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1.
White, fluffy cellulose/arabinoxylan mixtures (CAX) were generated from the solid residues remaining after corn fiber gum (CFG) production. Most CAX were produced using variations of a process in which a single alkaline hydrogen peroxide (AHP) step was used for delignification and for CFG (arabinoxylan) extraction. The optimal ratio of H2O2 to corn fiber to water was 0.1:1:20. Holding this ratio constant, time and temperature conditions were systematically varied, and yields of CAX and CFG determined. Parallel processes were conducted without H2O2 to determine its effect on CAX and CFG yield. CAX prepared under identical conditions but without H2O2 retained nearly twice the levels of CFG sugars, as revealed from L‐arabinose, D‐xylose, and D,L‐galactose levels. Even the CAX prepared under extreme AHP conditions (1 hr, 100°C), however, contained 32.9% of these CFG sugars. This CAX was obtained in a 25.1% yield, whereas those produced under less vigorous conditions were obtained in higher yields, because they retained more CFG. CAX prepared in the presence of H2O2 hydrated very effectively, as indicated by their high swollen volumes and water absorbance values. This suggests potential food applications for CAX as a bulking agent. In addition, the open structure of the CAX matrix would render these residues suitable for chemical derivatization and enzymatic saccharification.  相似文献   

2.
The ability of alphas1/beta-casein and micellar casein to protect whey proteins from heat-induced aggregation/precipitation reactions and therefore control their functional behavior was examined. Complete suppression (>99%) of heat-induced aggregation of 0.5% (w/w) whey protein isolate (pH 6.0, 85 degrees C, 10 min) was achieved at a ratio of 1:0.1 (w/w) of whey protein isolate (WPI) to alphas1/beta-casein, giving an effective molar ratio of 1:0.15, at 50% whey protein denaturation. However, in the presence of 100 mM NaCl, heating of the WPI/alphas1/beta-casein dispersions to 85 degrees C for 10 min resulted in precipitation between pH 6 and 5.35. WPI heated with micellar casein in simulated milk ultrafiltrate was stable to precipitation at pH>5.4. Protein particle size and turbidity significantly (P相似文献   

3.
小麦麸皮阿拉伯木聚糖碱提工艺条件优化研究   总被引:2,自引:0,他引:2  
为提高小麦麸皮中阿拉伯木聚糖的得率,本研究在考察了温度、时间、碱液与H2O2浓度和振荡速度等单因素对阿拉伯木聚糖得率影响的基础上,采用二次回归正交旋转组合设计对阿拉伯木聚糖的碱提工艺条件进行了优化并建立数学模型。结果表明,在提取温度88℃、时间200min、NaOH浓度0.16mol/L、H2O2浓度1.5%的条件下,阿拉伯木聚糖的得率达到最大值21.23%,验证实验结果与模型预测值相符。  相似文献   

4.
The overall objective of this research was to find a new way to valorize rye bran, by producing a gellifier from the enzymatic solubilization of arabinoxylans (AX). The effects of three pure endo-xylanases from Aspergillus niger (Xyl-1), Talaromyces emersonii (Xyl-2), and Bacillus subtilis (Xyl-3) and of Grindamyl S100 (GS100), a commercial enzyme preparation containing a Xyl-1 type endo-xylanase, were tested on rye bran to study the solubilization of water-unextractable arabinoxylans (WUAX). Eight different extrusion-treated rye brans were also used as substrates to find the best physical treatment to facilitate enzymatic arabinoxylan (AX) solubilization. Arabinoxylans were better solubilized from the bran extruded at high temperature using Xyl-3. This enzyme was then tested in combination with pure (1,4)-beta-d-arabinoxylan arabinofuranohydrolase (AXH) and endo-beta-d-glucanase or ferulic acid esterase (FAE), from A. niger. Only beta-glucanase in combination with Xyl-3 improved the AX extraction, but it did not have a marked effect on the viscosity of the extracts. Xyl-3 was then tested on a high-shear-treated rye bran, and results were compared to those obtained with the high-temperature-extruded rye bran. The high-shear treatment did not improve the bran AX enzymatic solubilization. The combination of FAE with Xyl-1 or Xyl-3 did not improve the AX extraction from untreated and high-shear-treated rye bran. Finally, to study the gelation capacity of the enzymatically solubilized AX, the effect of the hydrogen peroxide/horseradish peroxidase (H(2)O(2)/POD) was tested on the Xyl-3 high-temperature-extruded bran extracts. Solubilized AX did not gel in the presence of the oxidizing system.  相似文献   

