Alkali Extraction Research Articles

Effects of Extraction Methods on the Physicochemical Properties and Biological Activities of Polysaccharides from Polygonatum sibiricum.

Polygonatum sibiricum polysaccharides (PSPs) have important biological functions, such as antioxidation, immunomodulatory, and hypolipidemic functions. Different extraction methods have effects on their structures and activities. In this study, six extraction methods, including hot water extraction (HWE), alkali extraction (AAE), ultrasound-assisted extraction (UAE), enzyme-assisted extraction (EAE), microwave-assisted extraction (MAE), and freeze-thaw-assisted extraction (FAE) were used to extract PSPs, and their structure-activity relationships were analyzed. The results showed that all six PSPs had similar functional group compositions, thermal stability, and glycosidic bond compositions. PSP-As (PSPs extracted by AAE) exhibited better rheological properties due to their higher molecular weight (Mw). PSP-Es (PSPs extracted by EAE) and PSP-Fs (PSPs extracted by FAE) had better lipid-lowering activity due to their lower Mw. PSP-Es and PSP-Ms (PSPs extracted by MAE), which do not contain uronic acid and have a moderate Mw, had better 1,1-diphenyl-2-picrylhydrazyl (DPPH)-radical-scavenging activity. On the contrary, PSP-Hs (PSPs extracted by HWE) and PSP-Fs, with the Mw of uronic acid, had the best OH-radical-scavenging activity. The high-Mw PSP-As had the best Fe2+-chelating ability. In addition, mannose (Man) may play an important role in the immunomodulatory activity. These results indicate that different extraction methods affect the structure and biological activity of polysaccharides to varying degrees, and these results are helpful for understanding the structure-activity relationship of PSPs.

Extractions of Protein-Rich Alaria esculenta and Lemna minor by the Use of High-Power (Assisted) Ultrasound

Plant nutrients extracted from sustainable sources, namely Alaria esculenta and Lemna minor, have been evaluated for their nutritional value in an attempt to identify their potential as protein-rich sources. The implementation of green technologies such as high-power ultrasound to extract nutrients from these alternative biomasses was studied and compared to more traditional techniques. Probe sonicators fared better than bath sonicators in extracting bioactive compounds while ultrasound assisted with enzymes was more efficient than conventional or alkali extraction methods. Lemna minor was found to have the greatest extraction yield of nutrients.

Effect of Microbial Consortium Constructed with Lignolytic Ascomycetes Fungi on Degradation of Rice Stubble

Microbial degradation is an effective, eco-friendly and sustainable approach for management of the rice residue. After harvesting a rice crop, removal of stubble from the ground is a challenging task, that forces the farmers to burn the residue in-situ. Therefore, accelerated degradation using an eco-friendly alternative is a necessity. White rot fungi are the most explored group of microbes for accelerated degradation of lignin but they are very slow in growth. The present investigation focuses on degradation of rice stubble using a fungal consortium constructed with highly sporulating ascomycetes fungi, namely, Aspergillus terreus, Aspergillus fumigatus and Alternaria spp. All three species were successful at colonizing the rice stubble. Periodical HPLC analysis of rice stubble alkali extracts revealed that incubation with ligninolytic consortium released various lignin degradation products such as vanillin, vanillic acid, coniferyl alcohol, syringic acid and ferulic acid. The efficiency of the consortium was further studied at different dosages on paddy straw. Maximum lignin degradation was observed when the consortium was applied at 15% volume by weight of rice stubble. Maximum activity of different lignolytic enzymes such as lignin peroxidase, laccase and total phenols was also found with the same treatment. FTIR analysis also supported the observed results. Hence, the presently developed consortium for degrading rice stubble was found to be effective in both laboratory and field conditions. The developed consortium or its oxidative enzymes can be used alone or combined with other commercial cellulolytic consortia to manage the accumulating rice stubble effectively.

