Effects of latitude and weather conditions on contents of sugars, fruit acids, and ascorbic acid in black currant (Ribes nigrum L.) juice.

The genetic background determined the composition of black currants and the compositional response to weather conditions. The variety Melalahti had higher values for glucose and sugar/acid ratio and lower contents of fructose, citric acid, quinic acid, and vitamin C than the varieties Mortti and Ola (p<0.05). In comparison to black currants grown in northern Finland (latitude 66 degrees 34' N), the berries grown in southern Finland (latitude 60 degrees 23' N) had higher contents of fructose, glucose, sucrose, and citric acid (by 8.8, 6.1, 10.0, and 11.7%, respectively) and lower contents of malic acid, quinic acid, and vitamin C (by 31.1, 23.9, and 12.6%) (p<0.05). Fructose, glucose, and citric acid in Melalahti were not influenced by the weather, whereas their concentrations in Mortti and Ola correlated positively with the average temperature in February (Pearson's correlation coefficients = 0.53-0.79, p<0.01) and July (Pearson's correlation coefficients = 0.63-0.87, p<0.01) and negatively with the percentage of the days with a relative humidity of 10-30% from the start of the growth season until the day of harvest (Pearson's correlation coefficients = from -0.47 to -0.76, p<0.01). Positive correlations existed between fructose and glucose (Pearson's correlation coefficients = 0.95-0.96, p<0.01), citric acid and fructose (Pearson's correlation coefficients = 0.57-0.75, p<0.01), as well as between citric acid and glucose (Pearson's correlation coefficients = 0.56-0.70, p<0.01) in the three varieties because of the closely related metabolic pathways.