Supplementary MaterialsFIGURE S1: LC(ESI)-MS/MS spectra of chromatographic peaks obtained from reddish and white onions. quercetin aglycone in the structures of the CviR protein of ATCC 12472 than the glycosylated compound which corroborates the better inhibitory effect of the former over violacein production. On the other hand, the two quercetins were well placed in the AHLs binding pouches of the LasR protein of PAO1. Overall onion extracts and quercetin offered antimicrobial activity, and interference on QS regulated production of violacein and swarming motility. and (Nealson and Hastings, 1979). In addition to these bacteria, there are other model microorganisms such as in which QS has been well elucidated (Miller and Bassler, 2001; Waters and Bassler, 2005). There is great desire for these microorganisms as models to study QS, since many of JAK2-IN-4 the phenotypes are easily measured and are specifically regulated by QS. In several bacteria QS regulates a range of phenotypes, coordinating a group behavior that controls the expression of virulence factors, extracellular enzymes, biofilm formation, secondary metabolites, motility, among others (Whitehead et al., 2001; Waters and Bassler, 2005; Skandamis and Nychas, 2012). Many of these phenotypes can impact food spoilage, making the product undesirable or unacceptable for consumption. As an example, the expression of some microbial extracellular DP3 enzymes like proteases, pectinases and lipases is usually regulated by QS (Ammor et al., 2008; Martins et al., 2018). Therefore, researchers have tried to find strategies to disrupt this communication using inhibitory compounds and consequently improve food quality and security (Bai and Rai, 2011; Skandamis and Nychas, 2012). Many studies have shown the potential of herb organic extracts rich in phenolic compounds to interfere with QS in different bacteria. These compounds constitute a diverse group of chemical substances, with different chemical activities, important for plant reproduction, growth, and protection against pathogens attack (Martnez et al., 2002). They can be classified depending on the ring number and the type of elements that bind them into phenolic acids, stilbenes, lignans, and flavonoids (Rodrigues et al., 2016). The last group is an important class of natural products with polyphenol structure, widely found in fruits and vegetables (Panche et al., 2016). Its basic structural feature is the 2-phenyl-benzo–pyran compound which consists in two benzene rings (A and B) attached through a heterocyclic pyran ring (C) (Cushnie and Lamb, 2005). There is great desire for flavonoids because of their anti-inflammatory, antimicrobial, antioxidant and antitumor properties, among others (Cushnie and Lamb, 2005; Silveira, 2012; Rodrigues et al., 2016). In addition, flavonoids have also gained importance as potential inhibitors of the QS system. Different flavonoids such as taxifolin, kaempferol, naringenin, apigenin, baicalein, as well as others have demonstrated their ability to interfere in the QS system of microorganisms such as PAO1 and CV026 (Vandeputte et al., 2011), changing the transcription of QS-controlled target promoters and inhibiting the production of virulence factors (Paczkowski et al., 2017). One of the most representative flavonoids found in high concentrations in foods, especially onion (284C486 mg/kg) is usually quercetin (Behling et al., 2008). Different studies showed the inhibitory potential of this compound against some microorganisms with phenotypes regulated by QS. A research performed by Gopu et al. (2015) evaluated the ability of quercetin against the QS biosensor strain CV026 and tested the anti-biofilm house of the compound against food-borne pathogens such as spp., spp. spp., PAO1 (Ouyang et al., 2016). The authors observed that quercetin experienced a significant inhibition on biofilm formation, pyocyanin, protease and elastase production. It was also observed that this expression of genes was significantly reduced in response to quercetin (Ouyang et al., 2016). Different types JAK2-IN-4 of quercetins such as quercetin aglycone, quercetin 4-glucoside, quercetin 3,4-Lineu). The anthocyanin cyanidin has also been recognized in purple onion cultivars that give reddish or purple coloration to the bulbs (Lombard et al., 2005). The amount of quercetin in onions varies according to the color and type of bulb, being distributed mainly in the skins and outer rings (Arabbi et al., 2004; Lombard et al., 2005; Corzo Martnez et al., 2007; Kwak et al., 2017). Studies have suggested that quercetin, a flavonol present in high concentrations in onion (ATCC 12472 (30C/24 h), PAO1 (37C/24 h), and MG1 (30C/24 h). All cultures were produced in Luria Bertani (LB) agar or broth made up of peptone 1%, yeast extract 0.5%, sodium chloride 0.5% with 1.2% agar, as needed. Preparation, Extraction, and Characterization of Phenolic Compounds of Onion Varieties Preparation of Extracts The extracts were prepared in the Laboratory of Chemistry, Biochemistry and Molecular Biology of Food in the Faculty of Pharmaceutical Sciences of JAK2-IN-4 the University or college of S?o Paulo. Samples of 5 kg of white.