• essential oils
• GC-MS
• phytochemistry
• statistical analysis

Volatile Organic Compounds emitted by plants are a mixture of lipophilic compounds that exert a role in plant communication with other organisms as well as in plant defence against unfavourable environmental conditions. Due to their roles, the analysis of both spontaneously emitted volatiles and essential oil, may represent an important tool to be exploited in various important sectors, including agricultural and food ones, since it can provide a series of information on plant behaviour.
The first section of the dissertation consists of a brief introduction on plant volatiles, both spontaneously emitted and EO, as they represent a recurrent theme of the thesis.
In the second chapter, variations in the volatile emission as a response to environmental factors were evaluated. Indeed, the former study investigated the potential impacts of the UV-B exposition and the inoculation with the mycorrhizal fungi Funneliformis mosseae on the volatile chemical profile of Lactuca sativa L., an important annual herb widely cultivated as leaf vegetables. Results highlighted UV-B exposure as an important abiotic factor capable of influencing plant secondary metabolism. Conversely, mycorrhization, which could not be considered a biotic factor, but rather a mutualistic symbiosis, was not able to activate changes in the biosynthetic pathways involved in the volatile compound production in lettuce plants. The following two studies of this chapter evaluated the effect of narrowband LED light supplementation to ambient light on basil volatile metabolism. The former evaluated the chemical composition of the spontaneous volatile emission of two different varieties of sweet basil (Tigullio, TI and Red Rubin, RR) while the latter the variations of the chemical composition and hydrodistillation yield of the essential oil obtained only from Tigullio. Concerning volatile compounds spontaneously emitted from basil varieties, monochromatic wavebands have been shown to stimulate changes in the metabolic pathways, mainly in green-leafed basil, but also in red-leafed ones. In fact, the spontaneous volatile emission of basil plants was influenced by the light treatments, suggesting a practical application for greenhouse cultivation since it was able to confer a better pleasantness to the Tigullio cultivar, increasing the linalool content and reducing the biosynthesis of eugenol, which is considered one of the major unpleasant compounds in sweet basil. LED light supplementation was also able to affect the chemical composition of the essential oil obtained from O. basilicum cv. Tigullio. In particular, blue and green lights were more efficient in enhancing the biosynthesis of sesqui- and diterpenes, while red and white lights determined an increase of oxygenated monoterpenes, mainly of linalool and 1,8-cineole. Since basil plants producing good amounts of linalool are characterised by the highest consumer acceptability, the present study suggests, once again, a practical application of light modulation for greenhouse cultivation.
The fourth study of this section aimed to evaluate the presence of a pattern relating the chemical composition of EOs and volatile organic compounds spontaneously emitted by flowers and leaves of 12 species of Salvia L. to their geographical origin, as well as to their clade distribution. Therefore, since both the EOs and the spontaneous volatile emission obtained from flowers and leaves were evaluated, we were able to highlight which analysis was more suitable to show this correlation. A great variability was found in the chemical volatile profiles of the analysed Salvia species, which, however, seems to be strictly related to their genetic heritage and, in turn, to their geographical origin. The multivariate statistical analyses, indeed, evidenced a slight correspondence between the EO chemical compositions and both the geographical origin and the clade distribution of Salvia species, while the same trend was not found for both the flowers and the leaves emissions. Given that all the species analysed in the present study were cultivated under the same environmental conditions, the similarities and differences shown in the volatile profiles could be considered genetically determined. Finally, the last study of the second chapter deals with the investigation of the spontaneous volatile emissions of inflorescences and leaves of Olea europaea accessions, collected in different municipal areas of Toscolano Maderno territory and belonging to different autochthon cultivars, in order to evaluate the influence of cultivar, environment, and their interaction on the plant volatile profile. The interaction between cultivar and environment has proved to be the most effective factor able to affect the volatile emissions of both inflorescences and leaves, which, instead, were not significantly influenced by single factors. Multivariate statistical treatments, however, evidenced a tendency for the samples to gather according to the area of provenance rather than by cultivar, and a better partitioning was obtained by considering the volatile emissions of the inflorescences.
