Insights into the chemical composition and bioactivities of citrus peel essential oils

Citrus peel (CP), a by-product of the citrus fruit processing, comprises nearly forty to fifty percent of the fruit portion. Interestingly, the essential oil (EO) is primarily concentrated in the peel portion of the citrus fruit. Extraction of CP essential oil (CPEO) is an effective way of utilizing the citrus fruit processing waste. The CPEO can be more efficiently recovered from CP waste by improving the efficiency of conventional extraction processes. The main components of CPEO include monoterpenes, sesquiterpenes and their oxygenated derivatives. Specifically, limonene is the major oil component identified in the peel of different citrus species. The health promoting biological activities of CPEO are functioning as antioxidant, anti-inflammatory, analgesic, antimicrobial and anticancer agents, thereby can be used as a source of functional components and preservatives for the development of nutritionally safe newer food products. This paper provides an in-depth knowledge about the chemical constituents and bioactivities of EOs extracted from peels of different citrus species.

Chemical Composition of the Essential Oils from Different Morphological Parts of Pinus cembra L

The essential oils from needles, twigs, bark, wood, and cones of Pinus cembra were analyzed by GC-FID, GC/MS, and ¹ H-NMR spectroscopy. More than 130 compounds were identified. The oils differed in the quantitative composition. The principal components of the oil from twigs with needles were α-pinene (36.3%), limonene (22.7%) and β-phellandrene (12.0%). The needle oil was dominated by α-pinene (48.4%), whereas in the oil from bark and in the oil from twigs without needles there were limonene (36.2% and 33.6%, resp.) and β-phellandrene (18.8% and 17.1%, resp.). The main constituents of the wood oil as well as cone oil were α-pinene (35.2% and 39.0%, resp.) and β-pinene (10.4% and 18.9%, resp.). The wood oil and the cone oil contained large amounts of oxygenated diterpenes in comparison with needle, twig, and bark oils.

Sustainable heterologous production of terpene hydrocarbons in cyanobacteria

Cyanobacteria can be exploited as photosynthetic platforms for heterologous generation of terpene hydrocarbons with industrial application. However, the slow catalytic activity of terpene synthases (k _cat = 4 s^-1 or slower) makes them noncompetitive for the pool of available substrate, thereby limiting the rate and yield of product generation. Work in this paper applied transformation technologies in Synechocystis for the heterologous production of β-phellandrene (monoterpene) hydrocarbons. Conditions were defined whereby expression of the β-phellandrene synthase (PHLS), as a CpcB·PHLS fusion protein with the β-subunit of phycocyanin, accounted for up to 20 % of total cellular protein. Moreover, CpcB·PHLS was heterologously co-expressed with enzymes of the mevalonic acid (MVA) pathway and geranyl-diphosphate synthase, increasing carbon flux toward the terpenoid biosynthetic pathway and enhancing substrate availability. These improvements enabled yields of 10 mg of β-phellandrene per g of dry cell weight generated in the course of a 48-h incubation period, or the equivalent of 1 % β-phellandrene:biomass (w:w) carbon-partitioning ratio. The work helped to identify prerequisites for the efficient heterologous production of terpene hydrocarbons in cyanobacteria: (i) requirement for overexpression of the heterologous terpene synthase, so as to compensate for the slow catalytic turnover of the enzyme, and (ii) enhanced endogenous carbon partitioning toward the terpenoid biosynthetic pathway, e.g., upon heterologous co-expression of the MVA pathway, thereby supplementing the native metabolic flux toward the universal isopentenyl-diphosphate and dimethylallyl-diphosphate terpenoid precursors. The two prerequisites are shown to be critical determinants of yield in the photosynthetic CO₂ to terpene hydrocarbons conversion process.