Identification of odour-active compounds in ewes' raw milk commercial cheeses with sensory defects

The aim of this work was to identify key odorant compounds associated with main off-flavours (acid, rancid and faecal) and one defect related to the internal appearance (big irregular eyes) in ewes' raw milk commercial cheeses. Cheese samples were submitted to solvent assisted flavour evaporation (SAFE) and odorant compounds were detected by gas chromatography–olfactometry (GC–O). Odour-active compounds detected by GC–O were identified and quantified by gas chromatography–mass spectrometry (GC–MS). Partial least square regression was performed to determine relationships between relative abundances of the odour-active compounds and sensory defects of commercial cheeses. An imbalance in the concentration of short-chain free fatty acids, predominant compounds in all cheese samples, was associated with acid and rancid off-flavour, whereas faecal off-flavour was related to minor compounds such as 4-methylphenol and 3-methyl-1-butanol. No volatile compound could be related to the defect of big irregular eyes.     

Enhancement of volatile aromatic compounds in black raspberry wines via enzymatic treatment

Robus coreanus Miquel is widely used in the production of Korean black raspberry (KBR) wine owing to its health benefits and commercial value. The effects of three different commercially available glycosidase enzymes on the volatile compounds in KBR wines were investigated with large‐scale fermentation to develop a high‐flavour‐quality wine. Volatile aroma compounds from the wines were analysed using headspace‐solid phase micro‐extraction‐gas chromatography–mass spectrometry (HS‐SPME‐GC–MS) and sensory evaluations were performed to evaluate the flavour characteristics. KBR wines treated with commercial enzymes yielded high concentrations of terpenes and esters compared with the control wine because the odourless non‐volatile glycosides in KBR wines were converted to their corresponding free forms by the enzymes. HS‐SPME‐GC–MS‐SIM analysis showed that the primary monoterpene compounds in KBR wines treated by the enzymes were myrtenol, linalool, citronellol and a significant quantity of compounds such as 2‐phenyl ethanol and ethyl benzoate, which contributed to the flavour of KBR wine, as determined by GC‐FID. KBR wines treated with the enzymes exhibited different sensory characteristics from the control wine owing to higher intensity of floral and fruity aromas. KBR wine treated with CYTOLASE PCL5 on a large scale exhibited the highest sensory preference. Copyright © 2017 The Institute of Brewing & Distilling     

The detection of α‐dicarbonyl compounds in wine by formation of quinoxaline derivatives

A method to determine the most abundant α‐dicarbonyl compounds in wine was developed by reaction with 2,3‐diaminobenzene. Products such as quinoxaline derivatives were detected by high‐performance liquid chromatography (HPLC) or by gas chromatography with a mass‐selective detector (GC–MS) or a thermoionic detector (GC–NPD). HPLC and detection with a spectrophotometer (313 nm) were used for routine quantitative analysis of wines. The method is sensitive, linear and has good repeatability. Diacetyl, pentane‐2,3‐dione, glyoxal and methylglyoxal were quantified in a single run; these compounds are always encountered in wines, but levels vary with different types of wine and also during fermentation and maturation processes. A new dicarbonyl compound, phenylglyoxal, was found in wine. The evolution of dicarbonyl compounds during fermentation is reported in this paper. © 2000 Society of Chemical Industry     

Analysis of food taints and off-flavours: a review

Taints and off-flavours in foods are a major concern to the food industry. Identification of the compound(s) causing a taint or off-flavour in food and accurate quantification are critical in assessing the potential safety risks of a product or ingredient. Even when the tainting compound(s) are not at a level that would cause a safety concern, taints and off-flavours can have a significant impact on the quality and consumers’ acceptability of products. The analysis of taints and off-flavour compounds presents an analytical challenge especially in an industrial laboratory environment because of the low levels, often complex matrices and potential for contamination from external laboratory sources. This review gives an outline of the origins of chemical taints and off-flavours and looks at the methods used for analysis and the merits and drawbacks of each technique. Extraction methods and instrumentation are covered along with possible future developments. Generic screening methods currently lack the sensitivity required to detect the low levels required for some tainting compounds and a more targeted approach is often required. This review highlights the need for a rapid but sensitive universal method of extraction for the unequivocal determination of tainting compounds in food.     

Insoluble Grape Material Present in Must Affects the Overall Fermentation Aroma of Dry White Wines Made from Three Grape Cultivars Cultivated in Greece

ABSTRACT: Musts from 3 grape varieties were used to elucidate the effect of the presence of grape solids in must on the volatile composition of the resultant white wines. Volatile compounds were analyzed by GC/MS and GC/FPD except H₂S, which was measured spectrophotometrically. Increasing quantities of grape insoluble material decreased the substances that enhanced aroma of Savatiano and Batiki wines. Simultaneously, the levels of compounds that degrade wine aroma, when formed in large amounts, were increased. However, in Muscat of Hamburg wines, the levels of some volatiles were not influenced by must turbidity in the same way as in wines of the other cultivars.     

