Glycosidically bound volatiles as affected by ripening stages of Satsuma mandarin fruit

The effect of hot air treatment on volatile compounds in nectarine fruit and the regulation of glycosidically bound compounds by sugar

In order to investigate the impact of hot air (HA) treatment on the sugars and volatiles in postharvest nectarine fruit, nectarines were treated with HA at 40 °C for 4 h and stored at 1 °C for 35 days. Changes of sugars, free and glycosidically bound volatiles, β-glucosidase (β-Glu) activity, and the gene expression of UGT (UDP-glucosyltransferase) in nectarine fruit were determined. The results showed that compared with CK, HA treatment delayed the firmness decline of 48.01%, weight loss of 32.13%, internal browning index of 58.03%, and maintained the high commodity quality of nectarine fruit at the end of storage. HA could reduce the content of aldehydes and increase the content of esters. The bound linalool in HA increased by 171.41% compared with the CK. In addition, the results of in vitro experiments showed that glucose and sucrose systems could increase the content of free and bound linalool by up-regulating the expression of PpUGT85A2, promoted the accumulation of bound benzaldehyde and nonanal, and reduced the corresponding free volatile compounds, it showed that free aldehydes can be synthesized from soluble sugars into bound aldehydes.

Comparative Investigation of Aroma-Active Volatiles in ("Ruixue", "Liangzhi", "Crystal Fuji," and "Guifei") Apples by Application of Gas Chromatography-Mass Spectrometry-Olfactometry (GC-MS-O) and Two-Dimensional Gas Chromatography-Quadrupole Mass Spectrometry (GC × GC-qMS) Coupled with Sensory Molecular Science

Aroma dramatically impacts the overall flavor profiles and consumer acceptance; therefore, it is necessary to conduct a comprehensive analysis of the aroma characteristics of apples. In this study, the aroma differences among four popular apple varieties ("Ruixue", "Liangzhi", "Crystal Fuji," and "Guifei") were compared using two extraction methods (headspace-solid phase microextraction, and solvent-assisted flavor evaporation) coupled with gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-qMS). A total of 82 odorants were identified via GC-MS-O, and 143 volatiles were identified by GC× GC-qMS. Among them, 41 key aroma-active compounds (butanal, ethyl acetate, 3-methylbutanal, methyl butanoate, 2-methylpropyl acetate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, butyl acetate, hexanal, 2-methylbutyl acetate, 1-butanol, 2-methylpropyl butanoate, 3-methylbutyl acetate, (E)-2-hexenal, butyl butanoate, butyl 2-methylbutanoate, hexyl acetate, hexyl butanoate, hexyl, 2-methylbutanoate, 1-octen-3-ol, 3-methylthiopropanol, 1,3-octanediol, linalyl acetate, and so on) with high odor activity values (OAVs) and AI value (odor activity values ≥1 or aroma intensity ≥3) were identified. Partial least-squares-discriminant analysis showed that Ruixue exhibited a high "fruity" note, Guifei and Crystal Fuji had the greatest "wood," "floral," and "sweet" notes, while Liangzhi presented a significant "green" note. This study provided flavor chemistry support for the apple quality control and production.

Effects of juicing methods on the bioactive compounds and flavor quality of 'Black-seed' pomegranate from three producing areas

BACKGROUND

Color, nutrients and flavor are the key characteristics of pomegranate juice, but they are susceptible to processing methods and raw materials. In this study, the effects of aril juicing and whole fruit juicing methods on the composition of 'Black-seed' pomegranate juice from three producing areas were studied, including physicochemical parameters, color attributes, organic acids, sugars, phenolic compounds, and volatile compounds.

RESULTS

The whole fruit juicing method resulted in higher juice yields of pomegranate fruit with 69.01-72.59%, hue angle values were 5.95-6.45°, and the juice remained red. The highest level of citric acid (21.21 g L-1 ), total acids (24.78 g L-1 ), and total anthocyanin content (435.59 mg L-1 ) were found in whole fruit juice, and seven tannins were detected. The most abundant volatile compounds were (Z)-3-hexen-1-ol and 1-hexanol in all juice samples, with alcohol content increased and aldehydes content decreased by whole fruit juicing. Principal component analysis revealed that the 24 indexes (variable important in projection >1) clearly distinguished juice samples obtained by two juicing methods, with ellagic acid hexoside, (E)-2-heptenal, (+)-catechin, and octanoic acid having the best discriminatory potential.

