Differential hydrolysis of alk(en)yl cysteine sulphoxides by alliinase in onion macerates: flavour implications

Intact cells of Allium spp have no odour, but when cells are disrupted, the enzyme alliinase (EC 4.4.1.4) hydrolyses the S-alk(en)yl sulphoxides (ACSOs) to produce pyruvate, ammonia and the many volatile sulphur compounds associated with flavour and odour. In onions, there are three main sulphoxides: methyl, propyl and 1-propenyl, which gives rise to onion's tear-producing effect. The relative proportions of these are a factor in determining the subsequent flavour. γ-Glutamyl peptides, which are biosynthetic intermediates to ACSOs, are also present in significant amounts, but their contribution to flavour is not known. There is little work on the reaction of alliinase in vivo. The hydrolysis of ACSOs by alliinase was studied in rapidly macerated bulbs at intervals between 5 s and 2 h. ACSO and γ-glutamyl peptide levels were measured by HPLC, and pyruvate levels were measured spectrophotometrically. Although the hydrolysis of propenyl cysteine sulphoxide (PrenCSO) was immediate and almost 100% between 5 and 20 s after bulb maceration, the hydrolysis of propyl cysteine sulphoxide (PCSO) and methyl cysteine sulphoxide (MCSO) was incomplete. After 5 s maceration, about 50% PCSO and MCSO remained and thereafter no further hydrolysis occurred. The levels of ACSOs and the extent to which they were hydrolysed were dependent on the cultivar and sulphur environment in which it was grown. The addition of pyridoxal phosphate cofactor enhanced the extent of MCSO and PCSO hydrolysis. Additional purified alliinase per se had no effect. Substantial hydrolysis of γ-glutamyl peptides also occurred after maceration, and this was unexpected. Levels of pyruvate product were between 15 and 25% of the expected amount from ACSO hydrolysis assuming a stoichiometric relationship. The incomplete hydrolysis of MCSO and PCSO, enhancement of activity by additional pyridoxal phosphate and non-stoichiometric production of pyruvate are evidenced that reaction inhibition of alliinase may be occurring in onion macerates. © 1998 Society of Chemical Industry.     

Changes in onion (Allium cepa L.) flavour components resulting from some post-harvest processes

The effect of the following processes on the flavour of the product as compared with that of fresh onion has been investigated: pickling, canning, boiling and frying under domestic conditions, dehydration in hot air and by freeze-drying and freezing. Flavour assessments were based on determination of pyruvate, thiolsulphinate and volatile components in headspace, gas-liquid chromatograms as well as sensory testing in certain cases. All the methods of flavour assessment led to the conclusion that these processes were accompanied by large flavour losses. Quantitative estimates of the losses, varied with the analytical method in question, but were in general of the order of 90 to 95%. Freeze-drying gave a product which retained more of the characteristic flavour components of fresh onion, as judged by sensory tests, than the other processes and in this case the taste threshold test indicated a flavour loss of 95%, pyruvate (P_E) a loss of 25%, thiolsulphinate 26% loss and gas-liquid chromatography a loss of total peak area of 57%. Evidence that onions are consumed mainly for their flavour rather than as a source of nutrients in the classical nutritional sense is discussed and other factors which influence the flavour strength of the vegetable are reviewed.     

EFFECT OF SULFUR SUPPLY ON ALLIINASE, THE FLAVOR GENERATING ENZYME IN ONIONS

The characteristic flavor of onions occurs when the enzyme alliinase (EC 4.4 1.4) hydrolyzes S‐alk(en)yl‐L‐cystene sulfoxides (ACSOs) to form sulfur‐containing volatiles, pyruvate and ammonia. Two onion cultivars, Pukekohe Longkeeper and Grano, were grown to maturity at a high (4.0 meq S/L) and low (0.25 meq S/L) sulfur supply and assayed for alliinase specific activity and enzymatically produced pyruvate. Alliinase specific activity was greater (1.3–1.7 fold) at low sulfur supply in bulbs of both cultivars. Levels of enzymatically produced pyruvate were lower at low sulfur supply. Low sulfur supply has been previously shown to decrease levels of ACSOs and their biosynthetic intermediates but increase levels of proteins involved in sulfate uptake and mobilization. Alliinase may have an endogenous role in remobilizing ACSOs during conditions of sulfur deprivation.     

