Effect of Temperature on Growth and Diacetyl Production by Aroma Bacteria in Single- and Mixed-Strain Lactic Cultures

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Abstract
By the use of a differential plating medium, the growth of aroma bacteria (Leuconostoc citrovorum and Streptococcus diacetilac-tis) in mixed-strain lactic starter cultures was followed. Populations were greater at 30 C than at the temperature (21 C) normally used in the dairy industry for incubation of cultures for manufacture of fermented dairy products. At 30 C, peak level of diacetyl produced in mixed-strain lactic starters was lower than at 21 C, however, at the higher temperature there was an earlier initiation of the synthesis and the attainment of the peak level. Prompt cooling of cultures to 2 C inhibited diacetyl reductase activity and, consequently, loss of desirable flavor and aroma was prevented. The cooling, however, had to carried out when the diacetyl level was high and before complete destruction of the favor compound. By a careful combination of time and temperature of incubation and prompt cooling, the diacetyl flavor in milk cultures and cottage cheese dressed with cultured cream could be stabilized and improved.