Analysis of Bound Form Terpenes in Different Agricultural Byproducts

Traditional sample preparation for terpene analysis includes distillation, solvent extraction, and solid phase extraction and is followed by using gas chromatography with a mass spectrometer (GC-MS) to complete identification and quantification. The preparations rely on the volatility and low polarity of terpenes which exist in free form. However, terpenes in bound form are still largely retained in the extracted residues because, by binding with sugar moiety, they have high polarity and water solubility and low volatility. In this study, distributions and profiles of free and bound form terpenes in different fruit and crop byproducts were evaluated by using different extraction media followed by acid hydrolysis. The acid hydrolysis significantly broke down the binding between terpene and sugar moiety and freed the bound terpene. The concentration of bound terpenes in fruit peel or corn silk was much higher than that of originally existing free terpenes. For example, the terpene concentration in watermelon peel increased from 47.0 to 101 μg/g after hydrolysis. The profile of bound terpenes was also more diverse than that of free terpenes. Among the three extraction media, water, ethanol, and acetone, acetone was the best media to extract bound terpenes with over one and a half times higher total bound terpene extraction yield than ethanol or water extract. The findings of this study explored the bound form terpenes in agricultural products which are usually underexplored in current terpene research. It also demonstrated an effective sample preparation and approach for determining bound terpenes in plants. This study could be an initiating effort and work to assist in exploring rarely mindful bound terpenes in foods and plants. The odorless nature and high stability and water solubility of bound terpenes could provide them a great advantage over free terpenes in various applications requiring neutral scent.