Maja Mikulic Petkovsek

The influence of organic/integrated production on the content of phenolic compounds in apple leaves and fruits in four different varieties over a 2-year period

BACKGROUND Phenolics in fruit may be influenced by the fruit type, cultivation conditions of a plant, climatic conditions, growing season, storage conditions, and industrial processing. The aim of this study was to compare single phenolic compounds, total phenolics and antioxidant capacity of four varieties of apple grown under organic and integrated conditions over a 2-year period. RESULTS Several different phenolic compounds belonging to the groups of hydroxycinnamic acids, flavanols, dihydrochalcones, flavonols and anthocyanins were quantified. The levels of all analysed groups of phenolics were higher (not always significantly) in the organically grown apple leaves and fruit than in the leaves or apples from integrated production. Leaves from organic trees had 10-20% higher content levels of total phenols than the leaves from trees in the integrated growing system. In both years, organic production affected the increase in the antioxidant activity of apple peel. Organic apples have higher total phenolic content than the integrated grown ones. CONCLUSION Cultivation type had an important influence on the polyphenolic level and antioxidant capacity of the apple fruits and leaves. Apples from organic production showed a higher content of hydroxycinnamic acids, flavanols, dihydrochalcones, quercetins and total phenolics than apples from integrated cultivation.

Seasonal changes in phenolic compounds in the leaves of scab-resistant and susceptible apple cultivars

Leaf samples were collected from apple varieties susceptible and resistant to apple scab [Venturia inaequalis (Cke.) Wint.] from June to September for 2 yr between 2005 and 2006. These were analyzed for phenolic compounds, using high-performance liquid chromatography (HPLC). In the apple leaves, the following hydroxycinnamic acids were detected: chlorogenic, caffeic and p-coumaric acids; the following dihydrochalcone: phloridzin, and the following flavonoids: epicatechin, catechin, rutin and quercitrin. The total of phenolic compounds in apple leaves was determined spectrophotometrically, using the Folin-Ciocalteu method. During the growing season, the content of phenolic compounds changed and was related to the physiological stage of the tissue and cultivar used. Each phenolic compound had its own curve of seasonal changes in concentration. In 2005 there was no significant change in total phenols during the growing season. In 2006, their content changed significantly during the growing season; statistica...

Polyphenol metabolism of developing apple skin of a scab resistant and a susceptible apple cultivar

During fruit development, the concentration of main polyphenols (flavonols, flavanols, dihydrochalcones, hydroxycinnamic acids, anthocyanins) and the activities of related enzymes (phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, flavonol synthase, peroxidase) were monitored in apple (Malus domestica Borkh.). The seasonal survey was performed at five different sampling dates and included the healthy peel of the resistant cultivar ‘Florina’ and healthy peel, scab symptomatic spot and the tissue around the infected spot of the susceptible cultivar ‘Golden Delicious’. From all enzymes tested, chalcone synthase/chalcone isomerase had the highest activity in both cultivars, while phenylalanine ammonia lyase had the lowest. The healthy peels of the susceptible and the resistant cultivar did not show differences in the accumulation of the main polyphenol groups present in the apple skin. However, in the resistant cultivar ‘Florina’, an increase of polyphenol enzyme activities could be observed in late stages of fruit development, which seems to be related to the anthocyanin accumulation in ripe fruits. Significant differences in the polyphenol metabolism were observed in the three different tissues of the susceptible cultivar ‘Golden Delicious’. Increased concentrations of hydroxycinnamic acids, dihydrochalcones and flavan-3-ols were found in the scab symptomatic spots and surrounding tissues. Phenylalanine ammonia-lyase, dihydroflavonol 4-reductase, flavanone 3-hydroxylase and peroxidase showed higher activities in the scab symptomatic spot compared to other analysed tissues, whereas the activities of other enzymes remained unchanged. Highest induction of polyphenol accumulation after scab infection was observed in early developmental stages, whereas enzyme activities were increased in later stages.

Response of the phenylpropanoid pathway to Venturia inaequalis infection in maturing fruit of ‘Braeburn’ apple

SummaryThis study investigated the activities of key enzymes in the phenylpropanoid pathway and the accumulation of phenolic products in apple peel in response to infection with Venturia inaequalis [(Cooke) G. Wint.]. We compared healthy apple peel with apple peel showing symptomatic scab lesions, and with peel tissue from 1 – 2 mm around the scab lesions in fruit 1 month before maturity [140 d after full bloom (DAFB)] and at physiological maturity (175 DAFB). Infection with V. inaequalis enhanced the synthesis of some phenolic compounds. Compared to healthy peel, scab lesion tissue had ≤ 3.1-times higher hydroxycinnamic acid content, ≤ 1.3-times higher dihydrochalcone content, and ≤ 3.9-times higher flavan-3-ol content. Scab lesions showed slightly higher phenylalanine ammonia-lyase, chalcone synthase, chalcone isomerase, flavonol synthase, and dihydroflavonol 4-reductase activities. The total amount of phenolics remained relatively stable between the two sampling dates, except for epicatechin and caffei...Summary This study investigated the activities of key enzymes in the phenylpropanoid pathway and the accumulation of phenolic products in apple peel in response to infection with Venturia inaequalis [(Cooke) G. Wint.]. We compared healthy apple peel with apple peel showing symptomatic scab lesions, and with peel tissue from 1 – 2 mm around the scab lesions in fruit 1 month before maturity [140 d after full bloom (DAFB)] and at physiological maturity (175 DAFB). Infection with V. inaequalis enhanced the synthesis of some phenolic compounds. Compared to healthy peel, scab lesion tissue had ≤ 3.1-times higher hydroxycinnamic acid content, ≤ 1.3-times higher dihydrochalcone content, and ≤ 3.9-times higher flavan-3-ol content. Scab lesions showed slightly higher phenylalanine ammonia-lyase, chalcone synthase, chalcone isomerase, flavonol synthase, and dihydroflavonol 4-reductase activities. The total amount of phenolics remained relatively stable between the two sampling dates, except for epicatechin and caffeic acid which decreased in amount toward fruit maturity, and levels of catechin which increased in more mature fruit. During fruit maturation, only chalcone synthase and chalcone isomerase activities decreased in all tissues examined. This study showed that the phenylpropanoid pathway in apple fruit peel changed significantly following infection with the apple scab pathogen.