Cheese whey is one by-product that can be used to produce lactic acid. The processes of lactic acid production include two key stages which are (a) fermentation and (b) product recovery. In this project, lactic acid was produced from cheese whey using B. longum. After 48 hours of fermentation, nearly 100% of the lactose was converted and the lactic acid yield reached 0.73 g/g lactose utilized without any nutrient addition.

Ultrafiltration membrane was used to separate cells and protein from the above fermentation broth. About 94% of the proteins were retained by the ultrafiltration membrane with MWCO of 5,000 and 20,000 Daltons. Nanofiltration membrane was used to further separate lactic acid from lactose in the ultrafiltration permeate, 99-100% of lactose can be retained in the concentrate and 40-60% of lactic acid can be recovered in the permeate using a nanofiltration membrane of DS-5DK. Higher initial lactic acid caused significant higher permeate flux, lower lactose retention, and higher lactic acid recovery. Increased transmembrane pressure caused significant higher permeate flux, higher lactose retention, and lower lactic acid recovery.