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1.
Nonlignified cell walls from Zea mays (L.) cell suspensions were incubated with and without pectin methylesterase (PME) and a portion were artificially lignified to assess how methyl esters influence the release of pectic uronosyls and total sugars from cell walls by fungal enzymes. Treatment with PME reduced uronosyl concentrations from 97 to 92 mg/g, reduced uronosyl methylation from 57% to 21%, and increased Klason lignin concentrations in artificially lignified cell walls from 99 to 116 mg/g. Although PME treatment slightly enhanced uronosyl release from nonlignified cell walls, it reduced uronosyl release from artificially lignified cell walls by 55% after 4 h and by 7% after 72 h of enzymatic hydrolysis. Pectin hydrolysis in PME treated cell walls was probably impaired by enhanced benzyl ester cross-linking of uronosyls to lignin via quinone methide intermediates. Variations in uronosyl methylation had little effect on the overall release of total sugars from cell walls.  相似文献   

2.
Because pectins are released from potatoes and other plants under conditions that cleave ester linkages, it has been suggested that there are other galaturonoyl ester cross-links between pectin chains in addition to the known non-cross-linking methyl esters. A microscale titration method and a copper binding method were developed for the measurement of total polymer carboxyl (essentially pectic) ester content in potato cell walls. Relative to the uronic acid content of the cell walls, the degree of total esterification was 57-58%. Comparison with levels of methanol released on ester hydrolysis allowed nonmethyl uronoyl esters to be estimated to be 14-15% relative to total uronic acid. The possibility of nonmethyl-esterified linkages being formed in potato cell walls by a side-reaction catalyzed by pectin methyl esterase (PME) was investigated, but no increase in nonmethyl-esterified pectin was observed under conditions where pectin was being effectively de-esterified by endogenous PME activity.  相似文献   

3.
六种果皮原料果胶的理化及凝胶特性比较   总被引：4，自引：2，他引：2  
为了解不同品种水果的果皮(柚子皮、西番莲皮、脐橙皮、石榴皮、榴莲皮)以及向日葵盘所提取果胶的理化和质构特性,研究了不同原料果胶的得率、色泽、果胶酸含量、甲氧基含量、酯化度、黏度及质构特性,特别是采用高效液相色谱准确测定了各类果胶的分子量。结果表明:柚子皮、向日葵盘和脐橙皮果胶质量分数较高,分别为18.06%、14.61%和14.43%;西番莲皮果胶质量分数为8.76%;而石榴皮及榴莲皮果胶质量分数较低(均<3%)。从分子量看,石榴皮、脐橙皮果胶分子量较大(>1000kDa),向日葵盘果胶分子量最小(483kDa)。此外,几种果胶的溶胶均属低黏度值果胶(<25厘泊),且在pH值为7.0时黏度最大、在pH值为5.0时黏度最小。结合凝胶质构分析表明:石榴皮果胶分子量最大,凝胶强度最大,但为高甲氧基果胶,且得率较低;而向日葵盘果胶分子量最小,但得率较高,且为低甲基果胶,在非糖及含糖体系中均可形成性能优良的凝胶,因此是生产果胶的良好原料。该文为果胶的生产及应用提供参考。  相似文献   

4.
Pectin gels were induced by monovalent salts (0.2 M) concurrently with deesterification of high methoxy pectin using a salt-independent orange pectin methylesterase (PME). Constant pH was maintained during deesterification and gelation. If salt or PME was absent, the pectin did not form a gel. The gel strength was influenced by both pH and species of monovalent cation. At pH 5.0, the pectin gel induced by KCl was significantly stronger than the NaCl-induced gel. In contrast, a much stronger gel was produced in the presence of NaCl as compared to KCl at pH 7.0. LiCl did not induce pectin gelation at either pH. Molecular weights of pectins increased from 1.38 x 10(5) to 2.26 x 10(5) during NaCl-induced gelation at pH 7. One proposal to explain these pectin molecular weight changes is a hypothetical PME transacylation mechanism. However, these pectin molecular weight changes can also be explained by metastable aggregation of the enzymatically deesterified low methoxy pectin. We postulate that gelation was induced by a slow deesterification of pectin under conditions that would normally salt out (precipitate) low methoxy pectin in the absence of PME.  相似文献   

