Factors affecting the resistance of listeria monocytogenes to high hydrostatic pressure

Several factors relevant to food preservation had large effects on the resistance of L. monocytogenes to high hydrostatic pressure. Cells in the stationary phase of growth were much more resistant to pressures above 200MPa than those in the exponential phase. Following treatment for 10 min at 400 MPa viable numbers of stationary phase cells were reduced by only 1.3 log₁₀ units compared with more than 7 log₁₀ units for exponentially growing cells. Stationary phase cells were sensitised to pressure by butylated hydroxyanisole, potassium sorbate and by acid conditions. The most effective sensitiser was BHA which, at 1.55 mM, caused a 10⁴‐fold enhancement of killing by treatment at 300 MPa for 10 min. Propyl hydroxybenzoate, butylated hydroxytoluene and sodium ascorbate were without effect. Xylitol (15%) protected log phase cells against inactivation by pressure: after treatment at 350 MPa for 10 min viable numbers were reduced by only 0.24 log₁₀ units compared with 2.4 log₁₀ units in the absence of xylitol. The physicochemical environment can substantially increase or decrease resistance to pressure and these effects will require quantification if the microbiological effects of pressure are to be predicted.     

愈创木酚法合成香兰素工艺综述

文章简述了香兰素的用途,主要介绍了愈创木酚为原料反应合成香兰素的工艺,其中乙醛酸法具有收率高、质量好、环境污染轻等特点,目前该工艺已实现产业化。     

邻苯二酚与甲醇合成愈创木酚的热力学分析

邻苯二酚与甲醇气相单醚化合成愈创木酚因经济、环保、原料廉价易得、可实现连续化生产等优点而备受关注。为了有效利用资源,对该反应过程进行了较为详细的热力学分析。根据邻苯二酚(catechol)、甲醇、愈创木酚(guaiacol)及水的标准摩尔生成焓Δ_fH^θ_m、标准熵变ΔS^θ_m和热熔C_p,m等热力学数据,讨论了温度对邻苯二酚与甲醇气相合成愈创木酚反应的焓变Δ_rH_m、自由能变Δ_rG_m及平衡常数K的影响。结果表明,在400～800 K温度范围内,该反应是一个放热自发反应,可在较低温度下顺利进行,有较大反应平衡常数。因此,该反应的研究关键主要是较低温度下高活性催化剂的研发和最适宜反应条件的选择。     

Amelioration of smoke taint in wine by reverse osmosis and solid phase adsorption

Background and Aims: Wines made from grapes harvested from vineyards exposed to bushfire smoke can exhibit objectionable ‘smoky’, ‘cold ash’, ‘medicinal’ and ‘ashy’ aroma and flavour characters. This study evaluated a combined reverse osmosis and solid phase adsorption process as a potential amelioration method for the treatment of smoke‐tainted wines. Methods and Results: Smoke‐tainted wines were treated using either pilot or commercial scale reverse osmosis systems and the chemical composition and sensory properties of wine compared before and after treatment. The concentrations of smoke‐derived volatile phenols, including marker compounds, guaiacol and 4‐methylguaiacol, decreased significantly with treatment. As a consequence, diminished smoke‐related sensory attributes enabled treated wines to be readily differentiated from untreated wines. However, the taint was found to slowly return with time, likely because of hydrolysis of glycoconjugate precursors, which were not removed during the treatment process. Conclusions: Reverse osmosis and solid phase adsorption reduced the concentration of smoked‐derived volatile phenols and improved the sensory attributes of smoke‐tainted wines. Significance of the Study: This is the first study to evaluate the amelioration of smoke taint in wine using reverse osmosis and solid phase adsorption.     

分光光度计法快速检测果汁中嗜热耐酸菌

酸土脂环酸芽孢杆菌(Alicyclobacillus acidoterrestris)是果汁污染的主要嗜酸耐热菌。它可以将香草酸或者香兰素转化为愈创木酚,后者在过氧化物酶的作用下产生红褐色产物,从而可以快速检测该菌。根据这个原理,设计实验探究该颜色反应的最优培养条件以及实际体系中检测该菌的可行性。结果表明：在静止培养情况下,在BAM培养基中添加100μg/kg的香草酸最有利于愈创木酚的产生;不同浓度的嗜热耐酸菌芽孢液在上述条件下培养,随着浓度的降低产生高浓度愈创木酚时间依次延迟,最低浓度为3个/mL的芽孢培养21h后,愈创木酚含量用分光光度计测定的光密度值OD470为1.0以上,为肉眼可见的红褐色;模拟实际体系下的培养也出现了颜色反应,证明该方法确实可以实现果汁中嗜热耐酸菌的快速、简便、高灵敏度的检测。     

