## 3 Results and Discussion
### Bioactivity of the Kiwi Peel Extract Obtained under Optimized UAE Conditions
#### 3.6.3 Antimicrobial Activity  
The antimicrobial activity of the kiwi peel extract was tested against some bacteria, namely _Bacillus cereus_, _Staphylococcus aureus_, _Listeria monocytogenes_, _Escherichia coli_, _Enterobacter cloacae_ and _Salmonella Typhimurium_, and some fungi, namely _Aspergillus ochracues_, _Aspergillus niger_, _Aspergillus versicolor_, _Penicillium funcilosum_, _Penicillium aurantiogriseum_ and _Trichoderma viride_. To compare the effectiveness of the kiwi peel extract, two synthetic food preservatives, sodium benzoate (E211) and potassium metabisulfite (E224), were used as positive controls. Table 4 shows the obtained values of minimum inhibitory and bactericidal or fungicidal concentration (MIC, MBC and MFC, respectively). As shown in Table 4, _Staphylococcus aureus_ and _Escherichia coli_ were the most sensitive bacteria to the tested extract and _Aspergillus ochracues_, _Aspergillus versicolor_, _Penicillium funcilosum_ and _Trichoderma viride_ were the most sensitive fungi.  
For antimicrobial activity, the MIC and MBC values show that the kiwi peel extract behaves very similar to the synthetic preservative E224, when it was used against Grampositive bacteria, such as _Bacillus cereus_ and _Staphylococcus aureus_, but adopts a behavior similar to the preservative synthetic E211, when tested against Gram-negative bacteria, such as _Escherichia coli_ and _Enterobacter cloacae_. Regarding the bacteria _Listeria monocytogenes_ and _Salmonella Typhimurium_, the extract was less effective compared to the respective controls. In general, the kiwi peel extract appears to have a greater effect against fungi compared to bacteria, with lower MIC and MFC values. In addition, the extracts showed, for most of the microorganisms, better or equal activity than both synthetic preservatives.  
These results are in agreement with studies that describe the antimicrobial potential of _Actimide delicious_ extracts against bacterial and fungal growth, which may be useful to help prevent food deterioration processes and the occurrence of possible contamination [25]. [PERSON] et al. [32] studied the antimicrobial potential of kiwi, pomegranate and graprefruit peels, and found that, although all fruit peels have great antimicrobial power, in most cases the kiwi peel stood out from the other samples, regardless of the type of extraction and solvent used. [PERSON] [28] reported the antimicrobial activity of kiwi peel and bagasse flours against _Salmonella_ sp., _Bacillus cereus_ and _Staphylococcus aureus_. In a study on the isolation and characterization of an allergenic kiwi protein _in natura_, [PERSON] et al. [33] verified its antifungal activity against _Saccharomyces carlsbergensis_ and _Candida albicans_. Furthermore, [PERSON] and [PERSON] [34] verified the antifungal activity of fresh kiwi against _Fusarium oxysporum_. Therefore, the results presented in this study are somewhat in agreement with the results previously reported in the literature. It can also be concluded that the observed effects could be attributed not only to phenolic compounds, but also to other bioactive constituents of this plant by-product.