Effect of thermal and high hydrostatic pressure processing on antioxidant activity and colour of fruit smoothies

Fruit smoothie samples were thermally treated (P-70 >= 10 min) or high hydrostatic pressure (HHP) processed (450 MPa) with holding time of 1, 3 or 5 min and antioxidant activity, phenolic content and colour values (L*, a* and colour intensity) were determined. Significant reductions in antioxidant activity (p<0.001) and phenolic content (p<0.001) were observed at the applied pressure and a maximum treatment time of 5 min. Mean values for redness (a*) showed an increase (p<0.001) in HHP processed smoothies compared to fresh. As expected, storage also had a significant effect on colour variables but the effect was more pronounced in high pressure treated samples stored for 30 days. Both colour and antioxidant activity were significantly affected by high pressure processing. Therefore, process optimisation of high pressure systems should be considered by processors prior to its adoption as a preservation technique in order to minimise the effect on the quality of fruit smoothie products. Industrial relevance: Fruit smoothies have become popular with consumers and may significantly contribute to daily antioxidant intakes. Thermal processing has been shown to reduce the antioxidant activity of fruits, thus non-thermal methods of pasteurisation such as high hydrostatic pressure processing could help retain antioxidants in fruit smoothies offering a unique selling point for processors. The present study focussed on assessing the effect of thermal and high pressure processing on the antioxidant activity and phenolic content of fruit smoothies. Since decreases in levels of antioxidants were noted during long term storage it would appear that higher pressure treatments (>450 MPa) might be required for better retention of antioxidant compounds in fruit smoothies. (C) 2010 Elsevier Ltd. All rights reserved.