# Quantitative Characterization of _Geotrichum candidum_ Growth in Milk
## 3 Results  
### Primary Modelling of G. candidium Growth in Milk  
In this study, we used the primary mechanistic model proposed by [PERSON] and [PERSON] [30], which is the most appropriate in comparison with other primary models that are based on statistical indices [34]. Although it was primarily constructed for bacterial growth predictions, it has also been frequently used to describe fungal growth [12; 36; 37; 38; 39; 40]. The average initial counts (\(N_{0}\)\(\pm\) standard deviation) of \(G\). _candidium_ J in milk were 1.55 \(\pm\) 0.18 log CFU\(\cdot\)mL\({}^{-1}\) (coefficient of variation: \(CV\) = 11.6%) in all experiments without NaCl addition (\(n\) = 30) and 1.88 \(\pm\) 0.19 log CFU\(\cdot\)mL\({}^{-1}\) (\(CV\) = 10.3%) in milk with 1% NaCl. This density is in accordance with the inherent presence of \(G\). _candidium_ in raw milk [2; 13]. The growth curves of the isolate (Figure 1) in milk were characterised by a typical sigmoidal shape, with an exception at 37 \({}^{\circ}\)C, when the survival and subsequent decline of \(G\). _candidium_ counts were observed. However, during its cultivation in milk with 1% NaCl and in a suboptimal temperature range, we repeatedly observed a slight decline in \(G\). _candidium_ counts before the exponential growth phase. Since the lag phase represents the transient period of non-replication during which microorganisms adjust to the new environment, a decrease in the number of viable cells may also occur before the exponential phase [41]. Therefore, for the most appropriate fitting of the growth data by the modelling program (DMFit), we transformed the decreased counts of \(G\). _candidium_ into the average of the counts occurring in the lag phase (Figure 2). Figure 1: Growth curves of \(G\). _candidium_ isolate J in ultra-high temperature processed (UHT) milk without NaCl in the temperature ranges of 6–18 \({}^{\circ}\)C (**a**) and 21–37 \({}^{\circ}\)C (**b**). The points represent the observed values of counts of \(G\). _candidium_. The continuous lines represent fitted growth curve according to the DMFit modelling program. The growth parameters from the primary modelling are summarized in Table 1. The longest lag phase durations of _G. candidum_ growth in milk without and with 1% NaCl, respectively, were observed at the minimum cultivation temperature used in our study (6 \({}^{\circ}\)C) and lasted for almost 3 days. Despite this low incubation temperature, _G. candidum_ was able to grow and increased the initial counts by more than three logs within 9 days. Although this cooling temperature is used in practice to minimize microbial growth and to extend the shelf life of non-sterile dairy products [10], it is obvious from our results that the growth of _G. candidum_ is enabled under these circumstances, and it may lead to spoilage of dairy products. Organoleptic defects in certain dairy products (e.g., octage cheese and cream) are obvious when the fungal population is at least 10\({}^{\circ}\)-10\({}^{\circ}\)CFU g\({}^{-1}\)[42]. Based on our results, _G. candidum_ could reach that density in 7 or 8 days at 6 \({}^{\circ}\)C in milk without or with 1% NaCl, respectively. These data should be considered in dairy practices for controlling food quality and effective shelf-life management, including for predictions within consumers' households. Further increases in the cultivation temperature led to significantly (_p_ < 0.05) more intense growth of the isolate in milk. The highest growth rate and the shortest duration of the lag phase were observed at the cultivation temperature of 30 \({}^{\circ}\)C. Detailed knowledge of the lag phase duration and the rate of _G. candidum_ growth in milk at 30 \({}^{\circ}\)C, that is, the temperature of milk coagulation in cheese practices [43], may be helpful in the manufacturing of cheeses with the intentional addition of _G. candidum_ culture or in cheese production with raw milk. On the other hand, the effect of temperature on _G.