Understanding mild cell disintegration of microalgae in bead mills for the release of biomolecules

Cell disintegration is, in general, the first step in the biorefinery of algae, since it allows the release of biomolecules of interest from the cells into the bulk medium. For high-value commercial applications, the disintegration process must be selective, energy efficient and mild. Developing a process with such features would demand extensive experimental effort. In the present study, we attempt to provide a tool for developing an efficient disintegration process via bead milling, by proposing a modelling strategy that allows the prediction of the kinetics of cell disintegration while having as input not only process parameters but also strain-specific parameters like cell size and cell-wall strength. The model was validated for two different algal strains (Tetraselmis suecica and Chlorella vulgaris), at various values of bead size (0.3–1 mm) and bead fillings (2.5–75%) and at two different scales of 80 and 500 mL. Since the kinetics of disintegration is proportional to the kinetics of release of biomolecules, the model can be further used for scale-up studies and to establish a window of operation to selectively target cells or metabolites of interest. Furthermore, the energy consumption in the mill was evaluated and it was found that operating at high bead fillings (>65%) is crucial to ensure an energy efficient process.publishedVersionPaid Open Acces

Combined bead milling and enzymatic hydrolysis for efficient fractionation of lipids, proteins, and carbohydrates of Chlorella vulgaris microalgae

A combined bead milling and enzymatic hydrolysis process was developed for fractionation of the major valuable biomass components, i.e., proteins, carbohydrates, and lipids from the microalgae Chlorella vulgaris. The cells were treated by bead milling followed by hydrolysis with different hydrolytic enzymes, including lipase, phospholipase, protease, and cellulase. Without enzymatic hydrolysis, the recovery yield of lipids, carbohydrates, and proteins for bead milled biomass was 75%, 31%, and 40%, respectively, while by applying enzymatic treatments these results were improved significantly. The maximum recovery yield for all components was obtained after enzymatic hydrolysis of bead milled biomass by lipase at 37 degrees C and pH 7.4 for 24 h, yielding 88% lipids in the solid phase while 74% carbohydrate and 68% protein were separated in the liquid phase. The recovery yield of components after enzymatic hydrolysis of biomass without bead milling was 44% lower than that of the milled biomass.publishedVersionPaid Open Acces

Selective fractionation of free glucose and starch from microalgae using aqueous two-phase systems

Microalgae are a promising source of lipids, pigments, proteins and carbohydrates, which are valuable compounds for many industries. However, optimal fractionation and valorization of all produced compounds is necessary to improve the economic viability of microalgae production. This paper aims to understand the fractionation of microalgae carbohydrates (free glucose and starch) in aqueous two-phase systems. Three aqueous two-phase systems were investigated to efficiently and mildly separate carbohydrates from disrupted Neochloris oleoabundans. This strain contains 16 w/w% of proteins, 48 w/w% total fatty acids and 27 w/w% carbohydrates when cultivated under saline water and nitrogen depletion conditions. The protein content decreases and the amount of fatty acids and carbohydrates increases notably under stress conditions and glucose becomes the main carbohydrate in this microalgae. Glucose is present in the disrupted microalgae as part of polymeric carbohydrates (starch) or in monomeric form (free glucose). With the aqueous two-phase system Polyethylene Glycol 400 - Cholinium dihydrogen phosphate (PEG400-ChDHp) microalgal free glucose is fractionated up to a recovery of 99% to the most hydrated bottom phase in a single step. Simultaneously, a recovery of 70% is reached for microalgal starch in the interface after two additional liquid-liquid extractions with PEG400-ChDHp. The final fractions obtained were free of pigments.publishedVersionPaid Open Acces

Selective and mild fractionation of microalgal proteins and pigments using aqueous two-phase systems

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Multistep Fractionation of Microalgal Biomolecules Using Selective Aqueous Two-Phase Systems

