental varieties. The correlation between the quantitative parameters, and a trend between quantitative and qualitative parameters were described. During the cluster analysis, the parents were well separated into different groups. The parameters that played an important role in the clustering were the ratio of the probability of occurrence of molecular size ranges along with the quantitative traits of AX. The selected samples can be used for further targeted breeding while the methodology was used in this work can be suitable for selecting lines/varieties for special food or other industrial applications.     

白酒丢糟的酸酶联合水解糖化工艺

为充分利用白酒丢糟资源,探讨了酸酶联合水解法对其进行糖化以获得可发酵糖的可行性。以木糖和还原糖浓度为指标,研究温度、固液比、混合酸浓度和时间等因素对酸解效果的影响;在此基础上分析纤维素酶对酸解残渣(AHR)的酶解历程,并利用扫描电镜(SEM)、红外光谱(FTIR)和X-衍射(XRD)技术考察不同水解阶段丢糟的结构特性变化。结果表明,丢糟在温度为100℃、固液比为1:12g/mL和酸浓度为2.0%的条件下经混合酸水解120min可获得59.32g/L还原糖和6.49g/L木糖,该酸解阶段的半纤维素和纤维素转化率分别为77.38%和62.50%,木质素溶出率为43.50%。AHR在纤维素酶用量为4000U/g原料、温度为45℃和pH值为4.8的条件下继续作用2.5h可获得13.27g/L还原糖,该酶解阶段的纤维素转化率为66.67%,酶解率高达90.73%。结构特性研究表明,水解作用前后的丢糟形貌结构变化明显,孔隙率和比表面积增加,有利于纤维素酶对AHR中纤维结晶区的作用。FTIR和XRD结果显示,水解前后的特征组分所对应的吸收峰强度发生了变化,相对结晶度逐渐提高。白酒丢糟经酸酶联合水解作用转化为可发酵糖具有可行性。该研究可为丢糟生物质发酵制备乙醇提供理论基础。     

发酵木糖高产乙醇酵母菌株的选育

筛选获得的季也蒙毕赤酵母(Pichia guilliermondii)为出发菌株,采用紫外线和亚硝基胍(NTG)复合诱变,筛选高产乙醇突变株。结果表明,紫外诱变菌最佳稀释度为1×10-5,最佳照射时间为25 s;NTG诱变菌最佳稀释度为1×10-6,最佳诱变时间为40 min,经3轮紫外和亚硝基胍(NTG)交替诱变,获得高产乙醇突变株C3-10,其乙醇产量最高为13.2%,比原菌乙醇产量增加了8.05%,5次传代表现出较好的遗传稳定性。     

Metabolic and productive response to ruminal protein degradability in early lactation cows fed untreated or xylose‐treated soybean meal‐based diets

Effects of different dietary rumen undegradable (RUP) to degradable (RDP) protein ratios on ruminal nutrient degradation, feed intake, blood metabolites and milk production were determined in early lactation cows. Four multiparous (43 ± 5 days in milk) and four primiparous (40 ± 6 days in milk) tie‐stall‐housed Holstein cows were used in a duplicated 4 × 4 Latin square design with four 21‐day periods. Each period had 14‐day of adaptation and 7‐day of sampling. Diets contained on a dry matter (DM) basis, 23.3% alfalfa hay, 20% corn silage and 56.7% concentrate. Cows were first offered alfalfa hay at 7:00, 15:00 and 23:00 hours, and 30 min after each alfalfa hay delivery were offered a mixture of corn silage and concentrate. Treatments were diets with RUP:RDP ratios of (i) 5.2:11.6 (control), (ii) 6.1:10.6, (iii) 7.1:9.5 and (iv) 8.1:8.5, on a dietary DM% basis. Different RUP:RDP ratios were obtained by partial and total replacement of untreated soybean meal (SBM) with xylose‐treated SBM (XSBM). In situ study using three rumen‐cannulated non‐lactating cows showed that DM and crude protein (CP) of SBM had greater rapidly degradable fractions. The potentially degradable fractions were degraded more slowly in XSBM. Treatment cows produced greater milk, protein, lactose, solids‐non‐fat and total solids than control cows. Increasing RUP:RDP reduced blood urea linearly. Feed costs dropped at RUP:RDP ratios of 6.1:10.6 and 7.1:9.5, but not at 8.1:8.5, compared with the 5.2:11.6 ratio. Intake of DM and CP, rumen pH, blood glucose, albumin and total protein, faecal and urine pH, changes in body weight and body condition score, and milk lactose and solids‐non‐fat percentages did not differ among treatments. Results provide evidence that increasing dietary RUP:RDP ratio from 5.2:11.6 to 7.1:9.5 optimizes nitrogen metabolism and milk production and reduces feed costs in early lactation cows. Reduced blood urea suggests reprodutive benefits.     