Separation of dihydrosinapyl alcohol from reductive depolymerization products of lignin by multistage extraction and crystallization

Because of the high complexity of the product and the similar physicochemical properties between G and S counterparts, the separation of aromatic monomers is one of the greatest challenges in the lignin chemical valorization, which limits its further utilization and conversion. In this study, the preparation method of the dihydroconiferyl alcohol & dihydrosinapyl alcohol-enriched oil and high purity dihydrosinapyl alcohol from reductive catalytic fractionation products catalyzed by Pd/C was first reported. Moreover, a purification process with alkali extraction - organic solvent extraction - dichloromethane reverse extraction - crystallization in the KOH ethanol solution as the main unit operation was designed. As a result, a monomer-enriched oil in which dihydroconiferyl alcohol (G-3OH) and dihydrosinapyl alcohol (S-3OH) could totally account for more than 83% was obtained, and S-3OH with a purity of 90.2% was separated by crystallization. In addition, this purification process was scaled up to 10 times. The monomer-enriched oil with a G-3OH and S-3OH content of 87.2% was obtained. The recoveries of G-3OH and S-3OH were 81.0% and 91.5%, respectively. The purity of S-3OH was 89.4%, and the recovery was 51.6%. The integrated process realizes the effective separation of the reductive depolymerization products of lignin, which can provide technical support for its industrial production.

Selectively isolated hemicellulose with high whiteness and molecular weight from poplar by sodium perborate-assisted alkali extraction

Selectively isolated hemicellulose with high whiteness and molecular weight from poplar by sodium perborate-assisted alkali extraction

Sequential extraction of labile and recalcitrant fractions of soil organic matter: A case study focusing on antimony (Sb) in humic acids, fulvic acids and humin fractions of long-term aged contaminated soils

Soil organic matter (SOM) plays a key role in environmental chemistry of macro and micro nutrients as well as heavy metal (loids). In this research, a modified sequential extraction scheme was used to isolate labile and recalcitrant SOM from organic rich soils after 18 months of ageing with antimony. Humic substances were extracted with a mixture of 0.5 M sodium hydroxide +0.1 M sodium pyrophosphate solution from soils. Then soils deprived of humic substances were sequentially subjected to extraction with glycerol, citric acid, pre-treated with acid and extracted with boiling alkali mixture. The humic acids (HA) and fulvic acids (FA) of isolated SOM fractions were separated and HAs been characterized using FTIR, 1H NMR, and UV-VIS. Acid-alkali treatment of the most recalcitrant SOM fraction (A1-ROM) led to the extraction of sparingly soluble, highly aromatic compound with considerable amounts of N (44% of the extractable N), possibly due to the breakdown of bounds between aromatic rings and amine functional groups. Nevertheless, the highest content of C and TOC was associated with the glycerol extractable SOM. Substantial amounts of Fe and Al were extracted with glycerol, resulting in a dramatic rise of Sb in SOM extracts. The largest increase (60%) in Sb concentrations was observed after the removal of Fe with citric acid. The humic substances (HS) were responsible for 63% of extractable Sb, whereas even after exhaustive alkali extractions 22% of the total Sb remained in the residual humin fraction. Within the HS fraction, 95% of antimony was associated with the low molecular weight FAs. Antimony concentrations in organic fractions correlated significantly with TOC and N contents, possibly due to the role of amine functional groups in Sb complexation. The results of this research highlight the importance of Fe–Al-SOM bridging and humin fraction in sequestration of Sb in recalcitrant SOM pools.

Humic substances derived from unconventional resources: extraction, properties, environmental impacts, and prospects.

Humic substances comprise up to 70% of the total organic matter in soils, between 50 and 80% of the dissolved organic matter in water, and about 25% of dissolved organic matter in groundwater. Elucidation of the complex structure and properties of humic substances requires advanced analytical tools; however, they are of fundamental importance in medicine, agriculture, technology, and the environment, at large. Although they are naturally occurring, significant efforts are now being directed into their extraction owing to their relevance in improving soil properties and other environmental applications. In the present review, the different fractions of humic substances were elucidated, underlying the mechanisms by which they function in soils. Furthermore, the extraction processes of humic substances from various feedstock were illustrated, with the alkali extraction technique being the most widely used. In addition, the functional group and elemental composition of humic substances were discussed. The similarities and/or variations in the properties of humic substances as influenced by the source and origin of feedstock were highlighted. Finally, the environmental impacts of humic substances were discussed while highlighting prospects of humic acid production. This review offers enormous potential in identifying these knowledge gaps while recommending the need for inter- and multidisciplinary studies in making extensive efforts toward the sustainable production of humic substances.

