## 3 Results and Discussion
### Chicken Nugget Shelf Life
\(\bullet\)CTRL_1, \(\bullet\)CTRL_2, \(\blacksquare\) Samp_1, \(\blacksquare\) Samp_2, \(\blacksquare\) Samp_3, \(\blacksquare\) Samp_4. The curves are the best fit to the experimental data. \(\bullet\)CTRL_1; \(\bullet\)CTRL_2; \(\blacksquare\) Samp_1; \(\blacksquare\) Samp_2; \(\blacksquare\) Samp_3; \(\blacksquare\) Samp_4. The dotted line represents the threshold for acceptability (\(10^{7}\) cfu/g). derived from grape pomace completely inhibit Enterobacteriaceae growth. Therefore, Table 4 only reports MAL values for the two controls and lists an MAL higher than 13 days for the other four meat products. The lactic acid bacteria grew very slowly and reached counts of around \(10^{6}\) CFU/g after 9-10 days in all of the samples (data not shown). Only in two cases, Samp_1 and Samp_2, was a slight overlapping of the threshold set to \(10^{7}\) CFU/g recorded (see Table 4). The effects on the growth of different meat spoiling microorganisms, such as lactic acid bacteria, depend on polyphenol concentration, medium, and species [33]. Various studies have suggested that polyphenols may improve sugar metabolism in lactic acid bacteria, thereby stimulating proliferation [41; 42]. The pH of meat samples did not remain constant over time for any of the samples (data not shown), thus suggesting possible correlation with microbial growth. In the two control meat products a reduction was observed from about 6.7 to about 5.6, without any statistically significant differences among them (\(p>0.05\)). This recorded pH reduction is in line with other literature evidence [9]. When sole GPP was used, the pH started from about 5.2 and reached about 5.6 after 13 days of storage. When GPP was combined with LA (Samp_2) or was combined with PE (Samp_3) or was combined with LA and PE (Samp_4), it maintained values around 5.2 during the entire observation period. Therefore, the low pH of the active samples can be considered an inhibitory factor limiting the growth of bacteria [43]. Further study is still necessary to assess if the direct bactericidal action of tested active ingredients results from a pH decrease within bacterial cells. Figure 4 reports the data recorded on cooked samples. As one would expect, sensory properties decreased over time because the detrimental phenomena occurring in the meat also generally affect the parameters that are responsible for product acceptability after cooking [7]. A similar trend to that recorded in the uncooked samples was also found for the cooked products. As can be seen, while the meat of the two control products lost color, odor, appearance and proper texture properties after about 8 days, the other treated samples remained acceptable for more time and, in most cases, never reached any threshold (score = 5). Table 4 also lists the results of the fitting procedure for cooked products. As can be inferred, the two controls recorded SAL values of around 8, Samp_1 and Samp_2 of around 13 days and the last two samples recorded SAL values higher than 13 days. The results of sensory evaluation agree with microbial analyses and are also consistent with previous research where good correlations among sensory attributes and microbial quality were reported [7]. Comparing values of MAL and SAL, it is possible to infer the meat shelf life as the lowest value among them. Considering that the lowest values of acceptability were always recorded for microbiological quality, the shelf life of samples tested in the current study can be inferred from the data in Table 4 (Table 6). The first control product lasts less than one day for an unacceptable proliferation of psychrotrophic bacteria, whereas the control meat treated solely with LA lasts a slightly longer time due to the _Pseudomonas_ spp. proliferation. The same pseudomonads group is responsible for the shelf life of Samp_1, Samp_2 and Samp_3, whereas Samp_4 became unacceptable for its high growth of mesophilic bacteria.