The third chapter of this PhD thesis aims to increase the knowledge of Cannabis sativa L. EO, a valuable by-product obtained from hemp inflorescences, which are usually discarded by the main supply chains of this crop. Hemp EO has attracted increasing interest thanks to its various applications in different fields. However, its chemical composition and productivity seem to be influenced by various environmental and meteorological conditions and these factors, besides the lack of standardisation of growing and operating conditions, make the comparison among the data reported in diverse studies quite challenging. Thus, the objective of the first study of this section was to investigate the chemical composition and the yield of the EO obtained from eleven industrial genotypes of C. sativa, cultivated and collected for two consecutive growing seasons, under the same cultural conditions. The results of the present study showed a significant influence of both the genotype and the year of cultivation, as well as of their interaction on the EO chemical profiles and yields. The second study of this chapter, instead, aimed to evaluate the effect of the phenological development on the production of the EO obtained from the inflorescences of two genotypes that in the previous study gave interesting results: Codimono (monoecious) and Fibrante (dioecious). Terpenes and cannabinoids represented the major detected chemical classes. Among the former class, sesquiterpene hydrocarbons were the prevalent components in the EOs of all phenological stages even though they showed a tendency to decrease during the plant phenological development. Conversely, oxygenated sesquiterpenes and phytocannabinoids showed a trend to increase during the plant growth, likewise the EO productivity. Therefore, despite its variability, hemp EO is consistently characterized by terpenes and phytocannabinoids and, among terpenes, sesquiterpenes are the most variable components, both in their hydrocarbon and oxygenated forms. Taking this into account, the third study of this section deals with the evaluation of the ability of the EOs obtained from two industrial genotypes of C. sativa, characterized by different chemical compositions, to counteract the microglia-mediated neuroinflammation using a human microglia cell model (HMC3), and both the volatile oils exhibited good outcomes in terms of anti-inflammatory activity. Finally, the last work of chapter 3, aimed to investigate the in vitro inhibitory activity of the essential oils obtained from leaves and inflorescences of two genotypes of C. sativa L. against 21 antibiotic-resistant field strains of Staphylococcus pseudintermedius, a bacterium responsible for the canine pyoderma and otitis externa.
Finally, the fourth chapter reported different applications of volatile analysis and other analytical investigations in the food sector. A particular focus was dedicated to the traceability and authenticity of wine, which represent important factors for consumers’ and producers’ protection. Therefore, the aims of the first two studies of this section were the evaluation of volatile and multi-elemental analysis for the traceability of Italian wines coming from different regions. Volatile organic compounds, constituting important wine features able to influence consumer acceptability, have been reported by the literature as an important tool for wine authentication. In the present study, different chemometric approaches were applied to evaluate the ability of volatile fingerprints to discriminate Italian wines according to their region of origin. Multivariate statistical methods, in particular PCA and HCA, exhibited a primary separation of the wines according to their type (red and white) and a good separation of red wines according to their geographical provenance. Conversely, LDA did not return successful outcomes. Inorganic elements due to their greater stability have been widely used in the food industry for tracing the wine origin. Indeed, the preliminary results of the second work of this chapter evidenced the ability of multi-elemental analysis associated with supervised statistical methods to discriminate Italian wines according to their geographical origin. This study represented a starting point for future investigations involving an increased number of samples from each region, necessary to confirm the discriminating power of the proposed method. Volatile analysis associated with other phytochemical and sensorial analyses was also applied for the evaluation of the Hibiscus rosa-sinensis-flavoured beer and Citrus-based products discussed in the present chapter. Finally, in the last work of this dissertation, the EOs obtained from different Salvia L. species were investigated for their antimicrobial activity against Listeria monocytogenes, an important gram-positive bacterium able to contaminate food products causing human listeriosis. The obtained encouraging results suggest possible applications of the analysed EOs in the food industry in different delivery systems that can enhance the bio-efficacy of the EOs while mitigating the challenge posed by their strong aroma.