IMPROVED ORGANIC-ACID PRODUCTION BY CALCIUM ALGINATE-IMMOBILIZED PROPIONIBACTERIA

Propionic and acetic acid production by Propionibacterium cells immobi lized in calcium alginate beads was evaluated in 12-h repeated-batch f ermentations on glucose and lactate as primary carbon sources. Beads c ontained approximately 2 x 10(11) cells g(-1) (wet weight) and were ad ded at 40% of broth volume. High initial substrate concentrations (up to 115 gl(-1) glucose and up to 78 gl(-1) lactate) were utilized by th e immobilized cells. The best substrate utilization rates and acid yie lds were obtained al 75 gl(-1) initial glucose and 42 gl(-1) initial l actate; 34 gl(-1) and 22 gl(-1) propionate were produced respectively, at these substrate concentrations in 12 h. The ratio of propionic to acetic acid increased to 9:1 with increasing glucose concentration, bu r remained at 2:1 at the different initial lactate concentrations test ed. Glucose consumption and propionate production rates were higher in fermentations controlled at pH 6.0 than at pH 7.0, but yields of acid s from glucose were highest at pH 7.0. (C) 1998 Elsevier Science Inc.