Studies on Acetylmethylcarbinol and Diacetyl in dairy products

The importance of diacetyl from the standpoint of the desirable aroma of butter has been shown by various investigators. van Niel, Kluyver and Derx (6) found from 0.0002 to 0.0004 percent diacetyl in fine butter, and when these concentrations of diacetyl were added to butter neutral in odor an unmistakable aroma appeared. The important conclusion of these investigators was that diacetyl is either responsible for the aroma of butter or is the principal component of the aroma material. Schmalfuss and Barthmeyer (4) found diacetyl to be an aroma constituent of various materials, including butter. The diacetyl was considered to come from acetylmethylcarbinol. Margarine to which diacetyl had been added took on the aroma of butter. Four samples of butter, representing different conditions of feeding the producing animals, yielded from 0.0001 to 0.0006 grams of nickel salt (equivalent to diacetyl) per kilogram, and the quantity of diacetyl in the butter appeared to be correlated with the intensity of the aroma

The oxidation of Acetylmethylcarbinol to Diacetyl in butter cultures

1. The. addition of purified acetylmethylcarbinol to sterile skimmilk, adjusted to an acidity and a temperature satisfactory for the rapid production of the carbinol when the citric acid-fermenting streptococci are present, did not result in the formation of appreciable amounts of diacetyl in 48 to 72 hours. The results were the same when carbon dioxide, hydrogen, nitrogen, or oxygen was bubbled through the milk as when no gas was used. 2. The production of diacetyl in acidified skimmilk cultures of the citric acid-fermenting streptococci was definitely influenced by bubbling various gases through the freshly acidified cultures. Oxygen regularly gave a higher yield of diacetyl than the control through which no gas was bubbled, while carbon dioxide, hydrogen or nitrogen gave lower yields. With all of the gases there was commonly a greater production of diacetyl, as well as acetylmethylcarbinol plus diacetyl, when the cultures were acidified with a mixture of citric and sulfuric acids than when acidified with sulfuric acid alone. 3. Various gases had the same general effect on the production of diacetyl in butter cultures as in pure cultures of the citric acid-fermenting streptococci, but the actual quantities of diacetyl formed appeared to be smaller with the butter cultures than with the pure cultures. When oxygen was bubbIed through butter cultures prepared with various amounts of added citric acid, the yields of both diacetyl and acetylmethylcarbinol plus diacetyl were roughly proportional to the amount of citric acid added. 4. When acetylmethylcarbinol was added to milk and the milk inoculated with S. lactis, analyses after incubation showed no evidence of an oxidation of the carbinol to diacetyl. 5. The data obtained indicate that the oxidation of acetylmethylcarbinol to diacetyl in a butter culture is due to the activity of the citric acid-fermenting streptococci rather than to a direct chemical oxidation

The relationship of Acetylmethylcarbinol and Diacetyl to butter cultures

The value of selected cultures of bacteria for the development of a desirable flavor and aroma in butter has been thoroughly established through comparisons of butter made with and without culture and also through the extensive commercial use of cultures. There are two distinct types of organisms present in the butter cultures commonly used, one of which (Streptococcus lactis or, according to certain investigators, Streptococcus cremoris) attacks primarily the lactose with the formation of large amounts of lactic acid while the other type (Streptococcus citrovorus and Streptococcus paracitrovorus Hammer (4), or Betacoccus Cremoris Knudsen and Sorensen (11), or Leuconostoc dextranicus and Leuconostoc citrovorus Hucker and Pederson (9)) is characterized by the fermentation of citric acid. The growth of the two types in a butter culture results in the formation of various compounds that are responsible for the more or less characteristic flavor and aroma. Volatile acids constitute one of the groups of these compounds that has been studied extensively, particularly in connection with the differentiation of the butter culture organisms (4, 6). The volatile acids do not account for the desirable aroma of butter in which culture is used, although they may be a factor in this connection. Recent studies carried out in Europe indicate that diacetyl, a compound that is readily derived from acetylmethylcarbinol by oxidation, is of special significance from the standpoint of the desirable aroma of butter

Reduction of Acetylmethylcarbinol and Diacetyl to 2,3-Butylene Glycol by the citric acid fermenting streptococci of butter cultures

