Applicability of lactic acid and nisin to improve the microbiological quality of cold-smoked rainbow trout

 The effect of lactic acid and nisin whey permeate on the microbiological and sensory quality of cold-smoked rainbow trout was studied. Lactic acid and whey permeate were mixed with salt solution and injected into fish fillets in concentrations of up to 2.5 g/kg lactic acid, 30 g/kg whey permeate and 20 g/kg sodium chloride. After smoking at 28  °C for 6 h the fillets were sliced, vacuum packed and stored at 3  °C. The aerobic and anaerobic/facultative anaerobic counts were measured after 1, 8, 15, 22 and 29 days of storage. The influence of the treatment on the sensory characteristics was analysed after 8 and 22 days by sensory profiling. A triangle test was used in order to ascertain at which stage the sensory quality of the samples changed during storage. Bacterial counts of smoked fish stored for 29 days were lowest in those samples containing a combination of lactic acid, sodium chloride and nisin whey permeate. Lactic acid alone did not affect the odour or flavour characteristics of the fish but did affect their texture as determined by sensory evaluation making it less elastic when stored at +3  °C for 8 days. A combination of lactic acid and nisin whey permeate enhanced the characteristic fishy flavour of the product. Differences between treatments in elasticity and fishy flavour were not detected after 22 days of storage. According to the triangle test, the samples from all treatments remained unchanged over the first 15 days. Received: 23 March 1998 / Revised version: 19 June 1998