Two hundred isolates from San Francisco sour dough French bread fermentations (40 from each of five different bakeries) were screened by fermentation tests and for their ability to grow in the presence of cycloheximide (Actidione). All of the isolates from four of the bakeries and 70% of those from the fifth were unable to utilize maltose but grew well on other sugars, even in the presence of cycloheximide. The remaining few isolates from the fifth bakery utilized maltose but not galactose and were inhibited by cycloheximide. No bakers' yeast types were found. Sixteen of the maltose-negative and five of the galactose-negative isolates were subjected to more rigorous taxonomic procedures. All of the maltose-negative isolates were identified as asporogenous strains of Saccharomyces exiguus (Torulopsis holmii) and the galactose-negative ones, as S. inusitatus. The predominance of S. exiguus, its vigor in the particular acidic environment of the sour dough, and the correlation of its numbers with the leavening function constitute strong evidence on the role of this organism in the sour dough system.
SUMMARY Addition of sucrose to whole egg and yolk before spray drying has long been known to yield powders with improved performance value and stability. At levels commonly employed, however, sucrose greatly accelerates and intensifies off‐flavor development in air‐packed powders even at refrigerator temperatures. In commercial practice, low‐dextrose‐equivalent corn syrup solids have recently been substituted for sucrose at the same level to improve flavor stability. This has led to the general belief that sucrose addition induces instability over a wide range of levels and, conversely, that low‐dextrose‐equivalent corn syrup solids do not. Present findings show that, under mild oxidative conditions, comparable flavor stabilities and instabilities can be achieved with both sucrose and various corn syrup solids but at different levels of added carbohydrate. Typically, in each case, flavor stability was gradually improved at lower levels of added carbohydrates, reaching a maximum flavor stability, followed by an abrupt transition to marked flavor instability. This transition corresponded to a change in the physical state of the egg lipids from one of coalescence, where the lipids were readily extractable with mild solvent, to a finely dispersed or emulsified state, where the lipids were virtually non‐extractable. Chemical indices of oxidative flavor deterioration (peroxide, carbonyl, TBA) correlated fairly well with organoleptic findings for powders stored at low temperatures. Flavor and chemical stability relationships for yolk, fortified whole egg, and whole egg solids as a function of graded levels of added sucrose, and 24 and 42 dextrose equivalent corn syrup solids, are reported. Corn syrup solids gave as good protection as sucrose did against browning reactions at elevated temperatures, despite their containing substantial quantities of glucose and other reducing sugars. It is feasible to select levels of any of the carbohydrates studied which yield dried products that combine good retention and stability of performance quality with outstanding flavor stability.
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