葡萄及葡萄酒中的有机酸及降酸研究

为了探索降低葡萄酒中过量有机酸的有效方法,综述了葡萄和葡萄酒中有机酸的形成及变化,较系统地论述了国内外葡萄酒降酸研究的进展,着重介绍了本研究室以粟酒裂殖酵母与葡萄酒酵母为亲株,采用原生质体融合技术进行生物降酸的研究。     

DIETARY FATTY ACIDS AND AMINO ACIDS OF CAMELINA SATIVA SEED

Abstract Camelina sativa ( L. ) Crantz is an ancient oilseed crop. Camelina seed can be used as a food ingredient and raw material for the production of oil. The by-product from the production of oil by pressing (oil cakes) was traditionally used as fodder ingredient.
Camelina seed samples for analyses were collected from geographically remote localities in Europe and in Scandinavia (6° W - 25° E, 48 - 61° N). The seed was analyzed for the content of oil, fatty acids, total nitrogen and amino acids.
The mean content of oil in the seed was 43.3 ± 0.22%/DM. The predominating acid, α-linolenic (18:3 n-3), was 37.8 ± 0.17%; and others were oleic acid (18:1 n-6) 13.4 ± 0.13%; linoleic acid (18:2 n-6) 14.8 ± 0.12%; gondoic acid (20: 1 n-9) 15.4 ± 0.16% and erucic acid (22: 1 n-9) was 2.76 ± 0.07%/total FA.
Crude protein was 42.5 ± 0.46%/fat free DM. Considerable amounts of essential amino acids were present, such as arginine 8.15 ± 0.06%; glycine 5.44 ± 0.04%; isoleucine 3.96 ± 0.02%; leucine 6.63 ± 0.04%; lysine 4.95 ± 0.04%; phenylalanine 4.19 ± 0.04%; proline 5.09 ± 0.03%; threonine 4.25 ± 0.03% and valine 5.42 ± 0.04%. The methionine content was 1.72 ± 0.04% and cystine, 2.12 ± 0.05% (A.A. g/16 g N).     

PHENOLIC ACIDS IN BEERS AND WORTS

The total contents of phenolic acids measured by high-performance liquid-chromatography were 5–8 mg/litre in beers brewed in Ireland whereas 16–40 mg/litre were present in four other beers. In all beers the predominant phenolic acids were vanillic, p-coumaric and ferulic acids. Free phenolic acids were extracted from Emma barley grains and malt in very small amounts (15–28 mg/kg) but larger quantities (191 mg/kg) were released on mashing the malt. Little change occurred in the contents of phenolic acids on processing a lager wort through to the finished beer. Treatment with excess Polyclar AT removed astringent flavour and phenolic acids from an experimental ale but this flavour loss could not be accounted for by the adsorption of phenolic acids. The flavour threshold for a nine-component phenolic acid mixture in lager was between 50 mg/litre and 100 mg/litre.     

ORGANIC ACIDS AND GLYCEROL IN BEER

The concentrations of pyruvic acid, citric acid, L-malic acid, acetic acid, L-lactic acid and glycerol were determined in beers of different type and origin. Large differences in organic acid and glycerol contents were found, especially between different types of beer. The amounts of acetic acid, lactic acid and glycerol can be used as process parameters. During malting a decrease of the malic acid-citric acid ratio occurred due to the pathway of the TCA-cycle. The acetic acid content and glycerol contents showed increases during fermentation. The latter parameter is useful to indicate if alcohol-free beer has been produced by fermentation. Determination of apparent final attenuation degrees of worts according to the usual laboratory practice resulted in higher glycerol contents than was found for the corresponding beers, making the value of this assay questionable.     

DETERMINATION OF INDIVIDUAL ALPHA ACIDS AND BETA ACIDS OF HOPS BY GAS CHROMATOGRAPHY

A new method is described for determining α acids and β acids of hops by gas chromatography. The method consists of splitting off the side chains of the lower fatty acids (isobutyric, 2-methylbutyric and isovaleric acids) by oxidation with hydrogen peroxide in an alkaline medium. The corresponding fatty acids are disengaging from their salts by passage through an ion exchanger and they are then esterified in isopropyl alcohol. The esters are shaken out into ether and, after distillation, determined by gas chromatography.     

DIETARY FATTY ACIDS, TOCOTRIENOLS AND CANCER

High-fat diets may increase the risk of cancer at sites such as the breast, colon, pancreas and prostate, although the evidence is somewhat mixed. The type of fat can affect its influence on cancer in experimental animals, but in humans on diets of mixed foodstuffs the quantity rather than the quality of fat is likely to be more important. Dietary fat may influence carcinogenesis by altering energy balance and in mammary cancer the effects may be mediated by the mammary adipose tissue. A variety of minor dietary components have been reported to possess anti-cancer activity. Among these compounds, tocotrienols and flavonoids have been shown in our laboratory to inhibit proliferation of human breast cancer cells in culture, and to act synergistically with each other and with tamoxifen in the inhibition of these cells. This suggests that such combinations may be useful for prevention and/or treatment of breast cancer.     