CONCLUSION

Overall, the effects of juicing method on 'Black-seed' pomegranate juice were greater than those of raw-material-producing areas. These results confirmed the potential for using the whole 'Black-seed' pomegranate for processing, and also provided a theoretical basis for the healthy product development and utilization of dark-color pomegranate varieties. © 2023 Society of Chemical Industry.

Comprehensive in situ and ex situ β-glucosidase-assisted assessment reveals Indian mangoes as reservoirs of glycosidic aroma precursors

Mango, a valued commercial fruit in India is popular mostly because of its attractive flavour. Glycosidically bound volatiles (GBV), an underrepresented warehouse of aroma, remain completely unexplored in Indian mangoes. In this study, GBV were profiled in pulps and peels of 10 Indian mango cultivars, leading to detection of 66 GBV which were dominated by monoterpenoids and phenolics. Peels were quantitatively and qualitatively richer in GBV than pulps. Hierarchical clustering and principal component analysis indicated higher contribution of peel GBV to the distinctness of cultivars. Linalool, geraniol, and eugenol were the significant contributors based on the odour units. Direct β-glucosidase treatment to the juice resulted in the release of lesser number of volatiles than those released from the purified GBV extracts. Apart from providing a comprehensive catalogue of GBV in mangoes, our data suggests the need of critical assessment of the usefulness of β-glucosidases in aroma improvement of fruit juices.

Factors affecting aroma compounds in orange juice and their sensory perception: A review

Orange juice is the most widely consumed fruit juice globally because of its pleasant aromas and high nutritional value. Aromas, contributed by free and bound aroma compounds, are an important attribute and determine the quality of orange juice and consumer choices. Aldehydes, alcohols, esters, and terpenoids have been shown to play important roles in the aroma quality of orange juice. Many factors affect the aroma compounds in orange juice, such as genetic makeup, maturity, processing, matrix compounds, packaging, and storage. This paper reviews identified aroma compounds in free and bound form, the biosynthetic pathways of aroma-active compounds, and factors affecting aroma from a molecular perspective. This review also outlines the effect of variations in aroma on the sensory profile of orange juice and discusses the sensory perception pathways in human systems. Sensory perception of aromas is affected by aroma variations but also converges with taste perception. This review could provide critical information for further research on the aromas of orange juice and their manipulation during the development of products.

Citrus juice off-flavor during different processing and storage: Review of odorants, formation pathways, and analytical techniques

As the most widespread juice produced and consumed globally, citrus juice (mandarin juice, orange juice, and grapefruit juice) is appreciated for its attractive and distinct aroma. While the decrease of characteristic aroma-active compounds and the formation of off-flavor compounds are easy to occur in processing and storage conditions. This review provides a comprehensive literature of recent research and discovery on citrus juice off-flavor, primarily focusing on off-flavor compounds induced during processing and storage (i.e., thermal, storage, light, oxygen, package, fruit maturity, diseases, centrifugal pretreatment, and debittering process), formation pathways (i.e., terpene acid-catalyzed hydration, caramelization reaction, Maillard reaction, Strecker degradation, and other oxidative degradation) of the off-flavor compounds, effective inhibitor pathway to off-flavor (i.e., electrical treatments, high pressure processing, microwave processing, ultrasound processing, and chemical treatment), as well as odor assessment techniques based on molecular sensory science. The possible precursors (terpenes, sulfur-containing amino acids, carbohydrates, carotenoids, vitamins, and phenolic acids) of citrus juice off-flavor are listed and are also proposed. This review intends to unravel the regularities of aroma variations and even off-flavor formation of citrus juice during processing and storage. Future aroma analysis techniques will evolve toward a colorimetric sensor array for odor visualization to obtain a "marker" of off-flavor in citrus juice.

SPME-GC-MS combined with chemometrics to assess the impact of fermentation time on the components, flavor, and function of Laoxianghuang

