LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART I: EFFECT OF HOP DETERIORATION ON EXTRACTION EFFICIENCY AND EXTRACT QUALITY

Deteriorated hops were extracted with liquid carbon dioxide (LCO₂) and with ethanol. The degree of hop deterioration influences both the extraction efficiency and the composition of the resulting extracts.     

PRODUCTION-SCALE APPARATUS FOR THE INJECTION OF HOP EXTRACTS INTO BEER USING LIQUID CARBON DIOXIDE

Extracts of hops made with liquid carbon dioxide can be substituted for dry hops to introduce the flavour of hop oils into beer. Apparatus has been devised so that such extracts can be redissolved in liquid carbon dioxide and then metered into beer. Successful trials have been carried out on the commercial scale.     

PREPARATION OF HOP EXTRACTS WITHOUT USING ORGANIC SOLVENTS

Extraction of hops with liquid carbon dioxide at ambient temperature provides an attractive means of producing hop extracts which are rich in α-acids and free from hard resins, polyphenols, pigments and residual organic solvents. The resulting yellow extracts give beer with a clean bitter flavour when they are added during wort boiling. Manufacturing costs using the process are likely to be substantially less than in a conventional hop extraction plant.     

SOLUBILITY OF HOP α- AND β-ACIDS IN LIQUID CARBON DIOXIDE*: ADDENDUM: SOLUBILITY OF PESTICIDES IN LIQUID CARBON DIOXIDE

A procedure is described for determining the solubility of hop α- and β-acids in liquid carbon dioxide. Results have shown that the optimum temperature range for the extraction of hops with liquid carbon dioxide is +5 to +10°C. A number of pesticides used by hop growers are appreciably soluble in liquid carbon dioxide.     

USE OF EXTRACTS PREPARED WITH LIQUID CARBON DIOXIDE AS A SUBSTITUTE FOR DRY HOPS

Liquid carbon dioxide hop extracts were prepared for use as a substitute for dry hops. Many of these extracts were oil rich fractions containing up to 14% (w/w) hop oil. Extracts of Styrian Golding, Wye Target and Wye Northdown hops were used to treat ales prior to completion of beer processing and subsequent packaging. Emulsion/suspension systems were developed as carriers to facilitate addition of these extracts to beers before the chilling process. A loss of hop character from beer was found to occur during fining and filtration. Beers, treated with the extracts, exhibited natural though varietally distinct dry hop character. Production scale trials using these extracts have been successfully carried out to dry hop a brewery conditioned draught bitter and to match a traditionally dry hopped premium pale ale. The quantities of extract used indicated that economies in hop usage can be achieved when substituting liquid carbon dioxide hop extracts for dry hops.     

PROCESS ASPECTS OF THE EXTRACTION OF HOPS WITH LIQUID CARBON DIOXIDE

The time course of the extraction of α-acids by liquid carbon dioxide was investigated and it has been established that there are two zones with greatly differing rates of extraction. The rate in the first zone is governed by ‘solubility’ effects, while in the second zone the rate is limited by ‘diffusional’ effects. Consequently the rate of extraction in the first zone depends upon the flow rate of liquid carbon dioxide while that in the second zone depends upon the time of extraction. The effects on extraction performance of the depth of the bed of hops and the extent of milling were also explored.     

PILOT PLANT EXTRACTION OF HOPS WITH LIQUID CARBON DIOXIDE AND THE USE OF THESE EXTRACTS IN PILOT AND PRODUCTION SCALE BREWINGa

Several varieties of hop have been satisfactorily extracted using liquid carbon dioxide in a plant operating on the 1 kg scale. The extracts have been used in small scale (0·6 and 16 hl) and production scale (700–800 hl) brewing trials where both ales and lagers were produced. All beers were of sound quality and could not be distinguished organoleptically from controls brewed with either hops or commercial hop extracts.     

THE STABILITY OF HOP OILS IN LIQUID CARBON DIOXIDE EXTRACTS OF HOPS

Portions of extracts obtained by treating three varieties of hops with liquid carbon dioxide were stored in the cold and at ambient temperature for 18 months. During this period the composition of nop oils remained stable, except for the formation of two terpene methyl sulphides in extracts from all three varieties. Ales were ‘dry-hopped’ using portions of the stored extracts and, despite formation of the two sulphur compounds, the resulting hop character was satisfactory in all cases.     

