Chemodiversity in the Fingerprint Analysis of Volatile Organic Compounds (VOCs) of 35 Old and 7 Modern Apple Cultivars Determined by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) in Two Different Seasons

Rapid Determination of Different Ripening Stages of Occidental Pears (Pyrus communis L.) by Volatile Organic Compounds Using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS)

Determination of Occidental pear (Pyrus communis) ripening is difficult because the appearance of Occidental pears does not change significantly during the ripening process. Occidental pears at different ripening stages release different volatile organic compounds (VOCs), which can be used to determine fruit ripeness non-destructively and rapidly. In this study, VOCs were detected using proton-transfer-reaction mass spectrometry (PTR-MS). Notably, data were acquired within 1 min. Occidental pears harvested at five separate times were divided into three ripening stages: unripe, ripe, and overripe. The results showed that the composition of VOCs differed depending on the ripening stage. In particular, the concentrations of esters and terpenes significantly increased during the overripe stage. Three ripening stages were clearly discriminated by heatmap clustering and principal component analysis (PCA). This study provided a rapid and non-destructive method to evaluate the ripening stages of Occidental pears. The result can help fruit farmers to decide the optimum harvest time and hence reduce their economic losses.

Analysis of Volatile Esters and Alkanoic Acids by an Atmospheric Pressure Corona Discharge Ionization Collision-Induced Dissociation Mass Spectrometry in Positive-Ion Mode: Ionization, Fragmentation Patterns, and Discrimination between Isomeric Compounds

The ionization and fragmentation patterns of 24 compounds with elemental composition of CmH2mO2, including isomeric esters and alkanoic acids, were investigated by atmospheric pressure corona discharge ionization collision-induced dissociation (CID) mass spectrometry in the positive-ion mode. All compounds were ionized as protonated molecules and NH4+ adducts. In addition, fragment ions were observed in mass spectra of esters other than methyl esters, which are owing to the dissociation of the alkyl group in the alcohol side from the protonated molecules. In CID spectra, protonated alkanoic acids/methyl esters split off H2O/CH3OH and CO or the alkyl group in the acid side, depending on the carbon chain length. Protonated esters (other than methyl esters) mainly fragmented the alkyl group in the alcohol side. These general rules on ionization and fragmentation patterns can provide relevant information on the discrimination of isomers.

Monitoring Volatile Organic Compounds in Different Pear Cultivars during Storage Using HS-SPME with GC-MS

Aroma, which plays an essential role in food perception and acceptability, depends on various mixture of volatile organic compounds (VOCs). Meanwhile, as a field of metabolomics, VOC analysis is highly important for aroma improvement and discrimination purposes. In this work, VOCs in pear fruits were determined via headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) to study variations among different cultivars and storage stages. In 12 cultivars of pear fruits, a total of 121 VOCs were quantified, including 40 esters, 32 alcohols, 16 aldehydes, 13 alkenes, 11 ketones, 4 acids, and 5 other compounds. The types and amounts of VOCs in different cultivars varied dramatically, which were in the range of 13-71 and 3.63-55.65 mg/kg FW (fresh weight), respectively. The Dr. Guyot cultivar showed the highest level of VOCs, both in type and amount. After 21 days storage at 4 °C, total concentration of VOCs increased from initial levels of 50.76 to 101.33 mg/kg FW. Storage at 20 °C made a larger contribution to production for VOCs than that at 4 °C, resulting in the maximum content of VOCs (117.96 mg/kg FW) in fruit after 14 days storage at 4 °C plus 7 days at 20 °C. During storage, the content of esters showed a gradual increase, while the content of alcohols and aldehydes decreased. Based on the results presented, related alcohols were recognized as the intermediates of conversion from aldehydes to esters.

Changes in the Quality of Old Apple Cultivars After Freeze-Drying

There are several thousand different cultivars of apple trees but only a limited number are cultivated on an industrial scale. Old cultivars can be useful, for example, in the processing industry due to their different composition. In many cases, they have higher organic acid content. The content of mineral components, colour, and polyphenols in the fruit of 7 old apple tree cultivars, growing in the Wolinski National Park, was studied. The changes that occurred in the fruit after freeze-drying were also evaluated. The trees from which the fruit was picked for analysis, despite the lack of chemical protection, were fruiting and the apples had only a few symptoms of damage caused by pests or diseases. The fruit was characterised by a high soluble solids content (14.4-16.4%), in which sugars and especially fructose dominated. The number of organic acids varied greatly and ranged from 0.27 (Oberlander Himbeerapfel) g to 1.07 g/100 g (Winter Goldparmane). The content of polyphenols in fresh apples ranged from 186 mg (Horneburger Pfannkuchenapfel) to 354 mg/100 g (Winter Goldparmane) and increased after freeze-drying from 666 mg (Weisser Winterkalvill) to 1486 mg/100 g (Winter Goldparmane). The dominant group of polyphenolic compounds was phenolic acid. The freeze-drying process caused unfavourable changes in the colour of the pulp. The fruits of Oberlander Himbeerapfel cultivar were most susceptible to these changes. However, the least darkened fruit of Horneburger Pfannkuchenapfel.

Volatilomics: a non-invasive technique for screening plant phenotypic traits

BACKGROUND

Climate change represents a grand challenge for agricultural productivity. Understanding complex plant traits such as stress tolerance, disease resistance or crop yield is thus essential for breeding and the development of sustainable agriculture strategies. When screening for the most robust plant phenotypes, fast, high-throughput phenotyping represents the means of choice.

RESULTS

We have developed a plant phenotyping platform to measure the emission of volatile organic compounds (VOCs), photosynthetic gas exchange and transpiration under ambient, or abiotic and biotic stress conditions. These parameters are highly suitable markers to non-invasively and dynamically study plant growth and plant stress status, making them perfect test variables for long-term, online plant monitoring. Here we introduce the new phenotyping platform, termed VOC-SCREEN, and present results of a first case study with three barley cultivars, demonstrating that the plant's volatilome can be successfully applied to discriminate different barley varieties.

CONCLUSION

Volatilomics is a promising technique to non-invasively screen for plant phenotypic traits.