5.
The structures of barley ( Hordeum vulgare) arabinoxylans isolated from two industrial side fractions, barley husks (BH) and barley fiber (BF), were characterized. Arabinoxylans were extracted with saturated barium hydroxide after enzymatic pretreatment. Barium hydroxide was selective toward arabinoxylans, and only a minor amount of glucose-containing material was coextracted. Acid methanolysis followed by gas chromatography, 1H NMR spectroscopy, and specific enzymatic treatments followed by anion exchange chromatography with pulse amperometric detection (HPAEC-PAD) revealed that the chemical structure of barley husk arabinoxylan (BHAX) clearly differed from that of barley fiber arabinoxylan (BFAX). BFAX was more branched, containing more beta-D-xylopyranosyl (beta-D-Xylp) residues carrying alpha-L-arabinofuranosyl (alpha-L-Araf) units at both O-2 and O-3 positions. BHAX, on the other hand, contained more 2-O-beta-D-Xyl p-alpha-L-Ara f substituents than BFAX. BHAX and BFAX also differed with respect to the hydrodynamic properties investigated with multidetector size exclusion chromatography. BFAX had a higher weight-average molar mass and larger hydrodynamic volume, the latter indicating less dense conformation than BHAX. Mn, Mw /Mn, Rh, and the Mark-Houwink a value were also determined for both arabinoxylans.  相似文献   

6.
Structured lipids (SLs) containing palmitic, oleic, stearic, and linoleic acids, resembling human milk fat (HMF), were synthesized by enzymatic acidolysis reactions between tripalmitin, hazelnut oil fatty acids, and stearic acid. Commercially immobilized sn-1,3-specific lipase, Lipozyme RM IM, obtained from Rhizomucor miehei was used as the biocatalyst for the enzymatic acidolysis reactions. The effects of substrate molar ratio, reaction temperature, and reaction time on the incorporation of stearic and oleic acids were investigated. The acidolysis reactions were performed by incubating 1:1.5:0.5, 1:3:0.75, 1:6:1, 1:9:1.25, and 1:12:1.5 substrate molar ratios of tripalmitin/hazelnut oil fatty acids/stearic acid in 3 mL of n-hexane at 55, 60, and 65 degrees C using 10% (total weight of substrates) of Lipozyme RM IM for 3, 6, 12, and 24 h. The fatty acid composition of reaction products was analyzed by gas-liquid chromatography (GLC). The fatty acids at the sn-2 position were identified after pancreatic lipase hydrolysis and GLC analysis. The results showed that the highest C18:1 incorporation (47.1%) and highest C18:1/C16:0 ratio were obtained at 65 degrees C and 24 h of incubation with the highest substrate molar ratio of 1:12:1.5. The highest incorporation of stearic acid was achieved at a 1:3:0.75 substrate molar ratio at 60 degrees C and 24 h. For both oleic and stearic acids, the incorporation level increased with reaction time. The SLs produced in this study have potential use in infant formulas.  相似文献   

7.
The molecular characteristics of two purified arabinoxylan fractions derived from corn kernels, corn fiber gum-1 and -2 (CFG-1 and -2), have been studied and correlated with emulsifying properties. CFG-1 and -2 fractions were isolated from different corn fiber sources by 1) a sequential alkaline extraction and H2O2 bleaching to produce CFG-1; and 2) additional H2O2 treatment of the alkali-extracted residue at pH 11.5, yielding CFG-2. Multiangle laser light-scattering and online viscosity were used to measure the molar mass, polydispersity, structure compactness, and intrinsic viscosity of the generated CFG fractions. Emulsification properties in an oil-in-water emulsion system with 10:1 oil-to-gum ratio was investigated by measuring turbidity of an aliquot from the bottom of the diluted emulsion over 10 days. The isolated CFG-2 from each fiber source was higher in weight-average molar mass (Mw) polydispersity) (Mw/Mn) and structure compactness, and also lower in solution weight-average intrinsic viscosity (ηw) than the corresponding CFG-1. Average Mw and ηw values were 244–491 kDa and 1.35–1.84 dL/g, respectively. The emulsion stabilizing capacity of CFG-2 from each fiber source was superior to the corresponding CFG-1.  相似文献   