We aim to develop liquid-liquid extraction processes for the fractionation of microalgal components (proteins, pigments, lipids, and carbohydrates). The partitioning behavior of microalgal pigments and proteins in aqueous two-phase systems (ATPS) composed of the polymer polypropylene glycol with molecular weight 400 (PPG 400) + various cholinium based-ionic liquids was studied. A process for fractionation of multiple components from disrupted Neochloris oleoabundans was developed and evaluated. Results show that cholinium dihydrogen phosphate (Ch DHp) allows the fractionation of pigments in the PPG 400-rich phase and proteins in the Ch DHp-rich phase with high selectivity. It was demonstrated that a multiproduct approach can fractionate free glucose, and proteins in the ionic liquid-rich phase, pigments in the polymer-rich phase, while starch and lipids are recovered at the interface.</p

Fractionation of proteins and carbohydrates from crude microalgae extracts using an ionic liquid based-aqueous two phase system

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Selective and energy efficient extraction of functional proteins from microalgae for food applications

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Techno-Functional Properties of Crude Extracts from the Green Microalga Tetraselmis suecica

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An integrated and optimized process for cleaner production of ethanol and biodiesel from corn stover by Mucor indicus

A two-stage process was successfully developed for biodiesel and ethanol production from corn stover using zygomycetes fungus Mucor indicus. Dilute-acid pretreatment followed by enzymatic saccharification was applied to release the maximum amount of sugars (glucose and xylose) from the lignocellulosic structure of corn stover. Dilute-acid hydrolysis was optimized by a response surface design. Under the optimal reaction conditions (i.e., 1.8% v/v H2SO4, 121 °C for 22 min), the hydrolysis resulted in the production of 270 g glucose per kg of dry corn stover (57.8% theoretical yield) and 100 g xylose per kg of dry corn stover (84.0% theoretical yield). Validation of the model exhibited proper fit between predicted and observed values of glucose and xylose concentrations: 91.4% regression adjustment for xylose and 98.2% for glucose. In the first stage, cells fermented the enzymatic hydrolysate to the maximum amount of 74.5% (0.38 g g−1) ethanol as the main product. In the second stage, the dilute-acid hydrolysate was used for lipid accumulation in the fungal cells of the first stage fermentation. The hydrolysates were used without detoxification since the fungus is among the most resistant microorganisms to the inhibitors available in the acid hydrolysates. Effects of addition of different nutrient sources, including fungal extract and yeast extract along with mineral salts, were also investigated to maximize lipid yield. Overall, 21.4 g ethanol and 2.2 g biodiesel (obtained from 4.00 g accumulated lipid) were produced from 100 g dry corn stover.</p

An integrated and optimized process for cleaner production of ethanol and biodiesel from corn stover by Mucor indicus

A two-stage process was successfully developed for biodiesel and ethanol production from corn stover using zygomycetes fungus Mucor indicus. Dilute-acid pretreatment followed by enzymatic saccharification was applied to release the maximum amount of sugars (glucose and xylose) from the lignocellulosic structure of corn stover. Dilute-acid hydrolysis was optimized by a response surface design. Under the optimal reaction conditions (i.e., 1.8% v/v H2SO4, 121 °C for 22 min), the hydrolysis resulted in the production of 270 g glucose per kg of dry corn stover (57.8% theoretical yield) and 100 g xylose per kg of dry corn stover (84.0% theoretical yield). Validation of the model exhibited proper fit between predicted and observed values of glucose and xylose concentrations: 91.4% regression adjustment for xylose and 98.2% for glucose. In the first stage, cells fermented the enzymatic hydrolysate to the maximum amount of 74.5% (0.38 g g−1) ethanol as the main product. In the second stage, the dilute-acid hydrolysate was used for lipid accumulation in the fungal cells of the first stage fermentation. The hydrolysates were used without detoxification since the fungus is among the most resistant microorganisms to the inhibitors available in the acid hydrolysates. Effects of addition of different nutrient sources, including fungal extract and yeast extract along with mineral salts, were also investigated to maximize lipid yield. Overall, 21.4 g ethanol and 2.2 g biodiesel (obtained from 4.00 g accumulated lipid) were produced from 100 g dry corn stover.</p