Jane E. Lancaster

Determination of anthocyanins, flavonoids and phenolic acids in potatoes. I: Coloured cultivars of Solanum tuberosum L

The major anthocyanins, flavonoids and phenolic acids in the tubers (skin and flesh), flowers and leaves of 26 cultivars of Solanum tuberosum L with coloured skins and/or flesh have been identified and quantified using analytical HPLC. Red tubers contained mostly pelagonidin-3-(p-coumaroyl-rutinoside)-5-glucoside (200–2000 μg g−1 FW) plus lesser amounts of peonidin-3-(p-coumaroyl-rutinoside)-5-glucoside (20–400 μg g−1 FW). Light to medium purple tubers contained petunidin-3-(p-coumaroyl-rutinoside)-5-glucoside (1000–2000 μg g−1 FW) plus small amounts of malvidin-3-(p-coumaroyl-rutinoside)-5-glucoside (20–200 μg g−1 FW) whilst dark purple–black tubers contained similar levels of petunidin-3-(p-coumaroyl-rutinoside)-5-glucoside together with much higher concentrations of malvidin-3-(p-coumaroyl-rutinoside)-5-glucoside (2000–5000 μg g−1 FW). Tuber flesh also contained chlorogenic acid (30–900 μg g−1 FW) and other phenolic acids plus low concentrations of flavonoids (0–30 μg g−1 FW). Tuber skins showed much higher levels (1000–4000 μg g−1 FW) of chlorogenic acid. The major anthocyanins in flowers were present as the rutinosides or other glycosides of pelargonidin, petunidin and malvidin whilst glycosides of cyanidin and delphinidin were found in some flowers, together with many of the same phenolic acids as found in tubers. The commonest flavonoids included rutin, kaempferol-3-rutinoside and two quercetin-rhamnose-glucosides. Flowers and leaves contained higher concentrations of flavonoids which fell into two patterns, with some cultivars containing high concentrations of quercetin-3-glycosides, whilst others had much lower concentrations.

γ-Glutamyl peptides in the biosynthesis of S-alk(en)yl-l-cysteine sulphoxides (flavour precursors) in Allium

Abstract Pulse-chase experiments with 35 SO 4 2− fed for 10 min to leaves of Allium cepa (onion), A. sativum (garlic) and 4 A. siculum showed that label appeared in γ-glutamyl peptides within 15 min, reached a maximum amount at 1 hr and had decreased by 6 hr. Label was not detected in free S -alk(en)yl- l -cysteine sulphoxides (flavour precursors) until 6 hr after pulse feeding, and then increased steadily for at least 24hr and for onions until day 3. It is concluded that glutathione, and γ-glutamyl peptides are intermediates in the biosynthetic pathway to flavour precursors in Allium spp.

Developmental Changes in Enzymes of Flavonoid Biosynthesis in the Skins of Red and Green Apple Cultivars

Three enzymes of flavonoid biosynthesis (phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI) and glycosyltransferase (UFGT)) were assayed during the development of apple (Maluspumila Mill) fruit. Total flavonoid and anthocyanin concentrations were measured (by HPLC) during the same period. The same patterns of change in activity were observed with all three enzymes in both a red (‘Splendour’) and a green-skinned cultivar (‘Granny Smith’). Enzyme activities were high in the immature fruit, decreased during the middle of the season and rose on ripening, activity in ripe fruit was generally not as high as in immature fruit. Total flavonoid concentration correlated with the activity of CHI and UFGT throughout development. In ‘Granny Smith’ there was correlation between flavonoid concentration and PAL but not in ‘Splendour’ except during ripening, when the fruit reddened. In ‘Splendour’ the activity of all three flavonoid enzymes correlated with anthocyanin levels during reddening. At all stages enzyme activity in ‘Splendour’ was several-fold higher than ‘Granny Smith’; daily rates of synthesis of the flavonoids were also much higher.

Effect of polysaccharides on the colour of anthocyanins

The effect of a variety of plant polysaccharides and sugars on anthocyanin colour was investigated. The colour intensity (absorbance), but not the λmax, of solutions of different anthocyanins was found to be diminished in the presence of amylose, amylopectin and α- and β-cyclodextrins whilst glucose, maltose and sucrose caused an increase in colour. This colour change was more apparent at pH 4 than at pH 2.

