This work reveals that, at pH 5-9, a lactate level of up to 30 g l(-1) retarded hydrolysis rates in polysaccharide-rich potato samples. Lactate substantially limited carbohydrate hydrolysis and enhanced the hydrolysis of proteins. Statistical analysis identified the significance of numerous process factors in substrate hydrolysis. At fixed pH, dissociated lactate affected hydrolysis rates more strongly than its molecular counterpart. At a fixed lactate level, an alkaline environment favors carbohydrate hydrolysis; the effect of pH is secondary. Significant effects of lactate on substrate hydrolysis may be evident in fermenting organic substrates with high carbohydrate content.