8.
小麦秸秆纤维素均相醚化制备羧甲基纤维素工艺优化   总被引:1,自引:1,他引:0  
为了利用小麦秸秆通过均相反应制备羧甲基纤维素(CMC,carboxymethyl cellulose),采用氢氧化钠和过氧化氢回流加热法制备小麦秸秆纤维素。以加入氧化锌的氢氧化钠/尿素/硫脲体系为溶剂,采用冻融循环法溶解小麦秸秆纤维素,利用正交试验获得了该溶解体系的最佳组成。在溶解了小麦秸秆纤维素的氢氧化钠/尿素/硫脲/氧化锌的体系中,以氯乙酸钠为醚化剂制备CMC,并对其进行红外光谱分析和取代度(degree of substitution,DS)测定。结果表明:在固液比为1∶20 g/mL,质量分数为10%NaOH,反应温度为85℃,回流3.5 h和固液比为1∶30 g/m L,质量分数为3%H_2O_2,反应温度为85℃,回流3 h处理小麦秸秆,纤维素提取率最高为84.61%,同时能较好的脱除半纤维素和木质素;最佳溶解体系为:质量分数为7%NaOH,11%硫脲,5%尿素,0.05%氧化锌,0℃时,最大溶解度为2.880 1 g。红外光谱试验表明小麦秸秆纤维素与微晶纤维素特征吸收峰基本一致,醚化反应生成的CMC与商品CMC的特征吸收峰基本一致。CMC的取代度受纤维素用量、温度和氯乙酸钠与纤维素葡萄糖单元(AGU,anhydroglucose unit)的摩尔比影响,随纤维素用量和氯乙酸钠与纤维素AGU的摩尔比增大而提高,随醚化温度的增加先增大(55℃)后降低。研究结果为以小麦秸秆为原料,经NaOH和H_2O_2处理获得纤维素,溶解在加入氧化锌的氢氧化钠/尿素/硫脲体系中,与氯乙酸钠经过均相醚化反应合成取代度较高的CMC提供参考。  相似文献   

9.
Competitive adsorption of alpha(s)-casein and beta-casein from a bulk solution mixture to the triolein-water interface has been studied. Although the binding affinity of alpha(s)-casein to the triolein-water interface was lower than that of beta-casein in single-component systems, in a 1:1 mixture of alpha(s)-casein and beta-casein in the bulk solution the ratio of interfacial concentrations of alpha(s)-casein to beta-casein at equilibrium was about 2:1, indicating that alpha(s)-casein was preferentially adsorbed to the triolein-water interface. Furthermore, the equilibrium composition of alpha(s)-casein and beta-casein in the interfacial film at various bulk concentration ratios did not follow a simple Langmuir adsorption model. This deviation from ideal behavior was mainly due to thermodynamic incompatibility of mixing of these caseins in the interfacial region. The value of the incompatibility parameter, X(12), for these caseins at the triolein-water interface was much greater than that at the air-water interface. Displacement experiments showed that while alpha(s)-casein could dynamically displace beta-casein when the latter was in an unsaturated monolayer state at the interface, it could not do so when beta-casein was in a saturated monolayer film state. It is hypothesized that, because of thermodynamic incompatibility of mixing, the alpha(s)-casein and beta-casein mixed film at the oil-water interface may undergo two-dimensional phase separation.  相似文献   

