Factors affecting diacetyl production by lactic acid bacteria.

Recently it has been observed that the lactic acid bacteria are primarily responsible for the production of diacetyl during concentration of orange juice. The amount of diacetyl present is used as an indicator of the degree of contamination, even though it is not a major end product of fermentation. Its presence may be detected even though little change in total acidity or pH has been noted. A better understanding of factors influencing diacetyl production by lactic acid bacteria would be desirable. The relationship of the lactic acid bacteria to diacetyl production evolved from an early date. Hammer (1920) concluded that the organisms in butter cultures other than Streptococcus lactis were responsible for the volatile acidity, aroma, and flavor of the fermented dairy product. Van Niel in 1929 as stated by Hammer and Babel (1943) recognized that diacetyl was either responsible for the aroma of butter or was the principal component of the aromatic material. Michaelian et al. (1933) noted that butter cultures with satisfactory character contained considerable quantities of acetylmethylcarbinol and diacetyl. This fact is generally accepted. Hays (1951) and Hays and Riester (1952) identified spoilage organisms from orange juice as species of the genera Leuconostoc and Lactobacillus. Murdock et al. (1952) and Murdock and DuBois (1955) noted production of acetylmethylcarbinol and diacetyl by lactic acid bacteria grown in orange juice. Brokaw (1952) also employed plate counts and microscopic examination to follow the contamination of orange juice. Hill and Wenzel (1954b) developed a colorimetric method which has been used successfully as a quality control device. Michaelian et al. (1938) and Glenn and Prouty (1955) studied the effects of citric acid on the growth of Streptococcus lactis, Streptococcus citrovorum, Streptococcus cremoris, and Leuconostoc mesenteroides. While most reports recognize the role of the lactics in diacetyl production, conflicting reports do appear. Teunisson and Hall (1947) concluded that bacteria are probably not a major factor in influencing quality of orange juice since only one-third of their isolates were bacteria. Wolford and Berry (1948) and Purko et al. (1956)