HPLC-MS Analysis of Proanthocyanidin Oligomers and Other Phenolics in 15 Strawberry Cultivars

Abstract

The phenolic compounds of 15 strawberry cultivars grown in Spain were analyzed and quantified: anthocyanins (20.2-47.4 mg/100 g of fw) (cyanidin 3-glucoside and pelargonidin 3-glucoside, 3-rutinoside, and 3-malonyl glucoside), flavonols (1.5-3.4 mg/100 g of fw) (quercetin 3-glucuronide and kaempferol 3-glucoside and 3-p-coumaroyl-glucoside), proanthocyanidins (53.9-163.2 mg/100 g), p-coumaroyl-glucose (0.84-6.70 mg/100 g), ellagitannins (9.67-22.86 mg/100 g) (sanguiin H-6, lambertianin C, and galloyl bis-HHDP-glucose), and ellagic acid glycosides (0.88-2.06 mg/100 g of fw) (two ellagic acid deoxyhexosides). Proanthocyanidins, the main phenolic compounds, were characterized by phloroglucinol degradation. Their mean degree of polymerization ranged from 3.4 for cv. Chiflon to 5.8 for cv. Ventana, the average value being 4.3. The terminal unit of proanthocyanidin oligomers was always (epi)catechin (17.36-29.93%) and (epi)catechin (61.66-75.39%) or (epi)afzelechin (4.50-10.54%) as extension units. Different combinations of (epi)catechin and (epi)afzelechin were detected, and their sequence of linkage was characterized by HPLC-MS-MS. Relative percentages of dimers, trimers, tetramers, and pentamers were evaluated by the extracted ion chromatogram (EIC) analysis.

Nutrient and polyphenolic composition of industrial strawberry press cake

“…Their results confirm that proanthocyanidins are strongly bound in the press cake, despite the intensive processing procedures involving enzymatic treatment, pressing, and extraction. Mean degree of polymerization of SPC proanthocyanidins was 6.7, the value is slightly higher than data by Buendia et al [11] for fruits, where mean DP depended on cultivar and varied between 3.4 and 5.8. In researched SPC, polymeric flavanols were composed of (+)-catechin and (−)-epicatechin which are constitutive units of procyanidins (Fig 3.).…”

“…The content of anthocyanins in the press cake is as little as 0.2 % of total polyphenols, while in the fruits, they account for 13-45 % of total polyphenols [4,11]. Depending on the season, the studied press cakes contain from 47 to 87 mg of anthocyanins per 100 g DW.…”

“…This is further confirmed by other results reported by Oszmiański et al [10], who found that in a typical process of concentrated strawberry juice production, about 20 % of the proanthocyanidins present in the fruits are transferred to the juice (the content of proanthocyanidins in the raw material was not less than 1,417 mg per kg fresh weight). According to Buendia et al [11], the levels of proanthocyanidins in the fruits of various cultivars of strawberries, determined by HPLC following the phloroglucinolysis reaction, range from 539 to 1,681 mg/100 g DW (given 10 % mean dry matter content of the fruits). Their results confirm that proanthocyanidins are strongly bound in the press cake, despite the intensive processing procedures involving enzymatic treatment, pressing, and extraction.…”

“…In researched SPC, polymeric flavanols were composed of (+)-catechin and (−)-epicatechin which are constitutive units of procyanidins (Fig 3.). According to Buendia et al [11] and Gu et al [40], epiafzelchin (the unit of propelargonidin) composes strawberry proanthocyanidins as well, and its contribution as extension unit varies between 6.1 and 10.5 %, depending on cultivar. Hydrolysis of ellagitannins in an acidic or basic environment leads to release of hexahydroxydiphenic acid molecules, which undergo spontaneous lactonization to ellagic acid.…”

“…Their beneficial influence is exerted by means of various complementary mechanisms that involve a number of bioactive compounds such as tannins, flavonoids, and phenolic acids [7]. Strawberries are known to be a rich source of polyphenols, such as ellagitannins (ETs) [8,9], proanthocyanidins [4,10,11], anthocyanins [4,12], and flavonols (mostly quercetin and kaempferol glycosides) [2,13]. Ellagitannins are thought to be the most important polyphenols in strawberries.…”