Vitamin C is an essential vitamin for human nutrition; with the L-ascorbic
acid (AA) being the active form of vitamin C. Hence, determination of the
L-ascorbic acid in the natural and processed foods is very important. In the
past, plenty of methods based on the reversible redox reaction of AA
oxidation/DHA reduction were developed. Because of L-ascorbic acid
instability in aqueous solutions, it is useful to analyze various types of
extraction. The aim of this study is to compare three different methods and
three different extractants for the L-ascorbic acid determination. Fruits
(kiwi, lemon, orange, and grapefruit) were purchased from a local market. The
L-ascorbic acid in these four samples was determined by the three different
methods: the AOAC, the HPLC method with three different types of extractions,
and the colorimetric method using ascorbate-oxidase. For the HPLC
measurements, one part of the fruits was extracted with distilled water, the
second with potassium hydrogen phosphate, and the third with 3%
meta-phosphoric acid (MPA) in 8% acetic acid. The HPLC measurements of each
sample were repeated three times, the AOAC titration was repeated five times,
and in the calorimetric method three measurements were performed. The results
were statistically evaluated related to sample basis. Statistical analysis
shows that there is a significant difference between the results for all
three methods of extraction for all samples, except for the grapefruit sample
where no significant difference was observed between the results obtained
after the buffer extraction (E2) and the metaphosphoric acid in acetic acid
extraction (E3). Discriminative analysis for the HPLC determinations proves
that there is a clear difference and defined border between the samples in
relation to the methods of extraction during the HPLC determination.
Prospect of Using Ascorbate Oxidase from Satsuma Mandarin (Citrus unshiu Marc) for Ascorbic Acid Determination by the Difference Spectral Method.