Try oat hydrocolloid as a substitute for cocoa butter; mass transfer issues are a concern.

Cardiovascular disease continues to be the number one cause of death in the United States despite numerous efforts to reduce its prevalence. Interest has increased in the use of diet and lifestyle rather than drugs to prevent and manage hypertension and cardiovascular disease. Numerous studies have demonstrated that whole grains that are high in soluble fiber, such as oats and barley, are more effective in lowering blood cholesterol levels than are grains in which fibers are predominantly insoluble, such as wheat or rice.

The beta-glucan from oats has a biological capability to lower blood cholesterol levels. It may be possible to prepare a chocolate product containing an oat hydrocolloid that would decrease the chocolate fat content and add a soluble fiber substance--beta-glucan--that would increase the health benefits of chocolate.

USDA-ARS scientists prepared chocolate by replacing up to 25% of cocoa butter with an oat hydrocolloid containing 30% beta-glucan. Researchers noted some small differences in the quality of the chocolate when the beta-glucan was substituted in a range up to 25%.

However, the chocolate mouth-coating texture scores dramatically increased from the control at 2.6 with each 5% increase in the oat hydrocolloid content to 6.9 at the 25% substitution level. Fat content also declined continually with each 5% oat hydrocolloid increment substitution to 11.2% at the 25% level from the control level of 15%. Incorporating an oat hydrocolloid into chocolate products can decrease the chocolate's fat content without causing a substantial change in its sensory properties.

One issue with chocolate involves fat bloom, the whitish haze formed on chocolate. This phenomenon is not clearly understood. Most theories emphasize the importance of fat migration to the surface. British scientists and others have developed chocolate model systems that generate kinetic data on migrated fat and whiteness when the product is stored at a high temperature--30 C. They wanted to examine the relationship between the measured parameter and the associated microstructure of the product.

Bloom was assessed by measuring the amount of migrated fat to the surface of chocolate bars and the change in surface color. The initial microstructure of the bars was examined by confocal and electron microscopy, along with image analysis. The measurements showed an initial rapid increase, followed by a gradually decreasing gradient, until reaching an asymptotic value.

The increase in volume when cocoa butter melts because of a temperature rise (decrease in density) was comparable to the amount of migrated cocoa butter determined experimentally for all bars that were tested. Also, a higher fat migration rate occurred in small particle-size bars. Changes in density were key in facilitating bloom. It appears that mass transfer mechanisms other than diffusion play an important role in a food system.

Further information. On oats: George Inglett, USDA-ARS National Center for Agricultural Utilization Research, 1815 N. University St., Room 2306, Peoria IL 61604l; phone: 309-681-6363; fax: 309-681-6685; email: george.inglett@ars.usda.gov. On bloom: Leo Pyle, Department of Food Biosciences, University of Reading, P.O. Box 226, Whiteknights, Reading RG6 6AP, England, U.K.; phone: +44 118 378 8700; fax: +44 118 931 0080; email: food@reading.ac.uk.