Effects of Alkalization and Roasting on Polyphenolic Content of Cocoa Beans and Cocoa Powder
Open Access
- Author:
- Stanley, Todd Harvey
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 21, 2014
- Committee Members:
- Joshua D Lambert, Thesis Advisor/Co-Advisor
Ramaswamy C Anantheswaran, Thesis Advisor/Co-Advisor - Keywords:
- Cocoa
polyphenols
roasting
alkalization
HPLC-ECD - Abstract:
- Cocoa products are a rich source of dietary polyphenols. On a per serving basis, cocoa has a higher phenolic content and antioxidant activity than green tea and red wine. Cocoa polyphenols are primarily flavan-3-ol monomers and proanthocyanidins (PaCs) with degree of polymerization (DP) previously identified up to ten. Ongoing research suggests that these polyphenols may account for potential health benefits of cocoa products. Polyphenols are oxidatively unstable, and processing operations such as roasting and alkalization have been suggested to reduce total polyphenol (TP) content, measured as non-specific estimations of total phenolic content and low DP PaCs. There is a need for investigation of the effects of cocoa processing on high DP PaCs. The objectives of this thesis were to: (1) develop a new method for quantification of PaCs using high performance liquid chromatography coupled with electrochemical detection (HPLC-ECD), (2) investigate the effects of alkalization of cocoa powder on color, TP, and PaC composition, and (3) investigate the effects of whole bean cocoa roasting on color, TP, PaC composition, and aroma. For the alkalization study, commercial cocoa powder was dispersed in water and then heated to 92˚C in 6 min. Sodium hydroxide was added to achieve a pH of 8. Color (L, a, b, ΔE), pH, TP, and PaC concentration data was collected 0.5, 5, 15, 30, and 60 min after base addition. For the roasting study, 100 g cocoa beans were roasted in a convection oven for various time/temperature combinations (10, 20, 30, 40 minutes at 100, 130, 150, 170, 190˚C) using a full factorial design. Samples were analyzed for TP, color, and flavan-3-ol monomers, PaCs, and aroma. All alkalization treatments caused a significant change in color (p < 0.0001). (+)-Catechin increased by 40%, while EC and PaCs decreased by 23-66%. PaC loss was modeled using a two-phase exponential decay model. The fit was best for EC and PaCs of odd DP, with R2 > 0.7. Roasting treatments reduced TP up to 40%. All treatments at 190˚C, 170˚C, and 150˚C except 10 min, significantly decreased EC content and significantly increased (+)-catechin content as compared to unroasted beans (p < 0.05). For all PaCs DP 2-5, a decreasing trend in PaC content was observed with increasing time and temperature of roasting. Interestingly, DP 6 and DP 7 significantly increased from the unroasted control for some of the170˚C and 190˚C treatments, with upwards of 280% and 214%, respectively (p < 0.05). Formation of high DP PaCs are important when biological significance is taken into account, in terms on antioxidant activity and inhibition of digestive enzymes pancreatic lipase and phospholipase A2. Alkalization of cocoa powders does not reduce these compounds to the extent previously believed. Roasting cocoa beans at 170˚C or above results in the highest production of DP 6 and 7 PaCs. In addition to meeting the sensory quality based on consumer needs, processing conditions used to produce cocoa products should confer greater health benefits to consumers.