ABSTRACT
Flavonoids and hydroxycinnamic acid derivatives, which are located in the upper epidermis of plants, are well known to screen ultraviolet radiation, thus protecting the underlying tissue from these harmful wavelengths. Both classes of secondary products complement each other over the UV spectral region according to their absorption spectra: flavonoids are most efficient as UV-A attenuators while hydroxycinnamates (HCAs) screen well within the UV-B region. Analysis of epidermal transmittance revealed a substantial UV-A screen in Helianthus annuus L. cv. Peredovick. Identifying responsible pigments by HPLC-MS, we found surprisingly low amounts of flavonoids but dominant abundance of the HCA derivatives chlorogenic and di-caffeoyl quinic acid. Both display low UV-A absorbance and thus, should contribute only a little to UV-A protection. However, growth at high light led to a decrease of epidermal transmittance at 366 nm of up to 90%. Underpinning the screening role, HCA autofluorescence microscopy revealed storage to occur predominantly in vacuoles of the upper epidermis. UV-A treatment in the absence of D1-repair resulted in photosystem II inactivation proportional to epidermal UV-A transmittance. Our findings suggest that UV-A protection can be achieved solely with HCAs, apparently through accumulation of high amounts of these compounds.
Subject(s)
Coumaric Acids/chemistry , Helianthus/chemistry , Sunscreening Agents/chemistry , Ultraviolet Rays , Chromatography, High Pressure Liquid , Helianthus/metabolism , Microscopy, Fluorescence , Phenols/chemistry , Phenols/isolation & purification , Plant Extracts/chemistry , Plant Leaves/chemistry , Plant Leaves/metabolism , Spectrometry, Mass, Electrospray IonizationABSTRACT
Quillaja saponin extract comprises both, surfactants and phenolic compounds, which makes it interesting, in particular, for the formulation of sensitive functional food ingredients and its protection against oxidation. The aim of this study was to investigate the antioxidant effect of Quillaja saponin extract in oil/water emulsions. Emulsions stabilised by Quillaja saponin showed decreased oxidation stability due to naturally occurring metals but stability increased to a great extent when a chelating agent was added. Antioxidant efficiency of the saponin extract was determined photometrically by 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assay and by the use of electron paramagnetic resonance spectroscopy (EPR). EPR spectroscopy applying stable hydrophilic and hydrophobic radicals is advantageous, especially for characterisation of antioxidant efficiency at the interface. The extract showed antioxidant activity towards radicals in both environments, aqueous and hydrophobic, indicating the importance of phenolic compounds for the antioxidant properties of Quillaja saponin extract and their presence at the interface facilitated by saponin molecules.
Subject(s)
Emulsions/chemistry , Lipid Metabolism/physiology , Plant Extracts/chemistry , Quillaja Saponins/analysis , Quillaja/chemistry , Oxidation-Reduction , Phenols/chemistry , Surface-Active Agents/chemistryABSTRACT
The influence of postharvest UV-B on its own and in combination with fermentation (e.g. sauerkraut production) on formation and degradation of bioactive compounds was investigated in white cabbage, processed according to traditional Chinese fermentation methods. The pattern of polyphenols was affected by postharvest UV-B: Newly formed coumaroylglycoside, feruloylglycoside, caffeoylglycoside (up to 1 mg/g dry matter; 4 days) and quercetintriglycoside (0.4-0.5 mg/gdm; 4 days) might be related to postharvest increase in enzyme activity in the biosynthesis. Decreasing contents were observed for the glucosinolates glucobrassicin and 4-methoxyglucobrassicin, but the formation of the degradation products dihydroascorbigen and dihydro-4-methoxyascorbigen, which might be related to cell shrinking as mechanical damage. Fermentation resulted in deglycosidation of hydroxycinnamic acids. Newly generated cinnamic acid from coumaric acid aglycone was detected in fermented plant material combined with UV-B (50 µg/g). Glucosinolates and dihydroascorbigens were completely degraded. This study shows exemplary UV-B as a supplemental step to improve the nutritional quality of processed plants.
Subject(s)
Brassica/chemistry , Fermentation , Food Analysis/methods , Food Irradiation/methods , Plant Leaves/chemistry , Ultraviolet Rays , Brassica/radiation effects , Food Storage , Glucosinolates/analysis , Indoles/analysis , Plant Leaves/radiation effects , Polyphenols/analysisABSTRACT
A systematic investigation was carried out on the influence of fermentation on glucosinolates and their degradation products from fresh raw cabbage, throughout fermentation at 20 °C and storage at 4 °C. Glucosinolates were degraded dramatically between Day 2 and 5 of fermentation and by Day 7 there was no detectable amount of glucosinolates left. Fermentation led to formation of potential bioactive compounds ascorbigen (13.0 µmol/100 g FW) and indole-3-carbinol (4.52 µmol/100g FW) with their higher concentrations from Day 5 to Day 9. However, during storage indole-3-carbinol slowly degraded to 0.68 µmol/100 g FW, while ascorbigen was relatively stable from Week 4 until Week 8 at 6.78 µmol/100 g FW. In contrast, the content of indole-3-acetonitrile decreased rapidly during fermentation from 3.6 to 0.14 µmol/100 g FW. The results imply a maximum of health beneficial compounds after fermentation (7-9 days) in contrast to raw cabbage or stored sauerkraut.
