Production and biotransformation of 6-pentyl-alpha-pyrone by Trichoderma harzianum in two-phase culture systems

The final concentration of 6-pentyl-a-pyrone (6PP) produced in cultures of Trichoderma spp. is limited by the fact that inhibition of biomass growth occurs at 6PP concentrations as low as 100 mg/l. The aim of this work was to evaluate liquid-liquid extractive fermentation systems as an alternative to overcome the toxicity problems and to increase the production of 6PP by this fungus. Two alkanes (n-decane and n-hexadecane) and two dicarboxylic esters (dibutyl phthalate and dioctyl phthalate) were evaluated in shake flask cultures. The highest 6PP production (173 ppm) was achieved when n-hexadecane was used, being 3.5-fold the maximum 6PP concentration of a culture without the solvent. Cultivation of Trichoderma harzianum in a 10-1 bioreactor with n-hexadecane yielded 6PP production ninefold higher than that from control cultures. However, 6PP production in the bioreactor (83 ppm) was lower than in shake flasks. Differences in the power drawn to the fluid at each scale could account for such behavior. Even in the presence of the solvent, 6PP content decreased after reaching its maximal concentration.

The potential application of aqueous two-phase systems for in situ recovery of 6-pentyl-infinity-pyrone produced by Trichoderma harzianum

Commercial production of aroma compounds by de novo microbial biosynthesis has been principally limited by the low productivity so far achieved. Production of 6-pentyl-alpha-pyrone (6PP), a coconut-like aroma compound, by Trichoderma harzianum has been limited by the toxic effect that occurs even at low concentration (<100 ppm). This work evaluated the feasibility of the use of aqueous-two phase systems (ATPS), as in situ extraction systems, in order to overcome the toxic effects of 6PP and to improve culture productivity. The partition behaviour of 6-pentyl-alpha-pyrone and Trichoderma harzianum mycelium in polyethylene glycol (PEG)-salt and PEG-dextran two-phase systems was investigated and it is reported for the first time. The evaluation of system parameters such as PEG molecular mass, concentration of PEG as well as salt, volume ratio (Vr) and dextran molecular mass, was carried out to determine under which conditions the 6PP partitions to the opposite phase that mycelium does. PEG-dextran systems proved to be unsuitable for the in situ recovery of 6PP because either 6PP and biomass partitioned to the same phase or a large extraction phase was required for the process. ATPS extraction comprising Vr = 0.26, PEG 1450 (7.2% w/w) and sulphate (16.6% w/w) provided the best conditions for the maximum accumulation of the biomass into the bottom phase and concentrated the 6PP in the opposite phase (i.e. 86% of biomass and 56% of 6PP of the total amount loaded from the fermentation extract into the ATPS) for ex situ bioseparation. However, this system caused complete inhibition of the growth of the microorganism during the in situ bioseparation, probably as a consequence of the high ionic strength resulting from the salt concentration. Consequently, two ATPS PEG 8000-sulphate (12%/7% and 6%/14%) were evaluated and proved to be more suitable in the potential application for the in situ recovery of 6PP.

Effect of biological suspensions on the position of the binodal curve in aqueous two-phase systems

This study is concerned with the influence of biological suspension on the position of the binodal curve in aqueous two-phase systems (ATPSs). Three different biological suspensions (i.e., disrupted yeast, E. coli homogenate and fermentation broth from Trichoderma harzianum) were selected and their impact upon ATPS performance was evaluated on the basis of changing volume ratio (Vr) and the position of the binodal curve of biological ATPSs (added with biomass). Biological ATPSs with initial Vr greater than 1 and long (>40%, w/w) tie-line length (TLL), exhibited significant changes in Vr when compared with that from non-biological systems. Such behaviour was associated with the top phase biomass accumulation. It was shown that the addition of the biological suspensions used in this study to ATPSs caused the binodal curve to displace towards the origin, which was associated with the critical contribution of the bio-polymer (present in the systems) to the phase formation. The practical implementation of ATPSs for the purification of biological materials exploiting the information reported in this study is discussed.

Aroma compounds recovery from mycelial cultures in aqueous two-phase processes

This paper presents the evaluation of the potential use of aqueous two-phase systems (ATPS) for the recovery of 6-pentyl-alpha-pyrone (6PP) produced by Trichoderma harzianum. The partition behaviour of 6PP and Trichoderma harzianum mycelium (biomass) in polyethylene glycol (PEG)-salt (phosphate and sulphate) and PEG-dextran ATPS was investigated. The influence of defined system parameters (e.g. molecular mass of PEG and dextran, volume ratio, etc.) on the partition behaviour of 6PP and Trichoderma harzianum mycelium was evaluated to select under which conditions 6PP and mycelium partition to opposite phases. In PEG-dextran systems either large extraction phases were required or mycelium and 6PP partitioned to the same phase. ATPS comprising V(r)=0.23, PEG 8000 6.6% w/w and sulphate 14.0% w/w provided the best conditions to satisfy the process requirement of biomass accumulation into the bottom phase and 6PP concentration in the top phase.

Kinetics of phase separation under different process and design parameters in aqueous two-phase systems

A practical study is presented of the effect of height/diameter (H/D) ratio of settlers on the kinetics of phase separation in aqueous two-phase systems (ATPSs). Poly(ethylene glycol) (PEG) 1000-phosphate systems with the presence of undiluted and diluted whey and disrupted yeast were used in batch studies. The influence of the biological suspensions on the rate of phase separation was investigated. It was observed that, phase separation time is much faster when disrupted suspension was used. The addition of undiluted suspensions to ATPSs slowed the process of phase separation. When the batch settler with a large cross section area (H/D ratio less than one) was used, the phases separated much faster than in a settler with a H/D ratio greater than one. Conclusions are drawn concerning the characterisation of the process and design parameters involved in the phase separation for the design of appropriate equipment.

Influence of system and process parameters on partitioning of cheese whey proteins in aqueous two-phase systems

A practical study is described to characterise some problems encountered in the application of aqueous two-phase systems (ATPS) to protein recovery. These factors include practical design of extraction stages and the impact of ATPS compounding methods and biological suspension upon process performance. They were addressed using the recovery of whey proteins as a model. The known effects of system parameters (i.e. tie-line length, volume ratio and system pH) were exploited to define the specific operating conditions of a two-stage ATPS process for the recovery of whey proteins. The partition of whey proteins in ATPS assembled using different methods resulted in changes in the partition coefficient of the proteins. Such changes were associated with the initial location of the proteins in the polymer or salt-rich solutions of the ATPS. Cheese whey loaded into the ATPS caused the displacement of the binodal curve from the origin. Such behaviour was attributed to the residual fat present in the whey. These findings highlight those factors perceived as negative constraints on the wider adoption of ATPS processes for protein recovery from complex biological systems.

Impact of cell disruption and polymer recycling upon aqueous two-phase processes for protein recovery

A practical study is presented of the influence of cell debris and polymer recycling upon the operation of two-stage aqueous two-phase systems (ATPS) for the recovery of yeast bulk protein, pyruvate kinase and fumarase. Brewers' yeast was disrupted using one of two types of high-pressure homogenisers or a bead mill. The different cell debris suspensions were partitioned in a single PEG-phosphate ATPS extraction and the efficiency of solid-liquid separation was examined. A continuously operated two-stage ATPS process, using spray columns, is presented and practical problems of polymer recycling are discussed. Conclusions are drawn concerning the generic implementation and operational stability of ATPS in practical protein recoveries.