## 3 Results and Discussion
### Effects of Antimicrobials on Shelf Life  
To assess the effect of the active ingredient used alone and in proper combination with other compounds, the shelf-life values were used to calculate a normalized percent difference (\(\Delta\%\)). To demonstrate the effects of LA on the shelf life, samples CTRL and CTRL_LA were used to calculate the first normalized percent difference, which will be referred to as A%_1. According to the shelf-life values recorded for the above sample, a \(\Delta\%\_1=127\) was obtained. The data of the shelf life of the two controls are not statistically different (Table 4) and, therefore, the calculated index, despite the difference recorded between the two samples, is not statistically significant. As can be inferred from the data listed in Table 3, the microbial quality of the investigated samples is the factor that limits the shelf life. Therefore, the fact that \(\Delta\%\_1\gg 1\) clearly indicates that LA extended the shelf life of chicken nuggets by slowing down the microbial growth of the main spoilage microorganisms. In fact, lactic acid is known to be effective against microbial proliferation in poultry meat [39]. The effect of GPP on chicken nugget shelf life was assessed by comparing the CTRL and Samp_GPP samples. The calculated normalized percent difference between the two mentioned samples (\(\Delta\%\_2\)) is equal to 281.25. This result indicates that GPP is very effective in extending the shelf life of the investigated food. This is not surprising considering the abundant findings from literature dealing with pomace and its extracts applied to improve the safety and quality of meat products. It is worth noting that \(\Delta\%\_2\) is double \(\Delta\%\_1\), thus suggesting that GPP can be considered more effective than LA in extending the shelf life of chicken nuggets. Direct comparisons between LA and GPP on chicken nuggets from literature evidence are not possible because no studies have been found with similar treatments. However, there are several abilities that are attributed to the phenolic compounds generally contained in grape by-products that indicate a significant effectiveness against microbial proliferation when compared with organic acids. The mechanisms of action of these abilities are associated with the ability to inhibit cell wall synthesis and produce cell membrane alterations with consequent loss of crucial intracellular material, ability to chelate essential metals, to bind polysaccharides, and to proteins, thereby producing compounds that cannot be metabolized by microorganisms and which have the ability to bind vital components such as enzymes and cell transport proteins [40]. When comparing sample CTRL_LA and sample Samp_LA_GPP, an effect of GPP on the sample treated with LA was observed. In this case, the normalized percent difference (\(\Delta\%\_3\)) is equal to 280.60. As one would expect, the value of \(\Delta\%\_3\) is very similar to \(\Delta\%\_2\), thus proving once again that GPP strongly influences chicken nugget shelf life, due to the well-known properties of grape pomace on meat [33; 34]. To assess the effect of PE on microbial growth of our meat-based products, samples SAMP_GPP_PE and Samp_GPP were used to calculate the normalized percent difference (\(\Delta\%\_4\)). In this case a