Laoxianghuang, fermented from Citrus medica L. var. Sarcodactylis Swingle of the Rutaceae family, is a medicinal food. The volatiles of Laoxianghuang fermented in different years were obtained by solid-phase microextraction combined with gas chromatography–mass spectrometry (SPME-GC–MS). Meanwhile, the evolution of its component-flavor function during the fermentation process was explored in depth by combining chemometrics and performance analyses. To extract the volatile compounds from Laoxianghuang, the fiber coating, extraction time, and desorption temperature were optimized in terms of the number and area of peaks. A polydimethylsiloxane/divinylbenzene (PDMS/DVB) with a thickness of 65 μm fiber, extraction time of 30 min, and desorption temperature of 200 °C were shown to be the optimal conditions. There were 42, 44, 52, 53, 53, and 52 volatiles identified in the 3rd, 5th, 8th, 10th, 15th, and 20th years of fermentation of Laoxianghuang, respectively. The relative contents were 97.87%, 98.50%, 98.77%, 98.85%, 99.08%, and 98.36%, respectively. Terpenes (mainly limonene, γ-terpinene and cymene) displayed the highest relative content and were positively correlated with the year of fermentation, followed by alcohols (mainly α-terpineol, β-terpinenol, and γ-terpineol), ketones (mainly cyclohexanone, D(+)-carvone and β-ionone), aldehydes (2-furaldehyde, 5-methylfurfural, and 1-nonanal), phenols (thymol, chlorothymol, and eugenol), esters (bornyl formate, citronellyl acetate, and neryl acetate), and ethers (n-octyl ether and anethole). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a closer relationship between the composition of Laoxianghuang with similar fermentation years of the same gradient (3rd-5th, 8th-10th, and 15th-20th). Partial least squares discriminant analysis (PLS-DA) VIP scores and PCA-biplot showed that α-terpineol, γ-terpinene, cymene, and limonene were the differential candidate biomarkers. Flavor analysis revealed that Laoxianghuang exhibited wood odor from the 3rd to the 10th year of fermentation, while herb odor appeared in the 15th and the 20th year. This study analyzed the changing pattern of the flavor and function of Laoxianghuang through the evolution of the composition, which provided a theoretical basis for further research on subsequent fermentation.

Volatiles Accumulation during Young Pomelo (Citrus maxima (Burm.) Merr.) Fruits Development

As widely planted fruits with high nutritional and medical values, pomelos are managed systematically to achieve the largest economic benefits. But the annual shedding of young pomelos, which could be applied as feedstocks for essential oil extraction with their abundant volatiles, leads to a waste of source. The present study selected two commonly planted pomelo (Citrus maxima (Burm.) Merr.) varieties in Southern China, to investigate the volatile profiles during young pomelo fruits development. Combing transcriptomic analysis, this study aimed at identifying the prominent volatile components in young pomelo fruits in order to preferably extract profitable volatiles, as well, increasing the knowledge concerning regulatory roles of transcription factors (TFs) on volatiles accumulation in young pomelos. Totally 29 volatiles were identified, including 14 monoterpenoids and 13 sesquiterpenoids. Diprene was the principal component with the highest amount. Volatiles were generally decreased during fruits development but preferable stages were figured out for volatile collections. 12 and 17 TFs were related to developing time while ERF003 and MYC2 were highly correlated to monoterpenoids. These findings put forward the comprehensive usages of young pomelos and enriched the regulatory roles of TFs on both fruit development and volatiles metabolism.

Characterization of the Volatile Compounds in Camellia oleifera Seed Oil from Different Geographic Origins

Volatile flavor of edible oils is an important quality index and factor affecting consumer choice. The purpose of this investigation was to characterize virgin Camellia oleifera seed oil (VCO) samples from different locations in southern China in terms of their volatile compounds to show the classification of VCO with respect to geography. Different samples from 20 producing VCO regions were collected in 2020 growing season, at almost the same maturity stage, and processed under the same conditions. Headspace solid-phase microextraction (HS-SPME) with a gas chromatography–mass spectrometer system (GC–MS) was used to analyze volatile compounds. A total of 348 volatiles were characterized, including aldehydes, ketones, alcohols, acids, esters, alkenes, alkanes, furans, phenols, and benzene; the relative contents ranged from 7.80–58.68%, 1.73–12.52%, 2.91–37.07%, 2.73–46.50%, 0.99–12.01%, 0.40–14.95%, 0.00–27.23%, 0.00–3.75%, 0.00–7.34%, and 0.00–1.55%, respectively. The VCO geographical origins with the largest number of volatile compounds was Xixiangtang of Guangxi (L17), and the least was Beireng of Hainan (L19). A total of 23 common and 98 unique volatile compounds were detected that reflected the basic and characteristic flavor of VCO, respectively. After PCA, heatmap and PLS-DA analysis, Longchuan of Guangdong (L8), Qingshanhu of Jiangxi (L16), and Panlong of Yunnan (L20) were in one group where the annual average temperatures are relatively low, where annual rainfalls are also low. Guangning of Guangdong (L6), Yunan of Guangdong (L7), Xingning of Guangdong (L9), Tianhe of Guangdong (L10), Xuwen of Guangdong (L11), and Xiuying of Hainan (L18) were in another group where the annual average temperatures are relatively high, and the altitudes are low. Hence, volatile compound distributions confirmed the differences among the VCO samples from these geographical areas, and the provenance difference evaluation can be carried out by flavor.