10.
Val-Pro-Pro (VPP) and Ile-Pro-Pro (IPP) are antihypertensive tripeptides isolated from milk fermented with Lactobacillus helveticus and inhibit angiotensin-converting enzyme (ACE). We investigated whether these peptides were generated from beta-casein by digestive enzymes and whether they were resistant to enzymatic hydrolysis, using an in vitro model. VPP and IPP were not generated from beta-casein by gastrointestinal enzymes; instead, a number of longer peptides including VPP and IPP sequences were detected. The fermentation step would therefore be necessary to produce these antihypertensive tripeptides. VPP and IPP themselves were hardly digested by digestive enzymes, suggesting that orally administered VPP and IPP remain intact in the intestine, retaining their activity until adsorption. The present study also demonstrated that various functional peptide sequences in beta-casein were resistant to gastrointestinal enzymes. There may be a strong correlation between the resistance of peptides to gastrointestinal digestion and their real physiological effects after oral administration.  相似文献   

11.
Water‐extractable (WE) material was isolated from a Canadian barley malt (cv. Harrington). The purified WE material contained mainly arabinoxylans, β‐glucans, proteins, and small amounts of arabinogalactans and mannose‐containing polymers. WE material was treated with specific enzymes to obtain two fractions: one enriched in arabinoxylan (AX) and another enriched in β‐glucan (BG). The AX fraction was further fractionated by stepwise precipitation in (NH4)2SO4 into five arabinoxylan subfractions. 1H‐NMR spectroscopy and sugar analyses revealed a relatively high content of unsubstituted xylose residues (48–58%) as well as a relatively high content of doubly substituted xylose residues (28–33%) in the structure of the arabinoxylans. β‐Glucans constituted a minor portion of water‐extractable malt polysaccharides and were characterized by high levels of tri‐ and tetrasaccharide residues (93.4%) with a molar ratio of 2.19 for cellotriosyl to cellotetraosyl units. Size‐exclusion chromatography revealed that the WE material contained several polymer populations. One population had a very high molecular weight that appeared to be the result of aggregation. The AX fraction contained higher molecular weight polymers than the BG fraction.  相似文献   

12.
For the first time, alkaline hydrogen peroxide (AHP) extraction conditions were used to isolate hemicellulose (arabinoxylan) from destarched corn fiber. Yields of the water-soluble hemicellulose B ranged from 35% (24 hr extraction at 25°C) to 42% (2 hr extraction at 60°C). The hemicellulose B resulting from the 2 hr extraction (pH 11.5) was off-white in color, and a very low proportion (1.7%) of water-insoluble hemicellulose A was extracted. AHP treatment caused delignification and facilitated the alkaline extraction of hemicellulose from the lignocellulosic fiber matrix. In the absence of H2O2, yields were reduced by more than one-third when using otherwise identical extraction conditions of time, temperature and pH. In the standard protocol, corn fiber, NaOH solution, and H2O2 were mixed in a 1:25:0.25 (w/v/w) ratio. Extractions were conducted at pH 11.5 at 25°C or 60°C. The pH was adjusted to 11.5 by addition of NaOH at ambient and elevated temperatures. The optimum hemicellulose yield (51.3%; dry, starch-free basis) was obtained when the pH was increased to 12.5 for the final one-half of the extraction period. Products obtained after extraction at pH values greater than 11.5 were tan in color, however, and the goal of the research has been to isolate white hemicellulose B and then evaluate its properties. Under most conditions, the yields ofhemicellulose B, potentially the most useful form for food and industrial applications, exceeded those of hemicellulose A by more than 10-fold. The hemicellulose B products were lighter in color than those obtained using traditional alkaline extraction conditions of refluxing with calcium or sodium hydroxide. Steps prior to extractions with alkaline H2O2, such as grinding to 20 mesh and extracting with azeotropic toluene-ethanol, were found to be unnecessary.  相似文献   

