Chemical characteristics of yoghurt samples from the market

Some products sold in Italy, named as yoghurt and fermented milk (30 sample s), have been analyzed in order to verify the presence of lactose fermentat ion products, D-lactic acid (from Lactobacillus bulgaricus), and L-lactic a cid (from Streptococcus thermophilus) using an enzymatic method. The result s showed a clear predominance of the L-lactic acid (0.46-1.15 g/100 g) whil e the D-lactic acid in many samples has not been found or was present in ve ry low concentrations (0-0.84 g/100 g). Furthermore 14 samples have been al so submitted to the analysis of acetaldehyde (enzymatic method) and benzoic acid (HPLC), two secondary products in yoghurt.