Texture improvement of fermented minced pepper under vacuum impregnation with pectin methylesterase and CaCl2 during fermentation

Fermented minced pepper (FMP) usually suffers from the deterioration of texture quality during fermentation, which can affect sensory and consumer acceptance. In this study, vacuum impregnation (VI) with CaCl₂, pectin methylesterase (PME) and CaCl₂ and PME (PME + CaCl₂ + VI) were compared to improve the texture quality of FMP. FMP treated with PME + CaCl₂ + VI showed the relatively intact cells structure after fermentation. In that case, its firmness maintained high level, while water-soluble pectin (WSP) content was minimum after fermentation. Meanwhile, the molar ratio of most monosaccharides of WSP in PME + CaCl₂ + VI treated FMP decreased, while rhamnose (Rha) molar ratio significantly (p < 0.05) increased after fermentation. The high Rha content represents the stability of rhamnogalacturonan-I linear skeleton of WSP. The negative effect on molecular weight of WSP was delayed by PME + CaCl₂ + VI treatment, and its peak area and value increased after fermentation. Atomic force microscope images indicated that PME + CaCl₂ + VI treatment could retain the long chain and branch structures, and inhibit the degradation of WSP net-like structure at some extent. Hence, PME + CaCl₂ + VI treatment was effective to improve the texture of FMP and inhibit the solubilisation of WSP via the formation of cross-linked pectin chains between Ca²⁺ and demethylesterified pectin.     

Quality attributes and cell wall properties of strawberries (Fragaria annanassa Duch.) under calcium chloride treatment

Effects of CaCl₂ (0%, 1% and 4%) treatment on quality attributes and cell wall pectins of strawberry fruits stored at 4 °C for 15 d were investigated. Strawberry firmness was not significantly affected by CaCl₂ treatment. Compared to the other groups, the 1% CaCl₂ group had better quality attributes, including decay rate, weight loss and soluble solids content. The treatment with 4% CaCl₂ inhibited weight loss but caused phytotoxicity. During storage, the chain widths and lengths of water-soluble pectin (WSP), chelate-soluble pectin (CSP) and sodium carbonate-soluble pectin (SSP) decreased. Strawberry softening seemed to be due to modifications of CSP and SSP, especially the side chains. CaCl₂ treatment significantly slowed the breakdown of CSP and SSP chains by strengthening the ionic crosslinkages among these pectin molecules. These results illustrate the fundamental CaCl₂ effects and will help improve the application of CaCl₂ to postharvest fruits.     

番茄果胶和半纤维素抗氧化活性分析

为了探究番茄细胞壁中不同类型果胶和半纤维素的抗氧化活性,利用水、EDTA、Na₂CO₃、4% KOH和24% KOH溶液分步提取,得到水溶性果胶(WSP)、离子结合型果胶(CSP)、共价结合型果胶(SSP)、松散结合型半纤维素(LH)和紧密结合型半纤维素(TH)五种组分,对各组分进行了氧自由基吸收能力(ORAC)、DPPH自由基(DPPH·)清除能力、ABTS自由基(ABTS+·)清除能力和铁离子还原能力(FRAP)的分析。结果表明,番茄WSP含量显著高于CSP和SSP,为1.05 mg GalUA/g FW,TH含量显著高于LH(p<0.05),为0.09 mg Glu/g FW。番茄不同类型果胶和半纤维素均具有一定的抗氧化活性。其中,CSP的ORAC、DPPH·清除能力和ABTS+·清除能力较强,综合抗氧化活性较高。在5 mg/mL时,CSP的ORAC值相当于76.4 μmol/L Trolox,DPPH·和ABTS+·的清除率分别达到61.0%和99.8%。而SSP、LH和TH具有较强的FRAP。相关性分析表明各组分与抗氧化活性密切相关。研究结果为番茄的综合加工利用和作为功能性食品添加成分的开发提供了理论根据。     