Effect of sulphate nutrition on flavour components of onion (Allium cepa)

It is known that the volatile components of raw and cooked onions contain mono-, di- and tri-sulphides and other flavour-contributing sulphur compounds. The relationship between the sulphate nutrition of spring (salad) onion (Allium cepa) and its flavour strength determined by sensory, biochemical and chromatographic methods has been investigated. The plants were grown in sand culture in a glasshouse and the nutrient solutions contained five levels of sulphate from zero to an adequate amount. In their growth response, total sulphur content and visual symptoms, the plants showed characteristic essential nutrient deficiency. The sensory tests, and instrumental and biochemical assays showed that flavour strength increased approximately in proportion to sulphate concentration in the medium; lachrymatory potency also increased. There were significant coefficients of correlation between sulphate concentration of the nutrient medium and some aspects of flavour strength. The correlation coefficients between total sulphur content (% of the edible portion) and total peak area, n-propyl disulphide peak area and total pyruvate were also high. These observations suggest the possibility of control of onion flavour strength and lachrymatory potency, under field conditions, by control of sulphate nutrition. The question of loss of maximum potential onion flavour as a consequence of sulphur deficiency in soils is discussed. A headspace method for sampling onion flavour volatiles and for their introduction into gas chromatographs is described.     

UHT杀菌对绿茶饮料风味的影响研究

研究了UHT杀菌对绿茶饮料风味的影响，通过绿茶饮料在UHT杀菌前、后香气成分的定性．定量分析，说明UHT杀菌在杀死绿茶饮料中的有害及腐败微生物时．不仅可以极大程度地保留产品中的营养成分和风味成分，同时还增加了绿茶饮料的甜香成分．     

Ammonium nitrate fertility levels influence flavour development in hydroponically grown ‘Granex 33’ onion

High levels of nitrogen (N) fertility have been shown to influence bulb flavour characteristics in onion (Allium cepa L). To test the effects of lower levels of N fertility on onion bulb flavour, ‘Granex 33’ onions were grown hydroponically in a greenhouse with varying solution N levels. Eleven levels were tested by increasing the concentration of NH₄NO₃ in solutions from 20 to 140 mg l^?1 N. Mature plants were harvested and evaluated for plant leaf and bulb fresh weights (FWs), bulb soluble solids content (SSC), bulb total pyruvic acid, bulb total sulphur (S), and bulb sulphate (SO₄^2?). To determine the effect of N on the flavour biosynthetic pathway of onion, total and individual S‐alk(en)yl cysteine sulphoxides and related peptide intermediates were also tested. Leaf and bulb FWs responded quadratically to N concentration, as did total bulb S. Bulb SO₄^2? and SSC, though significantly influenced by N concentration, did not respond with a meaningful trend. Bulb pyruvic acid increased linearly with N level increases, as did (+)‐S‐propyl‐L ‐cysteine sulphoxide. Total precursors, (+)‐S‐methyl‐L ‐cysteine sulphoxide, and trans‐(+)‐S‐1‐propenyl‐L ‐cysteine sulphoxide responded quadratically to N levels. At lower N levels, trans‐(+)‐S‐1‐propenyl‐L ‐cysteine sulphoxide content was highest relative to the other precursors. However, at elevated N levels, (+)‐S‐methyl‐L ‐cysteine sulphoxide accumulated in the highest concentrations. Peptide intermediates 2‐carboxypropyl glutathione and γ‐glutamyl propenyl cysteine sulphoxide responded linearly and quadratically respectively to increasing N fertility levels. Nitrogen fertility levels can influence flavour intensity and quality and should be considered when growing onions for flavour attributes. Copyright © 2003 Society of Chemical Industry     

Investigations on the conversion of onion aroma precursors S‐alk(en)yl‐L‐cysteine sulphoxides in onion juice production