When acetylmethylcarbinol or diacetyl was added to a tomato bouillon culture of one of the citric acid fermenting streptococci normally present in butter cultures, there was a rapid disappearance of the added reagent and an increase in 2,3-butylene glycol. The amount of the glycol produced accounted, in a general way, for the acetylmethylcarbinol or diacetyl that disappeared. The added reagent did not usually disappear completely. In trials with acetylmethylcarbinol the change of the carbinol to the glycol was delayed when sulfuric acid was added in amounts to yield a pH of from 3.8 to 4.0. There was also a change of acetylmethylcarbinol or diacetyl to 2,3-butylene glycol when one of these reagents was added to a milk culture of one of the organisms. With the diacetyl there was an increase in the acetylmethylcarbinol as well as in the 2,3-butylene glycol, and the increase in the carbinol was greater than the increase in the glycol. The added reagent did not disappear completely in any of the trials. When various amounts of sulfuric acid were added to milk cultures of the organisms, acetylmethylcarbinol was not produced at the higher pH values but was produced at the lower values, while 2,3-butylene glycol was produced at both the higher and lower pH values. There was less of the glycol formed at the lower pH values than at the higher ones. The total molarities of acetylmethylcarbinol and 2,3-butylene glycol showed an increase as the pH was lowered, although there were some irregularities in the increase with one of the organisms. The addition of 0.65 percent citric acid to a milk culture of one of the organisms resulted in an increase in both acetylmethylcarbinol and 2,3-butylene glycol. The reduction of acetylmethylcarbinol, which had been added to a milk culture of one of the organisms, to 2,3-butylene glycol was not delayed by potassium nitrate in the quantity used but was delayed by the largest amount of hydrogen peroxide employed. In pure cultures of the citric acid fermenting streptococci which had been acidified with sulfuric acid to a pH of about 3.9, the addition of acetaldehyde or propionaldehyde increased the amount of acetylmethylcarbinol present after 96 hours at 21 °C. but decreased the amount of 2,3-butylene glycol and also commonly decreased the total molarities of the two compounds. These results suggest that the increased production of acetylmethylcarbinol is accounted for by a decrease in the reduction of the carbinol to the corresponding glycol, rather than to an aldehyde condensation involving, in part, the added aldehyde. In butter cultures the decrease in acetylmethylcarbinol was accompanied by an increase in 2,3-butylene glycol, and there was commonly an increase, from one examination to the next, in the total molarities of the two compounds. When ripened butter cultures were neutralized to a low acidity there was a rapid decrease in the acetylmethylcarbinol, and in some of the trials this was followed by an increase. The decrease in the carbinol was accompanied by a rapid increase in 2,3-butylene glycol, and there was also an increase in the total molarities of the two compounds. Hydrogen peroxide, in certain concentrations, delayed the reduction of acetylmethylcarbinol to 2,3-butylene glycol as did also 1 percent sodium fumarate or 12 percent sodium chloride. Ice water temperatures also delayed the reduction in either neutralized or unneutralized cultures, but the reduction was more rapid with neutralization than without

Bremsstrahlung of 350--450 MeV protons as a tool to study NNNN interaction off-shell

The $pp\to pp\gamma$ bremsstrahlung cross section is calculated within the method of coordinate space representation. It is shown that in the beam energy range of 350--450~MeV a deep attractive NN-potential with forbidden states (Moscow potential) and realistic meson exchange potentials (MEP) give rise to the cross sections that differ essentially in shape: the cross sections nearly coincide in the minima but differ by a factor of 5 approximately in the maxima. Therefore, the $pp\to pp\gamma$ reaction at energies $\sim$350--450~Mev can be used to study $NN$ interaction off-shell and to discriminate experimentally between MEP and Moscow potential.Comment: 5 pages, latex, 4 PS figures. Talk presented by Andrey Shirokov at the International Conference on Quark Lepton Nuclear Physics ``QULEN97'', May 20-23, 1997, Osaka, Japan; to be published in Nucl. Phys.

Chirality in Bare and Passivated Gold Nanoclusters

Chiral structures have been found as the lowest-energy isomers of bare (Au$_{28}$ and Au$_{55}) and thiol-passivated (Au$_{28}(SCH$_{3})$_{16}$and Au$_{38}(SCH_{3})_{24}) gold nanoclusters. The degree of chirality existing in the chiral clusters was calculated using the Hausdorff chirality measure. We found that the index of chirality is higher in the passivated clusters and decreases with the cluster size. These results are consistent with the observed chiroptical activity recently reported for glutahione-passivated gold nanoclusters, and provide theoretical support for the existence of chirality in these novel compounds.Comment: 5 pages, 1 figure. Submitted to PR

Metacognition as Evidence for Evidentialism

Metacognition is the monitoring and controlling of cognitive processes. I examine the role of metacognition in ‘ordinary retrieval cases’, cases in which it is intuitive that via recollection the subject has a justified belief. Drawing on psychological research on metacognition, I argue that evidentialism has a unique, accurate prediction in each ordinary retrieval case: the subject has evidence for the proposition she justifiedly believes. But, I argue, process reliabilism has no unique, accurate predictions in these cases. I conclude that ordinary retrieval cases better support evidentialism than process reliabilism. This conclusion challenges several common assumptions. One is that non-evidentialism alone allows for a naturalized epistemology, i.e., an epistemology that is fully in accordance with scientific research and methodology. Another is that process reliabilism fares much better than evidentialism in the epistemology of memory

Do Thiols Merely Passivate Gold Nanoclusters?

A Comment on the Letter by H. Hakkinen, R. N. Barnett, and U. Landman, Phys. Rev. Lett. 82, 3264 (1999)