Amp. Gomes et al., SURVIVAL OF PROBIOTIC MICROBIAL STRAINS IN A CHEESE MATRIX DURING RIPENING - SIMULATION OF RATES OF SALT DIFFUSION AND MICROORGANISM SURVIVAL, Journal of food engineering, 36(3), 1998, pp. 281-301
The growth and survival behaviours of Bifidobacterium lactis and Lacto
bacillus acidophilus in a semi-hard Gouda cheese at various axial loca
tions during 9 wk of ripening at 13 degrees C were assessed using non-
linear regression analysis. The final average salt levels ranged in 2-
4%(w/w). Viable numbers of both probiotic strains underwent a slow dec
line during the first 3 wk followed by a sharper decrease towards the
end of ripening; such decrease was more substantial for the outer than
for the inner cheese portions. Salt transport was successfully descri
bed by Fick's second law of diffusion, and the cheese was considered a
s a finite slab for modelling purposes. Salt diffusivity remained cons
tant with time and was estimated to be 0.2 cm(2)/day. Theoretical salt
concentration profiles were in good agreement with experimental data.
The mathematical models postulated and fitted to the microbial viabil
ity data encompassed both a linear relationship between specific death
rate and salt concentration and a constant death rate, following a me
thodology of increasing model complexity. Decision on the better model
was taken based on a F-test of the ratio of incremental sum of square
s of residuals to sum of squares of residuals of the more complex mode
l, and it was concluded that viability of the probiotic strains was be
tter described by a first order process independent of local salt conc
entration. Prediction of profiles of viable numbers of B. lactis and L
. acidophilus in cheese with respect to both ripening time and axial l
ocation for several overall salt concentrations is useful in attempts
to predict potential viability by the time of consumption. (C) 1998 El
sevier Science Limited. All rights reserved.