Polyphenol content and antioxidant capacity of apple fruit: effect of cultivar and storage conditions

The benefits of fruits and vegetables are often attributed to their high antioxidant content. Research supports a role of secondary plant metabolites particulary polyphenols in the prevention of degenerative diseases e.g. cardiovascular diseases and cancer. Apple fruit are an important source of secondary plant metabolites and one of the major phenol sources being consumed during the whole year. The present investigation was undertaken to determine antioxidant capacity in selected apple cultivars depending on cultivar and different modes of postharvest storage. Additional storage at 20 °C was tested to simulate the conditions at the consumers’ home (shelf life). Antioxidant capacity differed between the cultivars. Cold storage (1 °C) for 4.5 months increased the antioxidative capacity and polyphenol content in most of the cultivars. Shelf life led to a decrease in polyphenol content and in antioxidant capacity. Storage under controlled atmosphere led to low increases of both antioxidant capacity and polyphenol content. In some cultivars polyphenol content remained stable. After the shelf life period lower values for antioxidant capacity were determined, in combination with no changes in phenol content. Correlation analysis showed a positive correlation between total phenols and antioxidant capacity (TEACValue). Lipophilic antioxidants decreased during storage. Storage experiments indicated that a high content of polyphenols and antioxidants can be sustained by optimal storage conditions, these fruit may contribute to an antioxidant rich diet and may impart health benefits

UV-B induced damage and recovery processes in apple leaves as assessed by LIF and PAM fluorescence techniques

The capability of laser-induced chlorophyll fluorescence (LIF) and pulse-amplitude-modulated (PAM) fluorescence technique as well as RED/NIR-light reflection measurements for detection and quantification of UV-B induced damages was evaluated in greenhouse experiments with apple seedlings (Malus domestica Borkh.). Photosynthetic recovery from short-term UV-B stress was assessed during 7 days after UV-B treatment with the PAM fluorometer. The exposure of apple leaves to UV-B doses in the range of 10-26 W m-2 for 180 minutes (UV-BBE dose = 5.4-14 kJ m-2) affected neither chlorophyll content nor leaf reflection. Although UV-B damage was not visually evident 2 hours after irradiation, it could be detected by PAM and LIF fluorescence techniques with equivalent success. The intensity of LIF, estimated as the integral of fluorescence spectrum, was reduced after UV-B irradiation by 19-30%. A stronger decrease in F686 compared to F740 fluorescence resulted in significantly lower F686/F740 values in all UV-B treatments.Apple leaves displayed a strong and significant reduction in maximum fluorescence (Fm) and a slightly increase in ground fluorescence (Fo) 2 hours after UV-B treatment, as documented by PAM fluorescence measurement. Negative linear regressions between investigated UV-B doses and selected PAM parameters were found with determination coefficients (R2) of 0.50 for Fv, 0.48 for Fv/Fm, and 0.58 for Fv/Fo. Among the PAM and LIF parameters tested, the Fv/Fo ratio appeared most sensitive for detection of UV-B induced damages displaying greatest changes and strongest correlation with the applied UV-B doses. PAM fluorescence images of apple leaves visualised an enhanced spatial heterogeneity of photosynthetic activity with increasing UV-B dose. The disturbance in photosynthetic functionality was followed by a continuous recovery process as indicated by restoring Fo and Fm parameters. A decline in maximum photochemical efficiency Fv/Fm from 0.80 to 0.72 and 0.43 after exposure to 20 W m-2 for 240 and 360 minutes (UV-BBE = 14.4 and 21.6 kJ m-2), respectively, was followed by recovery at 7 x 10-4 and 5 x 10-3 units per hour during the first 48 hours after UV-B treatment. The recovery curves of Fm, Fv, Fv/Fm and Fv/Fo parameters during a week after UV-B irradiation were well fitted with exponential rise to maximum function, such as: y = yo + a (1 - e-bx). However, within 7 days after exposure to UV-B light, apple leaves displayed 14% or 4% lower Fm, and 5% or 1% lower Fv/Fm values compared with control plants, indicating only a partial recovery from photoinhibition and irreversible damages in PSII

Improvement of Mg uptake of grapevine by use of rapeseed oil ethoxylates for foliar application of Mg

To improve the uptake of foliar-applied Mg a new group of toxicological and ecotoxicological harmless surfactants (rapeseed oil ethoxylates) with an average of 5 (Agnique RSO 5®), 10 (Agnique RSO 10®), 30 (Agnique RSO 30®) and 60 (Agnique RSO 60®) units of ethylene oxide (EO) was evaluated as adjuvants for a MgSO4 and Mg(NO3) formulation. The impact of the surfactants on Mg penetration was studied using astomatous cuticular membranes isolated from mature tomato fruit. The biological efficacy of a formulation, containing castor oil, ionic and non-ionic surfactants with and without addition of RSO 5 was investigated in two vineyards at the Moselle valley, cvs Riesling and Regent. Especially RSO 5-surfactant increased Mg penetration through isolated cuticles. Under field conditions, Mg application enhanced significantly the Mg content in leaves. The Mg level in bunch stems merely increased when formulated 'Bittersalz' was applied. 'Magnisal' and formulated 'Magnisal' reduced markedly Mg deficiency symptoms in leaves and increased Mg content in leaves of cv. Regent.