Ascorbic acid
(AA), vitamin C and organic acids were analysed by HPLC, whereas total phenols and antioxidant capacity
(%DPPH) were measured by spectrophotometry. The results showed that conventional treatment led to a
significant decrease in citric acid (from 1538 to 1478 mg/100 g) and AA (from 36 to 34.3 mg/100 g),
whilst microwave pasteurisation preserved these compounds. Frozen storage maintained AA and vitamin
C, especially in treated samples. Frozen non-treated samples and conventional pasteurised ones preserved
about a 75% and 20% of the total phenols and antioxidant capacity, respectively, whilst in frozen
microwave pasteurised juices this preservation was of 82% and 33%. From these results, the use of microwave
energy may be proposed as an alternative to traditional heat pasteurisation in order to preserve the
natural organoleptic characteristics and essential thermolabile nutrients of grapefruit juice.