Failure to conserve lactose and glucose polymers during frozen storage of fecal specimens: methods for preservation

Freezing is often used to retard bacterial enzymatic activity in fecal specimens collected to quantify specific carbohydrates. The effectiveness of freezer storage on preservation of lactose and glucose polymers was assessed. The data showed that more than 50% of lactose that was added to fecal supernatants that were stored without treatment for more than 50 days at -20 degrees C was lost. Adjustment of pH with HCl (pH 4.9), with HgCl2 (pH 6.3 or 5.85), or with NaOH (pH 10) improved carbohydrate preservation (P less than 0.0004). Storage of the supernatants of fecal homogenates lessened the loss of carbohydrate compared with the total homogenates (P less than 0.001). In supernatants, degradation occurred via simple hydrolysis; in homogenates, degradation occurred by hydrolysis and fermentation to a variety of end-products. Unprocessed fecal specimens that were frozen for months, then retrieved and incubated with lactose or glucose polymers showed extensive fermentative capacity. Cumulatively, the data indicate that enzymatic activity in feces is not halted by storage in the freezer, even if bacteria have been filtered from the stool.