A Narrative Review of the Current Knowledge on Fruit Active Aroma Using Gas Chromatography-Olfactometry (GC-O) Analysis

Fruit aroma, a mixture of chemical compounds with odor, is a strong attractant derived from a complex mixture of different amounts and intensities (threshold) of chemical compounds found in fruits. The odor-producing compounds of fruit aroma are derived from carbohydrates, lipids, phenolic compounds, and mono- and sesquiterpenes, among others. The identification of compounds responsible for fruit aroma is usually conducted using gas chromatography coupled with olfactometry (GC-O). This technique separates the chemical compounds from the aroma of foods using a chromatographic column and divides the resultant outflow between the physical detector and a testing outlet (sniffing port). Trained judges describe the perceived odor in terms of the intensity of the odor zones perceived according to their training method. Moreover, the use of GC-O coupled with a mass detector (GC-MS-O) allows for the retrieval of chemical information such as identification and quantification of compounds, which can be correlated to sensory information. This review aimed to demonstrate the application of GC-MS-O in the identification of precursor compounds in fruit aroma, considering important factors for the application, main results, and most recent advances in this field.     

Changes in Phenols,Polysaccharides and Volatile Profiles of Noni (Morinda citrifolia L.) Juice during Fermentation

The change in phenols, polysaccharides and volatile profiles of noni juice from laboratory- and factory-scale fermentation was analyzed during a 63-day fermentation process. The phenol and polysaccharide contents and aroma characteristics clearly changed according to fermentation scale and time conditions. The flavonoid content in noni juice gradually increased with fermentation. Seventy-three volatile compounds were identified by solid-phase microextraction coupled with gas chromatography–mass spectrometry (SPME-GC-MS). Methyl hexanoate, 3-methyl-3-buten-1-ol, octanoic acid, hexanoic acid and 2-heptanone were found to be the main aroma components of fresh and fermented noni juice. A decrease in octanoic acid and hexanoic acid contents resulted in the less pungent aroma in noni juice from factory-scale fermentation. The results of principal component analysis of the electronic nose suggested that the difference in nitrogen oxide, alkanes, alcohols, and aromatic and sulfur compounds, contributed to the discrimination of noni juice from different fermentation times and scales.     

Flavonoid profiles of immature and mature fruit tissues of Citrus grandis Osbeck (Dangyuja) and overall contribution to the antioxidant effect

Citrus fruits are a valuable functional food and their peel is used in East Asian folk medicine. In this study, the polar components of the fruit tissues of Citrus grandis Osbeck were analyzed using high‐performance liquid chromatography–tandem mass spectrometry and compared with reported data. Among the 13 characterized compounds, eight flavonoids and one coumarin were identified for the first time in fruit tissues. The total amount of the identified components was the largest for the immature fruit peel, followed by mature fruit peel, mature fruit flesh, and immature fruit flesh. Naringin (2) and neohesperidin (3) were particularly rich in all samples. The antioxidant activity of the flavonoids extracted from fruit tissues increased in a dose‐dependent manner. The activity of the fruit peels was significantly higher than that of the fruit flesh. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterisation of free and glycosidically bound odourant compounds of Aragonez clonal musts by GC-O

To evaluate the potential aroma of Aragonez clonal red musts, several free and glycosidically bound odourant compounds were extracted. Then, the gas chromatography-olfactometry (GC-O) posterior intensity method was used to evaluate their odour intensity and the compounds were identified by gas chromatography-mass spectrometry (GC-MS). A group of eight sniffers evaluated free and bound fractions of Aragonez musts and perceived forty-three and twenty-two odourant peaks respectively. Furaneol (burnt sugar, candy-cotton) and vanillin (vanilla, sweet) were identified in both free and bound fractions of Aragonez musts, indicating their grape-derived origin. Principal component analysis (PCA) was applied to the posterior intensity method data and a relationship between the different odourant compound variables and the free fractions was established. Two principal components (PCs) were found which together explained 100% of the total variance. A large number of potentially important but yet unknown odourants was detected by the GC-O analysis.     

Characterization and comparison of volatile constituents of juice and peel from clementine, mandarin and their hybrids

The volatile compositions of juice and peel of clementine (Citrus reticulata x Citrus sinensis var. Commune), mandarin (Citrus reticulata Blanco var. Willow Leaf) and their hybrids were analyzed by headspace solid-phase extraction (HS-SPME) coupled with gas chromatography and either a flame ionization detector (FID) or a mass spectrometer (MS). The major compounds of the volatile fractions of clementine and mandarin were limonene and limonene/gamma-terpinene, respectively. The volatile compositions of juice and peel of the same fruit showed qualitative and quantitative differences. The data analysis established the existence of three main groups based on volatile compounds that correlated with sample genotypes (clementine and mandarin) and fruit samples (peel and juice).     

