Rheological Properties of Peanut Paste and Characterization of Fat Bloom Formation in Peanut-Chocolate Confectionery
Abstract
Fat bloom in chocolates is the gray-white discoloration and dullness that can occur
on the surface of the confectionery. Fat bloom is a common quality defect that can result
from temperature fluctuations during storage. Chocolates candies with peanuts or other nut
fillings are more prone to fat bloom compared to plain chocolates, due to a release of
incompatible nut oils into the chocolate matrix. The overall goal of this study was to
determine if differences in triacylglycerol (TAG) composition and rheological properties of
high, medium, and normal oleic peanuts influence fat bloom formation. All three peanut
varieties showed high concentrations of triolein. Normal oleic peanuts had a slightly
higher trilinolein than high and medium oleic peanuts, which contained trilinolein in trace
amounts. Peanut pastes from the three peanut varieties all had a minimum apparent yield
stress, and all pastes showed varying degrees of shear thinning. The apparent yield stress
of high and normal oleic pastes was higher than the apparent yield stress of medium oleic
paste. The absolute value of the flow index behavior was 1 for the high oleic peanut paste,
suggesting friction in the experimental apparatus, even with use of Teflon plates. The
peanut chocolate candies took around 45 days for significant dulling of the chocolates with
temperature cycling between 26-29 °C approximately every 26 hours. Optical microscopy
scans showed differences in glossiness and surface textural attributes of the unbloomed and
bloomed peanut chocolate confectionery. Consumer evaluation showed some differences
in the glossiness and significant differences in surface texture of unbloomed and bloomed
chocolates. A majority (62%) of the survey respondents had seen whitish discoloration in
chocolates and 40% of the respondents thought this is because the chocolate had grown old.
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- Doctoral Dissertations [14916]