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Fat bloom formation in peanut butter filled chocolate confectionary


NSF-funded researchers, Dr. Sean O’Keefe (Food Science and Technology), Dr. Richie Davis (Chemical Engineering), and MILES-IGERT trainee Emma (Vinodini) Buck are investigating fat bloom (formation of large crystals after melting and chocolate recrystallization) in chocolate confectionary. Chocolates are a popular confectionary consumed many times as comfort foods. Dark chocolate is now being marketed for their antioxidant functionality. No matter what the reason is for buying chocolates, it is important that the product consumers receive are of superior quality.

One of the reasons why chocolate consumers may be disappointed in their purchase is if the chocolate looks old. Most consumers assume that chocolate that is gray in color has undergone some chemical changes and is no longer safe to consume. The proper scientific term for this gray discoloration that occurs is known as fat bloom. Fat bloom in chocolates is the formation of large imperfect fat crystals on the surface of the confectionary. Fat bloom results in loss of appeal to consumers and loss of profit to manufacturers (figure 1). Fat bloom can originate from separation and migration of liquid triacylglycerides (TAG) to the surface of the chocolate, followed by re-crystallization of the solid TAG component. Fat bloom does not make the chocolate unsafe to consume nor does it affect taste, but a lot of chocolates appeal is in its rich shiny color and smooth texture.

Triglycerides are organic molecules that complex together to form crystal structures. When triglyceride molecules come together with different crystalline packing of the same ensemble of molecules, different polymorphs form. The Beta-V form is desired crystal structure of cocoa butter in properly tempered chocolates. The Beta-VI form is the larger more visible form observed after formation of fat bloom. The differences in TAG composition and viscosities of normal and high oleic peanuts (NOP and HOP) may show differences in the rate and size of crystals formed. Lower degree of saturation in TAG with high viscosity, in the center of the confectionary may hinder oil migration.

High oleic peanuts are a new cultivar of peanuts that have shown improved oxidative stability in chocolate. The structural properties (crystallization or melting temperature) of the high and normal oleic peanut oils heavily depend on their TAG composition. The orientation and arrangements of the fatty acids in TAGs may produce different melting points and will affect the crystallization of fats. This is most likely caused by the increased viscosity of the high oleic peanut oils which limits structural formation of the crystal network.

In this study, TAG analysis of normal and high oleic peanut oils were performed using gas chromatography-mass spectroscopy (GC-MS). Viscosities of peanut fillings made from NOP and HOP were measured at 5, 10, 18, 22, 25 and 28 ºC using an AR-G2 rheometer. The AR-G2 (TA instruments) has very sensitive temperature and steady torque control which gives good accuracy and reproducibility of results. HOP oil had a higher content of triolein TAG than NOP oil. NOP oil had a higher content of trilinoleic TAG than the HOP oil. Fatty acid analysis of peanuts showed high oleic peanut oil to have oleic acid content of 73 % and normal oleic peanut oil to have oleic oil content of 53% and a higher linoleic acid content than high oleic peanut oil. Oscillatory experiments showed differences in complex viscosities of the HOP and NOP paste. At lower temperatures HOP had higher viscosity than normal oleic peanut paste. With increasing temperature these differences were significantly reduced. Both findings indicate that chocolates containing peanut butter paste made from high oleic peanuts may have reduced fat bloom. Future work in this study involves utilizing differential scanning calorimetry to determine solid fat index and determine crystal properties. Scanning electron microscopy will be used to view crystal size and structure of chocolates made with high and normal oleic peanut paste.

Address Goals

Discovery: Foster research that will advance the frontiers of knowledge, emphasizing areas of greatest opportunity and potential benefit and establishing the Nation as a global leader in fundamental transformational science and engineering. Understanding the mechanisms of fat bloom formation will help ensure consumers receive chocolate confectionary that is superior of quality and free of defect in high oleic peanut butter filled chocolates. Based on these researchers findings, recommendations can be made to the food industry to reduce bloom formation in chocolates containing peanut butter fillings.