Chemical constituents and larvicidal activity of Hymenaea courbaril fruit peel

The chemical compositions of the essential oils from the peel of ripe and unripe fruits of Hymenaea courbaril L., obtained by hydrodistillation, were analyzed by GC and GC-MS. The main constituents of the essential oil from the peel of the ripe fruits were the sesquiterpenes alpha-copaene (11.1%), spathulenol (10.1%) and beta-selinene (8.2%), while germacrene-D (31.9%), beta-caryophyllene (27.1%) and bicyclogermacrene (6.5%) were the major compounds in the oil from unripe fruits. The essential oils were tested against Aedes aegypti larvae and showed LC50 values of 14.8 +/- 0.4 microg/mL and 28.4 +/- 0.3 microg/mL for the ripe and unripe fruit peel oils, respectively. From the peel of the ripe fruits, the diterpenes zanzibaric acid and isoozic acid were isolated, along with the sesquiterpene caryolane-1,9beta-diol. To the best of our knowledge, this is the first report of this sesquiterpene in the genus. The structures of all compounds isolated were identified on the basis of their spectral data (IR, MS, 1D- and 2D-NMR) and by comparison with literature spectral data.     

Chemical constituents of the essential oil from aerial parts and fruit of Anisosciadium orientale

The essential oils from aerial parts and fruits of Anisosciadium orientale DC. growing wild in Iran were obtained by hydrodistillation and analyzed by GC and GC/MS. Seventy-one compounds were identified in the fruit oil and fifteen in the oil from the aerial parts. The main oil components of the fruits and aerial parts were myristicin (33.5%-33.7%), alpha-terpinolene (22%-25.8%) and limonene (19.5%-19.7%). Some compounds, such as geranyl butyrate and germacrene-D, were only detected in the fruit oil.     

运用气相色谱检测数据定量评价加工果蔬汁的香气协调性变化

为了建立加工果蔬汁香气协调性变化程度的定量评价模式,运用数学方法归纳果蔬汁样品的气相色谱(GC)检测数据,以原果蔬汁为基准,计算经浓缩或其他加工处理后样品中含有的各挥发性组分的百分含量相对于原果蔬汁的整体变化值(即样品偏差值),用以定量描述果蔬汁处理前后香气组分的整体变化程度。当需要比较不同加工方法或工艺对果蔬汁香气协调性的影响时,可对其进行相同条件的GC检测获取数据并计算比较样品偏差值。用此方法将冷冻浓缩柠檬汁、真空蒸发浓缩柠檬汁与原汁进行了比较,结果显示冷冻浓缩柠檬汁不仅能够很好地保持柠檬汁香气成分的绝对含量,同时也很好地保持了天然柠檬汁原有的香气协调性。     

Comparison of volatile compound production in fruit body and in mycelium of Pleurotus ostreatus identified by submerged and solid-state cultures

Comparative analyses of the production of volatile compounds by Pleurotus ostreatus JMO.95 fruit body and its corresponding mycelium grown in liquid, on agar surface, and on solid support cultures were carried out by dynamic headspace concentration using gas chromatography/mass spectrometry and gas chromatography sniffing. The aroma produced by fruit body was owing essentially to the presence of octan-3-one and, to a lesser extent, to octan-3-ol. Other compounds, such as oct-1-en-3-ol, oct-1-en, 2-methylbutanol, and α-pinene were also present in low concentrations. Comparison of aromatic spectra of the fruit body with that of mycelia obtained under different culture conditions indicated that the main aromatic compounds present in the P. ostreatus fruit body and mycelium were produced in the same proportions on agar surface and on solid support culture, but not under submerged conditions.     