Changes in anthocyanin, flavonoid and phenolic acid concentrations during development and storage of coloured potato (Solanum tuberosum L) tubers

Changes in the anthocyanin concentration of coloured potato tubers have been investigated in cultivars with coloured skin and coloured or white flesh. The biosynthesis of anthocyanins coincided with tuber initiation in cultivars with intensely coloured mature tubers and, after a slight increase as the smaller tubers increased in size, anthocyanin concentrations remained relatively constant. Thus, because tubers were increasing in weight, anthocyanin was being synthesised to maintain a more or less constant concentration. In cultivars with less coloured tubers, the developing tubers remained white for a longer time, with anthocyanin concentrations increasing gradually up to a maximum at a certain tuber weight depending on the cultivar. The concentration of flavonoids was lower than that of anthocyanins but followed a similar pattern. Phenolic acid levels were about twice those of the anthocyanins and reached their maximum at a slightly lower tuber weight than anthocyanins and flavonoids. During cold storage (4°C) the anthocyanin concentration in coloured tubers increased, whereas tubers stored at higher temperatures did not show this increase. The increased colour in cold-stored tubers is discussed in terms of its relationship to ‘cold sweetening’ and the increased concentration of sugars in cold-stored tubers. The distribution of anthocyanins altered during tuber development and also during cold storage. In very small developing tubers the anthocyanins appeared first at the stem end of the tuber whilst the bud end remained white. As the anthocyanin concentration increased during tuber development, it increased over the whole tuber, but the concentration at the stem end was always higher than that at the bud end, until the tuber reached maturity, when the concentration became approximately equal at both ends. After cold storage, tubers had a higher concentration of anthocyanin in the bud end than the stem end; the opposite to that found in developing tubers. © 1999 Society of Chemical Industry

Metabolism of γ-glutamyl peptides during development, storage and sprouting of onion bulbs

Abstract Quantitative analysis of γ-glutamyl peptides in onion bulbs showed that γ-glutamyl trans-(+)- S -(1-propenyl)- l -cysteine sulphoxide (γ-glutamyl propenyl CSO) and S -2-carboxypropyl glutathione (2CPGTH) were absent prior to bulbing, and then at bulbing accumulated to levels of 2.1 and 0.4 mg g −1 fr. wt respectively. These levels were maintained throughout storage. The hydrolytic enzyme γ-glutamyl transpeptidase [EC 2.3.2.1] was of minimal activity in a stored bulb. During sprouting, activity increased ca five-fold. Levels of γ-glutamyl propenyl CSO and 2CPGTH decreased by 50% to 0.94 and 0.14 mg g −1 fr. wt respectively. These data support the hypothesis that the two major γ-glutamyl peptides function as storage compounds during the overwintering of onion bulbs.

Induction of flavonoids and phenolic acids in apple by UV-B and temperature

Summary The effect of UV-B irradiation at 10°C and 20°C on the quercetin glycosides procyanidins, chlorogenic acid and anthocyanin levels in the skin of detached fruit of five apple cultivars was investigated. UV-B responsiveness was compared between sides of the fruit that were outwardly facing (exposed) and inwardly facing (shaded) when on the tree. There were no common effects of UV-B irradiation and temperature across all cultivars. UV-B irradiation increased the quercetin glycoside levels in the shaded side of ‘Gala’, ‘Royal Gala’ and ‘Braeburn’ fruit and only at 20°C. UV-B irradiation of the exposed sides of the five cultivars, of either side at 10°C, and of ‘Pacific Rose’ and ‘Aurora’ at either 10°C or 20°C had no significant effect on quercetin glycoside levels. There was no effect of UV-B irradiation on procyanidin levels at any combination of treatments. However, levels of chlorogenic acid, although one tenth of those of quercetin glycosides and procyanidins, increased markedly with UV-B irradiation. Both exposed and shaded sides of fruit of all cultivars increased in chlorogenic acid levels at 10°C and 20°C after UV-B irradiation. UV-B irradiation increased anthocyanin levels in exposed and shaded sides of fruit of all cultivars at 20°C, and on ‘Braeburn’, and ‘Aurora’ at both 20°C and 10°C. UV-B irradiation at either temperature had no significant effect on either the relative proportions of the glycosides of quercetin (galactoside, rhamnoglucoside, glucoside, xyloside, arabinoside and rhamnoside) or the relative proportions of the procyanidins (Procyanidins B2, B5, epicatechin and catechin). The effect of UV-B irradiation was variable, depending on cultivar, previous light exposure, temperature and class of flavonoids examined.

