Polyphenol content and antioxidative activity in apple purees with rhubarb juice supplement

The purpose of the present study was to evaluate the effect of rhubarb juice addition and peeling in apple puree production and storage on its phenolic composition, antioxidant activity and colour. The apple material used in this study was of two varieties: Sampion and Idared. The apple purees prepared in three variants (control purees, peeling purees and purees with 5% of rhubarb juice) were stored for 3 and 6 months at 30 degrees C. Apple purees were investigated for their antioxidant activity, change of colour and contents of phenolic compounds plus the polymer procyanidins and degree of polymerization (DP). The preparation of purees from apples without peeling and the addition of rhubarb juice during puree preparation had significant influence on polyphenol content. The puree prepared from peeled apples of Idared variety had phenolic content 2.2 times lower than the control sample (non-peeled apples). The highest level of total polyphenols was found in Idared + rhubarb sample (129.82 mg 100 g(-1) puree). The content of this compound in Idared control sample was more than 2.8 times lower than in Idared purees with rhubarb. The use of non-peeled Idared apples and 5% of rhubarb juice in puree preparation significantly increased polymeric procyanidins from 11.68 to 75.20 mg 100 g(-1) and other phenolics from 9.23 to 54.62 mg/100 g. This effect for Sampion apples was smaller. The procyanidins during purees storage were more stable in samples with rhubarb juice addition. The puree samples with the addition of rhubarb juice had higher antioxidant activity measured using ABTS (2,2'azinobis-(3-ethylbenzthiazoline-6-sulphonic acid)) than puree samples without the addition (two times higher for Idared variety) of rhubarb juice. After 3 and 6 months of storage at temperature 30 degrees C, the antioxidant capacity decreased in all purees. Rhubarb juice had only high and positive effect on L* value in the case of Idared variety. The results showed that all Sampion apple purees had higher L* values than Idared.