Total phenol content and antioxidant activity of fruit smoothies during storage

A fruit smoothie is described as a 100 percent blend of a variety of fruits with no added sugar or additives, no added water and not made from concentrates. Phenols are compounds which contain a hydroxyl group (OH) bonded to benzene (aromatic) rings. Recently, phenols in foods have gained much attention owing to their antioxidant activity and possible beneficial implications in human health such as prevention of certain cancers and cardiovascular diseases1. Total phenols (TP) and antioxidant activity of three fruit smoothies (Blackberries, Raspberry and Boysenberry (BRAB), Mango and Passion fruits (MAP) and Blackcurrant, Acerola cherries and Rosehips (BACAR)) were determined during storage by Folin-Ciocalteu and ferric reducing antioxidant power (FRAP) assays respectively. All measurements were performed at least in three replicates. TP ranged from 1943±70.7 to 2692±21.6 mg gallic acid equivalent/L whereas FRAP ranged from 43217±1225 to 126125±2887 µmol Trolox equivalent/L for the three smoothies on opening. Both TP and antioxidant activity were highest in BACAR, followed by BRAB and lastly MAP. The differences in TP and antioxidant activity of these smoothies could be attributed to their respective fruit ingredients. The smoothies had significant decrease (p < 0.05) in TP during four weeks storage at 4 0C. The decrease in antioxidant capacity was significant (p < 0.05) for BRAB and MAP only. Results also showed that smoothies left unopened at room temperature (21±1 0C) for two days also experienced loss in TP but that of BACAR was insignificant (p > 0.05). There was a higher loss in TP and antioxidant activity when smoothies were opened, part sampled and the remaining stored at 4 0C for four consecutive days. It is therefore important that once a smoothie is opened, it should be consumed within the stated four days and should be quickly closed to minimize oxygen entry which causes the loss of antioxidants. However, the study revealed that the smoothies had high TP and antioxidant activity even during shelf-life at 4 °C which implies that consumption of smoothies may give considerable antioxidant benefits. Correlation between TP and antioxidant activity was strong and highly significant (r = 0.890, p < 0.0001).