Ultrafiltration flux of acid whey obtained by lactic acid fermentation

Acid whey was prepared from reconstituted ultra-low heat skimmed milk powder fermented with Lactobacillus helveticus, clarified by centrifugation, pH adjusted and ultrafiltered (cut-off limit 10 or 30 kDa) at 50 °C to a volume reduction ratio of 10. Centrifugation primarily removed the serum albumin and, to a lesser extent, immunoglobulins, considered the most critical membrane foulants during ultrafiltration of acid whey. Below pH 3.9 the flux improvement was directly dependent on pH lowering. At pH 3.9 a deviation point in the relationship between pH and flux of acid whey was observed. Above this pH a severe flux decline was detected and at pH 4.6 the fermented acid whey was non-filterable. Largest flux increase was obtained at a transmembrane pressure of 2.0 bar and 50 °C. Under these conditions the permeation flux achieved using a 30 kDa membrane was about 34 ± 5 kg h−1m−2, comparable with that for sweet whey.