Characterization of Crystals in Ciliate Paramecium bursaria Harboring Endosymbiotic Chlorella variabilis.

Protists, including ciliates retain crystals in their cytoplasm. However, their functions and properties remain unclear. To comparatively analyze the crystals of Paramecium bursaria, a ciliate, associated with and without the endosymbiotic Chlorella variabilis, we investigated the isolated crystals using a light microscope and analyzed their length and solubility. A negligible number of crystals was found in P. bursaria cells harboring symbiotic algae. The average crystal length in alga-free and algae-reduced cells was about 6.8 µm and 14.4 µm, respectively. The crystals of alga-free cells were spherical, whereas those of algae-reduced cells were angular in shape. The crystals of alga-free cells immediately dissolved in acids and bases, but not in water or organic solvents, and were stable at - 20 °C for more than 3 weeks. This study, for the first time, reveals that the characteristics of crystals present in the cytoplasm of P. bursaria vary greatly depending on the amount of symbiotic algae.

Self-flocculation behaviour of cellulose-based bioflocculant synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans.

The global energy crisis has spurred a shift from conventional to clean and sustainable energy sources. Biomass derived from microalgae is emerging as an alternative energy source with diverse applications. Despite the numerous advantages of microalgae, large-scale biomass harvesting is not economical and convenient. Self-flocculation is considered an effective phenomenon facilitated by extracting the flocculating substances from microalgae that assist aggregation of algal cells into flocs. A novel cellulose-based bioflocculant has been synthesized from sewage water grown Chlorella sorokiniana and Scenedesmus abundans for harvesting application. The produced bioflocculant amounted to 38.5% and 19.38% of the dry weight of S. abundans and C. sorokiniana, respectively. Analysis via FTIR, XRD, and FESEM-EDX revealed the presence of cellulose hydroxyapatite (HA) in algae-derived cellulose. Harvesting efficiencies of 95.3% and 89.16% were attained for S. abundans and C. sorokiniana, respectively, at a dosage of 0.5 g/L. Furthermore, the bioflocculant was recovered, enabling its reuse with recovery efficiencies of 52% and 10% for S. abundans and C. sorokiniana, respectively. This simple and efficient approach has the potential to replace other harvesting methods, thereby contributing to the economic algal biofuel production.

Comprehensive Analysis of Biomass from Chlorella sorokiniana Cultivated with Industrial Flue Gas as the Carbon Source.

Chlorella sorokiniana, isolated from a pond adjacent to a cement plant, was cultured using flue gas collected directly from kiln emissions using 20 L and 25000 L photobioreactors. Lipids, proteins, and polysaccharides were analyzed to understand their overall composition for potential applications. The lipid content ranged from 17.97% to 21.54% of the dry biomass, with carotenoid concentrations between 8.4 and 9.2 mg/g. Lutein accounted for 55% of the total carotenoids. LC/MS analysis led to the identification of 71 intact triacylglycerols, 8 lysophosphatidylcholines, 10 phosphatidylcholines, 9 monogalactosyldiacylglycerols, 12 digalactosyldiacylglycerols, and 1 sulfoquinovosyl diacylglycerol. Palmitic acid, oleic acid, linoleic acid, and α-linolenic acid were the main fatty acids. Polyunsaturated fatty acid covers ≥ 56% of total fatty acids. Protein isolates and polysaccharides were also extracted. Protein purity was determined to be ≥75% by amino acid analysis, with all essential amino acids present. Monomer analysis of polysaccharides suggested that they are composed of mainly D-(+)-mannose, D-(+)-galactose, and D-(+)-glucose. The results demonstrate that there is no adverse effect on the metabolite profile of C. sorokiniana biomass cultured using flue gas as the primary carbon source, revealing the possibility of utilizing such algal biomass in industrial applications such as animal feed, sources of cosmeceuticals, and as biofuel.

Process intensification for the enhancement of growth and chlorophyll molecules of isolated Chlorella thermophila: A systematic experimental and optimization approach.