PREPARATION,PURIFICATION AND SEPARATION BY HIGH PERFORMANCE LIQUID CHROMATOGRAPHY OF HUMULINIC ACIDS,DEHYDROHUMULINIC ACIDS,AND HULUPONES

Modification of published procedures are described for the preparation of humulinic acids, dehydrohumulinic acids and hulupone, using iso-α-acids as starting material. These procedures provide facile routes for preparation of these compounds in higher yields than was hitherto reported, and also in sufficient purity for their use as standards in quantitative High Performance Liquid Chromatography. An alternative and more feasible route to hulupones, using β-acids as starting material, is also outlined.     

FREE AMINO ACIDS AND DIPEPTIDES IN DRY-CURED HAM

Six types of dry-cured hams were chemically profiled for proximate composition and low molecular weight nonprotein nitrogen (NPN) fractions including free amino acids (FAA) and two dipeptides (carnosine and anserine). Results indicate that FAA were present in the six classes at different (mg/100g protein) concentrations, with Iberian and Serrano containing greater (P<0.05) amounts of most FAA. However, when analyzed as percentage (mg/100g total FAAs) values, FAA contents of Iberian and Serrano hams exhibited lower (P<0.05) tyrosine and greater (P<0.05) aspartic acid and threonine values. Within each class, large variation coefficients (>10%) for nonprotein nitrogen paralleled inconsistent values of salt content, to which NPN and FAAs were negatively correlated (P<0.01). NPN was also negatively affected by moisture in the dried muscle, indicating limited saltiness and greater muscle shrinkage as two major determinants in developing of nonprotein fractions, hence of free amino acids.     

FATTY ACIDS IN ISOMERIZED HOP EXTRACTS AND GUSHING

A procedure is described for the analysis of fatty acids (C₁₂-C₁₈ individually and C₁₈₊ as a group) in hops, hop extracts and isomerized hop extracts, and analytical results are quoted for twenty-one different samples of hops or hop products. Isomerized extracts varied widely in their content of fatty acids and isomerization and processing of hops appeared to eliminate some fatty acids selectively so that isomerized extracts were enriched in palmitic acid, linoleic acid and linolenic acid. Some hop extracts had a surprisingly high content of lauric acid. The analytical results are discussed in relation to gushing.     

LONG CHAIN FATTY ACIDS IN HEALTH AND NUTRITION

The typical western diet which is low in long chain omega-3 fatty acids and high in long chain omega-6 fatty acids may not supply the appropriate balance for optimal metabolism. The imbalance is believed to cause a variety of disease symptoms ranging from cardiovascular disease, hypertension, inflammatory and auto-immune disorders, depression and disrupted neurological functions. In the area of cardiovascular disease new research on arrhythmias is exciting and shows that application of omega-3 fatty acids can produce rapid results. In addition omega-3 fatty acids are showing benefits in preventing restenosis following angioplasty in approximately half of the reported studies. Significant research in infant nutrition indicates that long chain polyunsaturated fatty acids are "conditionally essential" for growth and development. Adequate intake of docosahexaenoic acid (DHA) and arachidonic acid (AA) is critical during pregnancy, lactation and infancy for proper development of the fetus and infant. Premature babies are particularly at risk for inadequacies. Thus, many specialist groups are recommending that infant formulas include long chain fatty acids at levels matching breast milk. Recommendations by many academic and governmental bodies propose that daily intakes on long chain omega-3 fatty acids be increased as a step in reducing certain chronic diseases.     

SENSORY AND CHEMICAL EFFECTS OFTOMATO JUICE ACIDIFIED WITH MALIC AND CITRIC ACIDS

Salted and unsalted tomato juice acidified with malic and citric acids were examined by sensory panel. For salted juice, panelists differentiated nonacidified from citrate acidified juice during the entire storage period. After 180 days of storage, panelists could not distinguish between nonacidified and malate acidified, salted juices. For unsalted juice, panel members could not distinguish between nonacidified juice and malate or citrate acidified juice. Malic acid increased the perception of saltiness in tomato juice. The pH of all juices decreased initially. After storage, the pH of nonacidified juice returned to initial raw juice levels, but the pH of the acidified juices maintained lower values.     

PREPARATION OF TRANS-ISO-ALPHA ACIDS AND USE OF THEIR DICYCLOHEXYLAMINE SALTS AS A STANDARD FOR ISO-ALPHA ACIDS ANALYSIS

The reaction between dicyclohexylamine and iso-alpha acids yields a crystalline product which consists of the dicyclohexylamine salts of trans-iso-cohumulone, trans-isohumulone and trans-iso-adhumulone. The presence of only the trans-isomers in the crystalline product was established by proton and carbon NMR. Pure trans-iso-alpha acids can be regenerated from the salt either by treatment with acid or in situ by the use of acidic buffers during HPLC analysis. The dicyclohexylamine salts of the trans-iso-alpha acids are stable for extended periods at room temperature, unlike the purified trans-iso-alpha acids, and are thus suitable for use as a standard for iso-alpha acids analysis.