Onion flavour develops when the cells are disrupted, allowing the enzyme alliinase (EC 4.4.1.4) to act upon the aroma precursors S‐alk(en)yl‐L ‐cysteine sulphoxides (ACSOs). For maximum flavour release, optimal cell disintegration and complete enzymatic conversion of ACSOs are desired. To assess an industrial scale onion juice extraction in regard to the extent of cell disintegration and the rate of enzymatic ACSO conversion, samples from all mass flows (ie onion, macerate, juice and pomace) were subjected to ACSO analysis. Applying a modified HPLC method, which allows baseline separation of the aroma precursors, three ACSOs, namely methyl‐, propyl‐ and 1‐propenyl‐L ‐cysteine sulphoxides (MCSO, PCSO and 1‐PeCSO), were determined. Initial ACSO ratios changed in the course of increasing degree of comminution from 17:83 to 100:0 (MCSO/1‐PeCSO). Only negligible amounts of PCSO were detected (<9.2 nmol g^?1 fresh weight (fw)), contributing less than 0.2% to the total ACSO content. For evaluation of the disintegration efficiency a chart was established consisting of an abscissa representing a percentage scale of ruptured cells and ordinates for the development of the marker parameters ACSOs and reaction product pyruvate relative to their initial contents. From this correlation a cell disintegration percentage after grinding of about 70% was deduced according to the determined ACSO contents. On a molar basis, macerate, juice and pomace showed 15, 0.6–2.4 and 0.7–1.0% of initial ACSO contents respectively. Only trace amounts of 1‐PeCSO were found in the juice (<16 nmol g^?1 fw). MCSO was converted to almost 90%, indicating that enzymatic transformation, in a practical sense, goes to completion. Copyright © 2004 Society of Chemical Industry     

Distribution of flavour components in onion (Allium cepa L.), leek (Allium porrum) and garlic (Allium sativum)

Dry bulb onions and leeks, at the marketable stage of development, were dissected into nine and ten fractions respectively, comprising the stem and leaves in succession from the oldest outer layers. Each fraction was separately analysed for flavour components by determination of thiosulphinate and pyruvate. Similarly, garlic cloves were divided into five fractions. There was a consistent pattern of flavour distribution in the seven onion varieties studied. The dried outer scales were virtually free from flavour components, the concentrations of which (on a fresh weight basis) increased progressively from a minimum value in the outer leaf to the innermost tissue and the stem. The latter often contained more than twice the concentration present in the outer leaf. The pattern in the roots and edible portions of leek differed in detail from that in onion. Flavour intensity increased progressively from the outer leaf to the inner tissues and the concentrations in both the roots and the stem were approximately equivalent to that of the fourth leaf numbered from the outer leaf. The pattern of flavour distribution in garlic cloves was simpler than that of onion and leek. The storage leaf accounted for the bulk of the weight of the clove as well as its flavour content. Some aspects of knowledge of the metabolism of inorganic nitrogen and sulphur compounds in roots and other tissues and transport of the corresponding metabolites have been briefly reviewed as the basis of a preliminary interpretation of the above observations. Attention has been drawn to the bearing of the results on preparation of onion for cooking and processing and on sampling for analysis.     

Influence of soil type and storage conditions on sensory qualities of fresh‐cut cantaloupe (Cucumis melo)

On‐farm cantaloupe (Cucumis melo) production as well as fresh‐cut storage duration can affect postharvest fruit sensory attributes. Both effects of soil type during production of cantaloupe fruits and storage temperature after fresh‐cut processing on sensory flavour and texture attributes were determined. Melons grown in sandy loam vs heavy clay soil were lower in sweet aromatic and sweet taste and higher in moisture release and fermented flavour. Fruity/melon, sweet aromatic, surface wetness, hardness and moisture release attributes decreased while fermented and sour flavour increased during storage regardless of soil type. During storage an increase in peroxidase activity occurred in fruits produced in sandy loam soil but decreased in fruits produced in clay soil. Clay soil appeared to have some advantages over sandy loam soil in producing cantaloupe fruits with better sensory quality attributes. Storage temperature conditions in this experiment (4 °C for 10 days or 4 °C for 4 days plus 10 °C for 6 days) did not have a statistically significant effect on these sensory attributes. Copyright © 2004 Society of Chemical Industry     

不同水煮时间对单环刺汤汁调味基料营养和呈味成分的影响

采用不同时间对单环刺螠进行水煮处理,测定处理后单环刺螠汤汁调味基料中的各种营养和呈味成分的变化,评价最佳水煮时间。实验结果表明:随着水煮时间0~3 h的延长,单环刺螠汤汁中可溶性蛋白含量先降低后升高;小于1000 u分子量组分和感官评分先升高后降低;鲜甜味游离氨基酸含量和有机酸含量逐渐升高;呈味核苷酸含量逐渐降低。单环刺螠汤汁调味基料获得更好风味的最佳水煮时间为0.5 h,获得更多可溶性蛋白和有机酸含量的水煮时间不低于3 h,此调味基料味道鲜美,营养丰富,可用于多种调味料开发。      

Sensory and chemical changes in five varieties of carrot (Daucus carota L) in response to mechanical stress at harvest and post‐harvest

