ARS | Publication request: AROMA CONTENT OF FRESH BASIL (OCIMUM BASILICUM L.) LEAVES IS AFFECTED BY LIGHT REFLECTED FROM COLORED MULCHES

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 17, 2003
Publication Date: N/A

Interpretive Summary: Basil is an herb that is used to add a distinct aroma and flavor to food. It is grown commercially and by home gardeners. The leaves are used fresh, or dried for use as a spice. This herb can be grown in a drip irrigated system using plastic soil covers (mulches) to conserve water and control weeds. By using colors other than the standard black for the soil covers, scientists at the Coastal Plains Soil, Water and Plant Research Center, Florence, South Carolina, were able to keep the benefits attributed to black mulch and alter the amounts of blue, red, and far-red light reflected to the developing leaves. The color of light reflected to the developing leaves affected their size and aroma. Basil leaves grown over red were larger and more succulent, but those grown over yellow and green had greater concentrations of aroma compounds. The concentration of aroma compounds emitted from fresh basil leaves was about 50 times higher than from dried leaves.

Technical Abstract: Sweet basil (Ocimum basilicum L.) is an herb that is used to add a distinct aroma and flavor to food. Aroma compounds emitted from fully-expanded fresh leaves that were grown in drip-irrigated field plots covered with different colors of polyethylene mulch were compared. The colors were selected to reflect a range of photosynthetic photon flux, far-red, red and blue light from the soil surface to developing leaves. The objective was to determine whether reflection from the different colors could influence concentrations of aroma compounds emitted from fresh leaves that developed in sunlight. Aroma compounds were isolated by dynamic headspace sampling, quantified by gas chromatography, and identified by gas chromatography-mass spectroscopy. Twenty-six compounds were identified, of which the terpenoids linalool and 1,8-cineole comprised more than 50% of the total yield. Leaves that developed over red were larger, but those grown over yellow or green surfaces emitted higher concentrations of aroma compounds. Altering the amounts of far-red, red and blue light reflected to the growing plants significantly affected the concentration of aroma compounds. The concentrations of aroma compounds from fresh basil leaves were about 50-fold higher than those from air-dried leaves in a previous study.