In our current work, we have optimized six physicochemical parameters (light intensity, light period, pH, inoculum size, culture period, and salt concentration) toward growth and chlorophyll synthesis using isolated fresh water microalgae Chlorella thermophila [contains ∼6% (w/w on dry biomass basis) chlorophyll]. Here, both experimental and computational [Taguchi orthogonal array (TOA), artificial neural network (ANN), and genetic algorithm (GA)] approaches were employed for the process intensification. Results revealed that the content of biomass and chlorophyll were enhanced by 118% and 95%, respectively, with productivity enhancement of 30% for biomass and 61% for chlorophyll from the optimization of physicochemical parameters. Further, optimum light intensity was found to be 128 µmol m-2 s-1 after conducting experiments in optimized chemical and physicochemical conditions, contributing to the enhancement of productivity of 46% for biomass and 106% for chlorophyll. Urea was found to be the most effective nitrogen source with an increase of 70% and 160% biomass and chlorophyll productivity, respectively. Moreover, sucrose as a carbon source contributed to an increase of 97% and 264% biomass and chlorophyll productivity.

Hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea and Chlorella sorokiniana possess synergistic hypoglycemic activity through inhibiting α-glucosidase and dipeptidyl peptidase-4 activity.

BACKGROUND: The prevalence of diabetes mellitus worldwide has increased in recent decades. Maintaining the level of blood glucose is the most basic and important issue for diabetics. This study aimed to investigate the hypoglycemic activity of a combination of hypoglycemic peptide-enriched hydrolysates of Corbicula fluminea (ACH) and Chlorella sorokiniana (PCH). RESULTS: Combined supplementation of ACH and PCH synergistically inhibited α-glucosidase and DPP4 activities in vitro. After 4 weeks of treatment with ACH and/or PCH, the plasma glucose concentration and insulin, homeostasis model assessment-estimated insulin resistance (HOMA-IR), total cholesterol (TC) and triglyceride (TG) levels significantly decreased. The hypoglycemic peptides in ACH and PCH were purified and assayed for α-glucosidase and DPP4 activity. The hypoglycemic peptides in ACH and PCH effectively decreased α-glucosidase and DPP4 activities. In silico assays showed that these two peptide types have different docking poses, which determined their inhibitory effect against α-glucosidase and DPP4 activity. CONCLUSION: Combined treatment with hypoglycemic peptide-enriched ACH and PCH could modulate blood glucose by synergistically inhibiting α-glucosidase and DPP4 activities. © 2021 Society of Chemical Industry.

Anti-Diabetic Potential of Chlorella Pyrenoidosa-Based Mixture and its Regulation of Gut Microbiota.

The aim of the present study was to investigate the anti-diabetic effect of CGSGCG and its beneficial effects on gut microbiota in type 2 diabetes (T2D) mice induced by streptozotocin and high sucrose and high fat diet. The results showed that treatment with CGSGCG reduced fasting blood glucose, improved oral glucose tolerance test, protected the liver from injury, and reduced inflammation in T2D mice. The contents of acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid and isovaleric acid in CGSGCG group were 2.49-, 1.74-, 3.31-, 1.93-, 1.36- and 1.30-fold than that of the model group. Moreover, administration of CGSGCG up-regulated the expression of INSR/IRS-1/PI3K/AKT/GLUT4 and mTOR but down-regulated the P38MAPK expression. Furthermore, the abundance of beneficial bacteria such as Verrucomicrobia, Proteobacteria, Osillibacter, Dubosiella and Lactococcus in intestinal tract increased, indicating that CGSCGG regulated and improved the bacterial community structure of T2D mice, which were closely related to glycometabolism.

Cellular and physiological approaches to evaluate the chelating effect of Chlorella on metal ion stressed lymphocytes.

Chlorella is a green alga consumed as dietary food supplement in pulverized form. In addition to its high nutritional value, it is reported as an excellent detoxifying agent. The pulverized Chlorella is partially soluble in water and insoluble portion has been reported for removal of mercury, cadmium and radioactive strontium from body. Chlorella contains a variety of metal-binding functional groups such as carboxyl, amino, phosphoryl, hydroxyl and carbonyl groups, which has high affinity towards various metal ions. The present study was envisaged to evaluate the chelating effect of water soluble fraction of Chlorella powder (AqCH) on metal ions. Fura-2 fluorescence ratio (F340/F380) was measured by fluorescence spectrometer (FS) after the exposure of chloride salt of metals viz., strontium, cobalt, barium, cesium, thallium and mercury to lymphocytes. Pretreatment of AqCH (0.1-20 mg mL-1) was given to evaluate the attenuating effect on fura-2 fluorescence ratio induced by metal ions. The intracellular levels of these metal ions were analyzed by atomic absorption spectrophotometer (AAS) and fluorescence microscopy (FM). Pretreatment with AqCH significantly attenuated the metal induced fluorescence ratio in dose-dependent manner. The results of AAS and FM were found in coherence with fura-2 fluorescence ratio which emphasized that AqCH significantly prevented the metal ions internalization. The present study suggests AqCH chelates with these metal ions and prevents its interaction with cells thereby reducing the intracellular mobilization of Ca2+.