Characterization of Volatile and Semi‐Volatile Compounds in Chinese Rice Wines by Headspace Solid Phase Microextraction Followed by Gas Chromatography‐Mass Spectrometry

The volatile and semi‐volatile compounds of Chinese rice wines were extracted by headspace solid phase microextraction (HS‐SPME) and analyzed by gas chromatography‐mass spectrum (GC‐MS). The original Chinese rice wine samples were diluted with deionized water to a final concentration of 6% (v/v) ethanol and then extracted by HS‐SPME. The samples were pre‐equilibrated at 50°C for 15 min and extracted with stirring at the same temperature for 45 min prior to injection into a GC‐MS. A total of 97 volatile and semi‐volatile compounds were identified from ten Chinese typical rice wine samples, including 13 alcohols, 8 acids, 28 esters, 4 aldehydes and ketones, 17 aromatic compounds, 3 lactones, 6 phenols, 3 sulphides, 9 furans and 6 nitrogen‐containing compounds, of which, 39 compounds were firstly reported in Chinese rice wine. By stepwise linear discrimination analysis, the ten Chinese rice wine samples could be classified into three groups according to the production area, and in particular, the production technologies.     

闪蒸品丽珠干红葡萄酒香气成分的GC/MS分析

采用溶剂萃取法提取闪蒸和传统品丽珠干红葡萄酒中的香气成分,经气相色谱-质谱联机分析,闪蒸干红酒鉴定出30种香气成分,包括16种酯、6种醇、3种萜烯类、4种酸和1种酮,传统干红酒鉴定出26种香气成分,包括14种酯、4种醇、4种萜烯类、2种酮、1种酸和1种醚.与传统品丽珠干红酒相比,闪蒸品丽珠干红酒酯类化合物相对含量提高29.43%,醇类化合物相对含量降低20.99%,葡萄酒香气更加浓郁、复杂、深沉.     

河西地区不同产地赤霞珠干红葡萄酒挥发性成分分析

以甘肃河西走廊产区5个不同产地葡萄园的赤霞珠葡萄为原料,分别发酵酿造干红葡萄酒,并对样品进行挥发性成分分析,共检测出107种物质,其中主要成分有58种,包括醇类物质19种,酯类物质18种、酸类物质5种、羰基类9种以及其他7种。对比不同产地赤霞珠干红酒发现其挥发性成分在种类和含量均有差异,并表现为各自特有的品质特性。     

Volatile composition of Bobal red wines subjected to alcoholic/malolactic fermentation with oak chips

The effect of wood, in the form of oak chips, on the volatile composition of Bobal red wines caused by adding oak chips at different stages of the fermentation process has been studied. Aroma compounds were isolated by solid phase extraction (SPE) for subsequent analysis by gas chromatography–mass spectrometry (GC/MS). Bobal control wine was produced according to traditional winemaking processes, without oak chips. Oak chips were added to the rest of the wines at two dose levels (3 and 6 g/L) at different stages of the winemaking process: at one week during alcoholic fermentation (AF), during malolactic fermentation (MLF) and in young, red Bobal wine. Wines fermented with oak chips during AF showed higher concentrations of the ethyl esters of straight-chain fatty acids and ethyl, hexyl and isoamyl acetates than the control wine. A similar, trend was observed for higher alcohols. Higher concentrations of benzene compounds, oak lactones and furanic compounds were found in wines in contact with oak chips during MLF followed by young Bobal oak wines. These results reveal that the point of addition during the winemaking process and the dose level of oak chips used have a significant effect on the volatile composition of Bobal red wines.     

Aroma characterization of red wines from cv. Bobal grape variety grown in La Mancha region

Bobal is an indigenous Spanish cultivar, principally grown in the region of Valencia. The volatile composition of young red wines made from the cv. Bobal grape variety grown in the La Mancha region of Spain has been studied over five vintages by instrumental analysis to determine the influence of grape variety on the aroma of wine. Free and glycosidically-bound aroma compounds were isolated by solid phase extraction (SPE) using dichloromethane and ethyl acetate respectively to later be analyzed using gas chromatography-mass spectrometry (GC/MS). One hundred and twelve (112) free aroma compounds and ninety-six (96) bound aroma compounds were identified and quantified in Bobal wines oven this five year period. Based on the result, Bobal wine presents a complex chemical profile with a wealth of aromas in its aromatic composition.     

