J. E. Hårdh
Yliopiston puutarhatieteen laitos, Viik
Analyses on the vitamin C content of black currants were performed in 1960—1963 using the method of ROBINSON and STOTZ (7) and amyl acetate for extracting (2, 4). 130 samples were examined yearly, two determinations on each. Samples of 21 black currant varieties from Viik (60° 10') and from Maaninka (63° 9') showed, as in previous tests, that among the varieties with the highest vitamin C content are Westwick Choice, Magnus, Roodknop, Boskoop Giant, Laxtons Tinker, Wellington xxx and Silvergieter, some of the poorest being Climax Black, Brödtorp and Holger Danske (Table 1). During the ripening the vitamin C content markedly decreases, as shown on 10 varieties, on fully ripe berries this was up to 30 % less than in unripe, green berries (Table 2). Fertilizer tests in 3 localities did not show any correlation between the nitrogen, phosphorus or potassium and the vitamin C content in the Brödtorp variety (Table 3). The weather factors during the growing season and the day length are discussed. The tests described here do not give reliable results in regard to these problems, but from Table 1 it is obvious that the low temperature in July 1962 preserved the vitamin C content during the ripening as compared with the data in 1960, 1961 and 1963. The interaction of the day length and the vitamin content can not be accurately determined in tests of this kind, but again it is possible that the 30 % higher vitamin C content in 1962 in berries grown in Rovaniemi (60° 30', mean daylength in July 20 h 10 m) as compared to the berries from Viik (60° 10', mean daylength in July 17 h 35 m) might be due to the longer day and to the higher total radiation energy during the growing time of the berries.
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