PREPARATION OF HOP EXTRACTS RICH IN PARTICULAR CONSTITUENTS*

When a column containing powdered hops is extracted with liquid carbon dioxide, chromatographic separation of hop components occurs. They are extracted in the order essential oils, β-acids, α-acids; and the separation is enhanced when finely milled hops are extracted. Early fractions (～0·5 hour) contain a high proportion of the available essential oils when hops are extracted at ?20°C and such extracts are suitable as a replacement for dry hops. Fractions can be obtained from extractions at ～7°C which are rich in α-acids and contain low levels of β-acids. Small amounts of fats and waxes are normally present in fractions collected towards the end of a run when seeded hops are extracted.     

Supercritical carbon dioxide extraction and fractionation of oregano oleoresin

The leaves of Origanum vulgare L. (Lamiaceae) harvested in different countries, three samples from Hungary and one from Turkey, were extracted with carbon dioxide in a high pressure apparatus with a 5 l extractor vessel volume. Total extractions with stagewise precipitation of the extracts were carried out in order to obtain essential oil-rich liquid and pasty products. A fractionated extraction with a stepwise increase of the extraction pressure was also performed to obtain portions of extracts of different quality. The extraction with carbon dioxide was compared to conventional steam distillation and to Soxhlet extraction with hexane, whith the goal of recovering essential oils and oleoresin products, respectively.     

LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART III- EFFECT OF HOP DETERIORATION ON UTILISATION AND BEER QUALITY

The quality of beers bittered with liquid CO₂ and ethanol extracts derived from fresh and deteriorated hops and the percentage utilization of alpha-acids therefrom were comparable. The importance of using analytical methods which measure bitterness substances per se is emphasized.     

ADDITION OF HOP EXTRACTS TO BEER USING LIQUID CARBON DIOXIDE*

A method is described for imparting hop character to beer using extract prepared by treating hops with liquid carbon dioxide. The long contact times required for conventional dry-hopping techniques are avoided, and the use of liquid carbon dioxide as a medium for dispersal of the extract obviates problems due to residual organic solvent or emulsion stabilizers. Beers in which hop character was introduced in this way were found to be similar in flavour to control beers treated with portions of the same hop extract dissolved in ethanol.     

YIELD AND QUALITY OF ONION FLAVOR OIL OBTAINED BY SUPERCRITICAL FLUID EXTRACTION AND OTHER METHODS

Methods of extraction of onion flavor oil were studied including supercritical fluid extraction using carbon dioxide (CO₂), liquid CO₂ extraction and steam distillation-solvent extraction. The effect of using entrainers with supercritical fluid extraction was also studied. The yield and the quality of onion extracts obtained from the different methods were compared. The maximum yield of 0.0324% was obtained by supercritical CO₂ extraction at 3600psi (24.5 MPa), 37C at a CO₂ flow rate of 0.5 L/min. Ethyl alcohol used as entrainer enhanced the yield of onion oil over that obtained by supercritical CO₂ experiment without entrainer at the CO2flow rate of 1.0 L/min. Gas chromatography and combined gas chromatography-mass spectrometry of the extracts indicated that the flavor profiles were different for extracts obtained by different methods. Supercritical and liquid CO₂ extracts had fresh onion-like flavor as opposed to a cooked flavor of the extract obtained by steam distillation-solvent extraction.     

枇杷叶熊果酸超临界流体萃取工艺的研究

采用超临界CO2流体萃取技术萃取枇杷叶中的熊果酸,并用高效液相色谱法测定萃取物中熊果酸含量;通过L9(34)正交试验对萃取条件进行优化,确定适宜的工艺参数。结果表明,枇杷叶熊果酸超临界CO2萃取的各因素影响程度为A>D>C>B(A为萃取温度,B为萃取压力,C为携带剂的添加量,D为萃取时间),最佳参数:萃取温度30℃,萃取压力15MPa,携带剂的添加量50ml,萃取时间90min。在最佳组合条件下进行萃取,粗提物含熊果酸15.66mg,含量为7.83%。     

超临界CO2杀菌过程中萃取机制研究

在相同工艺条件下对大肠杆菌菌悬液作超临界CO2 处理,对不同时间段萃取液的成分进行分析。结果表明,萃取物主要有两大类：非极性脂肪酸类及极性较弱的小分子氨基酸类物质,均为细胞的功能性物质。证实在超临界CO2 杀菌过程中确实发生了萃取作用。     

SUPERCRITICAL CARBON DIOXIDE SELECTIVITY TO FRACTIONATE PHENOLIC COMPOUNDS FROM THE DRY ETHANOLIC EXTRACT OF PROPOLIS

The global yield and composition of extracts obtained by supercritical carbon dioxide (SC-CO₂) extraction from a dry ethanolic extract of propolis were measured in order to determine the possibility of using SC-CO₂ to fractionate components of interest present in these extracts. The global yield extraction was measured, and also the concentrations of the following phenolic compounds in the resulting supercritical fluid extracts (SFEs): 3,5-diprenyl-4-hydroxycinnamic acid (known as artepillin C), 3-prenyl-4-hydroxycinnamic acid, 4-hydroxycinnamic acid ( p- coumaric acid) and 4-methoxy-3,5,7-trihydroxyflavone (kaempferide), of which artepillin C was the target component of greatest interest. The results showed extraction yields between 3.82 (at 150 bar) and 13.07% (at 350 bar), which could be highly correlated with the density of the SC-CO₂ at a constant temperature of 60C. The resulting concentrations in the SFE indicated that the selectivity of the carbon dioxide could be manipulated, and it was more selective at lower pressures, although with lower extraction yields.