A novel approach to production of Chlorella protothecoides oil-loaded nanoparticles via electrospraying method: Modeling of critical parameters for particle sizing.

Bioactive compounds in algae have chain rings that protect the tissue from chemical damage and disease symptoms. In addition, algal bioactive agents have the ability to stimulate the immune system, protective and therapeutic effects against many diseases, including various types of cancers, coronary heart disease, premature aging, and arthritis. These bioactive compounds also have antioxidant, anticoagulant, antiviral, and anti-inflammatory properties. It is very important to encapsulate these algal compounds for preserving bioactive properties. Two of the most efficient methods used for encapsulation are electrospraying and microemulsion techniques. Although electrospraying is a novel technique to produce nanoparticles in recent years, microemulsion is more conventional method compared with electrospraying. In this study, Chlorella protothecoides oil was encapsulated by using sodium alginate and chitosan biopolymers, and the effects of production parameters of electrospraying and microemulsion methods on the particle size and loading efficiency were investigated. Statistical modeling of critical parameters for particle sizing in microemulsion method and electrospraying technique, which is a novel approach to obtain microalgal oil-loaded nanoparticles, was also presented. It was seen that electrospraying is suitable for obtaining smaller nanoparticles (123.9-610 nm), homogeneous distribution, and higher oil loading efficiency (60%-77%) compared with microemulsion method (756.9-1128.2 nm and 57%-73%).

Enhanced whole-cell biotransformation of 3-chloropropiophenone into 1-phenyl-1-propanone by hydrogel entrapped Chlorella emersonii (211.8b).

OBJECTIVES: This study focuses on dehalogenation of halogenated organic substrate (3-Chloropropiophenone) using both free and hydrogel entrapped microalgae Chlorella emersonii (211.8b) as biocatalyst. We aimed at successful immobilization of C. emersonii (211.8b) cells and to assess their biotransformation efficiency. RESULTS: Aquasorb (entrapping material in this study) was found to be highly biocompatible with the cellular growth and viability of C. emersonii. A promising number of entrapped cells was achieved in terms of colony-forming units (CFUs = 2.1 × 104) per hydrogel bead with a comparable growth pattern to that of free cells. It was determined that there is no activity of hydrogenase that could transform 1-phenyl-2-propenone into 1-phenyl-1-propanone because after 12 h the ratio between two products (0.36 ± 0.02) remained constant throughout. Furthermore, it was found that the entrapped cells have higher biotransformation of 3-chloropropiophenone to 1-phenyl-1-propanone as compared to free cells at every interval of time. 1-phenyl-2-propenone was excluded from the whole-cell biotransformation as it was also found in the control group (due to spontaneous generation). CONCLUSION: Hence, enhanced synthesis of 1-phenyl-1-propanone by entrapped Chlorella (211.8b) can be ascribed to either an enzymatic activity (dehalogenase) or thanks to the antioxidants from 211-8b, especially when they are in immobilized form. The aquasorb based immobilization of microalgae is highly recommended as an effective tool for exploiting microalgal potentials of biocatalysis specifically when free cells activities are seized due to stress.

Molecular and Structural Characterizations of Lipases from Chlorella by Functional Genomics.

Microalgae have been poorly investigated for new-lipolytic enzymes of biotechnological interest. In silico study combining analysis of sequences homologies and bioinformatic tools allowed the identification and preliminary characterization of 14 putative lipases expressed by Chlorella vulagaris. These proteins have different molecular weights, subcellular localizations, low instability index range and at least 40% of sequence identity with other microalgal lipases. Sequence comparison indicated that the catalytic triad corresponded to residues Ser, Asp and His, with the nucleophilic residue Ser positioned within the consensus GXSXG pentapeptide. 3D models were generated using different approaches and templates and demonstrated that these putative enzymes share a similar core with common α/ß hydrolases fold belonging to family 3 lipases and class GX. Six lipases were predicted to have a transmembrane domain and a lysosomal acid lipase was identified. A similar mammalian enzyme plays an important role in breaking down cholesteryl esters and triglycerides and its deficiency causes serious digestive problems in human. More structural insight would provide important information on the enzyme characteristics.