5.
The use of protease and cellulase preparations to extract pectins from plant byproducts (chicory, cauliflower) was investigated. Different enzymatic preparations were characterized by their activities toward proteins, cellulose, and pectins. These preparations were then tested regarding pectin extraction, and extraction conditions (nature and concentration of enzyme, incubation time) were optimized. Enzymatic and acidic extractions were compared and also combined in sequential extractions. This study shows that it is possible to extract pectins by using cellulases and proteases. Enzymes can extract pectins with a higher yield ( approximately 35%) than acid (approximately 28%) but enzyme-extracted pectins have a smaller molar mass (300,000 g/mol) than acid-extracted pectins (500,000 g/ mol). Different hypotheses are tested and discussed to explain this mass difference.  相似文献   

6.
The effect of vacuum infusion on eggplant quality of a commercial fungal (Aspergillus niger) and citrus pectinmethylesterase (PME) with calcium chloride (4000 ppm) was investigated after processing and during storage. Firmness of infused eggplants using fungal or citrus PME was significantly increased compared to controls (fresh noninfused and water-infused control) after processing and during storage for 7 days at 4 degrees C. Activity of fungal PME-infused eggplant increased almost 32 times, whereas activity of eggplant infused with Marsh grapefruit PME increased 2-fold. Degree of esterification of pectin of eggplants infused with fungal or citrus PME decreased slightly. Cryo-SEM showed that samples treated with fungal PME/ CaCl2 displayed more integrity among cells as compared with water-infused control. The change of pectin in the cell wall was visualized using monoclonal antibodies JIM5 (low-esterified pectin) and JIM7 (high-esterified pectin). JIM5 showed more binding than JIM7 with the cell walls of eggplant tissues from fungal PME/ CaCl2 treatment.  相似文献   

7.
Strawberry cultivars differ in their sensitivity to NaCl; fruits of cv. Elsanta suffer from softening, whereas those of cv. Korona retain their firmness. The mean fruit fresh weight is reduced in cv. Elsanta up to 46% and in cv. Korona up to 26%. Cell walls of fruits grown under 0, 40, or 80 mmol/L NaCl were extracted and analyzed. In fruits of cv. Korona, the content of the alcohol-insoluble residue remained comparatively stable as salt levels increased but was reduced in cv. Elsanta. The water-soluble pectin fraction was not affected in cv. Korona, but the content of low methoxy pectinates increased significantly, indicative of the generation of calcium and magnesium bridges that stabilize pectin polysaccharides of cell walls. In cv. Elsanta, the content of water-soluble pectin rose, indicating pectin solubilization. For both cultivars, the significant negative correlation of fruit Cl(-) contents with the contents of NaOH-soluble pectinates, when expressed per fruit fresh mass, indicated that covalently bound pectic substances were degraded. Especially the response of cv. Elsanta is in line with the general observation that severe osmotic stress results in slower cell expansion and weaker cell walls.  相似文献   

8.
The effect of high-pressure processing (HPP) on cell wall polysaccharides in berries was investigated. HPP decreased the degree of methyl esterification (DM), probably by activation of pectin methyl esterase (PME), and improved the extractability of pectins. When commercial enzyme mixtures were added to mashed berries, a synergistic effect was observed between treatment with commercial enzymes and HPP. Compared to treatment at atmospheric pressure, pectic polysaccharides were degraded to a larger extent when HPP was used. In contrast, hemicelluloses were hardly affected by the added enzymes when HPP was included, although they were degraded during similar treatment at atmospheric pressure. Additionally, the activity of rhamnose-releasing enzymes present in minor quantities might be enhanced after HPP, resulting in a decrease of rhamnose in the polymeric cell wall material. These results exploring the effect of HPP at representative conditions clearly point out the potential of HPP for polysaccharide modification.  相似文献   

9.
A commercial high-methoxy citrus pectin was treated with a purified salt-independent pectin methylesterase (PME) isozyme isolated from Valencia orange peel to prepare a series of deesterified pectins. A series of alkali-deesterified pectins was also prepared at pH 10 under conditions permitting beta-elimination. Analysis of these pectins using high-performance size exclusion chromatography (HPSEC) with on-line multiangle laser light-scattering, differential viscometer, and refractive index (RI) detectors revealed no reduction in weight-average molecular weight (M(w); 150000) in the PME-treated pectin series, whereas a 16% reduction in intrinsic viscosity (IV) occurred below a degree of esterification (DE) of 47%. In contrast, alkali deesterification rapidly reduced both M(w) and IV to less than half of that observed for untreated pectin. PME treatment of a non-calcium-sensitive citrus pectin introduced calcium sensitivity with only a 6% reduction in the DE. Triad blocks of unesterified galacturonic acid were observed in (1)H nuclear magnetic resonance spectra of this calcium-sensitive pectin (CSP). These results demonstrate that the orange salt-independent PME isozyme utilizes a blockwise mode of action. This is the first report of the preparation of a CSP by PME treatment without significant loss of the pectin's M(w) due to depolymerization.  相似文献   

