CHEMICAL COMPOSITION AND SUGAR PROFILE ON NECTAR OF SOYBEAN FLOWERS (Glycine max. L. Merrill)

Abstract

Pollination is one of the main mechanisms for maintaining and promoting biodiversity. Floral nectar is an important reward for the pollinating visitors, and bees are responsible for much of the cross-pollination process. The aim of this study was to evaluate the chemical composition and to determine the sugar profile of nectar from flowers of soybean cultivars (Glycine max. L. Merrill) grown in the field. Nectar samples were collected from six cultivars (BRS 399RR, BRS 1001IPRO, BRS 388, Don Mario 6563IPRO, TMG 7063IPRO and Monsoy 6410IPRO). After collected, the samples were prepared by mixing 2 mL of soybean flower nectar in 550 mL with a stock solution containing TMSP-d4 (3- and 3-trimethylsilyl) propionic acid-2, 2, 3, 3-d4, 0.01%). Nuclear Magnetic Resonance (NMR) analyzes were performed at the Multiusers Laboratory of Natural Products Chemistry (LMQPN), Embrapa Tropical Agroindustry, Fortaleza, CE, Brazil. NMR spectra were obtained on the Agilent DD2, with One Probe (1H-19F/15N-31P) of inverse detection and field gradient in the “z”-axis. After characterization of the substances, nectar sugars were quantified through the integration of NMR signals. The main nectar compounds of soybean flowers were ethanol (alcohol), threonine, tyrosine and phenylalanine (amino acids) and acetic acid, as well as the sugars: fructose, β-glucose, α-glucose and sucrose. In cultivar BRS 399RR, higher levels of reducing sugars (glucose and fructose) were detected in relation to the other cultivars Don Mario 6563IPRO, TMG 7063IPRO and Monsoy 6410IPRO showed similar amount, but less than the first cultivar. Thus, the soybean flower nectar has levels of sugar and compounds that can help to provide food to the most commonly used pollinating agents, such as bees.