Contribution of non-volatile and aroma fractions to in-mouth sensory properties of red wines: Wine reconstitution strategies and sensory sorting task

This work explores to what extent the aroma or the non-volatile fractions of red wines are responsible for the overall flavor differences perceived in-mouth. For this purpose, 14 samples (4 commercial and 10 reconstituted wines), were sorted by a panel of 30 trained assessors according to their sensory in-mouth similarities. Reconstituted wines were prepared by adding the same volatile fraction (coming from a red wine) to the non-volatile fraction of 10 different red wines showing large differences in perceived astringency. Sorting was performed under three different conditions: (a) no aroma perception: nose-close condition (NA), (b) retronasal aroma perception only (RA), and (c) allowing retro- and involuntary orthonasal aroma perception (ROA). Similarity estimates were derived from the sorting and submitted to multidimensional scaling (MDS) followed by hierarchical cluster analysis (HCA). Results have clearly shown that, globally, aroma perception is not the major driver of the in-mouth sensory perception of red wine, which is undoubtedly primarily driven by the perception of astringency and by the chemical compounds causing it, particularly protein precipitable proanthocyanidins (PAs). However, aroma perception plays a significant role on the perception of sweetness and bitterness. The impact of aroma seems to be more important whenever astringency, total polyphenols and protein precipitable PAs levels are smaller. Results also indicate that when a red-black fruit odor nuance is clearly perceived in conditions in which orthonasal odor perception is allowed, a strong reduction in astringency takes place. Such red-black fruit odor nuance seems to be the result of a specific aroma release pattern as a consequence of the interaction between aroma compounds and the non-volatile matrix.     

The combination of gas chromatography-olfactometry and multidimensional gas chromatography for the characterisation of essential oils

A research area of great interest to the flavour industry is the analysis of odour active compounds in essential oils. In this paper, a methodology is presented for the identification of character-impact odorants in essential oil samples using (a) gas chromatography-olfactometry (GC-O); (b) comprehensive two-dimensional gas chromatography (GC x GC) combined to time-of-flight mass spectrometry (TOFMS) and (c) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The specific advantages and limitations of each technique are discussed. The advantage of combining these techniques in a strategy to identify character-impact odorants is demonstrated using examples from coriander leaf (Coriandrum sativum) and hop (Humulus lupulus) essential oils. In particular, resolution of co-eluting regions of compounds and evaluation of their individual odour activity is discussed. In coriander leaf, only E-2-dodecenal was found to contribute to a co-eluting odour region, E-2-dodecen-1-ol and 1-dodecanol being present below detection threshold. Using MDGC on a hop essential oil sample, eight significant peaks were resolved from an 18 s heart-cut where a potent odorant was perceived during GC-O.     

固相微萃取-气相色谱-质谱联用结合嗅觉检测法鉴定血橙汁中的香气活性化合物

采用固相微萃取-气相色谱-质谱法(SPME-GC-MS)和嗅觉检测法对血橙汁中的挥发性物质进行分析,确定了血橙汁中的香气活性化合物。采用二乙烯基苯/碳分子筛/聚二甲基硅氧烷共聚物(DVB/CAR/PDMS)萃取头在40 ℃条件下顶空萃取40 min。通过气相色谱-质谱联用结合保留指数,在所萃取的血橙汁的挥发性化合物中共鉴定出46种化合物。通过嗅觉检测法检测出34种具有气味的化合物,其中23种被定性。结果表明,对血橙汁香气起主要贡献的化合物是丁酸乙酯、辛醛、γ-松油烯、芳樟醇、4-乙酰基-1-甲基环己烯、癸醛、(-)-香芹酮、乙酸香叶酯、巴伦西亚桔烯以及保留指数分别为1020,1143,1169和小于800的4个未知化合物,这些香气强度较高的化合物的总相对含量为7.22%。     

Sensory quality, volatile compounds and color of pear juice treated with β-cyclodextrin

The effect of the addition of β-cyclodextrin (β-CD), the most used of natural CDs, on the pear juice quality was studied. Several properties of this fruit juice, such as color, odor and aroma have been evaluated in both the absence and presence of β-CD for the first time. A study of the aroma profile of pear juice showed that esters, aldehydes, alcohols and terpenes are the most important chemical families of volatile compounds present in this fruit juice. Furthermore, a trained sensory panel was used to quantify odor/aroma attributes of pear juices in both the presence and absence of increasing β-CD concentrations. The addition of β-CD at a concentration of 15 mM to pear juice significantly increased its global quality, color intensity and reduced its browning but without any significant decrease in aroma. For this reason, a concentration of 15 mM of this type of natural CD is recommended to be used in pear juice manufacturing.     

