John R.L. Walker

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.

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.

The selective inhibition of ortho- and para-diphenol oxidases

Abstract Ortho- and para-diphenol oxidases (DPOs) are often distinguished by substrate specificity tests which are not always unequivocal. This paper suggests that they may be differentiated by their response patterns to certain inhibitors and activators. In general o-DPOs (‘catecholases’) are inhibited by substituted cinnamic acids (cinnamic, p-coumaric and ferulic), or polyvinylpyrrolidone (PVP) and may be activated by anionic detergents. By contrast p-DPOs (‘laccases’) are unaffected by cinnamic acids and PVP but are inhibited by cationic detergents such as cetyltrimethylammonium bromide (CTAB). Thus in crude extracts these enzymes may be clearly distinguished by a simple combination of substrate and inhibitor specificity tests.

Phenolic biosynthesis during grain development in wheat: changes in phenylalanine ammonia-lyase activity and soluble phenolic content.

Changes in phenylalanine ammonia lyase (PAL) activity and the total phenolic content of several wheat cultivars have been monitored during grain development. PAL activity was maximal during the early milk stage of development and then declined. The level of soluble phenolics peaked 20-24 days after the PAL peak, just prior to the appearance of mature grain colour. Red cultivars showed higher PAL activities during early grain development and lower germination rates during maturation.

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

O-Diphenol oxidase activity, phenolic content and colour of New Zealand wheats, flours and milling streams.

Phenolic content, o -diphenol oxidase activity and bread crumb colour have been compared for flour streams from a local mill and for flours and wholemeals from six New Zealand wheat cultivars. Phenolic content and o-diphenol oxidase activity varied significantly betwen milling flour streams and between cultivars. Flour and bread crumb colour correlated significantly with phenolic content and o -diphenol oxidase activity in the milling flour streams. A similar relationship was observed also between o -diphenol oxidase activity and the colour of flour and bread prepared from the different cultivars. These observations suggest an involvement of o -diphenol oxidase and phenolics in the pigmentation of both wheat flour and bread.

The selective inhibition of catechol oxidases by salicylhydroxamic acid.

Abstract Salicylhydroxamic acid (SHAM) has been shown to be a powerful and selective inhibitor of catechol oxidases but was without effect on laccases. Inhabition was non-competitive at concentrations less than 10 μM

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.

Metabolism of phloroglucinol by Fusarium solani

A strain of Fusarium solani, isolated from soil, has been found to convert phloroglucinol to pyrogallol which was then metabolised via the meta-fission pathway to yield pyruvate.