The aim of this study was to investigate the influence of onion juice on the fermentation of milk by
Lactobacillus acidophilus. The onion juice significantly stimulated the growth and acidification of the
bacterial strain L. acidophilus NCFM. The viable cell counts in onion-supplemented fermented milk were
higher than that of the control sample and were maintained during cold storage. We considered the
whole constituents of onion juice such as polyphenols, sulfur compounds, fructans, and minerals
together to play the stimulatory roles and result in this beneficial effect for L. acidophilus viability during
fermentation and storage. After the milk was fermented by L. acidophilus NCFM, the antioxidant capacity
decreased greatly in the control and onion-supplemented fermented milk. The results suggested that it
was very necessary and crucial to scavenge radical for L. acidophilus growth. The onion juice was slightly
beneficial to enhancing the antioxidant capacity of fermented milk. The higher cell numbers, the less
fermentation time, the better antioxidant capacity, and more abundant flavor components were achieved
by onion-supplemented fermentation by L. acidophilus, demonstrating the potential for industrial
applications.