MicroRNAs and Transcripts Associated with an Early Ripening Mutant of Pomelo (Citrus grandis Osbeck)

'Liuyuezaoyou' is an early-ripening cultivar selected from a bud mutation of Citrus grandis Osbeck 'Guanximiyou'. They were designated here as MT and WT, respectively. The fruit of MT matures about 45 days earlier than WT, which was accompanied by significant changes in key phytohormones, sugar compounds and organic acids. Recent studies have showed that microRNAs (miRNAs) play an important role in regulation of fruit ripening process. The aim of this study was to compare MT fruits with WT ones to uncover if miRNAs were implicated in the ripening of C. grandis. Fruits of both WT and MT at four developmental stages were analyzed using high-throughput sequencing and RT-PCR. Several independent miRNA libraries were constructed and sequenced. A total of 747 known miRNAs were identified and 99 novel miRNAs were predicted across all libraries. The novel miRNAs were found to have hairpin structures and possess star sequences. These results showed that transcriptome and miRNAs are substantially involved in a complex and comprehensive network in regulation of fruit ripening of this species. Further analysis of the network model revealed intricate interactions of miRNAs with mRNAs during the fleshy fruit ripening process. Several identified miRNAs have potential targets. These include auxin-responsive protein IAA9, sucrose synthase 3, V-type proton ATPase, NCED1 (ABA biosynthesis) and PL1/5 (pectate lyase genes), as well as NAC100 putative coordinated regulation networks, whose interactions with respective miRNAs may contribute significantly to fruit ripening of C. grandis.

Elucidation of Endogenous Aroma Compounds in Tamarillo (Solanum betaceum) Using a Molecular Sensory Approach

Glycosidically bound volatiles (GBVs) are flavorless compounds in fruits and may undergo hydrolysis during fruit maturation, storage, and processing, releasing free aglycones that are odor active. However, the contribution of glycosidic aglycones to the sensory attributes of fruits remains unclear. Herein, the key odor-active aglycones in tamarillo fruits were elucidated through the molecular sensory approach. We extracted GBVs from three cultivars of tamarillo fruits using solid-phase extraction and subsequently prepared aglycone isolates by enzymatic hydrolysis of GBVs. Gas chromatography-mass spectrometry-olfactometry (GC-MS-O) coupled with odor activity value (OAV) calculation, comparative aroma extract dilution analysis (cAEDA), and omission tests were used to identify key aromatic aglycones. A total of 42 odorants were determined by GC-MS-O analysis. Among them, trans-2,cis-6-nonadienal, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF), linalool, 4-vinylguaiacol, geraniol, and α-terpineol showed high OAVs. The cultivar Amber had more aglycones with flavor dilution (FD) factors >16 than the Mulligan cultivar (27 vs 21, respectively), and the Laird's Large fruit showed the highest FD of 1024 for glycosidic DMHF. Omission tests indicated 14 aglycones as essential odorants related to GBVs in tamarillo fruits. Moreover, the enzymatic liberation of aglycones affected the sensory attributes of the tamarillo juice, resulting in an intensified odor profile with noticeable fruity and sweet notes. This study gives insights into the role of endogenous aroma during tamarillo-flavor perception, which lays the groundwork for developing tamarillo-based products with improved sensory properties.

Stage- and Rearing-Dependent Metabolomics Profiling of Ophiocordyceps sinensis and Its Pipeline Products

Cordyceps, a parasitic complex of the fungus Ophiocordyceps sinensis (Berk.) (Hypocreales: Ophiocordycipitaceae) and the ghost moth Thitarodes (Lepidoptera: Hepialidae), is a historical ethnopharmacological commodity in China. Recently, artificial cultivation of Chinese cordyceps has been established to supplement the dwindling natural resources. However, much is unknown between the natural and cultivated products in terms of nutritional aspect, which may provide essential information for quality evaluation. The current study aims to determine the metabolic profiles of 17 treatments from 3 sample groups including O. sinensis fungus, Thitarodes insect and cordyceps complex, using Gas Chromatography - Quadrupole Time-of-Flight Mass Spectrometry. A total of 98 metabolites were detected, with 90 of them varying in concentrations among groups. The tested groups could be separated, except that fungal fruiting body was clustered into the same group as Chinese cordyceps. The main distinguishing factors for the groups studied were the 24 metabolites involved in numerous different metabolic pathways. In conclusion, metabolomics of O. sinensis and its related products were determined mainly by the fruiting bodies other than culture methods. Our results suggest that artificially cultured fruiting bodies and cordyceps may share indistinguishable metabolic functions as the natural ones.