13.
Valuable information about possible types of linkages, reaction mechanisms, and sequences for oxidative coupling of phenolic compounds in planta is available from in vitro model systems. Ferulate oligomers were generated in a system using ethyl ferulate, peroxidase, and hydrogen peroxide under various conditions. A molar ferulate/H2O2 ratio of 1:1, an ethanol level of 30% in an aqueous sodium phosphate buffer (pH 6.0), and a reaction time of 10 min were considered to be ideal to produce maximal proportions of ferulate trimers and tetramers from ethyl ferulate as starting material. The dominant trimer and tetramer were each isolated from the reaction mixture and identified as 8-O-4/8-5(cyclic)-dehydrotriferulic acid triethyl ester and 8-5(cyclic)/4-O-5/8-5(cyclic)-dehydrotetraferulic acid tetraethyl ester. The structure of the 8-O-4/8-5(cyclic)-dehydrotriferulic acid triethyl ester revealed that a third ferulate unit is bound to a preformed 8-O-4-diferulate dimer, a surprising reaction sequence considering the dominance of 8-5-coupled dimers among dehydrodiferulates in H2O2/peroxidase-based model reactions. As 4-O-5-coupling is not favored in the dimerization process of ferulates, the main tetramer isolated in this study is probably formed by 4-O-5-coupling of two preformed 8-5(cyclic)-diferulates, a logical step in analogy with reactions occurring in lignin biosynthesis.  相似文献   

14.
Hexyl acetate, a short-chain ester with fruity odor, is a significant green note flavor compound and widely used in the food industry. The ability for immobilized lipase from Mucor miehei (Lipozyme IM-77) to catalyze the transesterification of hexanol with triacetin was investigated in this study. Response surface methodology and five-level-five-factor central composite rotatable design were adopted to evaluate the effects of synthesis variables, such as reaction time (2-10 h), temperature (25-65 degrees C), enzyme amount (10-50%; 0.024-0.118 BAUN), substrate molar ratio of triacetin to hexanol (1:1 to 3:1), and added water content (0-20%) on percentage molar conversion of hexyl acetate. The results showed that reaction temperature and substrate molar ratio were the most important parameters and that added water content had less of an effect on percent molar conversion. On the basis of canonical analysis, optimum synthesis conditions were as follows: reaction time, 7.7 h; temperature, 52.6 degrees C; enzyme amount, 37.1% (0.089 BAUN); substrate molar ratio, 2.7:1; and added water, 12.5%. The predicted value was 88.9% molar conversion, and the actual experimental value was 86.6% molar conversion.  相似文献   

15.
Corn fiber gum (CFG) is a hemicellulose (arabinoxylan)-enriched fraction obtained by the extraction of corn bran/fiber using a proprietary alkaline hydrogen peroxide process. When purified CFG prepared by this process was hydrolyzed with more concentrated base (1.5 N methanolic KOH at 70 degrees C for 1 hour), considerable amounts of hydroxycinnamic acids (up to 0.015% of mainly ferulic acid) and lipids (up to 0.43%) were released. The released phenolic acids and lipids were identified and quantified using high-performance liquid chromatography (HPLC) with detection by both UV and evaporative light-scattering detection (ELSD). During the wet milling of corn, two types of corn fiber are produced: coarse fiber, which is primarily from pericarp, and fine fiber, which is from the endosperm. The total phenolic acid content in CFGs purified from coarse corn fiber (pericarp fiber) is comparatively higher than that purified from fine corn fiber (endosperm fiber). It was also determined that the purified CFG samples contained significant amounts of strongly associated proteins, from 2 to 5% by weight. The presence of these phenolic acids, lipids, and proteins strongly associated or bound to CFG may contribute to its excellent ability to emulsify oil-in-water emulsions.  相似文献   

16.
A new spectrophotometric enzymatic method for the determination of total phenol content in tea and wine has been developed. The method is based on the peroxidase-catalyzed oxidation, by hydrogen peroxide, of phenols to phenoxyl radicals, which can react with aromatic substrates to form intensely colored adducts. In comparison with the widely used Folin-Ciocalteu method, this method appears to be more specific and more rapid and as a whole is not affected by the common interfering substances such as ascorbate, citrate, and sulfite. Numerous samples of teas and wines were analyzed by using the new method, and the results compared with those obtained by using the Folin and scavenging of DPPH methods. The differences of the total phenols content found by applying the three methods are discussed in terms of the different specificities of the analytical basis.  相似文献   

