Raman spectroscopy of chocolate bloom
Raman spectroscopy has been widely applied to the chemical analysis of food quality and, in particular, of chocolate. We perform Raman analysis of bloom formation in white and dark chocolates. We show evidence of sugar and fat bloom and investigate spectroscopic signatures of polymorphic changes in different phases.
Relation of fat bloom in chocolate to polymorphic transition of cocoa butter
A special chocolate with spray-dried sugar (50:50 w/w sucrose/20 Dextrose Equivalent corn syrup solids) was made to study the polymorphic changes in cocoa butter crystals using X-ray diffraction. Anhydrous milk fat (AMF) and high-, middle-, and low-melting milk fat fractions were used to replace 2% (w/w) of cocoa butter. Chocolates were tempered, and the consistency of temper among chocolate samples was verified by a temper meter. Chocolates were cycled between 19 and 29°C at 6-h intervals to induce fat bloom. The special chocolates were analyzed by X-ray spectroscopy and colormeter.X-ray analysis on the special chocolates showed polymorphic transition from the βV to the βVI form of cocoa butter. After a lag phase, the percentage of the βVI form rapidly increased. However, the sample made with the high-melting milk fat fraction transformed slowly to βVI. Visual bloom appeared rapidly on the special chocolates made with AMF, middle- and low-melting fractions, whereas visual bloom was very slow to appear on the special chocolates made with high-melting milk fat fraction and on the cocoa butter control. The commercial chocolate responded consistently; the control bloomed rapidly, the AMF exhibited some bloom resistance, and the high-melting fraction inhibited bloom. Despite the βV to βVI transition, the control chocolates with amorphous sugar did not bloom. Since the only difference in the chocolates was sugar microstructure, differences in bloom formation were caused by the microstructure, not the polymorphic transition.
Sterol metabolism. XLI. Cholesterol A-ring autoxidations
Abstract Chromatographic and spectral evidence is adduced for the presence of cholest-5-en-3-one, cholest-4-en-3-one, and cholest-4-ene-3,6-dione in samples of cholesterol aged naturally in air or subjected to irradiation in air by 60 Co gamma radiation. These findings establish an additional mode of air oxidation of cholesterol to A-ring 3-ketones. Moreover, the oxidation by air of cholest-5-en-3-one induced by 60 Co gamma radiation yielded cholest-4-en-3-one, cholest-4-ene-3,6-dione, and the epimeric 3-oxocholest-4-ene-6-hydroperoxides. Cholest-4-en-3-one was not altered by irradiation in air, nor was cholesterol isomerized to cholest-4-en-3β-ol upon irradiation. From these observations it is deduced that the radiation-induced A-ring dehydrogenation of cholesterol yields initially cholest-5-en-3-one which upon isomerization yields cholest-4-en-3-one not further oxidized and which by a second oxidation yields the epimeric 3-oxocholest-4-ene-6-hydroperoxides which decompose to cholest-4-ene-3,6-dione.