PECTIC SUBSTANCES AND FIRMNESS OF CUCUMBER PICKLES AS INFLUENCED BY CACL2, NACL AND BRINE STORAGE1

The effects of brine treatments (CaCl₂ and NaCl) and storage on pectic substances and texture of cucumber pickles were examined. Firmness of cucumber pickles was closely associated with the solubility characteristics and degree of esterification (DE) of pectic substances. Brining, storage, time of CaCl₂ addition and concentration of NaCl and CaCl₂ were all observed to influence the characteristics of pectic substances. Important to preventing softening was maintenance of pectic substances not extractable (NXP) by conventional methods, i.e., by water (WSP), the chelator sodium hex-ametaphosphate (CSP), and dilute alkali (OHSP). Erosion of NXP consistently resulted in increased levels of CSP and reduced firmness. Reducing the amount of demethylation of pectins was also associated with maintaining firmness. Although the DE declined rapidly during brining, tissues from treatments that enhanced firmness had pectic substances with the highest DE. CaCl₂ added to brine at the beginning of fermentation was most effective in preventing the demethylation of pectins and solubilization of NXP. In contrast, delayed addition of CaCl₂ and storage in low NaCl concentration (5% or less) caused greater pectin demethylation, erosion of NXP with concomitant increases in CSP and tissue softening.     

Effect of ice storage on the functional properties of pink perch and oil sardine meat

Ice storage of dressed pink perch (Nemipterus japonicus) and Indian oil sardine (Sardinella longiceps) for 16 and 20 days, respectively, resulted in a decrease in emulsifying capacity (EC), protein solubility (PS), relative viscosity (RV) of salt‐soluble proteins (SSP) and water‐soluble proteins (WSP), water binding capacity (WBC) in terms of absorbed moisture in water (AM_w), absorbed moisture in brine lpar;AM_b), retained moisture in water (RM_w) and retained moisture in brine (RM_b), WSP and SSP, and increase in cook loss (CL). Decrease in protein solubility influenced the EC, RV, CL and WBC in both the species of fish. Significant (P<0.05) correlations existed among various functional properties analysed, in both the fishes during the ice storage. © 1999 Society of Chemical Industry     

1-甲基环丙烯和不同贮藏温度对油桃果实硬度与细胞壁果胶的影响

以“中油 13 号”为试材,研究1-甲基环丙烯（1-Methylcyclopropene,1-MCP）和不同贮藏温度对油桃果实硬度与细胞壁果胶的影响。结果表明:1-MCP处理能有效地抑制常温下油桃果实硬度下降,贮藏第2 d,1-MCP处理组与未经1-MCP处理组油桃硬度分别下降12.31%和54.53%,差异极显著（P<0.01）,但贮藏后期抑制效果减弱,差异不显著（P>0.05）;而结合低温贮藏效果更好,贮藏至结束,1-MCP处理组与未经1-MCP处理组油桃硬度分别下降54.38%和62.96%,差异显著（P<0.05）。1-MCP主要通过影响油桃WSP半乳糖醛酸主链和阿拉伯糖支链的积累、CSP与SSP阿拉伯糖支链与半乳糖支链的分解,抑制油桃水溶性果胶（Water-soluble pectin,WSP）含量的升高与螯合性果胶（Chelate-soluble pectin,CSP）和碱溶性果胶（Sodium carbonate-soluble pectin,SSP）含量的降低,延缓油桃软化;低温主要通过抑制SSP阿拉伯糖支链与半乳糖支链的分解,减缓SSP含量降低,延缓油桃软化。油桃质地软化与果胶多糖的含量及主侧链变化密切相关,1-MCP处理和低温能有效地抑制贮藏期油桃硬度下降。     

Changes in firmness,cell wall composition and cell wall hydrolases of grapes stored in high oxygen atmospheres

