The authors of this article proposed a method of determining the levels of ascorbic acid and another similar method for carotenoids specifically lycopenes and β-carotene in mango, kiwi and four varieties of tomatoes: raf, cherry, daniela, rambo. The methods interface reverse phase liquid chromatography (LC) to mass spectroscopy (MS) detection which allows for the identification, quantification, and confirmation of carotenoids and ascorbic acid with good efficacy. Furthermore, the method was used to investigate how freezing affects the concentration of ascorbic acid in daniela and rambo tomatoes. Finally the authors analyzed the impact of processing on tomatoes by comparing ascorbic acid levels in unprocessed tomatoes to that of dried tomato and tinned tomato enriched. Previous studies in this area coupled liquid chromatography with UV-vis which could not give a definitive confirmation of the analyzed compounds. In addition, LC-MS was used to identify carotenoids but never for quantitative purposes.
In the experiments, ascorbic acid and carotenoids were recovered from fruits by extractions. Electrospray ionization probe (ESI) negative ion mode in MS was used to verify the presence of ascorbic acid through the detection of fragmental ion peaks. Chemical ionization atmospheric pressure (APCI) positive ion mode in which the carotenoids were protonated was used for the confirmation of lycopene and β -carotenes because the carotenoids could not be fragmented. To validate their methods, the authors constructed calibration curves of ascorbic acid, lycopene, and β -carotene in tomato matrix at different concentration levels through standard additions of the compounds.
The study found that mango and kiwi had low carotenoid levels. Interestingly, kiwi had the most ascorbic acid level followed by mango. Of the 4 tomatoes varieties raf has the highest amount of ascorbic acid and the highest carotenoid levels of all the fruits that were analyzed. The authors observed that freezing tomatoes reduce ascorbic acid content by approximately half of the original concentration. Processed tomatoes also result in a loss of ascorbic acid when dried tomatoes were discovered to have low ascorbic acid content. The authors attributed the loss to the oxidative reactions that occurred while the tomatoes were being processed.
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3 comments:
So in order to prevent tomatoes from decrease in ascorbic acid it needs special care. What condition did the author use to test the effect of freezing on ascorbic acid? I often put tomatoes in very low temp of refrigerator. What is the ideal condition for tomatoes?
Ernest,
Tomatoes should be stored at room temperature. Tomatoes that are oeverly ripe may be put in the fridge to prevent molding or rotting.
Many people refrigerate them by mistake.
When investigating the effect of freezing on tomatoes, the authors used ones that were frozen at -24◦C for one month which did not reflect real life scenarios. Many consumers would never freeze their tomatoes or keep them frozen for such a long period of time. It would be more beneficial to know the results using realistic conditions. In my critique I suggest that the authors should also try to investigate how freezing affects the ascorbic acid content in kiwi and mango. Freezing results in the loss of ascorbic acid in tomatoes but it might not be the case for kiwi and mango.
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