Abstract
The paper presents the chemical characteristics of ellagitannins isolated from raspberry (Rubus idaeus L.) fruit and their in vitro and in situ antifungal activity against Geotrichum candidum ŁOCK 0511. The study investigated a complex preparation containing various raspberry ellagitannins at a concentration of 86% w/w, as well as pure lambertianin C and sanguiin H-6. The ellagitannin preparation was obtained by extracting raspberry press cake and purifying the extract using Amberlite XAD resin, while individual compounds were isolated by means of preparative HPLC. The complex preparation was analyzed for the content of ellagitannins, anthocyanins, and flavan-3-ols using HPLC and LC-MS. The antifungal activity of the complex ellagitannin preparation and the isolated ellagitannins was determined for the strain Geotrichum candidum. The MIC and MFC values (10.0 mg/mL and 30.0 mg/mL, respectively) were found to be the same for lambertianin C, sanguiin H-6, and the complex ellagitannin preparation. The fungistatic activity of the studied ellagitannin preparation at a concentration of 10 mg/mL, as determined by the poisoned medium method, was 65.2% following 6 day incubation of Geotrichum candidum, with the linear growth rate of only 16.2 mm/day. The corresponding parameters for the control sample were 0% and 56 mm/day, respectively. The study demonstrated both in vitro and in situ antifungal activity of raspberry ellagitannins against Geotrichum candidum.
Highlights
Ellagitannins constitute a complex class of polyphenols characterized by one or more hexahydroxydiphenoyl (HHDP) moieties esterified with a sugar, usually glucose
Six ellagitannins were identified in the obtained raspberry extract (Table 1) in the process of gradient elution with polyphenols being purified on XAD 1600 resin
It should be noted that the first isomer fragmented to m/z 1235, which was associated with the loss of an HHDP residue as described by Kähkönen et al [11], while the second isomer fragmented to m/z 1265, which was linked to the loss of a galloylated glucose as described by Gasperotti et al [3]
Summary
Ellagitannins constitute a complex class of polyphenols characterized by one or more hexahydroxydiphenoyl (HHDP) moieties esterified with a sugar, usually glucose. The main raspberry ellagitannins are sanguiin H-6 (1871 g/mol) and lambertianin C (2805 g/mol) Both compounds are dimers and trimers of casuarictin (936 g/mol) respectively, which are formed by intermolecular C-O bonds between an HHDP group and a galloyl group on a neighboring monomer [1]. The content of these compounds in fresh raspberry fruit, depending on the cultivar, ranges from 360 to 750 mg/kg for sanguiin H-6 and from 280 to 630 mg/kg for lambertianin C [3].
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