Interaction between starter bacteria and adjunct Lactobacillus plantarum INF15D on the degradation of citrate, asparagine and aspartate in a washed-curd cheese

Washed-curd brine-salted cheeses were made with four different starters: citrate degrading (Cit+) heterofermentative mesophilic DL-starters (CHN-11 and CHN-19), a citrate negative (Cit−) mesophilic homofermentative O-starter (R-704) and a thermophilic starter TCC-20, all with the addition of an adjunct Lactobacillus plantarum INF15D to study the interaction between the starter and adjunct on the degradation of citrate to aspartate (Asp), diacetyl and acetoin in cheese. Citrate degradation by Lb. plantarum INF15D in cheese varied according to the type of starter used. In cheese made with Cit+ DL-starters, the degradation of citrate and Asp by the adjunct Lb. plantarum INF15D was less extensive as diacetyl and acetoin were produced from citrate via α-acetolactate by Cit+Lactococcus lactis subsp. lactis biovar. diacetylactis and/or Leuconostoc mesenteroides subsp. cremoris. In the presence of a Cit− O-starter, Lb. plantarum INF15D degraded citrate mainly to Asp which was further converted to acetoin and diacetyl. However, in the presence of a thermophilic starter, Lb. plantarum INF15D degraded citrate mainly to succinic acid. The highest degradation of asparagine (Asn) was found in cheese made with the Cit− O-starter (R-704) and adjunct Lb. plantarum INF15D. Both Lb. plantarum INF15D and the starter cultures were capable of deaminating Asn to Asp.