The ecology of non-starter lactic acid bacteria (NSLAB) and their use as adjuncts in New Zealand Cheddar

摘要

This paper reviews the recent New Zealand studies on non-starter lactic acid bacteria (NSLAB) in Cheddar cheese. In New Zealand, cheese adventitious NSLAB were usually strains of homofermentative lactobacilli and occasionally pediococci and heterofermentative lactobacilli. In Cheddar cheese., manufactured in six factories at different times and ripened over 24 months. over 140 NSLAB strains were identified using pulse field gel electrophoresis profiles and fermentation patterns on 22 carbohydrates. The majority of NSLAB isolates identified belong to two species: Lactobacillus paracasei subsp. paracasei and Lactobacillus rhamnosus. The composition of the NSLAB strains in a cheese was variable and dependent on the manufacturing factory, the date of manufacture and the age of the cheese. In most cheeses, no single NSLAB strain predominated during ripening. Up to six strains formed the majority (about 90%) of the NSLAB population. the remainder was represented by up to 15 other strains. In only about 10% of the cheeses investigated was one strain predominant throughout the 24 month ripening period. The acid and salt tolerance, effect of temperature, ability to produce biogenic amines and the lipolytic and proteolytic activities of the NSLAB strains were studied to screen strains for use as adjuncts. Sixty suitable strains were selected for further screening in a cheese model system. The NSLAB were incubated at 30 degreesC for 10 days in the model system and the flavour and biochemical changes were assessed. Twenty-three strains were eliminated as potential adjuncts because they produced defective flavours and a further 13 strains were eliminated on the basis of undesirable biochemical properties (e.g. excess fermentation of glutamate, lactate racemisation). The 24 remaining NSLAB strains that had acceptable microbiological biochemical and flavour properties were used as adjuncts in Cheddar trials. Seven of the 24 adjunct combinations studied (made up from 2-4 strains of NSLAB) provided consistent flavour benefits, Analysis of the cheeses during ripening in these trials provided significant understanding of the ripening mechanisms of the NSLAB adjuncts.