不同品种啤酒花中α-酸的微波萃取最佳工艺条件对比

通过应用单因素和正交实验设计,对马可波罗和青岛大花中α-酸的微波萃取工艺进行了优化,并比较了两者最佳工艺条件的异同。马可波罗α-酸微波萃取的最佳工艺条件为微波时间20s、微波功率267W、浸泡时间30min、料液比1:25,影响因素的主次顺序为微波时间>微波功率>料液比>浸泡时间;青岛大花α-酸微波萃取的最佳工艺条件为微波时间15s、微波功率为267W、浸泡时间为30min、料液比为1:15,影响因素的主次顺序为微波时间>料液比>微波功率>浸泡时间。结果表明:两个品种的最佳萃取工艺条件中仅微波功率参数、浸泡时间参数相同,而微波功率、料液比的主次影响顺序不同。由此得出,不同品种啤酒花中α-酸的微波萃取最佳工艺条件不能混用,而关于啤酒花α-酸微波萃取工艺的研究,很有必要针对不同品种来进行。     

反相高效液相色谱法(RP-HPLC)测定异构颗粒酒花中的异α-酸

利用反相高效液相色谱法(RP-HPLC)研究异构颗粒酒花中异α-酸的测定方法.结果表明:当检测波长270nm、流动相为甲醇:水:磷酸(85%):EDTA(ethylene diamine tetra aeeticacid)二钠盐(0.2mol/L)(770:210:5:1)、流速为1.0ml/min时,方法的精密度为1.09%,外加标回收率91.4%～97.1%之间.RP-HPLC的色谱柱为EC 250/4 Nuclesoil,100-5 C18(4.0×250nm,5 μm),保护柱为CC 8/4 Nuclesoil 100-5 C18.该方法可以简便、准确地测定异构颗粒酒花中异α-酸含量.     

NON-IMPLICATION OF HOP α- AND β- ACIDS AS SOURCES OF SULPHUR COMPOUNDS IN BEER

Whereas hop oil terpenoids can give rise to organoleptically undesirable sulphur compounds in beer brewed using hops dressed on the bine with sulphur, the hop resin α- and β-acids and their transformation products appear incapable of reactions with sulphur under analogous conditions. The evidence indicates that the hop resins are not potential sources of sulphur compounds in beer     

THE APPLICATION OF SALT FORMATION IN THE CHEMISTRY AND TECHNOLOGY OF HOP RESINS

In natural product chemistry the satisfactory isolation of chemical compounds of scientific and/or commercial significance normally follows a pattern of fractionation which involves the utilization of a range of physical and chemical properties of the compounds present in the mixture. Vapour pressure and solubility are the physical properties traditionally made use of in the initial stages of fractionation. Chemical properties normally enable somewhat more specific fractionation to be achieved. One chemical property that is widely used is the ability of a large number of compounds to form salts. In the case of the hop resins it is this specific chemical property which has played the most significant role in their isolation, characterization and commercial utilization. The historical development of this aspect of hop chemistry has been reviewed.     

Positional distribution of Δ5-acids in triacylglycerols from conifer seeds as determined by partial chemical cleavage

The positional distribution of various Δ5-acids in the seed triacylglycerols from several conifer species has been established after partial chemical degradation with Grignard reagent. The species studied were representative of four conifer families and were specially selected for their particularly high Δ5-acid contents. These species were Taxus baccata (Taxaceae; 5,9-18:2 acid, 11.9%), Larix decidua (Pinaceae; 5,9,12-18:3 acid, 28.5%), Sciadopytis verticillata (Taxodiaceae; 5,11,14-20:3 acid, 16.7%), and Juniperus communis (Cupressaceae; 5,11,14,17-20:4 acid, 19.8%). Calculations from the fatty acid compositions of triacylglycerols and of the mixture of 1,2- and 2,3-diacylglycerols generated by the Grignard reagent indicated that, for the four species, there was a considerable enrichment of Δ5-acids (generally more than ten times) in the 1,3-positions as compared to the 2-position, where Δ5-acids represented always less than 2% of total fatty acids esterified to triacylglycerols. This distribution was practically independent from the species (four families studied), the chainlength (18 or 20 carbon atoms), and the number of ethylenic bonds (two to four) in the Δ5-acids. Similar distributions were established for triacylglycerols from the seeds of three pine species that are available on a ton-scale: Pinus pinea, P. koraiensis, and P. pinaster. These observations confirm and extend previous studies conducted with other conifer species by similar techniques or by ¹³C-nuclear magnetic resonance spectroscopy. Consequently, the almost exclusive location of Δ5-acids in the external positions of triacylglycerols is now well established and appears to be a general feature of conifer seed oils.     

STUDIES ON THE EFFECT OF POLLINATION ON THE YIELD AND RESIN CONTENT OF HOPS (HUMULUS LUPULUS L.)

Pollination trials in otherwise male-free hop gardens are described. The results showed that a reduction in cone yield of up to 30% may be expected from seedless hops, but an increase in α-acid content of the cones more or less compensates for this yield reduction and the yield of α-acid per acre can be almost as high from seedless as seeded hops. Northern Brewer, in particular, performed better than other varieties when grown seedless but most of the high α-acid varieties gave reasonable results. It is suggested that the variation in response may depend on the number of resin glands present on the seeds of the different varieties, and differences in the distribution of resin glands on other parts of the cone.     

KINETICS OF HOP STORAGE

After an initial ‘delay period’ the storage losses of α- and β-acids follow a first-order rate equation and not a zero-order equation as has been suggested by others.     

THE STORAGE OF YEOMAN HOPS AND PELLETISED POWDERS

Studies have shown that on extended storage of up to 90 weeks at ambient temperature pockets of Yeoman hops lose α-acids less rapidly than do the other varieties of English hops which are rich in resins. As expected the rate of loss of α-acids is further reduced when Yeoman hops are stored in the cold. Pelletised powders made from Yeoman hops show excellent storage characteristics when commercial packs are kept for 12 months either at ambient temperature or in the cold.     

ON THE SUNSTRUCK FLAVOUR OF BEER

It has been confirmed that sunstruck flavour is due to the formation of 3-methyl-2-butene-1-thiol formed by photolysis of iso-α-acids in the presence of sulphur-containing amino acids.