Open access publications in the SLU publication database

Abstract

Apple (Malus × domestica Borkh.), a popular and widely cultivated fruit world-wide, contains bioactive triterpenes and phenolic compounds with potentially valuable pharmacological functions. This thesis investigated the effects of pre-harvest and postharvest factors on concentrations of these bioactive compounds in apples. It also studied the effect of ozone treatment, before or during storage, combined with cold storage on triterpene and phenolic compound concentrations in apples and the antifungal activity of triterpene-enriched crude extract.

Concentrations of two major triterpenes, oleanolic acid and ursolic acid, in apple peel varied significantly between cultivars, with the late-ripening cultivar ‘Gloster’ having higher concentrations than the earlier ripening ‘Discovery’ and ‘Aroma’. The concentrations were higher in peel from the shaded side than from the sun-exposed side of both ‘Discovery’ and ‘Gloster’ apples. Harvest time and storage methods had minor effects on the concentrations, although some between-cultivar variation was observed. Inoculation with Penicillium expansum decreased oleanolic acid concentration in ‘Discovery’ and ‘Gloster’ at harvest in one study year and decreased ursolic acid concentration in ‘Aroma’ after cold storage. Oleanolic acid and ursolic acid concentrations in apple peel showed non-consistent changes in different cultivars after bruising. On four of six harvest occasions during a two-year study of ‘Aroma’, the concentrations were higher in peel of apples from rootstock ‘MM106’ than from ‘M9’. Total polyphenolics concentration was higher in ‘Amorosa’ peel than in ‘Santana’ peel at harvest and after four months of storage.

Ursolic acid concentration in apple peel was almost unaffected by ozone treatment, but oleanolic acid concentration showed differing responses to varying ozone application. The concentrations of different bioactive compounds both increased and decreased after ozone treatment, but the changes were within the range of fluctuations observed in untreated apples during storage. Low-dose ozone treatment (0.5 ppm gaseous ozone one hour per day) during four months of cold storage did not affect total polyphenolics in ‘Amorosa’ and ‘Santana’ flesh, but increased total polyphenolics in ‘Amorosa’ peel and decreased them in ‘Santana’. Short-term ozone treatment (2.5 ppm gaseous ozone and ozonated water, alone or combined) before one month of cold storage reduced total polyphenolics content in apple peel, while inconsistent responses were observed in apple flesh.
Triterpene-enriched water significantly inhibited mycelial growth of all pathogens studied, but inhibited conidia production differently in each pathogen.