Roberto Afonso da Silva

Covalent immobilization of invertase on polyurethane, plast-film and ferromagnetic Dacron

Invertase was covalently immobilized on polyurethane (PU), inox plate covered with plast-film layer and ferromagnetic azide-Dacron. The immobilization processes, physico-chemical parameters and a model for coupling reactions were studied. The preliminary studies for selection of the support showed that the best activity was obtained for PU treated with HCl, polyethylenimine and glutaraldehyde (156.7+/-4.9 U/g support). All plast-film-invertase derivatives did not show activity and the Dacron-invertase derivative showed an activity of 105.39 U/g support. The invertase immobilized in presence of substrate (10% w/v sucrose) was the most efficient (832.74+/-1.48 U/g support). The optimal pH was shifted from 4.5 (free enzyme) to 5.0 (immobilized derivative) and optimal temperature was not affected. Activation energy values of free enzyme, Dacron-invertase and PU-invertase were 32.4+/-0.34 kJ/mol, 33.4+/-0.36 kJ/mol and 44.0+/-0.67 kJ/mol, respectively. The PU-invertase could be used over 2 months without considerable activity loss (68.5% activity retention) and retained 12.6% (287.97+/-27.9U/g support) of the activity after five cycles.

Kinetics and bioreactor studies of immobilized invertase on polyurethane rigid adhesive foam

A new support, polyurethane rigid adhesive foam (PRAF), which can be used to cover internal surface of metallic tubes, was used to immobilize invertase for application in an enzymatic bioreactor. The kinetic parameters were: Km--46.5±1.9 mM (PRAF-invertase) and 61.2±0.1 mM (free enzyme) and Vmax 42.0±4.3 U/mg protein/min (PRAF-invertase) and 445.3±24.0 U/mg protein/min (free invertase). The PRAF-invertase derivative maintained 50.1% of initial activity (69.17 U/g support) for 8 months (4°C) and was not observed microbial contamination. The bioreactor showed the best production of inverted sugar syrup using up-flow rate (0.48 L/h) with average conversion of 10.64±1.5% h(-1) at feeding rate (D) of 104 h(-1). The operational inactivation rate constant (kopi) and half-life were 1.92×10(-4) min(-1) and 60 h (continue use). The PRAF spray support looks promising as a new alternative to produce immobilized derivatives on reactor surfaces.

Biotechnological richness of the northeastern semi-arid region: antioxidant activity of casein hydrolysates from Moxotó goat milk (Capra hircus Linnaeus, 1758) obtained by papain action

This study aimed to identify antioxidant peptides from caprine casein hydrolysates by papain application using MALDI-TOF mass spectrometer, and a 2 2 full factorial design, with 4 axial points, in order to evaluate kinetic parameters (time and pH) effects on the degree of hydrolysis as well as the antioxidant activity of Moxoto goat milk casein peptides. Degree of hydrolysis was determined by total and soluble protein ratio in casein. Antioxidant activity was measured by ABTS method with 2, 2-cation-azinobis (3-ethylbenzothiazoline-6-sulfonic acid). TROLOX was used as standard. Peptide pattern and sequence of antioxidant amino acids were obtained using MALDI-TOF/MS. The highest degree of hydrolysis (28.5%) and antioxidant activity (2329.6 mmol.L TROLOX. mg –1 peptide) were observed in the permeate. NENLL, NPWDQVK and LLYQEPVLGPV peptides, detected in the permeate, were pointed as the responsible for antioxidant activity, suggesting their potential application as food supplement and pharmaceutical products.

Avaliação da microbiota bacteriana do queijo de coalho artesanal produzido na região Agreste do estado de Pernambuco

The aim of this study was to evaluate the microbiological quality and lactic-acid profile of artisanal coalho cheese. All cheese samples analyzed showed total coliforms, were thermotolerant, and had Escherichia coli, but all the values were within the standards established by current legislation in the country, and could be considered a food fit for human consumption. The cheese showed a heterogeneous microbiota, being constituted of all tested genus, such as lactobacilli, lactococcus, streptococcus and enterococcus, and confirmed the species: Enterococcus faecalis, Enterococcus faecium, Streptococcus thermophilus and Lactococcus lactis.

Brazilian Kefir-Fermented Sheep’s Milk, a Source of Antimicrobial and Antioxidant Peptides

Fermented milks are a source of bioactive peptides and may be considered as functional foods. Among these, sheep’s milk fermented with kefir has not been widely studied and its most relevant properties need to be more thoroughly characterized. This research study is set out to investigate and evaluate the antioxidant and antimicrobial properties of peptides from fermented sheep’s milk in Brazil when produced by using kefir. For this, the chemical and microbiological composition of the sheep’s milk before and after the fermentation was evaluated. The changes in the fermented milk and the peptides extracted before the fermentation and in the fermented milk during its shelf life were verified. The antimicrobial and antioxidant activities of the peptides from the fermented milk were evaluated and identified according to the literature. The physicochemical properties and mineral profile of the fermented milk were like those of fresh milk. The peptide extract presented antimicrobial activity and it was detected that 13 of the 46 peptides were able to inhibit the growth of pathogenic microorganisms. A high antioxidant activity was observed in the peptides extracted from fermented milk (3.125 mg/mL) on the 28th day of storage. Two fractions displayed efficient radical scavenging properties by DPPH and ABTS methods. At least 11 peptides distributed in the different fractions were identified by tandem mass spectrometry. This sheep’s milk fermented by Brazilian kefir grains, which has antioxidant and antimicrobial activities and probiotic microorganisms, is a good candidate for further investigation as a source for bioactive peptides. The fermentation process was thus a means by which to produce potential bioactive peptides.