A simple and fast experimental protocol for the extraction of xanthophylls from microalga Chlorella luteoviridis.

This study aimed to optimize the key parameters of extraction methods and to increase the recovery yields of intact xanthophylls (violaxanthin, zeaxanthin, astaxanthin) from microalgae (Chlorella luteoviridis). An effective, simple, and fast extraction protocol is described. It consists of a grinding pretreatment followed by a microwave-assisted extraction, using ethanol 90% as an environmentally preferable extraction solvent. Xanthopylls were quantified using high performance liquid chromatography. Irradiation time of 6 s only resulted in the extraction of violaxanthin (4.479 ± 0.009 mg/g), astaxanthin (4.154 ± 0.013 mg/g), and zeaxanthin (4.776 ± 0.120 mg/g). The described protocol seems to be the fastest extraction method of xantophylls compared to the literature and could be an advantage for industrial scale, while saving time and energy.

Green synthesis of mono and bimetallic alloy nanoparticles of gold and silver using aqueous extract of Chlorella acidophile for potential applications in sensors.

Bimetallic or alloy nanoparticles (NPs) have improved properties compared to their monometallic forms. Microalgae being rich in biocompatible reductants and being ecofriendly are potential sources to synthesize fuctionalized NPs. In this study, biosynthesis of silver, gold, and bimetallic NPs was carried out via bioreduction using aqueous extract of algal isolate Chlorella acidophile, inhabitant of non-arable land. C. acidophile is known to contain highly bioactive functional moieties, which can serve as nanobiofactories for metallic NPs. Various characterization techniques viz, UV-visible spectrophotometer, X-ray diffraction analysis, X-ray photo-electron spectroscopy, and Raman spectroscopy were employed to determine their composition, structure, and crystal phase. The monometallic and bimetallic particles were found to be crystalline state and generally in a spherical shape. Their size ranged from 5 to 45 nm and the corresponding FTIR spectra indicated that the specific organic functional groups from algal extract were involved in the bio-reduction. Furthermore, the core-shell in the case of Au-Ag NPs was formed due to the simultaneous reduction of gold and silver ions. An enhanced and more pronounced Raman spectra of Au-Ag NP compared to individual Au NP indicated the improved properties of bimetallic NPs, the latter having been of immense potential to be used as sensors in industries.

Chemical Characterization, Antiproliferative and Antioxidant Activities of Polyunsaturated Fatty Acid-Rich Extracts from Chlorella sp. S14.

Microalgae is a rich source of polyunsaturated fatty acid. This study was conducted to identify and isolate microalgal strain with the potentials for producing polyunsaturated fatty acids (PUFAs) and determine its cytotoxic effect on some cancer cells. The algal strain (Chlorella sp. S14) was cultivated using modified BG-11 media, and algal biomass obtained was used for fatty acid extraction. Gas chromatographic-mass spectrometry was used to identify and quantify the levels of the fatty acid constituents. The total content of monounsaturated fatty acids (1.12%) was low compared to polyunsaturated fatty acids (PUFAs) (52.87%). Furthermore, n-3 PUFAs accounted for (12.37%) of total PUFAs with the presence of α-linolenic acid (2.16%) and cis-11,14,17-eicosatrienoic acid (2.16%). The PUFA-rich extract did not exhibit a cytotoxic effect on normal cells. Treatment with the PUFA-rich extract (150 µg/mL) significantly reduced cell viability in MCF-7 (31.58%) and A549 (62.56%) cells after the 48 h treatment. Furthermore, treatment of MCF-7 with fatty acid extracts (125 and 150 µg/mL) showed a significant reduction in MDA levels, increase in catalase activities and decrease in GSH level compared to untreated cells. However, a slight decrease in MDA level was observed in A549 cells after the 48 h treatment. There are no significant changes in catalase activities and GSH level in treated A549 cells. However, a slight reduction of NO levels was observed in treated MCF-7 and A549 cells. These results indicate the potentials of PUFA-rich extracts from Chlorella sp. S14 to reduce viability and modulate redox status in A549 and MCF-7 cells.

