The discovery of a gene involved in determining the melting point of cocoa butter should lead to new varieties of the cocoa plant that could extend the climate and soil-nutrient range for growing the crop
Why does that matter? It's widely used in foods and pharmaceuticals and increasing the value of its yield also provides a boost to farmers' incomes in the cocoa-growing regions of the world.
Cacao, Theobroma cacao L., is an understory tropical tree domesticated in the Amazon basin and today widely cultivated in West Africa, Central and South America and Southeast Asia. Around the world, more than five million cocoa farmers -- and more than 40 million people total -- depend on cocoa for their livelihood, according to the World Cocoa Foundation.
The estimated annual cocoa production worldwide is 3.8 million tons, valued at $11.8 billion.
Cacao pods, each containing around 40 seeds, are harvested approximately 20 weeks after pollination. The seeds contain about 50 percent total lipids (cocoa butter), which provides a main raw ingredient for chocolate manufacturing as well as ingredients for pharmaceutical and cosmetic products.
Optimizing that is important because cocoa butter with altered melting points may find new uses in specialty chocolates, cosmetics and pharmaceuticals. For example, a chocolate with a higher or lower melting point would be useful for production of chocolate with specific textures and specialty applications.
"The 'snap' and 'melt' of chocolate are two very important textural features that determine the appeal of chocolate to consumers, and having new varieties of the cocoa plant that produce butter with different melting points would be a valuable resource to control those characteristics," says molecular biologist Professor Mark Guiltinan of Penn State. "Medical applications could include production of drug-delivery products with slower release of drugs than is possible with current cocoa-butter-based systems."
In a new study, a stearoyl-acyl carrier protein desaturase (SAD) gene family is examined in detail, and the expression patterns of each SAD gene in various cacao tissues is explored along with functional analysis to study how the enzyme works. They discovered that a single gene -- TcSAD1 -- is primarily involved in the synthesis of cocoa butter and is responsible for its melting point. This information can be used to develop biomarkers for screening and breeding of new cacao varieties with novel fatty acid compositions of cocoa butter. Notably, cocoa butter consists of almost equal amounts of palmitic acid, stearic acid and oleic acid. Its exact composition determines its melting temperature, which is very close to human body temperature, thus providing the smoothness and feel of chocolate in the mouth, as well as the creamy texture of cosmetics on skin.
"During cacao seed development, large amounts of fatty acids are synthesized that are rich in saturated and monounsaturated lipids," Guiltinan said. "An important part of this process is the activity of an enzyme produced by the SAD1 gene that creates a special double bond critical in determining the melting point of chocolate, that is very close to the human body temperature and makes cocoa butter quite unique."
Citation: Zhang Y, Maximova SN, Guiltinan MJ: Characterization of a stearoyl-acyl carrier protein desaturase gene family from chocolate tree, Theobroma cacao L. Frontiers in Plant Science 2015, 6(DOI 10.3389/fpls.2015.00239). DOI:10.3389/fpls.2015.00239