Nonstarter lactic acid bacteria biofilms and calcium lactate crystals in cheddar cheese

A sanitized cheese plant was swabbed for the presence of nonstarter lactic acid bacteria (NSLAB) bio-films. Swabs were analyzed to determine the sources and microorganisms responsible for contamination. In pilot plant experiments, cheese vats filled with standard cheese milk ( lactose: protein = 1.47) and ultrafiltered cheese milk ( lactose: protein = 1.23) were inoculated with Lactococcus lactis ssp. cremoris starter culture ( 8 log cfu/mL) with or without Lactobacillus curvatus or Pediococci acidilactici as adjunct cultures ( 2 log cfu/mL). Cheddar cheeses were aged at 7.2 or 10 degrees C for 168 d. The raw milk silo, ultrafiltration unit, cheddaring belt, and cheese tower had NSLAB biofilms ranging from 2 to 4 log cfu/ 100 cm(2). The population of Lb. curvatus reached 8 log cfu/ g, whereas P. acidilactici reached 7 log cfu/ g of experimental Cheddar cheese in 14 d. Higher NSLAB counts were observed in the first 14 d of aging in cheese stored at 10 C compared with that stored at 7.2 C. However, microbial counts decreased more quickly in Cheddar cheeses aged at 10 C compared with 7.2 C after 28 d. In cheeses without specific adjunct cultures ( Lb. curvatus or P. acidilactici), calcium lactate crystals were not observed within 168 d. However, crystals were observed after only 56 d in cheeses containing Lb. curvatus, which also had increased concentration of D(-)- lactic acid compared with control cheeses. Our research shows that low levels of contamination with certain NSLAB can result in calcium lactate crystals, regardless of lactose: protein ratio. Key words: nonstarter lactic acid bacteria, calcium lactate crystal, biofilm, Lactobacillus curvatus, regardless of lactose:protein ratio.