Current progress in valorization of food processing waste and by-products for pectin extraction

Food processing waste and by-products such as peel of citrus fruit, melon, mango, pineapple, etc. and fruit pomace can be utilized for manufacturing of several high-value products. Valorization of these waste and by-products for extraction of pectin, can help offset growing environmental concerns, facilitate value-addition of by-products and their sustainable uses. Pectin has many applications in food industries such as gelling, thickening, stabilizing, and emulsifying agent, and as a dietary fibre. This review elaborates on various conventional and advanced, sustainable pectin extraction techniques, and paints a comparative picture between them considering extraction efficiency, quality, and functionality of the pectin. Conventional acid, alkali, and chelating agents-assisted extraction have been profusely used for pectin extraction, but advanced extraction technologies e.g., enzyme, microwave, supercritical water, ultrasonication, pulse electric field and high-pressure extraction are preferred due to less energy consumption, better quality product, higher yield, and minimal or no generation of harmful effluent.

DEVELOPMENT OF AMMONIA-ALKALINE METHOD OF COMPLEX PROCESSING OF ALUNITE ORE

The results of research in the field of development of complex processing of alunite ore from the Zaglig deposit of Azerbaijan are presented. An ammonia-alkaline ore processing method is proposed, which provides for the extraction of alkali metal sulfates (K2SO4, Na2SO4) at the beginning of the technological process during the leaching of alunite ore. To recover alkali metal sulfates from dehydrated ore to ammonia processing, the dehydration product is leached with a slightly alkaline (0.5% NaOH) solution. After extraction of alkali sulfates from the ore, the solid insoluble residue is subjected to ammonia leaching. In this case, only ammonium sulfate passes into the solution, which is used as a fertilizer. Thus, the separation of alkali metal sulfates from the ore at the beginning of processing improves the conditions for subsequent hydrochemical processes. the following average values of the degrees of extraction of alkali metals and aluminum into the solution from leaching were determined, (%): Na+ = 90.93; K+ = 96.42; Al+3 = 0.055. Aluminum oxide, which is part of alunite, remains in the sediment under optimal leaching conditions. Aluminum oxide, which is not part of the alum part of alunite, that is, associated with silicate in kaolinite, is also not extracted and remains in the undissolved precipitate

Hepatoprotective effect of water bamboo shoot (Zizania latifolia) extracts against acute alcoholic liver injury in a mice model and screening of bioactive phytochemicals

AbstractIn this study, the hepatoprotective effect of alkali extract (NE) of water bamboo shoot (WBS) against acute alcoholic liver injury (ALI) in mice was evaluated, and its underlying mechanisms were explored. Animal experiment demonstrated that NE exhibited hepatoprotective effect on alcoholic intake‐induced ALI via significantly enhancing the hepatic activities of alcohol dehydrogenase (ADH), acetaldehyde dehydrogenase (ALDH), superoxide dismutase (SOD), glutathione peroxidase (GSH‐Px), and catalase (CAT), whereas significantly attenuated hepatic levels of malondialdehyde (MDA), interleukin‐1β (IL‐1β), interleukin‐6 (IL‐6), and tumor necrosis factor‐α (TNF‐α). The potential molecular mechanism and bioactive compounds of NE against ALI were explored by bioinformatics analysis and isosinensetin was found to be the major bioactive compounds in NE against ALI. The western blot analysis showed that NE inhibited phosphorylation of p65 and IκBα to suppress the NF‐κB pathway. Overall our result indicated that WBS possesses potential hepatoprotective effects against ALI.

Microwave-assisted separation hemicellulose from hemp stalk: Extracting performance, extracting mechanism and mass transfer model

Herein, a novel microwave-assisted alkali extraction process was proposed for further high-efficiency extraction of hemicellulose from hemp stalk. The hemicellulose extraction yield of the peeled hemp stalk surpasses 60% under mild conditions (4% alkali content, 80 °C, 30 min). Meanwhile, the hemicellulose presented a high weight-average and number-average molecular weight of 25331, 6067 g/mol. The improved efficiency could be thanks to the looser structure created by microwave expansion pretreatment via breaking the intricate structure and shielding of the hemp stalk cell wall, detailed as the specific surface area, total pore volume, and average pore size of the hemp stalk increased from 1.30 m²/g, 0.003 cm3/g, 10.66 nm to 1.85 m²/g, 0.006 cm3/g and 13.08 nm after the microwave expansion pretreatment. Furthermore, the higher expansion rate (36.74%) and water retention value (265%) of the hemp stalk also demonstrated the effective disrupting effect on the fiber structure. Finally, the empirical mass transfer model of extraction hemicellulose from hemp stalk was established. The predicted value and the experimental data showed a good correlation (R2 = 0.9998) and the model displayed excellent stability (relative deviation within 5%). Therefore, microwave-assisted alkali extraction has great potential application in the hemicellulose separation industry.