17.
The antioxidant hesperidin, a major flavonoid in sweet orange and lemon, was evaluated using chemical and biological systems. The chemical assay evaluates the hesperidin capacity to sequester 1,1-diphenyl-2-picrylhydrazyl (DPPH*). Biological studies were done using the eukaryotic cells of superoxide-dismutase proficient and deficient strains of Saccharomyces cerevisiae treated with hesperidin and the stressing agents hydrogen peroxide or paraquat (methylviologen; 1,1'-dimethyl-4,4'-bipyridinium dichloride). Hesperidin was able to reduce significantly the level of the free radical DPPH* with similar efficacy of trolox (positive control). When the yeast cells were exposed to the flavonoid hesperidin before the stressing agents, there was a significant increase in the survival of all strains. Paraquat induced higher catalase and superoxide dismutase than did hydrogen peroxide, which only increased catalase activity. Previous addition of hesperidin to these treatments was able to reduce significantly both enzymatic levels. These observations clearly demonstrate that hesperidin provides strong cellular antioxidant protection against the damaging effects induced by paraquat and peroxide hydrogen.  相似文献   

18.
The tyrosine-containing peptide Gly-Tyr-Gly (GYG) was oxidatively cross-linked by horseradish peroxidase in the presence of hydrogen peroxide. As products, covalently coupled di- to pentamers of the peptide were identified by LC-MS. Oxidative cross-linking of ferulic acid with horseradish peroxidase and hydrogen peroxide resulted in the formation of dehydrodimers. Kinetic studies of conversion rates of either the peptide or ferulic acid revealed conditions that allow formation of heteroadducts of GYG and ferulic acid. To a GYG-containing incubation mixture was added ferulic acid in small aliquots, therewith keeping the molar ratio of the substrates favorable for hetero-cross-linking. This resulted in a predominant product consisting of two ferulic acid molecules dehydrogenatively linked to a single peptide and, furthermore, two ferulic acids linked to peptide oligomers, ranging from dimers to pentamers. Also, mono- and dimers of the peptide were linked to one molecule of ferulic acid. A mechanism explaining the formation of all these products is proposed.  相似文献   

19.
The potential of a laccase from the fungus Pycnoporus cinnabarinus to cross-link feruloylated soluble wheat arabinoxylans was investigated using capillary viscometry, size-exclusion HPLC, and reverse-phase HPLC of phenolic compounds. The laccase results were compared with those for a hydrogen peroxide/horseradish peroxidase system. The oxidants provoked an increase in viscosity of a 0.2% (w/v) arabinoxylan solution. A gel was formed after 30 min with laccase. Hydrogen peroxide was consumed rapidly before a gel could be formed. Free ferulic acid, methyl ferulate, and vanillic acid inhibited the gelation, whereas fumaric acid had no effect. This suggests that the aromatic ring, and not the propenoic chain of ferulic acid, was the initiating site for arabinoxylan cross-linking. Ferulic acid and its 8-O-4′, 8-5′, and 5-5′ dehydrodimers were present in nonoxidized arabinoxylans. Upon oxidation, the 8-8′ and 8-5′ benzofuran dehydrodimers appeared and the 8-O-4′ and 8-5′ dimers increased. The production of dimers was proportional to the consumption of ester-bound ferulic acid. In cross-linked arabinoxylans, the major dimers were 8-5′ benzofuran, 8-8′, and 8-O-4′, whereas the 5-5′ dehydrodimer remained at the same level as in the nonoxidized solution.  相似文献   

20.
1,3-Dioleoyl-2-palmitoylglycerol, an important triacylglycerol in infant formulas, was effectively enriched by a two-step process: (a) dry fractionation of leaf lard and (b) enzymatic acidolysis of the fractionated leaf lard. In step a, the 1,3-dioleoyl-2-palmitoylglycerol content was increased from 16.77 to 30.73% after programmed temperature treatment of the leaf lard at 60 °C for 20 min followed by 34 °C for 10 h. In step b, 43.72% of the 1,3-dioleoyl-2-palmitoylglycerol content was obtained at the optimal conditions of enzymatic acidolysis: a substrate molar ratio of 1:4 (the fractionated leaf lard/camellia oil fatty acids), 6% (w/w) of enzyme loading, and 6 h of reaction time at 45 °C. On the basis of gas chromatography determination and "deducting score" principle, a model was properly established for characterizing the quality of triacylglycerols enriched with 1,3-dioleoyl-2-palmitoylglycerol. This approach would be a valuable contribution in structured lipids industries because only gas chromatography determination was involved.  相似文献   

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