AlOOH催化臭氧氧化降解愈创木酚的研究

以木素模型物愈创木酚(GL)模拟废水为目标物,采用拟薄水铝石(AlOOH)为催化臭氧氧化的催化剂,研究了催化剂及其投加量、臭氧进气量、初始溶液pH值等因素对200 mg/L愈创木酚溶液的降解效果和CODCr去除率的影响;通过液相图谱分析和添加羟基自由基捕获剂——叔丁醇(TBA)初步探讨了催化臭氧氧化的降解机理。结果表明,与单独臭氧氧化相比,催化臭氧氧化效果更佳;在臭氧质量浓度13.32 mg/L、臭氧进气量0.51 L/min、初始溶液pH值5.4、催化剂投加量5 g/L的条件下,反应40 min后,愈创木酚(200 mg/L)降解率能达到100%,CODCr去除率能达到89.3%;叔丁醇(TBA)的添加可以证明催化臭氧氧化反应是臭氧与羟基自由基共同作用的结果。     

焙烧温度对Au/TiO2催化愈创木酚加氢脱氧反应性能的影响

采用沉积-沉淀法制备了不同焙烧温度的Au/TiO₂系列催化剂,采用TEM、XPS、XRD、N₂吸附-脱附、ICP以及NH₃-TPD等手段表征了Au/TiO₂系列催化剂的物化性能。考察了Au/TiO₂系列催化剂在木质素模型化合物(愈创木酚)加氢脱氧反应中的催化性能,及反应条件对Au/TiO₂-1(焙烧温度为350 ℃)催化愈创木酚加氢脱氧反应性能的影响,并探讨了反应机理。结果表明,当焙烧温度由350 ℃升至650 ℃,Au/TiO2催化剂中Au颗粒平均粒径从2.7 nm增至7.9 nm,晶型保持为锐钛矿型,催化剂比表面积由90 m²/g减至49 m²/g;新鲜和反应后催化剂中的Au均以金属态存在。在愈创木酚加氢脱氧反应中,Au/TiO₂催化剂对酚类产物有很高的选择性。随着催化剂焙烧温度增加,其活性逐渐降低,产物中酚类物质的选择性基本不变;当催化剂上Au颗粒平均粒径小于6 nm时,出现了新的反应路径,即愈创木酚上甲氧基中的甲基加氢生成甲烷。不同反应温度与氢气压力的结果表明,Au/TiO₂催化剂能够高选择性地断裂1个C-O键,而苯环不会被饱和,酚类产物的分布基本没有变化。催化剂重复使用2次性能稳定。     

Aggregation pheromone system of adult gregarious desert locust schistocerca gregaria (forskal)

Six electrophysiologically active aromatic compounds, viz., anisole, benzaldehyde, veratrole, guaiacol, phenylacetonitrile, and phenol, were identified in the volatiles of older-adult male desert locust. Young adults and females of all age groups produced none or only trace quantities of these compounds. Comparison of the aggregation responses of young and older adults to the crude, older-adult, volatile extract and different synthetic blends of the six compounds showed that the aggregation pheromone system of the adult gregarious locust consists of phenylacetonitrile, guaiacol, phenol, and benzaldehyde. Like the crude volatile extract of older males, neither the synthetic blend of the six compounds nor the adult pheromone blend evoked any significant aggregation responses from nymphs. These results confirm our previous report of sexual differentiation in the production of adult aggregation pheromone in the desert locust and of the evidence of two distinct aggregation pheromone systems in the two stages of the insect.     

由邻苯二酚合成愈创木酚的反应过程和动力学研究

在连续固定床反应器中,以复合的固体酸为催化剂,以邻苯二酚和甲醇为原料,在270～300℃下进行了气固催化合成愈创木酚的反应过程研究,通过对实验结果进行分析,给出了适宜的反应条件并关联出了与实验吻合的宏观动力学方程。     

CONTROL OF FERULIC ACID AND 4-VINYL GUAIACOL IN BREWING

Phenolic acids in beer are important because they can be decarboxylated to phenols, which usually impart off-flavours. An improved high performance liquid chromatographic system was used to monitor phenolic acids and phenols during the brewing process. Ferulic acid was the most significant phenolic acid found in beers prepared from malted barley. Extraction of ferulic acid from malt involved an enzymatic release mechanism with an optimum temperature about 45°C. Mashing-in at 65°C significantly decreased the release of free ferulic acid into the wort. Wort boiling produced 4-vinyl guaiacol by thermal decarboxylation, in amounts (0.3 mg/L) close to its taste threshold, from worts that contained high contents of free ferulic acid (> 6 mg/L). The capacity of yeasts to decarboxylate phenolic acids (Pof⁺ phenotype) was strong in wild strains of Saccharomyces and absent in all lager brewing yeast and most ale brewing yeasts. Some top-fermenting strains, especially those used in wheat beer production, possessed a weak decarboxylating activity (i.e. Pof^δ). During storage of beers there were appreciable temperature-dependent losses of 4-vinyl guaiacol. These results indicated that the production of 4-vinyl guaiacol is amenable to close technological control.