Postharvest UV-C Irradiation Influenced Cellular Structure, Jasmonic Acid Accumulation, and Resistance Against Green Mold Decay in Satsuma Mandarin Fruit (Citrus unshiu)

Green mold caused by Penicillium digitatum is an important factor limiting the shelf life of mandarin fruit. In this study, the effect of ultraviolet-C (UV-C) irradiation on cellular structure, endogenous jasmonic acid (JA), and development of P. digitatum in satsuma mandarin fruit was investigated. UV-C treatments included 0 (untreated control), 3, and 10 kJ m−2 or the exposure time of 0, 1.18, and 4.52 min, respectively. The UV-C dose of 10 kJ m−2 significantly reduced the development of P. digitatum both in vitro and in vivo, resulting in the maintenance of the cellular structure of the albedo tissue. The production of malondialdehyde (MDA) was decreased upon UV-C treatment of 10 kJ m−2. The concentration of JA increased in the treatment of 10 kJ m−2 compared to the treatment of 3 kJ m−2 and the control. UV-C irradiation increased total phenolic and total flavonoid concentrations and DPPH radical scavenging capacity. These results suggest that UV-C at 10 kJ m−2 has a potential to control green mold caused by P. digitatum, maintain cellular structure, stimulate the accumulation of JA, and induce biochemical compounds in satsuma mandarin.

Characterization of key aroma compounds and enantiomer distribution in Longjing tea

By comparing the enantiomers of authentic Longjing tea, the authenticity of Longjing tea can be effectively distinguished. In this study, 18 enantiomers were identified using a chiral column. At the same time, the unique enantiomer ratio (ER) of Longjing tea (LG1, LG2, LG3, LG4, LG5) of different grades and origins was determined. The ER can provide a theoretical basis for distinguishing Longjing tea of different grades and origins, and for identifying the authenticity of Longjing tea. The ER ratio of (R)-(-)-1-octen-3-ol and (S)-(+)-1-octen-3-ol can be used to identify LG1 (71:29). The ER ratio of (S)-(+)-α-ionone and (R)-(-)-α-ionone can be used to identify LG2 (65:35). The ER ratio of (R)-(-)-dihydroactinidiolide to (S)-(+)-dihydroactinidiolide (71:29) can also be used to detect LG3. The ER ratio of (R)-(+)-Limonene and (S)-(-)-limonene can be used to identify LG4 (20:80). The ER ratio of (R)-(-)-linalool to (S)-(+)-linalool (12:83) was available to identify LG5.

Free and Glycosidic Volatiles in Tamarillo (Solanum betaceum Cav. syn. Cyphomandra betacea Sendt.) Juices Prepared from Three Cultivars Grown in New Zealand

This study investigated the free and glycosidic-bound volatiles in the juice samples of three tamarillo cultivars (i.e. Amber, Mulligan, and Laird's Large) that are widely grown in New Zealand. Juice samples were prepared from fruits at different ripening stages (green, middle, and ripe). Headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was applied to analyze the free volatiles in the samples. A total of 20 free volatiles were detected. Among the samples, the ripe Mulligan juice gave the highest contents of free terpenoids (424 μg/L) and esters (691 μg/L). The glycosidic-bound volatiles were prepared by solid-phase extraction. The matrix effect was evaluated based on the recovery rate of analytes containing multiple aglycone classes. From the results, phenyl β-d-glucopyranoside was selected to compensate the matrix effect caused by insufficient acquisition of glycosidic volatiles during analyte preparation. In all the ripe-fruit juice samples, the aglycones 4-hydroxy-2,5-dimethyl-3(2H)-furanone and trans-2, cis-6-nonadienal were found to give high odor activity values. According to multivariate statistical analysis, 11 free volatiles and 22 glycosidic volatiles could be potentially applied as volatile makers to distinguish the juice samples. This study has provided a comprehensive understanding of the flavor chemistry of tamarillo juices, with a focus on the potential role of glycosidic aglycones as aroma contributors to tamarillo products.

