| Summary: | The producers of essential oils from the Republic of Moldova care about the quality of their products and at the same time, try to capitalize on the waste from processing. The purpose of the present study was to analyze the chemical composition of lavender (<i>Lavanda angustifolia</i> L.) essential oil and some by-products derived from its production (residual water, residual herbs), as well as to assess their “in vitro” antimicrobial activity. The gas chromatography-mass spectrometry analysis of essential oils produced by seven industrial manufacturers led to the identification of 41 constituents that meant 96.80–99.79% of the total. The main constituents are monoterpenes (84.08–92.55%), followed by sesquiterpenes (3.30–13.45%), and some aliphatic compounds (1.42–3.90%). The high-performance liquid chromatography analysis allowed the quantification of known triterpenes, ursolic, and oleanolic acids, in freshly dried lavender plants and in the residual by-products after hydrodistillation of the essential oil. The lavender essential oil showed good antibacterial activity against <i>Bacillus subtilis</i>, <i>Pseudomonas fluorescens</i>, <i>Xanthomonas campestris</i>, <i>Erwinia carotovora</i> at 300 μg/mL concentration, and <i>Erwinia amylovora</i>, <i>Candida utilis</i> at 150 μg/mL concentration, respectively. Lavender plant material but also the residual water and ethanolic extracts from the solid waste residue showed high antimicrobial activity against <i>Aspergillus niger</i>, <i>Alternaria alternata</i>, <i>Penicillium chrysogenum</i>, <i>Bacillus</i> sp., and <i>Pseudomonas aeroginosa</i> strains, at 0.75–6.0 μg/mL, 0.08–0.125 μg/mL, and 0.05–4.0 μg/mL, respectively.
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