The polymerization of 2-hydroxyethyl methacrylate, in a methanol solution, proceeds efficiently using the photoinitiator safranine T in the presence of tertiary aliphatic amines. Polymerization rates were measured at several amine concentrations. These values increase with the amine concentration, reaching a maximum, and further amine addition slowly reduces the polymerization rate. The quenching of the dye excited states by amines was analyzed by static fluorescence and laser flash photolysis. The excited singlet quenching involves a charge-transfer process with rate constants near the diffusional limit. Flash photolysis studies of safranine in the presence of amines, in a methanol solution, yield the triplet species 3SH+ and 3S+ and the unprotonated semireduced radical. This latter transient follows a dependence with the amine concentration similar to that found for polymerization rates. All these results indicate that polymerization involves the interaction of the excited triplet with the amine, while quenching of the excited singlet inhibits the polymerization.

No abstract

No abstract

ResumoIsolados protéicos (IPs) foram obtidos a partir da farinha da semente de goiaba (Psidium guajava) por extração a diferentes pHs seguido de precipitação isoelétrica (pI 4,5). As condições para o preparo do IP foram defi nidas a partir da curva de solubilidade, em pH 10,0 e 11,5, na ausência de NaCl e em temperatura de 25 ± 3 °C. Essas condições levaram a um rendimento na extração de 45,19 e 66,23%, e teor protéico de 96,4 e 93,5% para IP 10,0 e 11,5, respectivamente. Capacidade de absorção de água e óleo de 1,05 ± 0,07 e 2,30 ± 0,01 mL.g -1 proteína e 1,65 ± 0,07 e 1,70 ± 0,07 mL.g -1 proteína foram obtidos, respectivamente, para IP 10,0 e IP 11,5. Não foram observadas diferenças entre os IPs quanto à atividade e estabilidade de emulsão, atingindo valores similares e superiores ao IP de outras sementes. Formação de gel, em pH neutro e ausência de sal, exigiram concentrações de 8 e 10% para IP 10,0 e IP 11,5, respectivamente. Maior capacidade de formação de espuma foi obtida para IP 10,0 em pH neutro e alcalino, apresentando valores de até 90% do volume inicial, por outro lado, para estabilidade de espuma, ambos IPs apresentaram boas propriedades até duas horas após a formação da espuma. Palavras-chave: Psidium guajava; semente de goiaba; propriedades funcionais; isolado protéico (IP). AbstractProtein isolates (PIs) were obtained from the guava seed fl our (Psidium guajava) by extracting different pHs followed by isoelectric precipitation (pH 4.5). The conditions for preparation of the PIs were defi ned from the solubility curve at pH 10.0 and 11.5, in the absence of NaCl and a temperature of 25 ± 3 °C. These conditions obtained protein isolated (PI) with extraction yield of 45.19 and 66.23%, with protein content of 96.4 and 93.5% for PI 10.0 and 11.5, respectively. The water and oil absorption capacity of 1.05 ± 0.07 and 2.30 ± 0.01 mL.g -1 protein and 1.65 ± 0.07 and 1.70 ± 0.07 mL.g -1 protein, respectively; were obtained for PI 10.0 and PI 11.5. Differences among the PIs regarding the emulsion activity and stability were not observed, reaching similar and higher values compared to IP of other seeds. The gel formation in neutral pH and salt absence require concentrations of 8 and 10% to PI 10.0 and PI 11.5, respectively. The highest foam formation was observed for PI 10.0 in neutral and alkaline pH, and it showed a capacity of up to 90% of the initial volume; however for the foam stability both IPs showed good properties of up to two hours after foam formation.

No abstract

No abstract

No abstract

The aim of this work was to evaluate the thermal and kinetic behavior of white lupin (Lupinus albus) oil obtained from its seeds. White lupin is a seed from the Lupinus albus species, and it presents physicochemical and physiological functional properties and is rich in fiber, protein, and lipids with a great application potential. Oil was extracted from the seeds, and its fatty acid profile indicates predominantly monounsaturated fatty acids (*65%). Thermo-gravimetry, derivative thermo-gravimetry, and differential scanning calorimetry (DSC) were used to characterize the thermal behavior of the oil fraction at high temperatures, showing a good thermal stability between 222 and 230°C and a large heat delivery at T = 400°C. Additionally, DSC was performed from 25 to-60°C, in which the crystallization behavior was verified. The kinetic behavior of the thermal decomposition was evaluated from several b values and mass samples (5 and 20 mg) under nitrogen and oxygen atmospheres to comparisons of the data.