蒸馏-萃取法与溶剂萃取法提取杏果实香气成分的比较

采用水蒸气蒸馏一萃取法和溶剂萃取法提取杏果香成分,用气相色谱一质谱联用测定其化学成分和质量分数,并对两种提取方法进行了比较。水蒸气蒸馏一萃取法提取的杏果香成分是74种,占总峰面积的73．604％;溶剂萃取法提取的杏果香成分是32种,占总峰面积的44．677％,两者相同的成分有21种。溶剂萃取法提取的主要是烷烃类化合物,水蒸气蒸馏萃取法提取的主要化合物为G醛类、C6醇类、内酯类、萜烯醇类、酮类、烷烃类等。结果表明：水蒸气蒸馏-萃取法能较好地提取杏果实香气成分。     

Screening of key odorants and anthocyanin compounds of cv. Okuzgozu (Vitis vinifera L.) red wines with a free run and pressed pomace using GC‐MS‐Olfactometry and LC‐MS‐MS

The principal purpose of the present work is to characterize the aroma, aroma‐active, and anthocyanin profiles of Okuzgozu wines and to observe the effect of the pomace pressing technique on these parameters. A total of 58 and 59 volatile compounds were identified and quantified in free‐run juice wine (FRW) and pressed pomace wine (PW). Alcohols were found as the most dominant group among aroma compounds followed by esters and acids. However, among all these compounds, only 11 and 13 of them could be considered as key odorants in aromatic extracts of FRW and PW, respectively. According to GC‐MS‐O analysis, ethyl octanoate (fruity), phenyl ethyl acetate (fruity), and 2‐phenyl ethanol (flowery) were found as the main contributors to the overall scent of both wines. Beyond the aroma profiles, anthocyanin contents of both types of wines were also investigated, and total 14 and 15 anthocyanins were identified and quantified in FRW and PW. Malvidin‐3‐glycoside and its acetyl and coumaroyl forms were identified as the dominant anthocyanins in both wines. It is worth noting the pressing application (2.0 atm) led to an increase of some unpleasant notes in the aroma providing chemical, pharmacy, and fermented aromas in wine. On the other hand, the wines produced with pressed pomace presented higher amounts of anthocyanins.     

Antifungal activity of the essential oil of Illicium verum fruit and its main component trans-anethole

In order to identify natural products for plant disease control, the essential oil of star anise (Illicium verum Hook. f.) fruit was investigated for its antifungal activity on plant pathogenic fungi. The fruit essential oil obtained by hydro-distillation was analyzed for its chemical composition by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). trans-Anethole (89.5%), 2-(1-cyclopentenyl)-furan (0.9%) and cis-anethole (0.7%) were found to be the main components among 22 identified compounds, which accounted for 94.6% of the total oil. The antifungal activity of the oil and its main component trans-anethole against plant pathogenic fungi were determined. Both the essential oil and trans-anethole exhibited strong inhibitory effect against all test fungi indicating that most of the observed antifungal properties was due to the presence of trans-anethole in the oil, which could be developed as natural fungicides for plant disease control in fruit and vegetable preservation.     

Limonene concentration in lemon (Citrus volkameriana) peel oil as a function of ripeness

The dependence of the limonene content of lemon (Citrus volkameriana) peel oil on the degree of ripeness of the fruit has been studied by using steam distillation and cold pressing to extract the oils from lemon fruit peel at different stages of maturation (green, greenish-yellow, and yellow-orange peel coloration). Samples of essential oils were analyzed by high resolution GC and GC-MS, using tetradecane as internal standard for quantitation. Forty components were detected; thirty eight were positively identified by comparison of their mass spectra (El, 70 eV) and Kováts retention indexes (determined using a non-logarithmic scale on capillary columns coated with both polar (DB-Wax) and non-polar (DB-1) stationary phases) with those of standards and with data reported in the literature. The limonene concentration reached a maximum level of 79.4% when the fruit was in the intermediate maturation stage characterized by greenish-yellow coloration.     

Characterization of Aroma Compounds in Cooked Sorghum Using Comprehensive Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry and Gas Chromatography-Olfactometry-Mass Spectrometry

Sorghum is the major raw material for the production of Chinese Baijiu (Chinese liquor) and has a great effect on the flavor of Baijiu. Volatiles in cooked glutinous and non-glutinous sorghum samples were extracted using solid-phase microextraction (SPME) and analyzed via comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS) and gas chromatography-olfactometry/mass spectrometry (GC-O/MS). A total of 145 volatile compounds and 52 potent odorant compounds were identified from both sorghum types according to the retention index, MS, aroma, and standards. Based on their aroma features, the compounds were grouped into eight general categories, and the intensities of each aroma group were summed. Moreover, most of the compounds detected in the cooked sorghums were also detected in commercial Chinese Baijiu, indicating that the aroma compounds produced during the sorghum cooking process have a direct and significant influence on the final flavor quality of Baijiu.