Degree

Doctor of Nutrition and Food Sciences (PNFS)

Department

Nutrition and Food Sciences

Document Type

Dissertation

Abstract

Six sweet potato (Ipomoea batatas) cultivars, New Orleans, Beauregard, Japanese, Hannah, Garnet, and Jewel were selected to determine the distribution of terpenes in their flesh and peel. The main terpenes were linalool and α-terpineol, which were present in a bound form. They were released as free-form, determined after acid hydrolysis, and detected by GC/MS. Ultrasonication-assisted acid hydrolysis decreased terpene levels since free-form terpenes evaporated or oxidized rapidly. The colored sweet potato cultivars had a higher level of bound terpenes than their white-colored counterparts. Also, the concentration of linalool and α-terpineol in the peel of each cultivar was approximately two times higher than in its flesh.

Three extraction techniques, namely, hydro-distillation (HD), vacuum distillation (VD), and water evaporation (WE) were used to evaluate the efficacy on the recovery of linalool and α-terpineol from sweet potato peel (SPP) solution. HD was effective in recovering α-terpineol, but not linalool. VD showed advantages in recovering both linalool and α-terpineol, with a greater yield of linalool than α-terpineol. The concentrations of linalool and α-terpineol increased by 12 and 14 times, respectively, when 90% of the water was removed from the SPP solution containing glycosidic terpenes. The three extraction methods generated more terpene compounds, mostly oxygenated monoterpenes. The exposure to high temperatures and extended exposure times during HD and VD led to the generation of 22 and 6 non-terpene artifacts, respectively. WE did not generate any artifacts.

The chemical composition of the two distillates and the concentrated SPP solution shed new light on linalool and α-terpineol as natural antifungal agents. The distillates from HD and VD did not alter the inhibition of A. flavus. However, the WE concentrate containing bound form terpenes inhibited A. flavus and altered the hyphal morphology with a MIC of 12.5 µg/mL. The distillates and the concentrate were also tested directly on tomato fruits. The concentrate solution rich in high stability and less volatility of bound terpenes acted effectively by inhibiting the growth and decreasing the size of lesions of the tomato’s fruits. Our finding demonstrates for the first time that concentrated SPP solutions can provide anti-fungal properties against A. flavus.

Date

6-26-2023

Committee Chair

Zhimin, Xu

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