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Bacteria of the Lactobacillus and Leuconostoc species are frequently encountered in Concentrated orange juice. Several strains have been identified with a type of spoilage known as "buttermilk off-flavor" characterized by the presence of diacetyl in the product. The processing conditions under which this substance is formed by the bacteria are not kinown. It is assumed, however, that the bacterial populations are probably large and that the enivironment in some stage of the evaporation process must be particularly favorable for the synthesis and accumulation of diacetyl. In support of this assumption, Hays anid Riester (1952) observed lactobacilli and leuconostoc in commercial citrus juice evaporators, particularly in the early stages where the concentration of the juice is relatively low. From orange concentrate showing this type of spoilage, Hays (1951) isolated Lactobacillus brevis and Lactobacillus plantarum var. mobilis strains which were capable of growing in 35 Brix conicentrate. He states that these organisms came from the fruit, gained access to the evaporators with the feed juice, and multiplied in the citrus solids which were not being continually washed free from the surfaces of the evaporators. Murdock et al. (1952b) found two of the most prevalent spoilage organisms causing this type of offflavor to be species of the genera Lactobacillus and Leuconostoc. They found that the development of offflavor depended on the strain of organisms, the size of the inoculum, and the period of incubation. They believed it could be possible for off-flavors to develop in some types of evaporators where recirculation allows the juice to stay in the first effect for unusually long periods of time. However, they considered that the condenser was the most likely point for a buildup of contaminants to occur. Hays and Riester (1952) described the cultural characteristics of Lactobacillus and Leuconostoc species recovered from spoiled orange concentrate. They reported Lactobacillus to be the predominant spoilage type in high-acid juices, and the less-acid-tolerant Leuconostoc in the lower acid juices. These species produced diacetyl as one of the products of fermenta-

Growth Rates of Lactobacillus and Leuconostoc Species in Orange Juice as Affected by pH and Juice Concentration