Development of volatile organic compounds and their glycosylated precursors in tamarillo (Solanum betaceum Cav.) during fruit ripening: A prediction of biochemical pathway

Key metabolites and flavour-regulation pathways in tamarillo were investigated to explore the development of free and glycosylated volatile organic compounds (VOCs) during fruit maturation. The concentrations of free and bound VOCs were determined by gas chromatography-mass spectrometry analysis. Changes of physical parameters, concentrations of flavour precursors, and activities of key endogenous enzymes were also monitored. A total of 22 free VOCs were identified with C6 alcohols and esters being the major compounds. From the 83 glycosylated VOCs detected, phenols and terpenoids were the dominant components. The concentration of total bound VOCs increased up to 4 times during fruit ripening. Lipoxygenase pathway is confirmed as an important biosynthetic mechanism for the generation of free and glycosylated VOCs during tamarillo ripening. This biosynthesis pathway is highly correlated with the activities of key enzymes and the contents of substrates, especially linolenic acid (p < 0.05 or p < 0.01).

Glycosidically bound aroma precursors in fruits: A comprehensive review

Fruit aroma is mainly contributed by free and glycosidically bound aroma compounds, in which glycosidically bound form can be converted into free form during storage and processing, thereby enhancing the overall aroma property. In recent years, the bound aroma precursors have been widely used as flavor additives in the food industry to enhance, balance and recover the flavor of products. This review summarizes the fruit-derived aroma glycosides in different aspects including chemical structures, enzymatic hydrolysis, biosynthesis and occurrence. Aroma glycosides structurally involve an aroma compound (aglycone) and a sugar moiety (glycone). They can be hydrolyzed to release free volatiles by endo- and/or exo-glucosidase, while their biosynthesis refers to glycosylation process using glycosyltransferases (GTs). So far, aroma glycosides have been found and studied in multiple fruits such as grapes, mangoes, lychees and so on. Additionally, their importance in flavor perception, their utilization in food flavor enhancement and other industrial applications are also discussed. Aroma glycosides can enhance flavor perception via hydrolyzation by β-glucosidase in human saliva. Moreover, they are able to impart product flavor by controlling the liberation of active volatiles in industrial applications. This review provides fundamental information for the future investigation on the fruit-derived aroma glycosides.

Free and Bound Aroma Compounds of Turnjujube (Hovenia acerba Lindl.) during Low Temperature Storage

Free and bound aroma volatiles from turnjujube during low temperature storage were extracted by headspace solid-phase microextraction. They were then characterized and identified using gas chromatography–mass spectrometry. Turnjujube was harvested and stored for 7, 14, and 21 days at 7 °C, the common temperature of display refrigerators in grocery stores. The results showed that 41 free and 24 bound aroma compounds were detected for the first time in turnjujube in both freshly harvested and stored turnjujube. The free and bound aroma compounds of turnjujube were markedly influenced by the storage time. The major free aroma compounds in turnjujube included esters, alcohols, aliphatic aldehydes, and aliphatic ketones. The major bound aroma compounds included borneol, eugenol, and isoeugenol, which contributed to sweet, floral, and herbaceous aroma after their hydrolysis. Freshly harvested turnjujube mostly had a fruity and herbaceous aroma, which diminished after storage at 7 °C. In contrast, the fatty aroma enhanced gradually over storage, and the floral aroma enhanced noticeably after storage for seven days. Foul odor was not detected even after storage at 7 °C for 21 days. The formation mechanisms of some aroma compounds were proposed.

Nanomaterial Gas Sensors for Online Monitoring System of Fruit Jams

Jams are appreciated worldwide and have become a growing market, due to the greater attention paid by consumers for healthy food. The selected products for this study represent a segment of the European market that addresses natural products without added sucrose or with a low content of natural sugars. This study aims to identify volatile organic compounds (VOCs) that characterize three flavors of fruit and five recipes using gas chromatography-mass spectrometry (GC-MS) and solid-phase micro-extraction (SPME) analysis. Furthermore, an innovative device, a small sensor system (S3), based on gas sensors with nanomaterials has been used; it may be particularly advantageous in the production line. Results obtained with linear discriminant analysis (LDA) show that S3 can distinguish among the different recipes thanks to the differences in the VOCs that are present in the specimens, as evidenced by the GC-MS analysis. Finally, this study highlights how the thermal processes for obtaining the jam do not alter the natural properties of the fruit.