10.
During the storage season changes in the chemical composition of the pectin moiety of the cell walls of raw potatoes were studied. This compositional analysis was performed for the cultivars Nicola and Irene, which represent two extremes with regard to sensory-perceived texture. Both cultivars were divided into three size categories. From each size category a dry matter (DM) distribution was made. From these distributions potatoes at the low and high ends of this distribution were selected for further analysis. In total 12 different samples were analyzed three times during the storage season. The analysis comprised a pectin fractionation study. Pectic fractions were extracted from the cell wall material (CWM) by increasing the harshness of the extraction procedure. This resulted in a calcium-complexed pectic fraction, two pectic fractions weakly bound to the CWM, and a residue fraction, respectively. It was shown that no statistically significant differences (p > or = 0.95), either in yield or in chemical composition, could be observed between the two cultivars studied (Nicola and Irene), between sizes (large, medium, and small), and between potatoes with either high or low DM contents. However, statistically significant effects of storage both on the yield and on the chemical composition of the pectic moiety of the CWM could be observed, irrespective of cultivar, size, and DM content. Despite the substantial changes in the composition of the pectic moiety of the CWM of the raw material, no to minimal changes in the sensory-perceived texture of the cooked potatoes were observed upon storage. This suggests that the observed changes in pectin composition upon storage are overruled by other aspects that contribute more importantly to the sensory-perceived texture of steam-cooked potatoes.  相似文献   

11.
Changes in the cell-wall polysaccharides (CWP) of the edible tissues of four winter squash cultivars during storage and after cooking were investigated. A procedure for isolating cell walls of tissues containing high levels of starch was used. The starch-free CWP were sequentially fractionated using CDTA, dilute Na(2)CO(3), and 4 M KOH. Cellulose made up 40-42% of the total CWP for three cultivars (Delica, CF 2, and CF 4) at harvest but was 35% in the softer Red Warren. The pectic polysaccharides of Delica, CF 2, and CF 4 cell walls are more branched than those from Red Warren squash. The higher proportion of uronic acid in the pectic polysaccharides of Red Warren squash correlates with its lower firmness. Cooking resulted in an increase in the water-soluble pectins and a decrease in the pectins associated with cellulose. The total CWP content of the squash cultivars remained unchanged for up to 2 months of storage and then markedly decreased between 2 and 3 months of storage. The galactose content of Delica and Red Warren cell walls remained relatively constant from harvest to 2 months of storage and then decreased markedly during 2-3 months of storage.  相似文献   

12.
Low-temperature blanching of vegetables activates the enzyme pectin methylesterase (PME), which demethylates cell wall pectins and improves tissue firmness. This temperature activation of PME has been investigated by measuring the formation of methanol in intact tissue of green beans and tomatoes. Rates of methanol formation at temperatures of 35-65 degrees C were obtained by measuring the release of methanol from thin slices of tomato pericarp or green bean pod material. Activation energies of 112 and 97 kJ mol(-1) were calculated for PME activity in green beans and tomatoes, respectively. These activation energies indicate that the rate of pectin demethylation at 65 degrees C will be nearly 100 times that at 25 degrees C. PME activity was also determined titrimetrically using a solubilized form of the enzyme and purified pectin at temperatures from 30 to 60 degrees C. Under these conditions, much lower activation energies of 37 and 35 kJ mol(-1) were obtained for green beans and tomatoes, respectively. Methanol accumulation during heating of whole intact green beans was also determined and yielded an activation energy similar to that obtained with sliced beans. Whole green beans held at room temperature did not accumulate any methanol, but sliced or homogenized beans did. If whole beans were first heated to 45 degrees C and then cooled, methanol accumulation was observed at room temperature. These results indicate that two factors contribute to the observed high rate of pectin de-esterification during low-temperature blanching: (1) An irreversible change, causing PME to become active, occurs by heating to > or = 45 degrees C. (2) The high activation energy for pectin de-esterification means that the rate of de-esterification increases substantially with increasing temperature.  相似文献   

