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Abstract  

The guava seed protein isolate (PI) was obtained from the protein precipitation belonging to the class of the gluteline (Ip 4.5). The conditions for the preparation of the PI were determined by both the solubility curve and simultaneous thermogravimetry-differential thermal analysis (TG-DTA): pH 11.5, absence of NaCl and whiteners and T=(253)C. Under these conditions a yield of 77.00.4%, protein content of 94.20.3, ashes 0.500.05% and thermal stability, T=200C, were obtained. The TG-DTA curves and the PI emulsification capacity study showed the presence of hydrophobic microdomains at pH 11.5 and 3.0 suggesting a random coil protein conformation and, to pH 10.0, an open protein conformation. The capacity of emulsification (CE), in the absence of NaCl, was verified for: 1 – pH 3.0 and 8.5, using the IP extracted at pH 10.0 and 11.5, CE≥3435 g of emulsified oil/g of protein; 2 – pH 6.60 just for the PI obtained at pH 11.5, CE≥1408 g of emulsified oil/g of protein.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Fontanari, G. Souza, J. Batistuti, V. Neves, I. Pastre, and F. Fertonani

Abstract  

Glutelin, the major protein fraction from guava seed, was obtained by fractioning as described by Osborne. The total proteins were extracted and the isolates obtained by isoelectric precipitation presented similar DSC curves, concordant with the results obtained by gel filtration chromatography and electrophoresis in polyacrylamide gel (PAGE-SDS). However, the DSC curves showed a higher enthalpy with regard to the denaturing protein isolate (PI) extracted at pH 10.0 when compared to a PI at pH 11.5. Such results are in accordance with those obtained for PI extracted at pH 10.0 using chromatography, this one being present in the form of molecular aggregates of greater molecular mass. The glutelin fraction, however, did not present a denaturation peak in the DSC curve, showing that the process for obtaining the same significantly altered its conformation.

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