响应面法优化酸水解稻秆制木糖的工艺参数

为了提高稀硫酸水解稻秆制木糖的收率,采用响应面法对稀硫酸水解稻秆制木糖的关键参数进行了优化研究,建立了木糖收率的二次多项式数学模型,并分析模型的有效性与因子间的交互作用。结果表明,3个因素对木糖收率的影响大小依次为酸浓度（质量分数）＞温度＞时间;稀硫酸水解稻秆制木糖的最佳工艺参数为：酸质量分数1.52%、温度121℃和时间为56 min。在此条件下,木糖的最高收率为78.12%。在最佳工艺条件下得到实验结果与模型预测值很吻合,说明所建立的模型是切实可行的。     

催化木糖制备 呋喃甲醛的研究

为了使呋喃甲醛的制备过程绿色化,以ZrOCl2为原料,利用沉淀-浸渍法初步制备了SO42-/ZrO2固体酸,并应用于催化木糖制备呋喃甲醛的反应。采用L9(34)正交试验确定了适宜的反应条件:木糖质量浓度10 g/L、催化剂用量20 g/L、反应温度220℃、反应时间3 h。之后采用单因素试验考察了催化剂制备条件对呋喃甲醛产率的影响。得到的催化剂最佳制备条件为:H2SO4浸渍浓度1.0 mol/L、焙烧温度550℃、焙烧时间5 h,呋喃甲醛产率达最大值47%。实验结果表明:SO42-/ZrO2固体酸在催化木糖制备呋喃甲醛方面,具有较大发展潜力。     

Phenolic compounds,antioxidant capacity and gelling properties of glucoarabinoxylans from three types of sorghum brans

Arabinose to xylose ratio (A/X), phenolics, antioxidant capacity and gelling properties were evaluated in glucoarabinoxylans (GAX) extracted from white (W-GAX), red (R-GAX) and high tannin (T-GAX) sorghum brans (SB). The characterization of arabinoxylans from corn fiber (CFAX) was used as benchmark. Sorghum GAX had higher branched structure (A/X 1.08–1.41) than CFAX (0.59). Nine 3-deoxyanthocyanins (3-DAs) were identified in SB and two glycosylated forms remained associated to the R-GAX and T-GAX extracts. T-GAX was the only that contained tannins (0.41 mg catechin equivalents (CE)/g dry basis (db)) and exerted the highest antioxidant capacity (81.75 mM Trolox equivalents (TE)/g db) followed by R-GAX (48.49 mM TE/g db), which contained the highest amount of 3-DAs (0.11 mg Luteolinidin equivalents (Lut eq)/g db), and W-GAX (35.45 mM TE/g db) that was not significantly different from the CFAX (25.83 mM TE/g db). Among sorghums, only the W-GAX gelled but it formed a weaker gel compared to CFAX likely due to its lower hydroxycinnamic acids (HCA) concentration. The presence of 3-DAs in the structure of R-GAX and T-GAX affected negatively their solubility and gelling properties. The different SB showed potential as sources of GAX with antioxidant capacity.     

Klebsiella oxytoca发酵木糖生产2,3-丁二醇的研究

利用一株克雷伯氏菌(Klebsiella oxytoca ZU-03)发酵木糖生产2,3-丁二醇,并对主要发酵工艺参数进行了优化.实验结果表明:在木糖质量浓度 90 g/L、玉米浆质量浓度 6 g/L、接种量 10 %(体积分数)、初始pH值5.5、 30 ℃的条件下发酵 96 h,木糖利用率为 89 %, 2,3-丁二醇的质量浓度为 36.22 g/L,得率为 0.45 g/g,达到了理论值的 90 %.