Conclusion

125 more complex tetramer A2 is the least UV-active compound (Pedan, Fischer, & Rohn, 2015a). Consequently, using (-)-epicatechin as standard underestimates the amount of oligomeric PAs in a sample. To minimize the problem of using less suitable standards, it is proposed to calculate the content of PAs expressed at hand of closely related standard compounds, e.g., for monomers as mg (-)-epicatechin, for dimers as proanthocyanidin B2 equivalents, for trimers as proanthocyanidin C1 equivalents and for fractions more complex or equal than tetramers as mg cinnamtannin A2 equivalents, as long as the corresponding standards are not available.

Most of the studies reported in the literature showed cascading, diminished levels of the polyphenol content from monomers to decamers. In this study, the calculation at hand of related standards provided evidence that raw cocoa beans possess a high amount of pentameric PAs with 7.1 mg cinnamtannin A2 equivalents/g compared to pentameric PAs with 4.3 mg ECE/g when calculated as (-)-epicatechin (Table 2). During the chocolate manufacturing process, the levels additionally decrease, whereby already after fermentation the pentameric PAs decreased significantly to 4.35 mg cinnamtannin A2 equivalents/g and more monomeric PAs are formed. There is a more than 1.5-fold difference in the response between the PAs expressed as (-)-epicatechin equivalent or expressed as related standard compounds. Furthermore, this kind of evaluation indicates that pentameric PAs are the most abundant compounds in raw cocoa beans with the highest antioxidant capacity.

As presented in Fig. 3a, the oligomeric PA profile of the model chocolate manufacturing expressed as (-)-epicatechin equivalent is more shaped as a cascade with a decrease from monomeric to oligomeric PAs. In contrast, Fig. 3b shows the oligomeric PA profile of the model chocolate manufacturing and the degree of polymerization expressed as proanthocyanidin equivalents, whereby the profile occurs more accented to tetrameric up to heptameric PAs.

The complexity of oligomeric PAs and an appropriate evaluation of analytical methods are also discussed by Schofield, Mbugua, & Pell (2001). They analyzed the relationship between the tannin concentration and the absorbance of three main standard compounds delphinidin, cyanidin, and quebracho at 550nm using the butanol/HCl assay. They showed a 30-fold difference in response between the UV-reactive delphinidin and the least UV-reactive quebracho. As a result, tannin concentration is underestimated when quebracho is used as standard for tannin-containing plants.

126 The highest content of phenolic compounds can be obtained for raw unfermented cocoa beans. During the chocolate manufacturing process, the total PA content decreased continuously, whereby the final chocolate contained only about 20 % of the initial PA content.

In the present study, the degree of polymerization also changed from a maximum of DP13 to DP11. The present study could confirm the main impact on the PA profile caused by fermentation resulted in a loss of the total PA content (™ DP1 - DP13) of approx. 11 % and a declination of the total PA content (™ DP1 - DP13) during roasting resulted of approx. 60 %.

In comparison with other literature, this study helps to understand the influence of time/temperature combination, which is often used in order to modulate and increase the functional properties of some foods. For a general understanding, more emphasis should be paid to the ‘PA hump’ and along with it oligomeric PAs with DP >1 3. This study clearly showed that the ‘PA hump’ increased during the fermentation process and dropped during roasting, whereby higher oligomeric PAs of higher molecular weight are formed during fermentation and decreased during roasting.

For the quantitative determination of the PA amounts, it should be considered that a calculation as epicatechin equivalents (ECE) leads to other results than the calculation as PA equivalents (PAE) up to DP4. Through calculation as ECE, the PA profile of raw cocoa beans appears to cascade down with DP1 > DP2 > DP3 etc. In contrast, when calculating the PA as PAE, the PA profile appears to have a peak at DP5 > DP4 > DP3 etc.

Finally, the major extractable PAs in cocoa could be determined using NP-HPLC-online-DPPH. A positive relationship was shown between DPPH scavenging activity and oligomeric PAs of higher molecular weight. Despite the complexity of cocoa polyphenols, a large number of novel cocoa flavonoids have already been identified recently (e.g., Patras, Milev, Vrancken, & Kuhnert, 2014). But further efforts need to be directed towards the analysis of polymeric PAs and the investigation of the ‘PA hump’.

Acknowledgments

We thank Esther Kokabi for providing the manufactured chocolate samples.

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Further reading

Kadow, D., Niemenak, N., Rohn, S., & Lieberei, R. (2015). Fermentation-like incubation of cocoa seeds (Theobroma cacao L.) - Reconstruction and guidance of the fermentation process. LWT – Food Science and Technology, 62, 357-361.

Oracz, J., Nebesny, E., & ĩyĪelewicz, D. (2015). Changes in the flavan3ols, anthocyanins, and flavanols composition of cocoa beans of different Theobroma cacao L. groups affected by roasting conditions. European Food Research and Technology, 241, 663-681.

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5. Weiterführende Ergebnisse und zusammenfassende

Im Dokument Charakterisierung von oligomeren Kakao-Proanthocyanidinen : Extraktion und chromatographische Trennung mit simultaner Bestimmung der antioxidativen Kapazität (Seite 135-141)