Effet combiné de l'oxygène et de la température sur l'acidification et les productions de diacétyle et d'acétoïne par Lactococcus lactis subsp lactis biovar diacetylactis

Abstract

N Bassit et al subsp lactis biovardiacetylactis was studied. The results were described by the methodology of response surface. Linear, squared and simple interaction effects were estimated after an orthogonal polynomial reparametrisation. The effect of temperature was higher than the effect of oxygen for acidification only. The opposite effect was observed for diacetyl and acetoin production and consequently for the ratio diacetyVacetoin (DIA). Optima were found on the limits of the experimental design. Diacetyl concentration and DIA ratio reached a maximum value at urc and 100% of oxygen concentration (0.3 mmoVl and 5.9%, respectively). Acetoin concentration was maximum (5.3 mmoVl) at 26"C and 100% of oxygen concentration. On the other hand, the maximum acidification rate reached its maximum value (0.23 unit pHlh) at 3CJ'Cand 0% of oxygen concentration. For the four variables tested, there was a significant interaction between temperature and initial oxygen concentration. diacetyl 1acetoin 1acidification 1 Lactococcus lactis subsp lactis

Osmotic‐Convective Dehydrofreezing Process for Drying Kiwifruit

“…An effect (P Ͻ 0.01) of temperature was observed on production of all metabolites (Table 4). An increase stimulated lactic acid production in YPC, which confirmed published results (Bassit et al, 1994(Bassit et al, , 1995Desmazeaud, 1983). An effect (P Ͻ 0.01) of temperature has been observed on diacetyl, acetoin and ethanol production.…”

“…Thus, increasing incubation temperature to 25ЊC stimulated the fermentation in all aspects, but a further temperature rise to 30ЊC only increased lactic acid production. These results on YPC basically confirmed those with citrate positive lactococci on dairy substrates (Bassit et al, 1994;Oberman et al, 1982;Pack et al, 1968).…”

Analysis of Volatile Compounds Produced by 2 Strains of Lactococcus lactis Isolated from Leben (Tunisian Fermented Milk) Using Solid‐Phase Microextraction‐Gas Chromatography

“…Fermentation conditions can greatly influence diacetyl production. The level of dissolved oxygen, either initially (Bassit and others 1994) or during fermentation (Takahashi and others 1990), has a direct influence on diacetyl production. The assumption was that dissolved oxygen levels were higher in stirred flasks (150 rpm) than in nonstirred ones.…”

Process–quality optimization of the vacuum freeze‐drying of apple slices by the response surface method

“…This experimental design enabled factor effects to be evaluated (linear, quadratic and interaction) and trial variability to be estimated with minimum experimentation. The response surface method (RSM) is the most widely used analysis for these experimental designs (Giovanni, 1983;Mudahar et al, 1990;Bassit et al, 1994). It is a linear multiple regression technique which consists of modelling the results using a second order polynomial equation of the two factors (quadratic model).…”

“…Factorial effects are not the coefficients of this function (6). To obtain directly interpretable and comparable effects, f must be rewritten according to the normalized orthogonal polynomials Q 0 , Q 1 , Q 2 ) of P c and T c (Noël et al, 1991;Bassit et al, 1994). The final model expression is:…”