The incidence of bacteria in cheese milk and Cheddar cheese and their association with flavour

SummaryThe numbers and types of non-starter lactic acid bacteria, lipolytic bacteria and group D streptococci in cheese milks and corresponding Cheddar cheeses have been studied and their relationship to cheese flavour discussed. Different milks, heat-treatments and starters were used, and their association with flavour investigated. The pH and fat, salt and moisture contents of the cheeses were also determined.The non-starter lactic acid flora consisted mainly of Lactobacillus casei, L. plantarum, L. brevis, L. buchnerii, Pediococcus spp. and Leuconostoc spp. Lactobacillus casei was nearly always present in the milks and cheeses, predominating in most of the cheeses, particularly in those made from milk which received the most severe of the three heat-treatments tested (160°F for 17 sec). Leuconostocs were not found in any of the cheeses. Other species sometimes occurred in approximately equal numbers to L. casei, particularly in cheeses manufactured from the milder heattreated milks. Cheeses made from milk receiving the highest heat-treatment contained fewest bacteria and scored lowest for flavour. The average flavour scores increased as the number of species contributing to the non-starter lactic acid flora at the time of tasting increased.The lipolytic organisms capable of hydrolysing butterfat consisted mainly of Gram-positive cocci, predominantly Staphylococcus saprophyticus. The group D streptococci occurred infrequently, Streptococcus faecium being the most commonly occurring species.A definite correlation was found to exist between the starters used and the flavour of the cheeses. The pH of the cheeses was associated with the flavour, but the fat, moisture and salt contents of the cheeses showed no definite effect.