, 2009, Kolusheva et al., 2000 and Su, 2005), chips (Kim et al., 2005 and Park et al., 2008) and biosensors (Lee et al., 2007 and Park et al., 2008). According to Reppy and Pindzola (2007) the optical properties of PDA vesicles and their susceptibility to their environment are the basis for the generation of signals in PDA-based biosensors. Thus, it is observed that the characteristics of colour

change in PDA vesicles, make them suitable as a material for the development of sensors for the food industry. This study investigated the effect of temperature, pH, and some solutions that simulate the chemical components of milk on colour properties selleck inhibitor of PCDA/DMPC vesicles, to verify their application in sensors for the food industry. This Bioactive Compound Library cost study focused on the UV–visible spectrophotometric detection of colour change. Vesicles were prepared using 10,12-pentacosadienoic acid (PCDA) 97.0% (Sigma®); 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) 99.8% (Merck, Darmstadt, Germany) and chloroform HPLC Grade 99.8% (Merck). NaOH ACS reagent 97.0% and HCl ACS reagent 37.0% (both Sigma–Aldrich, St Louis, MO) were used for the titration of vesicles. NaCl 99.95%; NaH2PO4·H2O 99.0%; C6H5Na3O7·2H2O 99.0%;

KCl 99.0%; KH2PO4 99.0%; CaHPO4 98.0% and MgHPO4·3H2O 99.0% (all from VETEC Química Fina Ltda, Rio de Janeiro, Brazil); CaCl2 99.0% (Merck); MgCl2 98% (Merck); d-lactose monohydrate, ACS reagent (Sigma); α-lactalbumin from bovine milk 90.0% (Fluka); β-lactoglobulin from bovine milk 90.0% (Sigma) and casein from bovine milk 90.0% (Sigma) Protein tyrosine phosphatase were used to simulate the chemical components of milk. The vesicles were prepared by separately dissolving 10,12-pentacosadienoic acid (PCDA)

and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in chloroform at a concentration of 1 mM and mixing them, at a ratio of 7:3 (v:v) to a final volume of 10 mL. Chloroform was evaporated using N2 gas. Then, 10 mL of Milli-Q deionised water (18.1 MΩ resistance) were added. The suspension was heated to 60 °C in a sonicator (Soni-tech ultrasonic cleaner, ultrasonic cleaning HW 800) for 1 h. It was then filtered through polyvinylidene filter (PVDF 0.45 μm, Mille; Millipore Corp., Billerica, MA). The filtrate was cooled to 4 °C for at least 4 h. The vesicles were polymerised by exposure to 254 nm UV light for 15 min. The vesicle suspension was stored at temperatures of 5, 12, 20 and 25 °C for 60 days and monitored by UV–Vis spectrum scanning from 700 to 400 nm (GBC UV/Vis 918; GBC Scientific Equipment, Braeside, Australia), to evaluate the effect of storage time and temperature on vesicle chromism. The spectroscopic analyses were performed on the day the PCDA/DMPC vesicles were produced and after 7, 15, 22, 30 and 60 days.