Carrots harvested by hand or machine and given additional mechanical stress by shaking in a transport simulator were analysed for taste, flavour and content of sugars, terpenes, 6‐methoxymellein and ethanol as well as for ethylene production and respiration. Carrots stressed by shaking had higher ethylene production and respiration, higher content of ethanol and 6‐methoxymellein and lower levels of total terpenes, several individual terpenes and sugars. This corresponded to a higher sensory score for ethanol flavour and odour, bitter taste, earthy flavour, terpene flavour, aftertaste and sickeningly sweet taste and a lower score for acidic taste and sweet taste as measured by an expert taste panel. Ethanol content was highly correlated with ethanol flavour and odour and sickeningly sweet taste. Of five varieties tested, ‘Bolero’ ‘Panter’ and ‘Yukon’ were most sensitive to mechanical stress, whereas ‘Napa’ and ‘Newburg’ were most resistant. Hand‐harvested carrots were not significantly different from machine‐harvested carrots as regards chemical or sensory variables. Principal component analysis showed only slightly different placing of these samples in the score plot. A digital carrot could monitor the degree of mechanical stress to which the carrots were subjected. © 2001 Society of Chemical Industry     

Amount of characteristic compounds in 15 cultivars of onion (Allium cepa L.) in controlled field trials

BACKGROUND: In order to develop the production of sweet onions (Allium cepa L.) and onions with a high content of flavonols and fibre in Norway, it was necessary to evaluate available cultivars with respect to their content of selected chemical compounds. A field trial with 15 different cultivars was conducted at Landvik in southern Norway. Compounds that reflect onion pungency and sweetness (pyruvate, sugars) and parameters known to have a beneficial impact on health (fructo‐oligosaccharides (FOS), flavonols, antioxidant capacity) were analysed. RESULTS: The sweetest onions with respect to low content of pyruvate and high amount of fructose and glucose ranged in pyruvate content from 2.7 to 3.6 µmol mL^?1. These cultivars were juicy and contained low amounts of FOS and total flavonols. The most pungent onions contained the highest amounts of FOS among the cultivars: 4.53, 3.80 and 5.81 g per 100 g fresh weight (FW) respectively. They also had a high content of flavonols (86.6, 159.2 and 97.6 mg per 100 g FW) and high dry weight content (14.6, 13.5 and 15.6 g per 100 g). CONCLUSION: The sweetest onion cultivars were found to be ‘NUN 9746’, ‘Musica’, ‘Domenica Supersweet’, ‘Colossus’ and ‘Cronus’. The most pungent cultivars were ‘Powell Brown’ and ‘Tilbury’, which also contained the highest amounts of flavonols and gave the highest Trolox equivalent antioxidant capacity (TEAC) values among the 15 cultivars. Copyright © 2007 Society of Chemical Industry     

Influence of sulphate nutrition on the flavour components of garlic (Allium sativum) and wild onion (A. vineale)

Investigation of the relationship between the sulphate nutrition of garlic (Allium sativum) and wild onion(A. vineale) and their flavour strength is now reported. The plants were grown in a glasshouse in sand culture at two concentrations of sulphate in the nutrient medium and their flavour strength determined by sensory, biochemical and gas chromatographic methods. These observations have furnished further examples of environmental control of flavour components. The garlic plants in the two groups differed significantly in their fresh weights per plant. Their sulphur contents also showed that deficiency of this nutrient had been established in spite of the relatively large amount of sulphur introduced in the original cloves. The ratios of total sulphur content in the two groups of plants and of their flavour strengths as determined by total pyruvate values and taste threshold concentrations, respectively, were approximately constant (about 5). Total peak areas in the gas chromatograms increased with increasing (sensory) flavour strength. The garlic plants grown in sand culture were morphologically atypical, possibly because of the high moisture content of the growth medium, but their odour, taste and gas chromatograms were qualitatively indistinguishable from those of field-grown garlic which grew normally. Similar but more pronounced differences of flavour strengths were obtained with A. vineale and in this case the difference in flavour strengths between the deficient and normal plants was about 13-fold. The gas chromatograms of the deficient plants were almost completely lacking in the peaks which are characteristic of Allium sp. The discrepancies between initial and final sulphur contents of the deficient plants are discussed.     

