Changes in flavonoids and nonphenolic pigments during on-tree maturation and postharvest pericarp browning of litchi (Litchi chinensis Sonn.) as shown by HPLC-MSn

Polyphenols, chlorophylls, and carotenoids were characterized by HPLC-DAD-MS(n) in the pericarp of unripe to over-ripe 'Hong Huey' and 'Chacapat' litchi fruit at harvest and during subsequent storage (5 °C, 90% RH, 21 days). (-)-Epicatechin and A-type procyanidins always predominated quantitatively. Besides these ortho-diphenolic compounds, minor novel litchi flavonoids included monohydroxylated structures. Chlorophyll degradation by 73-92% and 7-38-fold anthocyanin accumulation affected pericarp color throughout the last 15-20 days of on-tree maturation. Postharvest, anthocyanins and (-)-epicatechin largely degraded within the first 3 days, accompanied by severe pericarp browning. Without packaging of the fruit, desiccation initially accelerated polyphenol oxidase-induced oxidation of (-)-epicatechin, but then hindered its further progress. Constant levels of the monohydroxylated (epi)afzelechin indicated no involvement of peroxidase. Acting as antioxidants, anthocyanins retarded (-)-epicatechin degradation. Hence, pinkish-red fruit with a molar ratio of cyanidin 3-O-rutinoside to (-)-epicatechin of >3:100 retained flavonoids best. However, brown polymers masked remaining red pigments.     

Yield and quality of pectins extractable from the peels of thai mango cultivars depending on fruit ripeness

Pectins, recovered from the peels of four mango ( Mangifera indica L.) cultivars by mimicking industrial techniques, were evaluated in terms of yield, composition, macromolecular properties, and technofunctional quality. Freeze-dried peels of mature-green fruits, after major mesocarp softening, and at full ripeness were extracted using hot acid. The pectins were precipitated in propan-2-ol and their crude yields quantified as alcohol-insoluble substance. Like apple pomace, the dried peels provided hardly acetylated (DAc < 6.3%) rapid-set to ultrarapid-set high-methoxyl pectins at starch-adjusted yields of 11-21 g/100 g. However, despite similar high molecular weight fractions and galacturonic acid/rhamnose ratios, their average molecular weight was markedly reduced by a characteristic, almost monodisperse fraction of 16000-19000. Expanded galactans, indicated by galactose/rhamnose ratios of 15-24 mol/mol, probably represented arabinogalactan side-chain fragments withstanding hot-acid extraction at pH 1.5 and 2.0, as implied by arabinose/galactose ratios of 8-15 and 33-56 mol/100 mol, respectively. Limited galacturonic acid contents made the mango peel pectins less valuable than commercial apple pectins with regard to gelling capacity and thickening properties. Whereas starch and matrix glycan fragments almost completely degraded during ripening, depolymerization of pectins and galactans was insignificant. Technofunctional properties, modulated by extraction at different pH values, were ascribed to structural differences influencing macromolecular entanglements.     

Constituents of the leaves of Holarrhena pubescens

The leaves of Holarrhena pubescens yielded a new naringenin glycoside (1), together with naringin, naringenin 7-O-beta-D-glucoside, lupeol, lupeol beta-hydroxyhexadecanoate and ursolic acid. The structure of 1 was determined by spectral analysis.     

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees—The possible participation of endogenous hormones: II. Low temperature and potassium chlorate effects on hormone concentrations in and their export out of leaves

Floral induction in longan (Dimocarpus longan Lour.) trees by low temperature (LT) or potassium chlorate (KClO₃) treatment, is supposed to act, at least partially, by their interference with the hormonal concentration and/or export out of leaves. Therefore the effect of LT and KClO₃ on hormone concentration and transport rate of leaves was investigated in these experiments. Results of experiments below show that LT-, but not KClO₃, treatment considerably increased the leaf export of N⁶ (Δ²-isopentenyl) adenine/N⁶ (Δ²-isopentenyl) adenosine (iP/iPA) together with indole acetic acid (IAA). Export rates of Zeatin/Zeatin riboside (Z/ZR) and gibberellins (GA) were very low and often below the detection limit (<10 ng). Practically no correlation between the concentrations of IAA, and iP/iPA-type CK of leaves and their export rates out of leaves after LT- or KClO₃ treatment were observed. This suggests a specific and independent export rate regulation by these two treatments. Potassium chlorate also strongly increased the production of ethylene in leaves. Whether this burst in ethylene is involved in the FI process, or is merely a stress response of the plant against the herbicide KClO₃, is unknown but could easily be tested by using inhibitors of ethylene biosynthesis/action. The results of these experiments and their effect on hormonal change and FI in the shoot (results of Part I experiments) are discussed.     

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees: Part I. Low temperature and potassium chlorate effects on FI and hormonal changes exerted in terminal buds and sub-apical tissue

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees was achieved in controlled greenhouse experiments by low temperature (LT) and by the application of potassium chlorate at high temperature (HT + KClO₃) during two consecutive seasons. The latter treatment was successful also at temperatures above 20 °C. The present experiment was conducted to investigate possible alterations in the concentrations of plant hormones exerted by these two methods and to relate them to the floral induction process. The following hormones were examined by radioimmunoassay in the shoot apical buds (SAB), and in sub-apical bark and wood: the auxin indole-3-acetic acid (IAA); gibberellins (GAs); and the cytokinins zeatin/zeatin riboside (Z/ZR) and isopentenyl-adenine/isopentenyl-adenosine (iP/iPA).     

Accumulation of all-trans-beta-carotene and its 9-cis and 13-cis stereoisomers during postharvest ripening of nine Thai mango cultivars

Accumulation of beta-carotene during postharvest ripening of nine Thai mango cultivars was assessed after verifying extraction and high-performance liquid chromatographic quantification of the beta-carotene stereoisomers for this sample matrix. No relevant trans-cis isomerization was induced by the analytical procedure. The vitamin A potential of mangoes was evaluated at different ripening stages unequivocally defined by a ripening index (RPIWB). Being rather stable throughout postharvest ripening, the cultivar-specific proportion of cis-beta-carotene isomers ranged from 14 to 40% of the total beta-carotene content. Subjected to the same postharvest ripening conditions, only the cultivars Kaew, Maha Chanok, Chok Anan, and Nam Dokmai #4 developed a bright yellow-orange mesocarp coloration at their fully ripe stage (RPIWB = 1.5-1.8, sugar-acid ratio approximately 50), resulting in total beta-carotene contents of 6544-11249 microg/100 g mesocarp dry weight (DW) and vitamin A values of 892-1573 retinol equivalents (RE)/100 g DW. Contrarily, poor-colored cultivars Mon Duen Gao, Rad, Kiew Sawoei, Okrong Kiew, and Okrong Thong reached total beta-carotene contents of 1019-2195 microg/100 g DW and vitamin A values of 136-298 RE/100 g DW at comparable sugar-acid ratios. Exponential development of mesocarp color (hue angle, H degrees ) and all-trans-beta-carotene levels, respectively, with RPIWB was described for each cultivar, allowing good prediction of mesocarp color and vitamin A value at consumption ripeness.