Comparative metabolites profiling of harvested papaya (Carica papaya L.) peel in response to chilling stress

BACKGROUND

Papaya, as one of the most important tropical fruits in the world, is easily subjected to chilling injury (CI). Research on the effect of chilling temperature storage on the metabolic changes of papaya peel is limited.

RESULTS

Chilling temperature (4 °C) inhibited fruit ripening and induced CI on papaya fruit. Additionally, low temperature altered the concentrations of 45 primary metabolites and 52 aroma volatile compounds in the papaya peel. Papaya fruit stored at different temperatures could be separated using partial least squares-discriminant analysis (PLS-DA) with primary metabolites and volatile compounds as variables. In total, 18 primary metabolites and 22 volatiles with variable importance in projection (VIP) score higher than one might be considered as potential markers in papaya peel in response to chilling stress. Metabolites related to aroma, such as organic acid, amino acids, hexanal, carbonic acid, pentadecyl propyl ester and methyl geranate, caryophyllene accounted for major part of the metabolism changes of papaya peel and contributed a lot in response to cold stress.

CONCLUSION

This study added new insights regarding effect of chilling stress on metabolites in papaya peel. Some important metabolites might be indicator for chilling stress and detection of these metabolites will guide us to regulate the storage temperature to avoid chilling and to prolong storage of papaya fruit. © 2019 Society of Chemical Industry.

Integration of Metabolite Profiling and Transcriptome Analysis Reveals Genes Related to Volatile Terpenoid Metabolism in Finger Citron (C. medica var. sarcodactylis)

Finger citron (Citrus medica var. sarcodactylis) is a popular ornamental tree and an important source of essential oils rich in terpenoids, but the mechanisms behind volatile formation are poorly understood. We investigated gene expression changes combined with volatile profiling of ten samples from three developing organs: flower, leaf, and fruit. A total of 62 volatiles were identified with limonene and γ-terpinene being the most abundant ones. Six volatiles were identified using partial least squares discriminant analysis (PLS-DA) that could be used as markers for distinguishing finger citron from other citrus species. RNA-Seq revealed 1,611,966,118 high quality clean reads that were assembled into 32,579 unigenes. From these a total of 58 terpene synthase (TPS) gene family members were identified and the spatial and temporal distribution of their transcripts was measured in developing organs. Transcript levels of transcription factor genes AP2/ERF (251), bHLH (169), bZIP (76), MYB (155), NAC (184), and WRKY (66) during finger citron development were also analyzed. From extracted subnetworks of three modules constructed by weighted gene co-expression network analysis (WGCNA), thirteen TPS genes and fifteen transcription factors were suggested to be related to volatile terpenoid formation. These results provide a framework for future investigations into the identification and regulatory network of terpenoids in finger citron.

Free and bound volatile compounds in the Rubus coreanus fruits of different ripening stages

The aim of the present study was to investigate the free and bound volatiles in the Rubus coreanus (RC) fruits of different ripening stages. Thirty-seven free volatiles and 28 bound volatiles were identified in RC fruit for the first time. The contents of free (E)-2-hexen-1-ol, 1-hexanol, 2-heptanol, β-myrcene, (E), (Z)-β-ocimene, allo-ocimene, linalool, cosmene, α-terpineol, methyl salicylate, eugenol, and β-damascenone remain high, and increased with the ripening of RC fruit. The contents of 11 bound volatiles decreased during the ripening, and became lower than the contents of their free volatiles in the ripe fruit. The ripe black fruit is closely correlated to the free nonanal, sulcatone, (E)-2-hexen-1-ol, 1-hexanol, 2-heptanol, 1-heptanol, 1-nonanol, (E)-linalool oxide (furanoid), and β-damascenone, and bound (E)-2-hexen-1-ol and (E)- β-ocimene. The ripe RC fruit is more fruity and floral than unripe fruit. The gradually hydrolyzed bound volatiles can enhance the fruity, floral, and herbaceous odors. PRACTICAL APPLICATIONS: Rubus coreanus (RC) fruit is a functional natural fruit. Both fresh and processed Rubus coreanus fruits including jams, confitures, wine, yogurt, vinegar, and beverages, as well as ingredients in functional foods or cosmetics have been extensively consumed. However, the free and bound aroma compounds in RC fruit have not been well understood. This work illustrates the contributions of free and bound volatiles to the flavor of RC fruit.

