Use of an immobilized cell bioreactor for the continuous inoculation of milk in fresh cheese manufacturing.

A system was developed to continuously acidify and inoculate skim milk for the production of fresh cheese. Four strains of mesophilic lactic acid bacteria were entrapped separately in kappa-carrageenan/locust bean gum gel beads and used in a stirred bioreactor operated at 26 degrees C with a 25% (v/v) gel load. The pH in the reactor was controlled at 6.0 by adding fresh milk using proportional integrated derived regulation. The bioreactor was operated during 8-h daily cycles for up to 7 weeks with different milks (heat treatment, dry matter content) and differing starting procedures. The heat treatment of the milk was an important factor for process performance: a dilution rate increase of 57% and an inoculation level decrease of 63% were observed with sterilized UHT skim milk (142 degrees C - 7.5 s) compared with pasteurized skim milk (72 degrees C - 15 s). The dry matter content of the milk (8-13% w/w) had no detectable effect on these parameters. A convenient starting procedure of the system was tested; steady-state was reached in less than 40 min following an interruption period of 16-60 h. These results combined with our published data on process performance show the feasibility of using an integrated immobilized cell bioreactor for milk prefermentation in cheese manufacture.