Sugar and acid-related quality attributes and enzyme activities in strawberry fruits: Invertase is the main sucrose hydrolysing enzyme

This paper presents sugar and organic acid content and composition, the principal determinants of flavour, of strawberries of the cultivars Festival and Ventana at four consecutive developmental stages. The metabolite profiles of these two cultivars were very similar. Glucose was the predominant sugar at approximately twice the concentration of fructose and sucrose. Total acid concentrations were five times lower than total sugar concentrations in ripe berries, with citrate comprising roughly two thirds of the total acid content. The maximum extractable catalytic activities of key enzymes in the relevant metabolic pathways were also quantified during berry development, in an attempt to elucidate possible correlations. Sucrose synthase activity was very low or undetected, while neutral invertase activity was relatively high, suggesting that sucrose synthase does not make a significant contribution to sink strength in these cultivars. Three enzymes, invertase, pyrophosphate-dependent phosphofructokinase (PFP) and fructose-1,6-bisphosphatase (FBPase), showed distinct activity patterns during development and may affect sugar and acid accumulation and sugar composition of strawberries.