engleski

Identification of polyphenols and methylxanthines in teas, herbal infusions, coffee and cocoa products by near infrared spectroscopy (NIRS) compared to high performance liquid chromatography (HPLC).

Bioactive compounds of plant origin are widely used in food industry as functional ingredients. Tea, medicinal plants and coffee are among the richest sources of bioactive compounds (polyphenols and methylxanthines), proven to exhibit positive health effects. Application of bioactive compounds imply development of advanced analytical techniques which enable the identification of new phytochemicals, characterization of their chemical structure, quantification, quality control, etc. High performance liquid chromatography (HPLC) is the most extensively used but quite time consuming analytical technique for quantification of bioactive compounds. Therefore, use of near infrared spectroscopy (NIRS) was evaluated as the alternative. Six types of „true“ teas (black, white, oolong), six herbal infusions and four different coffee brews were analyzed by HPLC technique in order to evaluate the contents of most representative polyphenolic compounds and methylxanthines. The results of HPLC analysis were compared to the ones obtained by NIRS and in order to determine whether the NIRS can be used as an identification technique for the analysis of bioactive compounds. The obtained results revealed a variability in epigallocatechin gallate (EGCG) and caffeine content of true teas. Green tea (Sencha) contained the highest content of EGCG (226.88 mg/L), while black tea (Bherjan) contained the highest content of caffeine (358.23 mg/L). The content of caffeine and chlorogenic acid in coffee was affected by brewing technique. Instant coffee contained the highest content of caffeine (8.09 g/L). Rosmarinic acid was identified only in herbal infusions. The principal component analysis of NIRS spectra confirmed the possibility to identify the chosen polyphenols and methylxanthines using this analytical technique, and revealed a high correlation of the NIRS spectra with the results of HPLC analysis. The obtained results imply on the potential of using NIRS for the rapid identification of various phytochemicals in food products.

caffeine; high performance liquid chromatography; NIRS; polyphenols; teas

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