Amp. Gomes et al., VIABILITY OF BIFIDOBACTERIUM-LACTIS AND LACTOBACILLUS-ACIDOPHILUS IN MILK - SODIUM-CHLORIDE CONCENTRATION AND STORAGE-TEMPERATURE, Journal of food processing and preservation, 22(3), 1998, pp. 221-240
The growth and viability of Bifidobacterium lactis and Lactobacillus a
cidophilus per se and for both strains as a coculture were studied in
reconstituted skim milk so as to assess their dependence upon temperat
ure (5, 10 and 15C), NaCl concentration (0, 0.51 and 1.03 mol L-1), an
d storage time (0-8 weeks). Cultures of B. lactis exhibited no signifi
cant loss of viability either with increasing NaCl concentration or in
creasing storage temperature within the ranges studied. On the other h
and, viability of L. acidophilus decreased with increasing temperature
and increasing NaCl concentration under similar conditions. When cocu
ltured with L. acidophilus, B. lactis was significantly less tolerant
to higher NaCl levels and higher temperatures than when in pure cultur
e, although final numbers were still above the threshold required for
commercial application. Coculturing with B. lactis had no detrimental
effect on viability oft. acidophilus. A mechanistic model, which consi
ders the behavior of the pure and mired microbial populations is descr
ibed by specific death rates which vary with temperature (following Ar
rhenius relationships) and NaCl levels (following simple inhibition ki
netics) in the milk medium. Activation energies for the death rates of
B. lactis and L, acidophilus were 14 kcal mol(-1) and 9-15 kcal mol(-
1), respectively.