## 3 Results  
In this study, the evolution of the microbial quality during the refrigerated storage of Giuncata cheese was assessed by monitoring the growth of both _Pseudomonas_ spp. and total coliforms as representative spoilage microbial groups [3; 15; 31]. In addition, to evaluate the effects of the two different natural compounds on the cheese quality, the viable cell concentration of lactic acid bacteria was monitored. The results are reported in the following for each group. Figure 1 shows the evolution of _Pseudomonas_ spp. 's viable cell concentration in the control cheese and some of the investigated samples (runs 1, 5, 7 and 11). Data related to the control cheese showed a short lag phase, followed by an increase in the viable cell concentration until the stationary phase was attained (about 8 log(CFU/g)). A different trend was found when chitosan or lemon extract was used during the process. As can be inferred from the data shown in Figure 1, the presence of the antimicrobials slowed down the growth of _Pseudomonas_ spp. compared with the control sample. In fact, a more pronounced lag phase and a reduced microbial concentration at the stationary  
Figure 1: Best fit of modified Gompertz equation (Equation (1)) to the experimental data on the growth kinetics of _Pseudomonas_ spp. Experimental data are presented as means \(\pm\) standard deviation. Control (\(\Circle\))—Giuncata without any compounds; run 1 (\(\blacklozenge\))—Giuncata with 250 ppm lemon extract and 30 ppm chitosan; run 5 (\(\blacksquare\))—Giuncata with 500 ppm lemon extract and without chitosan; run 7 (\(\circ\))—Giuncata with 60 ppm chitosan and without lemon extract; run 11 (\(\square\))—Giuncata with 500 ppm lemon extract and 60 ppm chitosan. phase were found in all the samples obtained with active agents (runs 1, 5, 7 and 11). Some further differences between these runs can be highlighted. Specifically, in run 1, the kinetic growth was more similar to the control and, therefore, _Pseudomonas_ spp. proliferation reached the threshold within the first 4 days, which also happened for the control cheese. In contrast, a significant delay in microbial proliferation was recorded in runs 5, 7 and 11. To quantitatively determine the effectiveness of the tested compounds regarding inhibiting the _Pseudomonas_ spp. growth cycle, Equation (1) was fitted to the experimental data. The value of log(N\({}_{\rm max}\)) was set to 6 because at this level of contamination with _Pseudomonas_ spp., alterations in the product begin to appear [4; 5]. The fitting procedure allowed for determining the MAL values related to _Pseudomonas_ (MALP) for each combination of the two preservatives under study (Table 2). The data shown in the first column of Table 2 highlight that most combinations of chitosan and lemon extract improved the microbial stability because they promoted a significant delay of the _Pseudomonas_ spp. proliferation. In fact, in most cases, a MALP value higher than that of the control cheese was found, thus suggesting that chitosan alone, lemon extract alone or their proper combination contributed to controlling microbial proliferation. The antimicrobial effects of chitosan are well-known in the literature; however, it is also recognized that the antimicrobial activity of chitosan varies because this activity is associated with its physicochemical characteristics and depends on the type of microorganism [18]. Regarding lemon extract, data relating to dairy applications show that it may exert an inhibitory effect on the spoilage of mozzarella cheese [15; 32]. Literature data recorded on different food matrices also confirmed the pronounced antimicrobial effect of citrus essential oils [33; 34]. The significant increases in the MALP values for runs 5 and 11, compared with the sample without any active agent (CNT), suggest that synergies between the tested natural compounds occurred and that they could be advantageously used in the Giuncata cheese production process.