The impact of onion juice on milk fermentation by Lactobacillus acidophilus

- Onion juice significantly stimulated the growth and acidification of Lactobacillus acidophilus.
- Onion juice was beneficial to maintain the viability of L. acidophilus.
- The antioxidant capacity decreased after the milk was fermented by L. acidophilus.
- Onion juice could slightly enhance the antioxidant capacity of fermented milk.
- Adding onion juice into milk increased the volatile compounds of fermented milk.

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.