Off-flavours in wines through indirect transfer of volatile organic compounds (VOCs) from coatings

This paper assesses the impact of volatile organic compounds (VOCs) from the drying of coatings on the sensory characters of corks and wines. According to Italian National Standard Method 11021:2002, a small-scale chamber was used (1) to expose wines to the drying of coatings with both low and high VOCs, and (2) to expose corks to the same coatings. After exposure to the coatings, the corks were then placed in direct contact with wine. Different styles of white, red and rosé wines were tested. In both directly exposed wines and in wines after contact with the exposed cork, the taste and smell off-flavour perception and intensity were assessed by a panel of eight experienced wine tasters using a five-point numerical scale according to International Organization for Standardization (ISO) standard methods. The results showed that the sensory characters of wines, especially taste, were influenced by the VOC content of the coatings. The taste off-flavour perception was found to be higher than the smell in wines exposed to coatings with either high or low VOCs contents. Analysis of variance (ANOVA) and Duncan analysis prove that: (1) panellist's answers were significantly different, (2) it was difficult to differentiate the off-flavour perception on the high-level scale, and (3) the panellist off-flavour perceptions versus wine style discriminated the wines into two groups (red and white/rosé). For all the wine styles, Pearson's test showed no significant correlation between off-flavour perception levels and the main chemical characters of the wines. For the wines that were in direct contact with the exposed corks, the panellists detect the off-flavours according to the levels of VOCs in the coating and wine styles and they assessed the highest levels of alteration were to the taste.     

Guaiacol and 4‐methylguaiacol accumulate in wines made from smoke‐affected fruit because of hydrolysis of their conjugates

Background and Aims: Taint in smoke‐exposed grapes have been associated with elevated levels of guaiacol and 4‐methylguaiacol. Previous research has reported guaiacol and 4‐methylguaiacol in both fruits and wines. In some cases, these compounds were not detected, or were detected at low levels in the fruit while high levels were subsequently identified during or after winemaking. Later research indicated that this was due to the presence of glycosidic conjugates. Here we report a method for the routine analysis of guaiacol and 4‐methylguaiacol released after acid hydrolysis of glycoside precursors. Methods and Results: Chardonnay, Merlot, Shiraz, Sangiovese and Cabernet Sauvignon fruits were collected following bushfire events in 2006–2007 in the King Valley wine region of NE Victoria, Australia. Gas chromatography‐mass spectrometry (GC‐MS) was used to detect free guaiacol and 4‐methylguaiacol in both fruits and wines. Low levels of free and bound forms were present in fruit not exposed to smoke. Substantial levels of free guaiacol and 4‐methylguaiacol were detected in the wines made from the smoke‐affected fruits. These compounds increased during bottle storage. Acid hydrolysis of wines and berries resulted in a several‐fold increase in free guaiacol and 4‐methylguaiacol. Conclusions: The validated GC‐MS method is suitable for monitoring free and glycosidically bound guaiacol and 4‐methylguaiacol after acid hydrolysis in both fruits and wines. Acid hydrolysis of wines provided evidence that bound volatiles, most probably glycosidically, act as reserve for guaiacol and 4‐methylguaiacol, which are released during ageing of wines. Significance of the Study: This is the first study published in a refereed journal to demonstrate that smoke taint‐associated volatiles increase during ageing of wine and bound forms of guaiacol and 4‐methylguaiacol represent an aroma reserve for smoke taint in ageing/bottled wines.     

Chemical tainting of foods

Taints and off-flavours in food are a major cause of consumer rejection of the food product, and consequently the occurrence of such flavour defects is of great concern also to the manufacturer. Unacceptable flavours in foods may develop within the food through chemical or microbial action on food components, or they may be inadvertently introduced into the food during processing or storage, by absorption of chemicals from airborne, waterborne or packaging-related sources. The chemicals responsible for taints and off-flavours are usually volatile organic compounds, which are frequently found at concentrations of less than 1 μg kg⁻¹, and cause flavour problems because of their low odour-threshold values. This paper discusses the possible origins of off-flavours and taints in foods, and describes some incidents in which food taints have been caused by chemical contamination from the environment.     

Polyphenolic content of Vranec wines produced by different vinification conditions

Macedonian Vranec wines were analysed by HPLC coupled with DAD and MS detections and by spectrophotometric methods. ESI-IT MS and MS–MS methods with alternating ionisation polarity were used for identification of the phenolic compounds. Both, nonflavonoids (stilbens, hydroxybenzoic and hydroxycinnamic acids and derivatives) and flavonoids (flavonols, flavan-3-ols and anthocyanins) were detected in the samples. Vranec wines were produced under different fermentation conditions: maceration time of 3, 6 and 10 days, two doses of SO₂ (30 and 70 mg l⁻¹) and two yeasts for fermentation, in order to examine their effects on the extraction of phenolic compounds from grapes into the wine.