Extraction of dietary fiber and phytochemicals from bottle gourd seeds (Lagenaria siceraria), its physicochemical properties and application in food model

This research aimed to extract dietary fiber and phytochemicals from matured bottle gourd (Lagenaria siceraria) seeds and use as ingredients in the preparation of cookies. Extraction of dietary fiber was performed using alkaline (AEDF), enzymatic (EEDF), and ultrasound-assisted alkali extraction (UAE). UAE gives a higher yield of 75.81% dietary fiber where the optimized conditions are solute: solvent; 1: 23.90 mg/ml, time; 27.20 min and amplitude; 47.76%. Comparison of physicochemical and functional properties of extracted dietary fiber was done and ultrasound-assisted alkaline extracted dietary fiber (UDF) was found to be the best. Extraction of phytochemicals using ultrasound-assisted alkaline extraction under the condition of 70% amplitude, 45 °C temperature, and duration of 15 min, and identification was done using RP-HPLC analysis and encapsulated using sodium alginate solution (2%) as the wall material. Fiber enriched cookies were developed by incorporating the extracted dietary fiber (3, 6, 9, 12 and 15%) and encapsulated phytochemicals beads (1, 1.5, 2, 2.5 and 3%) in 5 different formulations. The result of this study revealed that matured bottle gourd seeds can serve as a potential, inexpensive dietary fiber source and phytochemicals, which can further be used to develop functional foods.

Phosphorylation of Alkali Extracted Mandua Starch by STPP/STMP for Improving Digestion Resistibility.

The chemical modifications of starch granules have been adopted to improve the characteristics, viz., paste clarity, resistant starch content, thermal stability, and so forth. The modified starch has been applied as a biopolymer in developing various preparations of food, nutraceutical, and pharmaceutical importance. The present work is focused on phosphorylation of alkali extracted mandua starch for improving digestion resistibility. The phosphorylation of mandua starch extracted from grains of Eleusine coracana (family Poaceae) was carried out by sodium tripolyphosphate/sodium trimetaphosphate at alkaline pH. After chemical treatment of mandua starch, the resistant starch (RS) content was increased significantly. The digestibility of chemically modified starch (CMS) was decreased down after treating by the phosphorylation process. The digestibility of CMS and alkali extracted mandua starch (AMS) in simulated intestinal fluid was found to be 32.64 ± 1.98% w/w and 61.12 ± 2.54% w/w, respectively. After chemical modification of mandua starch, a decrement was observed in amylose content, water-binding capacity, and swelling power. In the three-stage decomposition pattern of CMS studied by thermal gravimetric analysis, the significant changes in decomposition behavior also affirmed the impact of cross-linking in the improvement of stability of internal structure and resistibility of starch. In Fourier transform infrared (FTIR), the formation of the P=O bond was observed in CMS at 1250 cm-1. The acute and sub-acute toxicity studies in terms of behavioral, haematological, and enzymological parameters for CMS were not different significantly from AMS and control (p > 0.05). The cellular architecture of the liver and the kidney were found normal after consumption of CMS. The results revealed that significant increment in RS fraction occurred after cross-linking of mandua starch. The prepared starch may be applied in developing various formulations of food and pharmaceutical importance.

A Beefy-R culture medium: Replacing albumin with rapeseed protein isolates

The development of cost-effective serum-free media is essential for the economic viability of cultured meat. A key challenge facing this goal is the high-cost of recombinant albumin which is necessary in many serum-free media formulations, including a recently developed serum-free medium for bovine satellite cell (BSC) culture termed Beefy-9. Here we alter Beefy-9 by replacing recombinant albumin with rapeseed protein isolate (RPI), a bulk-protein solution obtained from agricultural waste through alkali extraction (pH 12.5), isoelectric protein precipitation (pH 4.5), dissolution of physiologically soluble proteins (pH 7.2), and concentration of proteins through 3 kDa ultrafiltration. This new medium, termed Beefy-R, was then used to culture BSCs over four passages, during which cells grew with an average doubling time of 26.6 h, showing improved growth compared with Beefy-9. In Beefy-R, BSCs maintained cell phenotype and myogenicity. Together, these results offer an effective, low-cost, and sustainable alternative to albumin for serum-free culture of muscle stem cells, thereby addressing a key hurdle facing cultured meat production.