13.
Global structure of microwave-assisted flash-extracted sugar beet pectin   总被引：3，自引：0，他引：3  
The global structure of microwave-assisted flash-extracted pectins isolated from fresh sugar beet pulp has been studied. The objective was to minimize the disassembly and possibly the degradation of pectin molecules during extraction. These pectins have been characterized by high-performance size exclusion chromatography with light scattering, viscometric detection, and atomic force microscopy (AFM). Analysis of molecular parameters was performed on 15 and 8 microm size column packings. Samples analyzed with 15 microm packing gave weight-average molar masses that ranged from 532,000 to 1.2 million Da, radii of gyration from about 35 to 51 nm, polydispersities from 1.78 to 2.58, intrinsic viscosities from about 3.00 to 4.30 dL/g, and recoveries from 8.40 to 14.81% of dry weight. Chromatography revealed that a bimodal distribution of high molar mass spherical particles and lower molar mass coils was obtained. AFM images of pectin corroborated this conclusion and further revealed that these strands and spherical particles were integrated into networks. It is demonstrated that microwave-assisted extraction of sugar beet pulp under moderate pressure and at relatively low temperature could extract under acid conditions high molar mass, moderate-viscosity pectin in minutes rather than hours as required by conventional heating.  相似文献   

14.
Highly esterified citrus pectin was de-esterified at pH 4.5 and 8.0 by a fungal pectin methyl esterase (PME) that was shown to have an acidic isoelectric pH (pI) and an acidic pH optimum and by a plant PME that was characterized by an alkaline pI and an alkaline pH optimum. Interchain and intrachain de-esterification patterns were studied by digestion of the pectin products with endo-polygalacturonase and subsequent analysis using size exclusion and anion-exchange chromatography. No effect of pH was observed on the de-esterification mode of either of the two enzymes. Acidic, fungal PME converted pectin according to a multiple-chain mechanism, with a limited degree of multiple attack at the intrachain level, both at pH 4.5 and at pH 8.0. A multiple-attack mechanism, with a high degree of multiple attack, was more appropriate to describe the action mode of alkaline, plant PME, both at pH 4.5 and at pH 8.0.  相似文献   

15.
Yellow passion fruit (Passiflora edulis f. flavicarpa Degener) rind pectic substances were fractionated with water, ammonium oxalate, and dilute acid solutions. The extracted pectins were rich in anhydrogalacturonic acid and had a low degree of methyl esterification. Moreover, their acetyl groups and neutral sugar contents were relatively low. Furthermore, a low amount of proteinaceous material was also found within them. Their gelling ability and viscoelastic properties as evaluated by the SAG and small amplitude oscillatory shear tests, respectively, were comparable to those of a commercial citrus low-methoxyl pectin. Hence, yellow passion fruit rind occurs as a potentially good source of naturally low-methoxyl pectin.  相似文献   

16.
Measurements revealed that LiAc/HAc buffer, when compared with other solvents, gave relatively low values of turbidity for five commercial pectins with various apparent molar masses and degrees of methyl esterification (DE). Therefore, HPSEC with on-line light scattering and viscosity detection was employed to compare LiAc/HAc buffer against NaNO(3) solution, a commonly used mobile phase for measuring the molecular properties of these pectins and an additional pectin prepared by microwave extraction. Microwave-extracted pectin was included in the study for its higher molar mass and DE compared with commercial pectins. Most commercial samples were more soluble and had a higher molar mass when dissolved in NaNO(3) than in LiAc/HAc buffer, whereas the microwave-extracted pectin was more soluble in LiAc/HAc buffer and had about the same molar mass. Furthermore, association fragments of pectin contained in samples were more dissociated by LiAc/HAc buffer than by NaNO(3). For the samples studied, weight-average molar masses ranged from about 41000 to 307000, weight-average intrinsic viscosities from about 0.86 to 9.76 dL/g, z-average radii of gyration from about 13 to 45 nm, and Mark-Houwink constants from about 0.62 to 0.94.  相似文献   