Characterization of purified γ-glutamyl transpeptidase in onions: Evidence for in vivo role as a peptidase

Abstract γ-Glutamyl transpeptidase, from sprouting onion bulbs, was purified to homogeneity and characterized as a glycoprotein of M r , 56 700. Studies to determine the mode of action of purified enzyme were carried out using the synthetic substrate γ-glutamyl p -nitroanilide. At pH 6.0, equal amounts of two products, glutamic acid and p - nitroaniline, were formed, demonstrating hydrolysis of the γ-glutamyl substrate. Between pH 6.0 and 9.0, the ratio of p - nitroaniline to glutamic acid increased from 1:1 to 17:1 indicating autotranspeptidation of γ-glutamyl p -nitroanilide. The enzyme showed a wide range of substrate specificity for intermediates in the biosynthetic pathway to flavour precursors. γ-Glutamyl transpeptidase was detected in leaves, roots and bulbs of the growing plant, but not in dormant bulbs. In vivo the enzyme acts as a hydrolase of γ-glutamyl peptides during the biosynthesis of flavour precursors.

Determination of anthocyanins, flavonoids and phenolic acids in potatoes. II: Wild, tuberous Solanum species

The distribution of anthocyanins, flavonoids and phenolic acids in the tubers (skin and flesh), flowers and leaves of eight wild Solanum species has been compared to that found in coloured, cultivated, S tuberosum. Principal component analysis (PCA) of these results revealed a strong association between the various coloured S tuberosum cultivars with distinct differences from the other wild Solanum species. Similarly, PCA showed that there were close correlations between the tuber skin and flesh components. Diseased tubers of S sanctae-rosae showed large increases in levels of flavonoids and phenolic acids.

Differential hydrolysis of alk(en)yl cysteine sulphoxides by alliinase in onion macerates : Flavour implications

Intact cells of Allium spp have no odour, but when cells are disrupted, the enzyme alliinase (EC 4.4.1.4) hydrolyses the S-alk(en)yl sulphoxides (ACSOs) to produce pyruvate, ammonia and the many volatile sulphur compounds associated with flavour and odour. In onions, there are three main sulphoxides: methyl, propyl and 1-propenyl, which gives rise to onions tear-producing effect. The relative proportions of these are a factor in determining the subsequent flavour. γ-Glutamyl peptides, which are biosynthetic intermediates to ACSOs, are also present in significant amounts, but their contribution to flavour is not known. There is little work on the reaction of alliinase in vivo. The hydrolysis of ACSOs by alliinase was studied in rapidly macerated bulbs at intervals between 5 s and 2 h. ACSO and γ-glutamyl peptide levels were measured by HPLC, and pyruvate levels were measured spectrophotometrically. Although the hydrolysis of propenyl cysteine sulphoxide (PrenCSO) was immediate and almost 100% between 5 and 20 s after bulb maceration, the hydrolysis of propyl cysteine sulphoxide (PCSO) and methyl cysteine sulphoxide (MCSO) was incomplete. After 5 s maceration, about 50% PCSO and MCSO remained and thereafter no further hydrolysis occurred. The levels of ACSOs and the extent to which they were hydrolysed were dependent on the cultivar and sulphur environment in which it was grown. The addition of pyridoxal phosphate cofactor enhanced the extent of MCSO and PCSO hydrolysis. Additional purified alliinase per se had no effect. Substantial hydrolysis of γ-glutamyl peptides also occurred after maceration, and this was unexpected. Levels of pyruvate product were between 15 and 25% of the expected amount from ACSO hydrolysis assuming a stoichiometric relationship. The incomplete hydrolysis of MCSO and PCSO, enhancement of activity by additional pyridoxal phosphate and non-stoichiometric production of pyruvate are evidenced that reaction inhibition of alliinase may be occurring in onion macerates.