Enhancing the saccharification of pretreated chestnut burrs to produce bacteriocins

 Journal of Biotechnology, 329, 13-20

The present study aims to valorize chestnut burrs, an important lignocellulosic waste, through a biorefinery concept. A solid residue rich in glucan (41.36 ± 0.59 %) and lignin (39.06 ± 0.01 %) obtained from a previous process of pre-hydrolysis was subjected to four treatments with water or NaOH to enhance enzymatic hydrolysis. Saccharification was performed using different ratios of commercial cellulases and β-glucosidases and at controlled pH 4.8 or 6.0 (with citrate buffer) or uncontrolled pH. Carbohydrate-rich solutions with or without nutrients were used to produce bacteriocins by Lactobacillus plantarum CECT 211. The use of NaOH at high temperatures (120 and 130 °C) was the most suitable treatment to improve saccharification. Regarding the production of bacteriocins, the best result was obtained using the enzymatic solution obtained at controlled pH 6.0, supplemented with MRS broth nutrients (except glucose). Thus, the concentrations of bacteriocins obtained in this culture medium (9.21 BU/mL) was 1.22 and 1.98 times higher than those obtained in the nutrient supplemented medium buffered at pH 4.8 (7.56 BU/mL) and in the commercial MRS broth (4.65 BU/mL), respectively. These results highlight the feasibility of the technology developed in this work.

High hydrostatic pressure as pretreatment and adjuvant for the enzymatic release of ferulic acid from corn cob

Process Biochemistry

https://doi.org/10.1016/j.procbio.2017.04.011

Bioprocesses based on the use of enzymes can be employed for the obtainment of ferulic acid by its solubilization from corn cob, which is a natural source of this phenolic compound. In order to overcome the limitations caused by the recalcitrance of biomass, the application of pretreatments is advisable. The utilization of high hydrostatic pressure on the enzymatic release of ferulic acid from corn cob with three feruloyl esterase extracts was studied applying pressurization at 600 MPa as a pretreatment in combination with a mild thermal treatment at 130 °C/2 h. Additionally, pressurization at 200 MPa during the enzymatic hydrolysis step was assessed to increase the ferulic acid yield. The results showed that the application of a high pressure pretreatment at 600 MPa/40 °C/15 min to thermally treated corn cob increased by 20% the ferulic acid release in comparison with the thermal treatment for Ultraflo® L, but not for the Aspergillus extracts. Pressurization at 200 MPa during the hydrolysis stage affected differently the enzymes stability and ferulic acid release depending on the extract and the pretreatments applied, showing that the effects of pressurization are complex and must be assessed in each case.

Feruloyl esterase production by Aspergillus terreus CECT 2808 and subsequent application to enzymatic hydrolysis

Enzyme and Microbial Technology, 91 (2016) 52–58

http://dx.doi.org/10.1016/j.enzmictec.2016.05.011

Ferulic acid esterases (FAE) were produced by Aspergillus terreus CECT 2808 from vine trimming shoots (VTS) and corn cob. Later, the fungal extracts thus obtained were used to enzymatically release ferulic acid (FA) from both substrates. Our findings showed a higher FAE activity in the enzymatic extracts produced on corn cob (0.070 ± 0.004 U/mL). Nevertheless, the enzymatic extracts produced on VTS demonstrated a better performance for FA release from both corn cob (2.05 ± 0.01 mg/g) and VTS (0.19 ± 0.003 mg/g). This result was probably because of the higher xylanase/FAE ratio determined in VTS extract. Therefore, an additional assay was carried out by supplementing corn cob extract with a commercial xylanase to test the influence of FAE/xylanase ratio in FA release. The results revealed the relevance of the FAE/xylanase ratio for an optimal FA release.

Structural and thermo-rheological analysis of solutions and gels of a β-lactoglobulin fraction isolated from bovine whey

Food Chemistry, 198 (2016) 45–53

http://dx.doi.org/10.1016/j.foodchem.2015.11.090

A β-Lactoglobulin fraction (r-βLg) was isolated from milk whey hydrolysates produced with cardosins from Cynara cardunculus. The impact of the technological process on the r-βLg structure and how in turn this determined its heat-induced gelation was investigated. Results were analysed taking pure β-Lg (p-βLg) as control sample. The process induced changes in the r-βLg native conformation causing exposure of hydrophobic groups, lower thermal stability and also, shorter thermal treatments needed to give rise to non-native and aggregated species.

At pH 3.2, r-βLg and p-βLg solutions exhibited two gelation steps, with the advantage that r-βLg protein may form stable gels at lower temperature than p-βLg. At pH 7.2, a specific thermo-viscoelastic stability to 73 °C was found, which corresponded to the gel point in both protein solutions. The difference was that while for p-βLg solution in sol state δ < 45° (solid-like), however for r-βLg solution δ > 45° (fluid-like).

Influence of pH on viscoelastic properties of heat-induced gels obtained with a β-Lactoglobulin fraction isolated from bovine milk whey hydrolysates

Food Chemistry, 219, 2017, 169–178

http://dx.doi.org/10.1016/j.foodchem.2016.09.137

A β-Lactoglobulin fraction (r-βLg) was isolated from whey hydrolysates produced with cardosins from Cynara cardunculus. The impact of the hydrolysis process on the r-βLg structure and the rheological properties of heat-induced gels obtained thereafter were studied at different pH values. Differences were observed between r-βLg and commercial β-Lg used as control. Higher values for the fluorescence emission intensity and red shifts of the emission wavelength of r-βLg suggested changes in its tertiary structure and more solvent-exposed tryptophan residues. Circular dichroism spectra also supported these evidences indicating that hydrolysis yielded an intermediate (non-native) β-Lg state.

The thermal history of r-βLg through the new adopted conformation improved the microstructure of the gels at acidic pH. So, a new microstructure with better rheological characteristics (higher conformational flexibility and lower rigidity) and greater water holding ability was founded for r-βLg gel. These results were reflected in the microstructural analysis by scanning electron microscopy.