Enhanced bio-ethanol production from bamboo residues by alkali-aided Fenton reaction pretreatment and enzymatic saccharification

Alkali extraction was used to assist the Fenton pretreatment for overcoming the recalcitrance of bamboo and producing more sugar-based chemicals and bioethanol. The alkali-aided Fenton pretreatment showed the delignification of 55.33% and xylan removal of 80.76%. The surface lignin coverage, hydrophobicity, specific surface area, and cellulose crystallinity index were obviously changed by the combined pretreatment, which made cellulose accessibility increased by about 2-folds than Fenton pretreatment alone. The cleavage of β-O-4 linkage, the decrease of condensed structure and syringyl unit were observed in the residual lignin from the NaOH-Fenton pretreated D. brandisii, all of which reduced the nonproductive adsorption between enzymes and lignin. When NaOH-Fenton pretreated four bamboo residues were performed enzymatic hydrolysis, glucose yields of 66–74% and ethanol concentration of 11–16 g/L were obtained. The sequential NaOH-Fenton pretreatment should be considered as an environmentally-friendly bamboo biorefinery technology in the future.

Yield optimization, physicochemical characterizations, and antioxidant properties of food grade agar from Gracilaria tenuistipitata of Cox's Bazar coast, Bangladesh.

The present study was aimed at investigating the optimization of extraction variables for food grade quality agar from Gracilaria tenuistipitata, so far, the first study on Bangladeshi seaweed. Water (native)- and NaOH (alkali)-pretreated agars were comparatively analyzed by several physicochemical parameters. All extraction variables significantly affected the agar yield in both extraction conditions. Alkali-pretreated agar provided a better yield (12-13% w/w) and gel strength (201 g/cm2) in extraction conditions as followed by 2% NaOH pretreatment at 30°C for 3h, seaweed to water ratio at 1:150, and extraction temperature at 100°C for 2h. Gelling and melting temperatures, color, and pH values of both agars were found to be comparable with commercial agar. Significantly higher sulfate contents including organic and inorganic and total carotenoids were reported in native (3.14% and 1.29 μg/mL) than that in alkali-pretreated agar (1.27% and 0.62 μg/mL). FTIR spectrum demonstrated the purity of the agar as characterized by the stronger relative intensity with higher degree of conversion of L-galactose 6-sulfate to 3,6-anhydrogalactose in alkali pretreatment group than that of native ones. Moreover, antioxidant activity (% DPPH scavenging) was observed and confirmed by IC50 values of 5.42 and 9.02 mg/mL in water- and alkali-pretreated agars, respectively. The results suggested that agar from G.tenuistipitata with optimized alkali extraction conditions could promote cost-effective yield with improved physicochemical characteristics and biofunctional values upon consumption by the consumers as food materials.

Anticoagulant Property of a Sulfated Polysaccharide with Unique Structural Characteristics from the Green Alga Chaetomorpha aerea.

Sulfated polysaccharides from marine algae have attracted a great amount of attentions for the development of marine drugs due to their unique structural features, and they are great potential sources of naturally occurring anticoagulant agents. The genus Chaetomorpha is one of the largest genera in green algae and has a worldwide distribution. In the present study, a homogeneous polysaccharide from Chaetomorpha aerea, designated as PCA, was obtained by alkali extraction, anion-exchange and size-exclusion chromatography. Based on the results of chemical and spectroscopic analyses, PCA was a sulfated galactoarabinan which was mainly constituted of a backbone of →4)-β-l-Arap-(1→ unit, partially sulfated at C-3 of →4)-β-l-Arap-(1→ and C-4 of →6)-α-d-Galp-(1→. The side chains consisting of →6)-α-d-Galp-(1→ and →5)-α-l-Araf-(1→ residues were in C-2 of →4)-β-l-Arap-(1→ unit. PCA had a strong anticoagulant activity in vitro as evaluated by the assays of activated partial thromboplastin time, thrombin time and fibrinogen level. The obvious anticoagulant activity in vivo of PCA was also found. PCA significantly inhibited the activities of the intrinsic coagulation factors XII, XI, IX and VIII, and exhibited weak inhibition effects on the common coagulation factors II and X. The anticoagulant mechanism of PCA was attributed to strong thrombin inhibition potentiated by heparin cofactor II or antithrombin III, and it also possessed an apparent inhibition effect on coagulation factor Xa mediated by antithrombin III. The investigation demonstrated that PCA could be a promising anticoagulant agent for health promotion and the treatment of thrombotic diseases.

