ELECTRICAL PROPERTIES OF APPLE CULTIVARS DURING RIPENING AND STORAGE

Abstract

Apple cultivars belonging to conc. Jonathan (Jonnee, Jonagold, Jonathan M41) and conc. Golden (Goldenspur, Mutsu) were used to study their electrical properties during ripening and storage. Based on ripening observations and maturity changes in September, the apples were harvested at three different times and were stored for 5, 6 or 7 months. Fruit bioelectric parameters were ascertained in the collenchyma and parenchyma cells under the epidermis. The theoretical basis of determining bioelectric parameters is the Hayden's low frequency RC model of the biological material. The |Z| values in the frequency range of 10 to 20 kHz can be fitted to a straight line with probability higher than 95%. The slope of this line - the differential coefficient - has a high value for unripe (early harvested) apples and shows a decreasing tendency during ripening (for apples later harvested). The Hayden's model was tested for the different apple varieties by t-distribution of two samples. The Hayden's model can also be used for characterization of the apple cultivars during storage. Significant differences were seen in 'Jonathan M41' apples harvested at different dates. In the case of 'Jonagold' ('Golden Delicious' hybrid) and 'Gloster' ('Delicious' hybrid) there was no significant difference in apples harvested at different dates. It is important to emphasize that our results, together with maturity indices, the cultivation and storage technological experiments can be applied to choose optimal harvest and storage times. Using the simple Hayden's model the resistance of cytoplasm and the cell wall was also determined from the complex impedance. There was no significant change in the resistance of the cytoplasm during ripening and storage, but there was a significant decrease in the resistance of the cell wall. At the end of the 7-month storage, in the resistance of cell wall tended to equalize for 'Jonagold' and 'Jonathan' apples.