Tetramethylpyrazine in Chinese sesame flavour liquor and changes during the production process

Tetramethylpyrazine (TTMP) is a key bioactive alkaloid and flavour compound found in Chinese sesame flavour liquor. Changes in TTMP concentration during the production of sesame flavour liquor have received little attention. Here, TTMP was tracked from raw material, fermented grains and fresh liquor in storage using high‐performance liquid chromatographic–tandem mass spectrometry (HPLC‐MS/MS). The results showed that TTMP was formed during stack fermentation, solid‐state fermentation and distillation, while no TTMP was produced during the storage process of fresh liquor. Furthermore, a higher temperature fermentation and bacterial starter culture were beneficial to TTMP generation. Accordingly, technology strategies for increasing the concentration of TTMP in sesame flavour liquor include raising the temperature of stack fermentation and distillation, reducing the distillation speed and screening for high TTMP producing Bacillus species. © 2018 The Institute of Brewing & Distilling     

Quantitative analysis of flavour precursors and pyruvate levels in different tissues and cultivars of onion (Allium cepa)

Onions of three different cultivars were dissected as in commercial peeling operations to give four tissue types: the dry, brown skin, the top/bottom sections, the outer fleshy leaf bases and the inner fleshy leaf bases. All tissue types were assayed for alliinase-produced pyruvate and for flavour precursors (alk(en)yl cysteine sulphoxides) and a positive correlation was observed between the levels of these classes of compounds. In all cultivars, the top and bottom onion sections have the highest levels of both pyruvate and flavour precursors with levels in the dry, brown skin being low or absent. Significant increases in levels of both pyruvate and flavour precursors were observed in inner tissues and top/bottom sections after storage under commercial conditions.     

Comparison of gas chromatographic volatile profiling methods for assessing the flavour quality of kenyan black teas

A comparison is made of the various ratios used to quantify black tea aroma such as: ratio of sum of gas chromatographic peak areas of compounds eluting before linalool (3,7-dimethyl-1,6-Octadien-3-ol) to those eluting after linalool (Wickremasinghe-Yamanishi ratio); gas chromatographic peak areas of compounds imparting sweet flowery aroma (Group II volatile flavour compounds) to those imparting green grassy aroma (Group I volatile flavour compounds), Owuor's flavour index; ratio of the sum of gas chromatographic peak area of the terpenoids to non-terpenoids, i.e. Mahanta ratio; and gas chromatographic peak area of linalool to E-2-hexena1, i.e. Yamanishi-Botheju ratio. The Wickremasinghe-Yamanishi ratio and Owuor's flavour index showed a significant relationship, the Mahanta ratio showed a significant but poor relationship, and the Yamanishi-Botheju ratio had no relationship with the tasters evaluation of Kenyan clonal CTC black teas. Similar results were obtained from orthodox black teas manufactured from different varieties.     

Estimation of volatile onion aroma and flavour compounds

Summary. The Chemical Oxygen Demand (COD) method was used for the evaluation of onion aroma components. the method was found to be reliable and to correlate well with odour threshold values for raw onions and with taste scores for dehydrated onion products. Odour threshold values could not be used for the latter products due to the development of undesirable off-odour after exposure to high temperature or prolonged storage.     

扇贝香味料的研究

扇贝香味料是以新鲜扇贝汁为原料精制而成的。本文探讨了控制扇贝香味料质量的方法,确定了最佳工艺路线。     

Beef broth flavour: study of flavour development

Of the range of preparation conditions studied here, the beef broths with the most favourable sensory characteristics (P ≤ 0.05) were those manufactured with minced meat in a 7.5 g l⁻¹ NaCl solution in proportions of 1:2 (w/v), heated at 85 °C for 60 min (the beef broth flavour was clean, clear, without any off‐flavour). Our data indicate the importance of accurately determining the heat treatment, since intermediate treatments yielded beef broths of good quality, whereas less intense treatments produced broths with raw meat and bloody and metallic flavours, and intensely heated broths had a warmed‐over or sour and astringent flavour. At higher temperatures the cooking time required to obtain a good‐quality broth decreased. From the analysis of variance of the sensorial data, temperature plays a more important role than cooking time in the development of the sensory properties of beef broths. © 2000 Society of Chemical Industry     

同时蒸馏萃取和固相微萃取与气相色谱-质谱法分析洋葱的挥发性风味成分

羊葱是百合科葱属的一种世界性的蔬菜,具有很高的营养价值和药用价值。洋葱的多种含硫化合物使其具有特殊的辛辣气味。本文采用传统的同时蒸馏装置和固相微萃取技术结合气相色谱-质谱分析了洋葱的挥发性风味成分。通过对固相微萃取的纤维头、萃取时间和解吸时间的选择来优化其实验条件。共鉴定出52种成分,其中硫醇类、硫醚类是洋葱挥发性风味成分的主要贡献物质。