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Utilization of milk citrate by lactic acid bacteria and ‘blowing’ of film-wrapped cheese

Summary A study was made of the utilization of citrate in milk by some lactic acid bacteria. When Streptococcus diacetilactis 1007 was grown alone or with either Streptococcus cremoris 924 or Lactobacillus casei B 142/C or with both these latter organisms, > 99% of the milk citrate was utilized within 5 days. L. casei B 142/C and L. casei/Str. cremoris utilized 57 and 14% of the citrate, respectively. When L. casei C 2 and L. casei C 5 were grown in milk in which Str. cremoris 924 had been previously grown, 94 and 64%, respectively, of the citrate was utilized after 7 days at 30°C. Cheeses were made using a citrate-fermenting and a non-citrate-fermenting starter and citrate concentrations of the milks, wheys and curds were determined during cheese-making. With Str. cremoris 924, citrate was preferentially retained in the curd at pressing, the concentration in the curd moisture being 2·9 times that in the whey. With the mixed starter Str. cremoris 924/Str. diacetilactis 1007, the curd at pressing and from the press contained only 27 and 5%, respectively, of the citrate present in the Str. cremoris curd at these times. Cheeses were made using Str. cremoris 924, combinations of Str. cremoris/Str. diacetilactis 1007, or with δ-gluconic acid lactone instead of starter, with and without the addition of L. casei C 5, in order to examine the ability of the latter organism to produce ‘blowing’ in the sense of distension of the Cryovac wrapping of film-wrapped cheeses. L. casei C 5 neither accelerated the decrease in cheese citrate nor produced blowing of the film-wrapping. Possible reasons for this behaviour are discussed.