Submitted to: European Food Research and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/10/2007
Publication Date: 1/10/2008
Citation: Nystrom, L., Moreau, R.A., Lampi, A., Hicks, K.B., Piironen, V. 2008. Enzymatic hydrolysis of steryl ferulates and steryl glycosides. European Food Research and Technology. 227:727-733. Interpretive Summary: Fruits, vegetables and cereals contain little or no cholesterol but they do contain similar compounds called phytosterols or plant sterols. Numerous clinical studies have demonstrated that eating 1-2 grams of phytosterols per day can lower the levels of serum cholesterol by 10-15% and lower the risk of cardiovascular disease by 20-30%. In fruits, vegetables and cereals, four types of phytosterols are found. Only two of these have been extensively studied and demonstrated to be effective at lowering serum cholesterol. In the current study the other two forms of phytosterols, steryl ferulates and steryl glycosides were studied. Studies were conducted to evaluate the ability of various natural digestive enzymes to break down (hydrolyze) steryl ferulates and steryl glycosides. Steryl ferulates were readily hydrolyzed by two pancreatic enzymes. Steryl glycosides were not hydrolysed by any digestive enzymes, but one commercial enzyme from a micro-organism was found to effectively hydrolyze them. These results help us to understand the physiological effect of the various forms of phytosterols. In addition, these results provide information which for the first time identifies enzymes that could potentially be used to provide a "green chemistry" replacement to the destructive acid hydrolysis methods that are currently used as the main analytical procedure for steryl glycosides.
Technical Abstract: Steryl ferulates and steryl glycosides are phytosterol conjugates found characteristically in cereals. Their properties in enzymatic hydrolysis are, however, not yet well known. Steryl ferulates and steryl glycosides were extracted and purified from rye and wheat bran. Their rates of hydrolysis with different enzymes were studied using normal phase HPLC with UV detection for steryl ferulates and evaporative light scattering detector for steryl glycosides. Steryl ferulates were hydrolysed by mammalian digestive steryl esterases. It was further demonstrated that a mixture of steryl ferulates from rye and wheat was hydrolysed much more effectively than a steryl ferulate mixture from rice (commonly known as g-oryzanol), suggesting better bioactive properties of the non-rice steryl ferulates. Steryl glycosides were hydrolysed by a commercial microbial b-glucosidase preparation (cellobiase), but were not effectively hydrolysed by two other highly purified b-glucosidases. These results demonstrate for the first time the potential use of enzymes as a replacement for acid hydrolysis in analytical procedures for steryl glycosides.