PRACTICAL APPLICATIONS

Supercritical fluid extraction is an interesting process for the production of natural extracts because it is a clean process, and extractions using carbon dioxide (CO₂) as the solvent have been gaining attention in recent years. This study presented important aspects with respect to the fractionation of a dry ethanolic extract of propolis using supercritical carbon dioxide, and it is important to explore the potential applications of propolis extracts and the biological properties of its fractions in the food, pharmaceutical and cosmetic industries, such as in dental hygiene products, wound healing creams and antibacterial soaps.     

Free radical-scavenging activity of Aloe vera (Aloe barbadensis Miller) extracts by supercritical carbon dioxide extraction

The free radical-scavenging activities of extracts of Aloe vera of leaf skin by supercritical CO₂ extraction and solvent extraction were determined. An orthogonal array design matrix of L₉ (3⁴) was considered to optimize supercritical carbon dioxide extraction processing at a CO₂ flow rate of 12–36 l h⁻¹, 35–45 MPa and 32–50 °C. The optimum extracted yield of 1.47% was provided at 50 °C 36 l h⁻¹, 35 MPa and 20% of modifier of methanol. These four factors were all demonstrated to be significantly crucial in the supercritical carbon dioxide extraction operation, as two-variable interactions. The extracts of A. vera rind by supercritical carbon dioxide extraction and solvent extracts provided significantly higher free radical-scavenging activities of 33.5% and 39.7%, respectively, than extracts of A. vera gel extracted by ethanol with a free radical-scavenging activity of 14.2%. The inhibition percentage of extracts of A. vera and reference antioxidants followed the decreasing order: Trolox (76.8%) > ethanol extracts of A. vera skin (39.7%) > BHT (35.9%) > the extract of supercritical carbon dioxide extraction (33.5%) >α-tocopherol (25.6%) > ethanol extracts of A. vera pulp (14.2%). Compared to BHT and α-tocopherol, the extracts of A. vera skin, by supercritical carbon dioxide extraction and ethanol, showed stronger antioxidant activities. Components in the rind of A. vera are responsible for the higher antioxidant activity of A. vera extracts.     

THE STORAGE OF PELLETED POWDERS MADE FROM WYE NORTHDOWN HOPS

Pelleted hop powder from seeded Wye Northdown hops of the 1976 crop shows small losses in lead conductance value (LCV) when stored in commercial packs for ca. 12 months after processing. The losses for hop pellets stored at ambient temperature are slightly more rapid than for those stored at 0 to 4°C. Losses in LCV of pellets during storage in the cold or at ambient temperature are substantially less than those of seeded Wye Northdown cone hops stored in pockets under comparable conditions. The hop pellets showed no significant loss in oil content or bittering potential over the storage period. Taste panels were unable to detect differences in flavour when comparisons were made of beers bittered with pellets stored in the cold and at ambient temperature.     

DETERMINATION OF HOP ALPHA-ACIDS BY SEMI-AUTOMATIC CONDUCTOMETRIC TITRATION

The conductometric method for determination of α-acids in hops consists of extraction of the hops with organic solvent, followed by conductometric titration of α-acids in the extract. A method is now described for semi-automatic conductometric titration of the extracts.     

High pressure extraction of vitamin E-rich oil from Silybum marianum

The efficiency of high pressure extraction in the production of oil with a high concentration of vitamin E, from seeds of Silybum marianum, was investigated. The solvents used in extraction were liquid or supercritical carbon dioxide and liquid propane. Operating parameters were 100, 200, 300 bar and 25, 40, 60 and 80°C for CO₂ and 60, 150, 200 bar and 40, 60 and 80°C for propane, respectively. The influence of process parameters on the total yield of extraction, vitamin E composition and acid value of the extracts was investigated. Results were compared with those obtained for conventional extraction with organic solvents (n-hexane, petroleum ether, dichloromethane, chloroform). The mathematical model based on the adsorption–desorption equilibrium of oil from solid tissue, the diffusion of oil to the surface and mass transfer through external film into the bulk, described the experimental extraction results well.