To investigate the effects of high oxygen (O₂) atmospheres on the firmness of ‘Kyoho’ grapes (Vitis vinifera L. X V. labrusca L.), changes in cell wall constituents and hydrolase activities were examined during 60 days of controlled atmosphere storage in air (control), 40% O₂ + 30% CO₂ or 80% O₂ (high O₂) at 0 °C and 95% relative humidity. Grapes stored in high O₂ retained greater firmness than grapes stored in air. The cell wall contents of high O₂-stored fruits contained less water-soluble pectin (WSP), more Na₂CO₃ soluble pectin (SSP) and higher hemicelluloses than air-stored fruits. The levels of cellulose and CDTA-soluble pectin (CSP) did not significantly change. The effects of high O₂ on enzyme activity were dramatic for polygalacturonase and β-galactosidase, moderate for cellulase, and very low for pectinesterase. No pectate lyase was detected. Taken together, WSP, SSP and hemicelluloses appeared to have major structural roles in retaining the firmness and preventing the deterioration of fruits kept in high O₂.     

Effect of debranching on the rheological properties of Ca-pectin gels

Water-soluble pectin (WSP) extract was subjected to controlled carrot pectin methylesterase treatment, thereby producing de-esterified pectin (DEP). Both WSP and DEP were incubated with a mixture of endo-arabinanase and α-L-arabinofuranosidase to yield partially debranched pectins (WSP_DBr and DEP_DBr respectively). Pectin samples were characterised in terms of degree of methylesterification (DM), neutral sugar content, and degree of branching (DBr). The characterised pectins were used for the preparation of pectin gels with high and low calcium ion (Ca²⁺) concentrations. The rheological characteristics of the produced gels were evaluated by means of small-amplitude oscillatory tests. These characteristics include network development of the gel, gel strength (G′), gel elastic character and gel type. Partial debranching of pectin resulted in a reduction of the arabinose content (by approximately 50%) and caused a slight decrease in polymer DBr. Gels produced from semi-dilute solutions of partially debranched pectins showed network development profiles similar to those prepared from semi-dilute solutions of the corresponding non-debranched polymers. Yet, the former gels showed lower G′ values, poor gel elastic character and a “weaker” nature as compared to the latter. Next to Ca²⁺ cross-links, the presence of long arabinose-containing side chains is suggested to play an important role in the rheological characteristics of Ca²⁺-pectin gels.     

Structural Characteristics of Pumpkin Pectin Extracted by Microwave Heating

Abstract: To improve extraction yield of pumpkin pectin, microwave heating was adopted in this study. Using hot acid extraction, pumpkin pectin yield decreased from 5.7% to 1.0% as pH increased from pH 1.0 to 2.0. At pH 2.5, no pectin was recovered from pumpkin flesh powder. After a pretreatment at pH 1.0 and 25 °C for 1 h, pumpkin powder was microwave‐extracted at 120 °C for 3 min resulting in 10.5% of pectin yield. However, premicrowave treatment at 60 °C for 20 min did not improve extraction yield. When microwave heating at 80 °C for 10 min was applied after premicrowave treatment, final pectin yield increased to 11.3%. When pH was adjusted to 2.0, the yield dropped to 7.7% under the same extraction conditions. Molecular shape and properties as well as chemical composition of pumpkin pectin were significantly affected depending on extraction methods. Galacturonic acid content (51% to 58%) of pumpkin pectin was lower than that detected in commercial acid‐extracted citrus pectin, while higher content of neutral sugars and acetyl esters existed in pumpkin pectin structure. Molecular weight (M_w) and intrinsic viscosity (η_w) determined for microwave‐extracted pumpkin pectins were substantially lower than acid‐extracted pectin, whereas polydispersity was greater. However, microwave‐extracted pectin at pH 2.0 had more than 5 times greater M_w than did the pectin extracted at pH 1.0. The η_w of microwave‐extracted pectin produced at pH 2.0 was almost twice that of other microwave‐extracted pectins, which were comparable to that of acid‐extracted pectin. These results indicate that extraction yield of pumpkin pectin would be improved by microwave extraction and different pectin structure and properties can be obtained compared to acid extraction. Practical Application: Pumpkin is a promising alternative source for pectin material. Pumpkin pectin has a unique chemical structure and physical properties, presumably providing different functional properties compared to conventional commercial pectin sources. Depending on the conditions to produce pumpkin pectin, diverse molecular structures can be obtained and utilized in various food applications.     

