Glycerol esters of wood rosin (GEWR) are complex mixtures of diglycerides and triglycerides of wood rosin resins with residual monoglycerides. In addition, neutral substances (non-acid saponifiables and unsaponifiables) and residual free resin acids are present. Wood rosin is obtained by solvent extraction of aged pine stumps, followed by a liquid-liquid solvent refining process. Refined wood rosin is composed of approximately 90% resin acids and approximately 10% neutral substances. The resin acid part is a complex mixture of isomeric diterpene monocarboxylic acids, with a typical empirical formula C20H30O2, and its main components are dehydrogenated rosin and rosin acid. GEWR is produced by esterifying resin acids with food-grade glycerol. The product is then purified by steam stripping or direct countercurrent steam distillation.
These specifications exclude substances derived from rosin, the exudate of live pine trees, and substances derived from tall oil rosin, a by-product of kraft (paper) pulp processing.

The IR spectrum of the sample film ester of rosin (potassium bromide disk) corresponds to the typical IR spectrum below
negative
Weigh 40-50 mg of sample into a test tube and add 1-2 drops of 20% (w/v) sodium formate solution. Place a strip of lead acetate test paper over the mouth of the test tube. Heat the tube until smoke forms that contacts the test strip. Continue heating for 2-5 minutes. The formation of black spots of lead sulfide indicates the presence of sulfur-containing compounds. (Detection limit: 50mg/kg sulfur)

Sample Preparation
Resin acid analysis was performed following the sample preparation method up to the centrifugation step. Use a pipette or syringe to remove the toluene layer and part of the water layer, leaving about 2 ml of water layer in the centrifuge tube. Add 1 drop of phenolphthalein solution to the remaining water layer in the centrifuge and neutralize it with sodium hydroxide solution (aluminum salts will precipitate). Pipette 5 ml of the internal standard solution into the tube, dilute to 15 ml with distilled water, add a stopper, shake well, and then centrifuge at 2800-3200 rpm for 5 min. Inject 1 μl of the clarified supernatant into a gas chromatograph operated under the following conditions and record the chromatogram. Inject 1 μl of glycerol solution and record the chromatogram. Measure the retention time of any observed peak relative to 1,4-butanediol. Compare retention times to glycerol standards.
Chromatographic conditions
- Column: DB-WAX polyethylene glycol (bonded and
Cross-linked), wide-bore capillary (inner diameter 15 m x 0.53 mm,
1.0 micron)
- Flow rate: Carrier gas (He): 30 ml/min at 60 psi,
Hydrogen: 30 ml/min and
- Air: 240 ml/min
- Temperature: Column: programmed, 120 to 200o at 6o
/min; Injector: 250o,
- and detector: 250o
© FAO/WHO 2018
7 points out of 8 points
Gas Chromatography Analysis of Resin Acids in GEWR (as alcohol)
Typical GC-FID chromatogram of a GEWR sample. Retention times correspond to picarinol (18.8 min), isopimarol (22.4 min), longiferol (23.1 min), dehydroabienol (25.9 min), rosinol (29.6 min) and neoabienol (35.2 min) . This is a plant-derived product that can exhibit significant variability and relative strength.