Optical purity is an important feature of the resultant acid in certain applications, including poly(lactic acid) production [21]. When yield is optimized (batches 4 and 5 at pH 5.5, 41◦C), the optical purity was 59 ± 2% l(+)-lactate which corresponds with 24–28 g L−1l(+)-lactate. When the loading rate was increased to maximize con-centration (batch 3, pH 5.3, 41◦C), the optical purity is slightly lessat 54% l(+)-lactate or 31.5 g L−1l(+)-lactate. Overall, this opticalpurity is lower than in the optimization of the digestion of food