Lag phase of growth

Typical units for productivity are kg m 3 h 1. Factors that influence productivity include the production time of the fermentation, the time required to dean and set up the reactor, the sterilisation time and the length of the lag phase of growth. Figure 2.2 shows how total productivity and maximal productivity can be calculated for a batch fermentation. The dedsion as to when the fermentation is terminated (maximum or total productivity) depends on the operating costs, which include the capacity of the fermentation vessel, energy costs and labour costs. 

In continuous fermentation, maximum productivity equals total productivity since the preparation time and the time in lag phase of growth are small relative to the total fermentation time. 

The strain adapted to pectate showed lag phase by cultivation on this medium corresponding to the first phase of growth on pectin, but after short storage period (two weeks) on malt agar it lost completely the ability to grow on pectate (Fig. 2). There was a possibility to restore this ability to grow on pectate by primary cultivation on pectin. It seems, in conclusion, there is a primary utilization of methanol released from pectin by Candida boidinii and the secondary path, the utilization of D-galacturonate chains, required an... 

Figure 7. Variation of arogenate dehydrogenase levels as a function of the physiological phase of growth in suspension cultures of Nicotiana sil-vestris. A stationary-phase inoculum was diluted into fresh medium and followed throughout the lag (L), exponential (E), and stationary (S) phases of growth. The hatched bar indicates the activity levels of EE cells, i.e., cells maintained continuously in exponential growth for 10 or more generations (53). Profiles are shown in which activity is related to soluble protein (specific activity), to cell number, or to dry weight.

When a more detailed analysis of microbial systems is undertaken, the limitations of unstructured models become increasingly apparent. The most common area of failure is that where the growth is not exponential as, for example, during the so-called lag phase of a batch culture. Mathematically, the analysis is similar to that of the interaction of predator and prey, involving a material balance for each component being considered. 

At the end of the lag phase, when growth begins, the division rate increases gradually and reaches a maximum value in the exponential growth period, as shown by the rising inflection at B in Figure 6.1. This transitional period is commonly called the accelerated growth phase and is often included as a part of the lag phase. 

The closer the pH of a medium is to the pKa of an acid, the greater the lag phase of microbial growth is expected to be (Livingston et al., 2004). Organic acids used for food preservation are weak acids with the pKa range between pH 3 and 5 which possess some levels of buffer activity (Doores, 1993 Fang and Tsai, 2003). 

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