Quantitation of vitamin C content in herbal juice using direct titration

Vitamin C content in fresh and freeze-dried herbal juice, such as guava (Psidium guajava Linn.) emblic myrobolan (Phyllanthus embica Linn.), lemon (Citrus aurantifollia Swing), sweet pepper (Capsicum annuum Linn.) Garcinia schomburgkiana Pierre and passion fruit (Passiflora laurifoia Linn.) was determined by direct titration with iodine. The method showed excellent linearity (r(2) > 0.99) over the concentration ranges tested (100-500% of the amount found in the juice samples), good precision (R.S.D. < 1.5%) and recovery (> 97%). The limit of detection and limit of quantitation were 2.2 and 7.3 mg, respectively. The amount of vitamin C found were 80.1 mg/100 g for guava, 226.0 mg/100 g for emblic myrobolan, 52.8 mg/100 g for sweet pepper, 39.1 mg/100 g for passion fruit, 10.5 mg/100 g for lemon and 4.6 mg/100 g for G. schomburgkiana. The stability of vitamin C during the first 4 weeks was remarkably improved after freeze-dried process. The percent reductions of vitamin C after freeze-dried process were 41.4 and 20.4% for guava and emblic myrobolan, respectively. After 8 weeks, the freeze-dried samples contained only traces amount of vitamin C tested by thin layer chromatography. (C) 2002 Elsevier Science B.V. All rights reserved.