S. Huerta-Ochoa

Physiological, morphological, and mannanase production studies on Aspergillus niger uam-gs1 mutants

Mutant strains from Aspergillus niger UAM-GS1 were produced by UV radiation to increase their hemicellulolytic and cellulolytic activity production. The mutant strains showing more enzymatic activity were those labelled GS1-S059 and GS1-S067. These strains also showed the largest relationship between diameter of hydrolysis zone and colony diameter. The mutant GS1-S067 showed a colony radial extension rate and a biomass growth rate [g biomass/(cm 2 h)], 1.17 times higher than that achieved by strain UAM-GS1. The high invasive capacity makes this mutant strain a promising alternative for its use in solid substrate fermentation (SSF). The morphological properties of the two mutant strains were evaluated by using scanning electron microscopy. The diameter of the sporangium of the mutant strains GS1-S059 and GS1-S067 was significantly larger ( P P

Assessment of the limiting step of mass transfer in n-hexadecane biodegradation in a bubble column reactor

A mathematical model was developed to assess limiting step of mass transfer in the n-hexadecane (HXD) biodegradation by a microbial consortium. A double Monod kinetic (oxygen and HXD) for biomass production was successfully used to describe the experimental data. Good fitting (r²=0.92) between the model solution and experimental data was obtained. The overall mass transfer coefficients for HXD, k(L)a(HXD), and oxygen, k(L)a(O₂), were experimentally determined and biosurfactant production was indirectly determined through surface tension measurements in the aqueous phase. It was observed that a surface tension reduction from 65 (0 h of culture) to 47 mN m⁻¹ (240 h of culture) was related to a decrease of 52% in the HXD droplet diameter and to an increase of 63% in k(L)a(HXD), respect the initial values. Conversely, k(L)a(O₂) was repressed up to 37% compared to the initial value. The maximum rate analysis based on the mathematical model showed that HXD transfer was up to 5-fold lower than its consumption. On the contrary, oxygen transfer was always higher than its consumption. Thus, the limiting step under the working conditions was the HXD transfer to the aqueous phase. However, slight reductions in k(L)a(O₂) could result in oxygen transfer limitations during the last 60 h of the cultures.

Whole Cell Bioconversion of (+)-valencene to (+)-nootkatone in 100 % Organic Phase using Yarrowia lipolytica 2.2ab

Abstract The aim of this work was to assess the whole cell bioconversion of (+)-valencene to (+)-nootkatone in 100 % organic phase (orange essential oil) using a stirred tank bioreactor. Yarrowia lipolytica 2.2ab was used to perform bioconversion experiments; 600 mL of orange essential oil was inoculated with 50 cm3 of cell paste containing 13.5 g of biomass previously permeabilized with 0.2 % (w/v) of cetyl trimethylammonium bromide (CTAB) and enriched with 2.0 mM niacin. Experiments were conducted at 200 rpm, 0.5 vvm and 30 °C. The highest (+)-nootkatone yield was ca. 773 mg L−1 after 4 days of conversion. Bioconversion percent and volumetric productivity increased to 82.3 % and 8.06 mg L−1 h−1 compared to those reported previously using a three-phase partitioning bioreactor. The absence of free water in the system did not affect the performance of Y. lipolytica 2.2ab.

On the Understanding of the Adsorption of 2-Phenylethanol on Polyurethane-Keratin based Membranes

Abstract Polymers and specifically hybrid polymeric membranes have been identified as effective formulations in adsorption processes. Nevertheless, the adsorption mechanisms associated with their thermodynamics and kinetics are not fully understood, particularly when these polymeric membranes are used to adsorb 2-Phenylethanol (2-PE) to intensify its production in a specific bioconversion process. This work was aimed at giving phenomenological insights on the adsorption of 2-PE on a set of novel porous hybrid membranes based on polyurethane and keratin biofiber obtained from chicken feathers. Feathers, considered as a waste by-product of the poultry industry, represent an alternative source of keratin, a biopolymer that can be used to design low-cost materials from natural resources. Two types of hybrid membranes were prepared. i. e. composite and copolymer. Firstly, these materials were characterized by scanning electron microscopy (SEM), infrared spectroscopy (FT-IR) (before and after the adsorption process) and X-Ray (WAXD) analysis. Secondly, these materials, including the reference ones (keratin biofiber and polyurethane), were evaluated during the removal of 2-PE, relating their adsorption capabilities to physiochemical properties elucidated during the characterization. Particularly a composite with 0.1 g of chicken-feather-keratin (C1) presented the highest removal percentage (60.68%), a significant initial adsorption rate (0.2340 mgPE.h−1.gA −1), the maximum adsorption capacity (12.13 mgPE.gA −1) and the best stability and mechanical properties at studied operating conditions. In comparison with results reported in literature, in this composite carbonyl functional groups from polyurethane showed rather major affinity to 2-PE than amino groups from the keratin biofiber. To this end, parameters associated with its industrial application were obtained, namely thermodynamic and kinetic information was obtained from a proper design of experiments and phenomenological models based on adsorption macroscopic fundamentals.