Red light induces starch accumulation in Chlorella vulgaris without affecting photosynthesis efficiency, unlike abiotic stress

International audienceMicroalgae show great promise as sources of starch, one of the most widely consumed macromolecules. In this study, we evaluated the impact of three starch-inducing factors, namely nitrogen deprivation, supra-optimal temperature, and red light, on the physiology and starch accumulation capacity of Chlorella vulgaris. This starch accumulation was monitored by measuring the total carbohydrate content and transmission electron microscopy (TEM) imaging. Nitrogen deprivation and a supra-optimal temperature of 39 °C resulted in carbohydrate contents of 69.7 and 64.3 % of dry weight (DW) respectively. This constituted a 5.3- and 3.3-fold increase in carbohydrate productivity compared to the control, after 4 days of cultivation. During this period, carbohydrates represented over 80 % of the produced material (DW basis). However, nitrogen deprivation and supra-optimal temperature were accompanied by extensive stress, leading to lower cell division rates and damage to the photosynthetic apparatus. Red light illumination resulted in a more moderate production of carbohydrates. After 4 days of cultivation, the carbohydrate content reached 46.8 %, representing a 3.0-fold increase in productivity compared to control. The composition of the starch formed under red light was surprisingly poor in amylose, similar to transitory-type starch rather than storage starch. Most notably, the starch accumulation under red light was sustained over 7 days without affecting the rate of cell division and quantum yield efficiency. To the best of our knowledge, red light is the only factor reported so far to induce a significant starch accumulation without hindering cell division and photosynthesis efficiency, even after long-term exposure (7 days). Furthermore, all three conditions induced a cell wall thickening, albeit without affecting the recovery of accumulated starch by high-pressure homogenization. These results highlight the potential of red light as a starch inducer in Chlorella vulgaris and open up perspectives for the production of starch-based bioplastics from microalgae

From raw microalgae to bioplastics: Conversion of Chlorella vulgaris starch granules into thermoplastic starch

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From raw microalgae to bioplastics: conversion of Chlorella vulgaris starch granules into thermoplastic starch

Microalgae are emerging as a promising feedstock for bioplastics, with Chlorella vulgaris yielding significant amounts of starch. This polysaccharide is convertible into thermoplastic starch (TPS), a biodegradable plastic of industrial relevance. In this study, we developed a pilot-scale protocol for extracting and purifying starch from starch-enriched Chlorella vulgaris biomass. From 430.3 ± 0.5 g (dry weight - DW) of microalgae biomass containing 42.2 ± 3.4 % of starch, we successfully extracted 205.8 ± 1.2 g DW of purified starch extract containing 86.9 ± 3.0 % of starch, resulting in a final recovery yield of 98.5%. We have characterized this extracted starch and processed it into TPS using twin-screw extrusion and injection molding. Microalgal starch showed similar properties to those of native plant starch, but with smaller granules. We compared the mechanical properties of microalgal TPS with two controls, namely a commercial TPS and a TPS prepared from commercial potato starch granules. TPS prepared from microalgal starch showed a softer and more ductile behavior compared to the reference materials. This study demonstrates the feasibility of recovering high-purity microalgal starch on a pilot scale with high yields, and highlights the potential of microalgal starch for the production of TPS using industrially relevant processes

Bridging the gap from raw microalgae to bioplastic: conversion of Chlorella vulgaris into thermoplastic starch

International audienceStarch, a glucose polymer and major storage molecule in photosynthetic organisms, is extensively used in food industry. However, its low cost and multiple functionalities also make starch highly demanded for non food applications, representing nearly half of its market in 2020 [1]. The dual role of starch, serving as both a glucose reservoir and a versatile polymer, has positioned it as a primary feedstock for the bioplastics industry. Indeed, several biobased-biodegradable plastics can be obtained from starch, either through fermentation processes following saccharification (such as polylactic-acid PLA and polyhydroxyalkanoates PHA) or through direct polymer plasticization (thermoplastic starch TPS). Starch resources have therefore emerged as a viable alternative to petroleum based materials, further intensifying the demand on amylaceous feedstock. Within this context, Chlorella vulgaris microalgae have been identified as a promising source of starch, with pilot-scale area yields surpassing by almost 2-fold those of traditional crops [2]. Within the framework of EU projects SEALIVE and Nenu2PHAr ([3, 4]), we successively produced a starch enriched Chlorella vulgaris at pilot scale, achieved sustainable starch extraction and converted this microalgal starch into thermoplastic starch. A 360L culture of Chlorella vulgaris was produced in greenhouse under natural light, with starch-enrichment reaching 42%wt after nutrient deprivation. This biomass was mechanically disrupted using a high-pressure homogenizer (HPH) until 95% of the cells were broken. A single centrifugation step separated starch granules from the biomass broth, resulting in starch purity of 85%wt in the recovered starch pellet. Raw starch was subsequently washed using successive water rinses until complete whitening. Interestingly, the non-starch fractions were enriched in lipids and proteins, making them appropriate for additional valorization in a biorefinery scheme with multiple product outputs. At the end of the process, 179 gDW of pure starch was obtained from a microalgae biomass containing initially 181 gDW of extractable starch. The starch granules were found to be smaller than plant starch, whereas crystallinity, phase transitions as well as amylose/amylopectin ratio were similar, making algal starch suitable for bioplastics formulation. Finally, the extracted microalgal starch was successfully plasticized with water and glycerol into thermoplastic starch in a twin-screw microcompounder, and then shaped into injection-moulded specimens