Novel Spray Dried Algae-Rosemary Particles Attenuate Pollution-Induced Skin Damage.

The present study investigated the effect of spray-dried algae-rosemary particles against pollution-induced damage using ex-vivo human biopsies exposed to diesel engine exhaust (DEE). For this, the complexation of hydroalcoholic rosemary extract with Chlorella (RCH) and Spirulina (RSP) protein powders was conducted. The process efficiency and concentration of rosmarinic acid (RA), carnosic acid (CA), and carnosol (CR) phenolic compounds of both products were compared. The RSP spray-dried production was more efficient, and RSP particles presented higher CR and CA and similar RA concentrations. Therefore, spray-dried RSP particles were prioritized for the preparation of a gel formulation that was investigated for its ability to mitigate pollution-induced skin oxinflammatory responses. Taken altogether, our ex-vivo data clearly demonstrated the ability of RSP gel to prevent an oxinflammatory phenomenon in cutaneous tissue by decreasing the levels of 4-hydroxynonenal protein adducts (4HNE-PA) and active matrix metalloproteinase-9 (MMP-9) as well as by limiting the loss of filaggrin induced by DEE exposure. Our results suggest that the topical application of spirulina-rosemary gel is a good approach to prevent pollution-induced skin aging/damage.

Behavior of concentrated emulsions prepared by acid-hydrolyzed insoluble microalgae proteins from Chlorella protothecoides.

BACKGROUND: Microalgae are a promising alternative source to meet the increasing global demand for protein. The insoluble microalgae protein fraction that makes up over half of the protein composition of the biomass has shown potential to serve as a functional emulsifier after acidic hydrolysis. However, creaming was observed due to the flocculation of emulsion droplets, suggesting a preferable use in concentrated emulsions. RESULTS: In this study, we examined the emulsifying behavior of the untreated insoluble microalgae protein fraction and two of its hydrolysates obtained in 0.5 mol L-1 HCl for 4 h at 65 °C (Hydrolysates 65) or 85 °C (Hydrolysates 85), at a concentration of 3% (w/w), and elevated levels of oil (50-70%). The results showed an increase in droplet size and apparent viscosity with increasing oil content in the emulsions. The emulsions made with Hydrolysates 85 had the smallest droplet size and the highest apparent viscosity. The gravitational separation was hindered when oil content was increased. The Hydrolysates 85 stabilized emulsions had a gel-like structure and were stable against coalescence or creaming during a 7 day storage test. CONCLUSION: The results suggest that the thermal acid-treated fraction Hydrolysates 85 may, in particular, be a good emulsifier to formulate concentrated emulsion-based foods with oil content over 50%, such as mayonnaise, salad dressings, or dips. © 2020 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The N-glycans of Chlorella sorokiniana and a related strain contain arabinose but have strikingly different structures.

The many emerging applications of microalgae such as Chlorella also instigate interest in their ability to conduct protein modifications such as N-glycosylation. Chlorella vulgaris has recently been shown to equip its proteins with highly O-methylated oligomannosidic N-glycans. Two other frequently occurring species names are Chlorella sorokiniana and Chlorella pyrenoidosa-even though the latter is taxonomically ill defined. We analyzed by mass spectrometry and nuclear magnetic resonance spectroscopy the N-glycans of type culture collection strains of C. sorokiniana and of a commercial product labeled C. pyrenoidosa. Both samples contained arabinose, which has hitherto not been found in N-glycans. Apart from this only commonality, the structures differed fundamentally from each other and from that of N-glycans of land plants. Despite these differences, the two algae lines exhibited considerable homology in their ITS1-5.8S-ITS2 rDNA sequences. These drastic differences of N-glycan structures between species belonging to the very same genus provoke questions as to the biological function on a unicellular organism.

Effect of fluorescent dye positioning and concentration on the growth parameters and lipid content of Chlorella sp. in a flat panel photobioreactor.

