A new immobilized biocatalyst based on Rhizopus oryzae fungal cells entrapped in poly(vinyl alcohol)-cryogel was evaluated in both the batch and semi-batch processes of L(+)-lactic acid (LA) production, when glucose, acid hydrolysates of starch or gelatinized potato starch were used as the main substrates. Under the batch conditions, the immobilized biocatalyst developed produced LA with yields of 94% and 78% from glucose and acid starch hydrolysates, respectively. Semi-batch conditions enabled product yields of 52% and 45% to be obtained with the corresponding substrates. The highest process productivity (up to 173 g L-1) was reached under semi-batch conditions. Potato starch (5-70 g L-1) was also transformed into lactic acid by immobilized R. oryzae. It was shown that long-term operation of the immobilized biocatalyst (for at least 480 h) produced a low decrease in metabolic activity. (c) 2006 Society of Chemical Industry.