Sesame seed lignan transformation and recovery under supercritical carbon dioxide

Abstract

Sesame seed is one of the well-known oilseed with rich source of nutritive values. It is ranked 2nd next to flax seed, in its lignan content. It is considered to be one of the most valuable oilseed primarily because of the presence of highly bioactive lignan components. These components gave sesame oil excellent stability due to the strong antioxidant properties. Sesamin and sesamolin are the main lignans in sesame oil, and relatively very small amount of sesamol also exists. Actually, sesamol does not exist naturally in sesame seed, rather its derived from sesamolin during sesame seed pre-treatment such as roasting, bleaching, and degumming. Even after the treatments only small amount of sesamol is detected in the oil. However small the amount of sesamol is, it exhibits the strongest antioxidant property compared to both sesamin and sesamolin. For this reason, the acidic conversion of sesamolin to sesamol under supercritical carbon dioxide was performed using solid catalyst (Amberlyst-15) having strongly acidic functional group. Previously, the transformation of sesamolin to sesamol and samin was performed in toluene, with the addition of strong oxidizing agents such as hydrogen peroxide. However, in this research work, sesamolin under supercritical CO2 was efficiently transformed mainly to sesamol and small amount of other lignans such as samin and sesaminol. Here, no oxidizing agent was used, only small fraction of water was added to furnish hydroxide ion in the solution. The two main advantages of using supercritical CO2 is; first it replaces relatively toxic chemical (toluene) with a green solvent (CO2). Second, product purification is not important, as CO2 can easily be separated by depressurization. The other important work in this research is, the recovery of water soluble bioactive components from the solid residue (defatted sesame meal) using CO2 assisted hydrothermal process. Defatted sesame meal (DSM) just like sesame oil, it is also rich source of pharmaceutical components. With the ever-growing demand for novel natural drugs, the utilization of green and efficient techniques to obtain highly biologically active natural products from unexplored herbal/medicinal plants is becoming increasingly important. Herein, the efficiency of green hydrothermal extraction (HT-extraction) for the recovery of bioactive compounds from DSM was investigated. The effects of the extraction temperature, extraction time, and ratio of CO2 added on the product yields and physicochemical, and structural properties of the DSM extracts were systematically investigated. In addition, the antioxidant activities of the HT extracts were examined using different in vitro methods, such as DPPH• scavenging capacity assay, and ABTS•+ scavenging capacity assay, and the correlations between the composition of the HT extract and the antioxidant activities of the resulting extracts were analyzed to determine the origin of the antioxidant activity of the extracts. Both extraction temperature and time were found to influence the extraction yields and product quality. The addition of CO2 even at lower temperature has showed the presence of more bioactive compounds and better antioxidant activities were achieved compared to conventional extraction. In vitro, anticancer cell effects on human breast cancer cells were checked for the extract solutions and a promising anticancer effect with lesser effect on normal cells was observed.