Ethanol treatment improves the sensory quality of cherry tomatoes stored at room temperature

The effects of ethanol treatment on quality characteristics of cherry tomatoes were investigated over 11 days of storage at room temperature (25 °C). Results showed that sensory quality was improved after ethanol treatment, with redder, softer fruits at the edible stage (11 days) compared with control fruit. In addition, the contents of ascorbic acid, sucrose and fructose were elevated after ethanol treatment as well as the concentration of 6-methyl-5-hepten-2-one. Conversely, decreased levels of methyl salicylate (MeSA), guaiacol, (Z)-3-hexenal and (E)-2-hexenal were observed. Selected consumers showed a preference for ethanol-treated cherry tomato fruits compared with controls. Taken together, 0.1% ethanol application has the potential to improve the quality characteristics of cherry tomatoes stored at room temperature.

Changes of the free and bound volatile compounds in Rubus corchorifolius L. f. fruit during ripening

The changes of free and bound volatile compounds in Rubus corchorifolius fruit during ripening were determined with a headspace SPME-GC-MS method. The results suggest that the free aldehydes, alcohols, esters and phenols increases, while that of free terpenoids decreases, with the ripening of the fruit. The bound aldehydes, alcohols, terpenoids, esters and phenols gradually decreases during ripening because these bound compounds are hydrolyzed to their free form. The characteristic free aroma compounds of ripened red fruit were found to be hexanal, 2-heptanone, ethyl hexanoate, 4-terpineol, geranial and methyleugenol. The free aroma compounds in red and yellow fruits exhibit similar odor profiles, and both of them are much sweeter, more floral and greener than the green fruit. The overall aroma of the fruits all ripening stages are mainly attributed to the free aroma compounds including β-damascenone, hexanal, 2-hexenal and linalool. The formation mechanisms of some volatile compounds were proposed.

UDP-glucosyltransferase PpUGT85A2 controls volatile glycosylation in peach

The monoterpene linalool is a major contributor to aroma and flavor in peach (Prunus persica) fruit. It accumulates during fruit ripening, where up to ~40% of the compound is present in a non-volatile glycosylated form, which affects flavor quality and consumer perception by retronasal perception during tasting. Despite the importance of this sequestration to flavor, the UDP-glycosyltransferase (UGT) responsible for linalool glycosylation has not been identified in peach. UGT gene expression during peach fruit ripening and among different peach cultivars was analyzed using RNA sequencing, and transcripts correlated with linalyl-β-d-glucoside were selected as candidates for functional analysis. Kinetic resolution of a racemic mixture of R,S-linalool was shown for PpUGT85A2, with a slight preference for S-(+)-linalool. PpUGT85A2 was shown to catalyze synthesis of linalyl-β-d-glucoside in vitro, although it did not exhibit the highest enzyme activity between tested substrates. Subcellular localization of PpUGT85A2 in the cytoplasm and nucleus was detected. Application of linalool to peach leaf disks promoted PpUGT85A2 expression and linalyl-β-d-glucoside generation. Transient expression in peach fruit and stable overexpression in tobacco and Arabidopsis resulted in significant accumulation of linalyl-β-d-glucoside in vivo. Taken together, the results indicate that PpUGT85A2 expression is a major control point predicting linalyl-β-d-glucoside content.

GC-MS study of changes in polar/mid-polar and volatile compounds in Persian lime (Citrus latifolia) during fruit growth

BACKGROUND

Citrus fruits possess a high content of bioactive compounds whose changes during fruit maturation have not been studied in depth. Fruits were sampled from week 1, after fruit onset (7 days after flowering), to week 14. Volatile compounds isolated by headspace-solid-phase microextraction and polar extracts from all samples were analyzed by gas chromatography-mass spectrometry.

RESULTS

The relative abundance of 107 identified metabolites allowed differences among samples at different stages of fruit growth to be established. Principal component analysis showed a clear discrimination among samples, and analysis of variance revealed significant differences in 94 out of the 107 metabolites. Among total volatiles, monoterpenes increased their relative abundance from 86% to 94% during fruit growth, d-limonene, γ-terpinene and β-pinene being the most abundant; conversely, sesquiterpenes decreased from 11.5% to 2.8%, β-bisabolene and α-bergamotene being the most concentrated. Sugars, in general, exhibited a gradual increase in abundance, reaching a maximum between weeks 9 and 12. Citric and malic acids, representing approximately 90% of the total identified carboxylic acids, reached a maximum concentration at commercial maturity (week 14).

CONCLUSION

Of the 107 tentatively identified metabolites during Persian lime growth, sugars, carboxylic acids, and volatiles were those that experienced more significant changes and more clearly created differences among fruit growth stages. © 2018 Society of Chemical Industry.