A sulfated polysaccharide from Dictyosphaeria cavernosa: Structural characterization and effect on immunosuppressive recovery

A homogeneous sulfated polysaccharide DCS1 was obtained from Dictyosphaeria cavernosa by alkali extraction and chromatography purification. On the basis of chemical and spectroscopic analyses, DCS1 was a novel mannan-type sulfated polysaccharide and had a molecular weight of 15.48 kDa. DCS1 consisted of a main chain of (1 → 4)-α-d-Manp units with partial sulfate substitution at C-2 and branches at C-2/C-6. DCS1 possessed a potent immune-enhancing effect in vitro evaluated by the assays of lymphocytes proliferation and macrophage phagocytosis. The immunomodulatory effect of DCS1 in vivo was further investigated using immunosuppressed mice induced by cyclophosphamide (Cy). The data showed that DCS1 markedly increased the spleen and thymus indexes, and ameliorated the Cy-induced damage to spleen and thymus. Moreover, DCS1 had a significant effect on hematopoietic function recovery, and promoted the secretion of the interleukin-2 and tumor necrosis factor-α. Notably, DCS1 reversed the reduction of CD4+ T cells, improved the disorder of CD4+/CD8+ T cells and enhanced the immune response. The investigation demonstrated that the sulfated polysaccharide DCS1 with novel structure could be a hopeful immunomodulatory agent.

Isolation of clean-label faba bean (Vicia faba L.) proteins: A comparative study of mild fractionation methods against traditional technologies

Plant protein isolation by mild wet processing methods that are free of alkali/acid and thermal treatments were investigated in order to address the fast growing consumer demand for clean-label ingredients. The impact of different mild wet fractionation conditions was established in terms of yield, purity and recovery of faba bean protein concentrates/isolates (PCs/PIs) from both Snowbird (low tannin, LT) and Athena (high tannin, HT) cultivars. Although salt-soluble globulins (74 to 75%) were the primary proteins found in faba beans, PIs resulting from dialysis (LT: 93.2 ± 0.1% and HT: 96.4 ± 0.3%) or micellization (LT: 99.1 ± 0.1% and HT: 98.7 ± 0.2%) following water extraction at 35 °C (W35) at a solvent/feed (S/F) ratio of 2 had higher protein contents than PCs from aqueous NaCl extraction followed by dialysis (LT: 79.1 ± 0.1% and HT: 81.6 ± 0.5%) or alkali extraction followed by acid precipitation (LT: 87.1 ± 1.4% and HT: 86.3 ± 0.2%). These differences in protein extractability of water- and salt-based methods could be attributed to the high levels of endogenously present minerals. Although methionine and cysteine were limiting amino acids, the W35 methods resulted in overall higher amino acid content and in high-quality PIs compared to the rest due to the presence of albumins as confirmed by SDS-PAGE. The W35-PIs were low in raffinose family oligosaccharides, tannins and trypsin inhibitory activity and can be considered chemical-free alternatives to alkali extracted-acid precipitated PCs.

Effect and characterization of polysaccharides extracted from Chlorella sp. by hot-water and alkali extraction methods

This study characterized and compared the physicochemical properties and antioxidant activity of polysaccharides from Chlorella sp. extracted by hot-water extraction method at different temperatures (60–180 °C) and alkali extraction method at different alkali concentrations (0–4 %). Results showed that the dissolution percent of polysaccharides of the two methods reached maximum values of 71.19 % and 58.79 % at 120 °C and 4 % alkali concentration, respectively. All these polysaccharides contained the same monosaccharide components at different proportions. The molecular weight of polysaccharides extracted by alkali method were larger than that extracted by hot-water method. High temperature and alkali concentration both degraded polysaccharides into the lower molecules and destroyed the carboxyl group in polysaccharides. The polysaccharides from alkali method showed the better antioxidant activity, and the polysaccharide extracted by 1 % alkali concentration showed the highest antioxidant activity with 85.17 % (4 mg/mL) and 96.75 % (1 mg/mL) scavenging rates of DPPH and OH, respectively. This study concludes that the determination of the extraction condition of Chlorella polysaccharides should consider the great effect of physicochemical properties and antioxidant activity.