| Abstrakt: |
A brew (1 rye flour: 2 water) was fermented by its indigenous microflora at temperatures (T) of 10, 15, 20, 25, 30, 35 and 40°C. A direct relationship was observed between the fermentation temperature and the absolute values of the ‘b' (the t coefficient) and ‘c' (an indicator of the width of the parabola) parameters of the fitted quadratic equations: pH=a+bt+ct2. Setting the first derivative of the quadratic fitted function to zero, dpH/dt=b+2ct=0, and solving for t gives the duration of the lag-phase period. When the temperature was increased from 10 to 35°C, the lag phase period (no net change in pH) of the fermentation was reduced by >sixfold from 17.8–2.9 h and the fermentation time to attain a pH of 5.0 was reduced by >13 times from 132–9.9 h. The fermentation rate (F) of rye flour within each of the three periods increased as the fermentation temperature increased up to 35°C. To predict the fermentation time to pH 5.0 at temperatures other than these examined in this study but within the range of these temperatures an exponential function, t5.0={exp[a+(b×T0.5)+c×exp(−T)}, was fitted. The Arrhenius plot of the acid production rate ([H+] h−1) vs the reciprocal of the absolute temperature showed a ‘breakpoint' at 15°C; indicating that 15°C may be the minimum metabolically efficient temperature for the lactic acid fermentation of rye flour. The activation energy (Ea) was 1.4 and 16.0 cal mol−1above and below the 15°C breakpoint; an additional indication that at temperatures <15°C the fermentation is less metabolically efficient. |
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