Bridging the gap from raw microalgae to bioplastic: conversion of Chlorella vulgaris into thermoplastic starch

International audienceStarch, a glucose polymer and major storage molecule in photosynthetic organisms, is extensively used in food industry. However, its low cost and multiple functionalities also make starch highly demanded for non food applications, representing nearly half of its market in 2020 [1]. The dual role of starch, serving as both a glucose reservoir and a versatile polymer, has positioned it as a primary feedstock for the bioplastics industry. Indeed, several biobased-biodegradable plastics can be obtained from starch, either through fermentation processes following saccharification (such as polylactic-acid PLA and polyhydroxyalkanoates PHA) or through direct polymer plasticization (thermoplastic starch TPS). Starch resources have therefore emerged as a viable alternative to petroleum based materials, further intensifying the demand on amylaceous feedstock. Within this context, Chlorella vulgaris microalgae have been identified as a promising source of starch, with pilot-scale area yields surpassing by almost 2-fold those of traditional crops [2]. Within the framework of EU projects SEALIVE and Nenu2PHAr ([3, 4]), we successively produced a starch enriched Chlorella vulgaris at pilot scale, achieved sustainable starch extraction and converted this microalgal starch into thermoplastic starch. A 360L culture of Chlorella vulgaris was produced in greenhouse under natural light, with starch-enrichment reaching 42%wt after nutrient deprivation. This biomass was mechanically disrupted using a high-pressure homogenizer (HPH) until 95% of the cells were broken. A single centrifugation step separated starch granules from the biomass broth, resulting in starch purity of 85%wt in the recovered starch pellet. Raw starch was subsequently washed using successive water rinses until complete whitening. Interestingly, the non-starch fractions were enriched in lipids and proteins, making them appropriate for additional valorization in a biorefinery scheme with multiple product outputs. At the end of the process, 179 gDW of pure starch was obtained from a microalgae biomass containing initially 181 gDW of extractable starch. The starch granules were found to be smaller than plant starch, whereas crystallinity, phase transitions as well as amylose/amylopectin ratio were similar, making algal starch suitable for bioplastics formulation. Finally, the extracted microalgal starch was successfully plasticized with water and glycerol into thermoplastic starch in a twin-screw microcompounder, and then shaped into injection-moulded specimens

Bridging the gap from raw microalgae to bioplastic: conversion of Chlorella vulgaris into thermoplastic starch

International audienceStarch, a glucose polymer and major storage molecule in photosynthetic organisms, is extensively used in food industry. However, its low cost and multiple functionalities also make starch highly demanded for non food applications, representing nearly half of its market in 2020 [1]. The dual role of starch, serving as both a glucose reservoir and a versatile polymer, has positioned it as a primary feedstock for the bioplastics industry. Indeed, several biobased-biodegradable plastics can be obtained from starch, either through fermentation processes following saccharification (such as polylactic-acid PLA and polyhydroxyalkanoates PHA) or through direct polymer plasticization (thermoplastic starch TPS). Starch resources have therefore emerged as a viable alternative to petroleum based materials, further intensifying the demand on amylaceous feedstock. Within this context, Chlorella vulgaris microalgae have been identified as a promising source of starch, with pilot-scale area yields surpassing by almost 2-fold those of traditional crops [2]. Within the framework of EU projects SEALIVE and Nenu2PHAr ([3, 4]), we successively produced a starch enriched Chlorella vulgaris at pilot scale, achieved sustainable starch extraction and converted this microalgal starch into thermoplastic starch. A 360L culture of Chlorella vulgaris was produced in greenhouse under natural light, with starch-enrichment reaching 42%wt after nutrient deprivation. This biomass was mechanically disrupted using a high-pressure homogenizer (HPH) until 95% of the cells were broken. A single centrifugation step separated starch granules from the biomass broth, resulting in starch purity of 85%wt in the recovered starch pellet. Raw starch was subsequently washed using successive water rinses until complete whitening. Interestingly, the non-starch fractions were enriched in lipids and proteins, making them appropriate for additional valorization in a biorefinery scheme with multiple product outputs. At the end of the process, 179 gDW of pure starch was obtained from a microalgae biomass containing initially 181 gDW of extractable starch. The starch granules were found to be smaller than plant starch, whereas crystallinity, phase transitions as well as amylose/amylopectin ratio were similar, making algal starch suitable for bioplastics formulation. Finally, the extracted microalgal starch was successfully plasticized with water and glycerol into thermoplastic starch in a twin-screw microcompounder, and then shaped into injection-moulded specimens