## 3 Results
### Effect of Dipping on Browning  
The visual impact is an important trait associated with quality of fresh fruits and vegetables as well as of fresh-cut products. In particular, the quality is expressed by the surface color of fresh cuts and their changes during storage, parameters which greatly influence the purchase decision of consumers [44]. Fresh-cut products are subject to enzymatic browning of cut tissues due to the contact between enzymes and cytoplasmic and nucleic substrates, normally protected in different cell compartments [45]. Enzymatic browning reaction in fruits is primarily catalyzed by polyphenoxidase (PPO) in the presence of oxygen [46]. PPO released during cutting acts on phenols, primarily causing browning of cut-apple surface [47]. Wounding may also determine the ethylene-induced activation of phenylalanine ammonia lyase (PAL) that regulates the biosynthesis of phenolic compounds, thus affecting their metabolism [48].  
During the storage at 20 \({}^{\circ}\)C, differences in surface color of apple cubes among dipping treatments adopted in these experimental conditions were observed (Figure 1).  
After 2 h of storage time (Figure 2), the browning appearance was evident in control dipping (DW) which showed the highest \(\Delta\)BI, while adding the preservative agents, the tissue browning was significantly reduced (\(p<0.05\)). The potato extracts, both water (PW) and ethanol (PE) solutions, showed an anti-browning effect comparable to the standard compounds. The beneficial effect exerted by P extracts could be linked to their phenolic content. Phenols have shown different behavior in enzymatic browning, depending on the type of compounds involved [49]. In the case of potato peels, the phenolic fraction contains substances, such as chlorogenic acid and caffe acid [34], able to inhibit the PPO activity [28].  
In particular, both potato extracts, used in combination with CA had a beneficial effect also after 4 h of storage similar to AA-CA, confirming the efficacy of organic acids in preserving low pH values. In this experimental trial, the AA alone showed a higher efficiency than AC. However, their combination was proved to exert the maximum anti-browning effect.  
The storage condition at 4 \({}^{\circ}\)C (Figure 2) showed a less severe browning degree in comparison to storage at room temperature. In general, the oxidation grade of tissues dipped with PE (Figure 2) was similar to DW. When PE and CA were combined, they produced a synergic effect inducing a strong browning inhibition. Thus, PE were able to retain color and control enzymatic browning alone or in combination with CA, similarly to results obtained at room temperature.  
This finding could be due to the influence of CA whose anti-browning effect in MP fruits and vegetables has been well known [28; 50] because of its copper chelating or acidulant role inactivating the PPO [51].  
Figure 1: Changes of browning index (BI) expressed as values of \(\Delta\) Browning Index (\(\Delta\)BI) of fresh-cut apples treated with different preservative media (Table 1) Data are referred to storage at 20 \(\pm\) 1 \({}^{\circ}\)C (\(t\) = 2 and 4 h) and 4 \(\pm\) 1 \({}^{\circ}\)C (\(t\) = 1 and 3 days). Values are means \(\pm\) SE and different letters indicate significant statistical difference (\(p\)\(\leq\) 0.05).