In this study, two different concentrations of fluorescent dye Rhodamine 6G (R6G) with two different strategies were used in a double layer flat panel photobioreactor (PBR) for investigation of its effect on growth parameters of microalgae Chlorella sp. Results showed that in the first strategy, when the light passed through the dye before reaching the broth, biomass productivity rate (P) and maximum specific growth rate (µmax) relative to control case, were increased up to 60 and 23% respectively. Increasing in these parameters were more, for the low dye concentration. Also, in the second strategy, when the light passed through the microalgae before reaching the dye solution, P and µmax for lower concentration increased about 9 and 15%, respectively. But using high dye concentration growth of the algae was decreased. Furthermore, using R6G caused increase in the lipid and chlorophyll content of the microalgae Chlorella sp.

Enhanced nitrogen removal of aerobic denitrifier using extracellular algal organic matter as carbon source: application to actual reservoir water.

Man-made organic matter acting as carbon source for oligotrophic aerobic denitrification has been studied extensively, while less attention has been paid to the actual organic matter derived from drinking water reservoir. In this study, the effect of extracellular organic matter (EOM) released from Microcystis aeruginosa and Chlorella sp. and organic matter in actual reservoir water on aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9 has been investigated, by measuring nitrogen removal and determining changes in the properties of organic matter. Results indicated that the Acinetobacter johnsonii strain WGX-9 showed effective nitrogen removal efficiency when cultural conditions were low C/N of 5, pH of 5-11, and low temperature of 8 °C. The nitrate removal efficiency with EOM as the sole carbon source was relatively higher than that with intracellular organic matter or natural organic matter as the sole carbon source. This is probably due to that EOM exerts a lower molecular weight and better ability of donating electrons. Besides, the findings can elucidate that nitrate and total organic matter removal efficiency with actual high-density algal water as the carbon source was higher than that with actual low-density algal water as the carbon source. This was attributed to that more EOM was released in high-density algal water, which highlighted the aerobic denitrification performance of Acinetobacter johnsonii strain WGX-9. This study will provide a reference for the application of aerobic denitrifier in drinking water reservoirs.

Cyanobacteria and Microalgae as Sources of Functional Foods to Improve Human General and Oral Health.

In the scenario of promising sources of functional foods and preventive drugs, microalgae and cyanobacteria are attracting global attention. In this review, the current and future role of microalgae as natural sources of functional foods for human health and, in particular, for oral health has been reported and discussed in order to provide an overview on the state of art on microalgal effects on human oral health. It is well known that due to their richness in high-valuable products, microalgae offer good anti-inflammatory, antioxidant, antitumoral, anti-glycemic, cholesterol-lowering, and antimicrobial activity. Moreover, the findings of the present research show that microalgae could also have a significant impact on oral health: several studies agree on the potential application of microalgae for oral cancer prevention as well as for the treatment of chronic periodontitis and different oral diseases with microbial origin. Thus, beneficial effects of microalgae could be implemented in different medical fields. Microalgae and cyanobacteria could represent a potential natural alternative to antibiotic, antiviral, or antimycotic therapies, as well as a good supplement for the prevention and co-adjuvant treatment of different oral diseases. Nevertheless, more studies are required to identify strains of interest, increase overall functioning, and make safe, effective products available for the whole population.

An erosion-type hydrolysis behavior of insoluble protein fraction from Chlorella protothecoides.

BACKGROUND: Acid-induced hydrolysis of proteins has been used to improve the solubility and functional properties of various proteins, and could be a promising tool to facilitate the use of currently underutilized insoluble microalgae protein-rich fractions in food applications. However, the results of a prior study showed an unusual resistance of an insoluble microalgae protein-rich fraction to acid hydrolysis at room temperature. RESULTS: In the present study, the insoluble protein-rich fraction extracted from microalgae Chlorella prothothecoides was treated with 0.5 mol L-1 hydrochloric acid at 25, 45, 65 or 85 °C for 0-4 h. The results showed that hydrolysis of the fraction at 85 °C for 4 h led to decreases in the amount of insoluble protein-rich aggregates and the formation of fragments with a lower molecular weight, as well as an increase in protein solubility by approximately 40%. Nevertheless, some aggregated insoluble protein-rich particles remained, even after hydrolysis at 85 °C for 4 h. CONCLUSION: The higher temperature improved the efficiency of the acid hydrolysis of the insoluble protein fraction from microalgae Chlorella prothothecoides, which is highly acid-resistant. Overall, an erosion-based mechanism was suggested for the acid hydrolysis of insoluble microalgae protein fraction. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.