The vitamin C analogue 2-O-β-D-glucopyranosyl- L-ascorbic acid in fruits from the Solanaceae family

Peer-Reviewed Manuskript (Original) eingereicht: 19.08.2019 Überarbeitung angenommen: 30.01.2020

Introduction

For centuries, goji berries (Lycium spp.) from the Solanacea family have been used in the traditional Chinese medicine for their bioactive compounds content [1]. Most of these bioactives are antioxidants such as ascorbic acid (AA), which are known to protect lipids, proteins and nucleic acids against oxidation. Other Solanaceae fruits are also well known for their antioxidant activities. According to Toor et al. [2], tomatoes present an antioxidant capacity, partly due to their AA content. Similar properties have been reported for cape gooseberries [3], for chili peppers [4, 5], and for different kinds of eggplants [6].

Rather recently, the interest has been put on the 2-O-β-D-glucopyranosyl-L-ascorbic acid (2-β-gAA), a stable AA analogue, which is one of the main biologically active components of goji berries [7]. As an analogue of AA, 2-β- gAA possesses antioxidant activities and prevents oxidative stress [8, 9]. Toyoda-Ono et al. reported an increased level of AA and of intact 2-β-gAA in the portal vein blood of rats, after oral administration of the analogue [10]. According to their findings, 2-β-gAA to some extend maintains the level of AA in the rat tissues and hence acts as a provitamin C. They even proposed the 2-β-gAA as a stable AA substitute for clinical applications. Synthetic access to this promising compound by either chemical or enzymatic approach is not efficient [11, 12]. Therefore, reliable natural sources are needed. The presence of 2-β-gAA in different goji berries has been studied extensively [12–15]. However, analogue’s occurrence in other fruits or berries have never been confirmed despite some unsuccessful studies on solanacea species.

Abstract

Goji berries from the Solanacea family are used in traditional Chinese medicine for their bioactive compounds, mostly antioxidants like ascorbic acid. Recently, an ascorbic acid analogue from goji, the 2-O-β-D-glucopyranosyl- L-ascorbic acid has been reported. In rats, this analogue is absorbed intact and as free ascorbic acid and has been consequently proposed as provitamin C. Since synthesis of the analogue is not promising, reliable natural sources are searched. However, knowledge concerning the analogue’s occurrence in other Solanacea fruits is lacking. In the present study, the presence of the analogue is evaluated in cherry tomatoes, cape gooseberries, different eggplants, and green chili peppers. Surprisingly, the analogue was found in all fruits investigated, but in considerably lower contents when compared to goji berries. For the first time, the presence of 2-O-β-D-glucopyranosyl- L-ascorbic acid is confirmed in fruits from the Solanacea family, other than goji berries.

Keywords: Solanacea, fruits, 2-O-β-D-glucopyranosyl-L-ascorbic acid, ascorbic acid, ascorbic acid analogue

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