The study published in the Journal of Food Processing and Preservation by Zzaman et al. said that the new method had the edge over conventional convection roasting.
“Superheated steam roasting could be more appropriate and flexible than conventional method because the higher total phenol and antioxidant properties are preserved using the same temperature and time.”
“This method takes a short time to achieve the optimum roasting characteristics whereas the conventional method takes too long which may contribute to loss of antioxidant properties of the products.”
Losses from convection roasting
Earlier work by the researchers found that around 70% of phenolic compounds and most antioxidant properties were destroyed by prolonged heating during convection roasting, which typically uses temperatures from 150°C-250°C for between 30 and 120 mins.
“There are no acceptable processing techniques to avoid polyphenol degradation in the conventional cocoa industry,” they said.
Superheated steam roasting: Hot dry gas
Under the present study, the researchers used Forastero cocoa beans from the Malaysian Cocoa Board and heated at 150°C, 200 and 250°C for between 10 and 50 mins in a superheated steam oven.
Superheated steam roasting performs as a hot dry gas. It involves reheating saturated steam above the boiling temperature of water..
In the past decade, researchers have reported that the method had advantages in shrimp and scallop processing.
The researchers measured total phenolic and flavonoid content as well as antioxidant activity and capacity for the cocoa beans roasted under Superheated steam.
Phenol content preserved
Phenol content before roasting was around 47 mg per gram. Phenol losses from superheated steam roasting varied from 2.88% to 24.57%. The losses increased when the beans were exposed to longer and greater heat.
Previous research with Arriba cocoa beans from Ghana found that the losses were at around 54.74% for convection roasting.
Reduced flavonoid losses
Before roasting, the raw cocoa powder used by the researchers contained 8.33 mg per grams of flavonoids.
Total flavonoid content losses from superheated steam roasting varied from 3.10% to 35.31%.
Earlier research found flavonoid losses up to 67% for the conventional roasting method.
“The lowest loss of total phenol and flavonoid content was found using superheated steam method rather than conventional method,” said the researchers.
“This is because of low oxygen environment and even the degree of heating during superheated steam roasting process.”
Polyphenol extraction is known to be effected by other factors such as drying, solvents used in extraction and the cocoa variety.
A recent study by Kothe et al . found that cocoa flavanol losses from roasting varied significantly depending on the bean orgin. Ivorian beans for example registered a 30% increase while cocoa flavanols from Java beans declined by about half.
Phenolic compounds prevent or delay lipid oxidation. Phenolics have been linked to reduced risk of cardiovascular diseases and cancer.
Unfermented cocoa beans contain 12-18% (dry weight) of phenolic compounds.
These compounds are mainly procyadin (oligomers), epicatechin and catechin (flavanol monomers).
Journal of Food Processing and Preservation
‘Effect of Superheated Steam Roasting on the Phenolic Antioxidant Properties of Cocoa Beans’
Authors: Wahidu Zzaman, R. Bhat, Tajul A. Yang