17.
Two potato cultivars representing extremes with regard to the texture of the cooked product were divided into subcategories based on size and dry matter (DM) content. The effects of the preheating temperature and time on both the instrumentally determined firmness and the sensory-perceived firmness were measured and compared. Increasing the preheating time at 60 degrees C followed by cooking resulted in greater force required to fracture the tissue, an increase in perceived firmness, and a less mashable product. A principal component analysis showed that with higher DM contents of the potato samples, preheating resulted in a larger force required to fracture the tissue and a firmer product. The changes in fracture force were not linearly related with the changes in perceived firmness. The effects of preheating on the pectin methylesterase (PME) activity, the enzyme assumed to be responsible for the firming effect upon preheating, showed that the activity of this enzyme remained rather constant during preheating at 60 degrees C for 1 h. Preheating at 78 degrees C for 10 min abolished virtually all PME activity. To obtain insight into the consequences of preheating and preheating followed by steam cooking on the yield and composition of the cell wall material (CWM) of potatoes, a cell wall isolation followed by a pectin fractionation study was performed. Attention was also paid to the consequences of the processing conditions applied on the chemical composition of the CWM and the sequentially extracted pectic fractions. Preheating resulted in an increase in yield of the CWM of cooked potatoes and, as a consequence, all of the sequentially extracted fractions, including the residue. Preheating did not have a pronounced effect on the composition of the pectin of the sequentially extracted fractions. This altogether strongly indicates that preheating causes a PME-based firming effect, resulting in an decrease in pectin degradation and, as a consequence, a larger yield of CWM. It seems reasonable to assume that this increase in amount of CWM results in a firmer texture. The contribution of starch-based degradation products to the texture after preheating can, however, not be excluded.  相似文献   

18.
The effect of dietary fiber in the form of apple cell walls and pectin extracts on natural antioxidants was examined. Cell walls (CW), isolated from apples ( Malus domestica Borkh. cv. "Pacific Rose"), were incubated with ascorbic acid (AA) or quercetin in N-2-hydroxyethylpiperazine- N'-2-ethanesulfonic acid (HEPES) buffer (pH 6.5) at 37 degrees C for 2 h. The resulting supernatants were characterized by a ferric reducing antioxidant power (FRAP) assay and cyclic voltammetry (CV). The experiments were repeated with pectin isolated from the apple cell walls and commercial pectins and showed that polysaccharide preparations stabilized AA effectively but offered little protection against quercetin oxidation. The water-soluble components from cell walls appeared to be responsible for the observed effects of cell-wall polysaccharide preparations on antioxidant activity.  相似文献   

19.
微波辅助提取桔皮果胶的理化及凝胶特性比较   总被引：1，自引：1，他引：0  
为了增加桔皮利用率,提高桔皮中果胶得率和品质,以5种新鲜桔皮(丑橘、砂糖橘、芦柑、金橘、贡桔)为原料,采用微波辅助法提取桔皮中果胶,对果胶理化特性和凝胶特性进行研究。分析果胶理化及凝胶特性的相关性,并采用主成分分析法确定影响果胶凝胶特性的主要因素,优化微波辅助法提取工艺参数。结果表明:5种桔皮果胶都是高酯果胶,5种果胶理化及凝胶特性存在显著差异(P0.05),其中芦柑果胶得率和半乳糖醛酸质量分数最高,分别为12.36%、78.61%;且5种果胶理化及凝胶特性呈显著相关性(P0.05),主成分分析法确定甲氧基质量分数和果胶得率分别为主成分1和2中主要影响因子,甲氧基质量分数决定果胶种类,因此果胶种类和得率是桔皮果胶提取的主要因素。微波提取优化参数:以芦柑桔皮为原料,料液比为1:26 g/g,p H值1.30,微波功率440 W,微波时间62 s,果胶得率为16.00%。研究结果为桔皮果胶加工和应用提供理论指导。  相似文献   

20.
Commercial pectinase preparations are applied in winemaking to improve wine processing and final quality. These preparations contain pectolytic enzyme activities such as polygalacturonases, pectin esterases, pectin lyases, and rhamnogalacturonases. These enzymes modify the polysaccharide and oligosaccharide composition of wines. The influence of various commercial enzyme preparations on wine oligosaccharide composition was studied, on Merlot wines from the Bordeaux area. Wine oligosaccharides were isolated by high-resolution size-exclusion chromatography on a Superdex-30 HR column. The glycosyl residue and glycosyl linkage compositions of the oligosaccharide fractions obtained were determined. The MS spectra of the Merlot oligosaccharide fractions from control and enzyme-treated wines were recorded on an AccuTOF mass spectrometer equipped with an electrospray ionization (ESI) source and a time-of-flight (TOF) mass analyzer. Oligosaccharides in the control wines were partly methylated homogalacturonans, corresponding to smooth regions of pectins, whereas those of the enzyme-treated wines were mostly rhamnogalacturonan-like structures linked with neutral lateral chains, arising from the hairy regions. The enzyme preparations used thus cleaved the rhamnogalacturonan backbone of the hairy zones and demethylated and hydrolyzed the smooth regions. Besides, different structures were detected, depending on the enzyme preparation used, indicating that they contained rhamnogalacturonase activities with different specificities. The oligosaccharide profiles can serve as a marker of enzymatic treatments.  相似文献   

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