Lactic acid production by batch-fed fermentation of deproteinized whey, using immobilized cells of Lactobacillus pentosus-4023 in a spirally wound fibrous-sheet packed-column reactor, has been investigated. This fermentation process has been studied to produce low-cost lactic acid 'in situ' and to investigate its direct use for the demineralization of crayfish chitinous fraction (exoskeleton). Chitin obtained by this procedure was chemically and spectrometrically (FT-IR and C-13-NMR) characterized.