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Abstract
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(PhD thesis for Pennsylvania State University)
Chocolate has recently gained attention for its high levels of flavanol antioxidants. These compounds, implicated in protection against cardiovascular disease, inflammation, and cancer, have become the object of a large quantity of research that seeks to fully appreciate the significance of flavanols for human health. Continuing in that vain, this thesis aims to recognize the bioactive role of flavanols in chocolate, but points out that flavanols are important not only in terms of human health, but also to other issues in chocolate production. Flavanols contribute to chocolate flavor and may also offer disease resistance to cacao seeds prior to harvest.
Both flavor and disease resistance are difficult to breed for and a better understanding of their association through flavanols could greatly assist in more efficient management of the crop. The goal of this thesis is to develop a marker for economically important traits through these central flavanol compounds. Since pigments in fresh cacao seeds are flavanols themselves, the thesis proposes that fresh seed color may be a ready indicator of native flavanol content in the fresh seed.
Two hundred seeds from 14 different varieties, chosen to cover the full range of color, were studied in order to develop a marker for flavanol content. Seeds were assessed in terms of light reflectance properties and mapped on scales of observable color based on a standard human observer. The measurements were compared to a chemical characterization of color based on anthocyanin concentrations from individual seed extracts. Through HPLC-MS, four anthocyanin pigments were identified, two of which were previously unknown in cacao. A significant correlation was found between total anthocyanin concentration and lightness of the seed. Additional variation in seed color was explained through in vivo effects such as copigmentation and pH of the cell environment.
In order to assess the ability of color to act as a marker for flavanols, concentrations of other flavanols (catechins, and procyanidins) were measured as well. Seeds were found to contain total extractable flavanol concentrations ranging from 1.25 to 26 µg/ml catechin equivalents per gram seed dry weight. A positive relationship was uncovered in the sample set between procyanidin and anthocyanin concentrations recorded for seeds. This trend was consistent for subsets of the data grouped by pod, with the exception of one pod whose seeds showed a negative relationship between anthocyanins and procyanidins. Apparently, all flavanol subspecies are coregulated in seeds throughout the species, although there is opportunity for exceptions or fine-tuning mechanisms.
In testing observable color as a predictor for flavanol content, a statistically significant relationship was established. Lightness of the outer surface of the seed was found to be the best measure of the flavanol content, with lighter seeds containing low levels of flavanols, and darker seeds containing higher concentrations. Colorimetric measurements of seed lightness can be used to estimate flavanol concentrations to within ± 4 µg/mL catechin equivalents per gram seed dry weight (on average). |