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Analysis of high and normal oleic peanut oil and their effect on fat bloom formation in peanut butter filled chocolate confectionary


NSF-funded MILES IGERT trainee, Vinodini Emma Buck, and MILES faculty, Sean F. O’Keefe, Richey Davis and Susan Duncan, studied the effect of triacylglycerol composition on oxidative stability and physical properties of peanut-chocolate interfaces. The overall goal was to determine if differences in triacylglycerol composition and rheological properties of high, medium and normal oleic peanuts affected fat bloom formation in peanut chocolate confectionery.

Our study concluded that all peanuts analyzed in this study released high concentrations of low melting incompatible (with cocoa butter) triglycerides causing increased softness of the chocolate and this may significantly increase the chances of fat bloom formation in chocolates. The triglyceride analysis was performed using matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS) with assistance from Dr. W. Keith Ray at the Virginia Tech Mass Spectrometry Incubator facility. The rheological properties of the peanut pastes were determined using a modified imperfect squeeze flow method. All three peanut pastes made only from peanuts showed varying degrees of shear thinning behavior and a minimum yield stress. The yield stress was significantly lower than the yield stress of commercial peanut butter due to the absence of stabilizers such as palm oil, sugar, molasses. The rheological properties measured show the importance of stabilizers in foods and the effect of buoyancy force in measurements using the imperfect squeeze flow method.

This project was done in collaboration with Dr. Richey Davis from the Virginia Tech Chemical Engineering department. The third objective of this project was to characterize bloom formation using sensory analysis and microscopy. The commercial peanut chocolates took 45 days of temperature cycling between 26-29 C every 26 hours for significant dulling. Sensory analysis revealed significant textural differences between unbloomed and bloomed chocolates but no significant differences between glossiness of unbloomed and bloomed chocolates. Surface texture and glossiness were examined using optical microscopy. The microscopy scans showed significant difference in glossiness and surface texture. This project was presented (poster) at the Virginia Tech Graduate Student Research forum and will also be presented at the American Oil Chemist Society Annual Meeting in May 2010.

Address Goals

Fat bloom results in undesirable discoloration of the product and loss of appeal to consumers. Though the product is not harmful to consumers, the issue results in loss of profit to manufacturers. This research hopes to reduce fat bloom formation and make recommendations to manufacturers regarding which peanut variety to use as fillings. Triglyceride analysis of peanut oils helps understand the structural properties of oils extracted and how the oils will crystallize in foods. Squeezing flow rheology was applied to study the viscoelastic behavior of peanut butter. The method proved to be reliable and remarkably reproducible, eliminating the current problems of slip associated with oscillatory experiment. Squeezing flow rheology can be applied to study the properties of other materials with similar texture.