10-hydroxy-cis-12 octadecenoic acid (10-HOE) is a type of octadecenoic acid with a hydroxyl on the C-10 carbon. It is generated from linoleic acid (LA) catalyzed by linoleate hydratase in lactobacilli, which was initially named as myosin-cross-reactive antigen (MCRA). In lactobacilli, 10-HOE is the first intermediate in the production of conjugated LA (CLA). Although MCRA from bifidobacteria can generate 10-HOE, the precise role of 10-HOE in CLA production in bifidobacteria remains unknown. In the current work, 10-HOE and LA were added to the medium as the substrate both separately and synchronously to analyze their influence on CLA production. Using 10-HOE as the substrate, bifidobacteria were able to generate CLA by first converting it to LA, followed by CLA accumulation. Recombinant MCRA catalyzed the conversion of 10-HOE to LA, indicating that bifidobacterial MCRA can account for the reversible conversion between LA and 10-HOE. This is the first report to demonstrate the precise role of 10-HOE in the process of CLA production among bifidobacteria.