Refractometric determination of water content in royal jelly

Abstract - A correlation was found between the measured refraction index of royal jelly and its water content as determined by vacuum oven drying. Twenty-seven different royal jelly samples were analysed for their water content by performing 24 hour vacuum drying at 48 °C, obtaining values that covered almost the entire range reported in literature. The refraction index values for the same samples were measured using a thermostated Abbe refractometer. A simple linear relationship (R² = 0.96) between refraction index and water content was found proving the fitness of a refractometric measure for quality control purposes. The relationship provides estimates of water content that are similar to those resulting from the Wedmore equation (R² = 0.9999) used to estimate water content in honey. The refractometric evaluation of the water content provides sufficient reliability for the routine quality control of royal jelly and is faster and simpler than currently used methods.