Untersuchungen an Polysaccharid-, Pektin- und Ballaststoff-Fraktionen von Sanddornbeeren

The alcohol-insoluble substance (AIS) was prepared from freshly picked buckthornton berries (Hippophae rhamnoides L.) (4.70% of the fresh substance). By sequential extraction with water, ammonium oxalate, 0.05 N HC1 and 0.05 N NaOH, the following quantities of galacturonan/ 100 g AIS were obtained: 0.15 g, 0.4 g (ca.), 0.94 g, 2.29 g resp. These pectin extracts were purified as Cu²⁺ salts. After dialysis they were fractionated into a water-soluble and a water-insoluble part. In these fractions Glc, Gal and Xyl were the predominant neutral saccharide units. Ara, Rha and Man were present in smaller amounts. A higher GalA content (in g per 100 original AIS) was found in the soluble fractions (with the exception of the alkali extract). The pectins from buckthornton berries are middle-esterified and partially acetylated. The composition of the AIS was determined as 9.25% pectin, 34.8% protein and 38.9% total polysaccharides. In the residue after sequential pectin extraction (RE), which contained 60.0% of the AIS, 3.89% pectin, 12.9% protein and 28.0% total polysaccharides were found. By the enzymatic method the percentages of soluble and insoluble dietary fiber were estimated as 13.6 % and 34.1% respectively, whereas the RE contained 5.1% soluble and 34.4% insoluble fiber. The following dietary fiber fractions were determined by the detergent method for both preparations: in case of AIS 36.2% NDF, 3.0% NDF filtrate, 28.0% ADF and 9.6% lignin were found to be present, whilst in the RE, the following components were estimated: 32.8% NDF, 1.4% NDF filtrate, 26.1% ADF and 10.1% lignin. The data presented relates to 100 g original AIS. The water binding capacity was observed to decrease from 7.50 g H₂O (AIS) to 4.26 g H₂O (RE) per 1 g original AIS. For both of these preparations, more than 40 % of bound water was found in the NDF fractions and approximately 30% in the ADF fractions.

     

Manipulate and stretch single pectin molecules with modified molecular combing and fluid fixation techniques

Manipulating and stretching single pectin molecules offer convenience to determine the chain lengths and further illustrate the action between pectins and other macromolecules. Pectin molecules on mica surfaces, which were imaged in air with atomic force microscopy (AFM), can be aligned and stretched through applying modified molecular combing and fluid fixation techniques. Modified molecular combing showed more effective and powerful for manipulation than fluid fixation. Chelate-soluble pectin (CSP) can be straightened into line to one direction by molecular combing while sodium carbonate-soluble pectin (SSP) shows ‘V’ structures. The differences may be the result of the different parts of the pectins which touched the mica surface firstly during the dropping, and the lengths of the chains. CSP was relatively long and initially touched the mica with the end point while SSP was short and touched the mica firstly with its middle part.The same contribution to the first author.     

Non-enzymatic Depolymerization of Carrot Pectin: Toward a Better Understanding of Carrot Texture During Thermal Processing

ABSTRACT Pretreated carrot discs were thermally processed (90 °C to 110 °C) in closed containers and the resulting textural characteristics were analyzed. The pretreatment conditions used include conventional high‐temperature blanching (90 °C, 4 min), low‐temperature blanching (LTB = 60 °C, 40 min), LTB combined with 0.5% calcium chloride soaking, LTB combined with 2% sodium chloride soaking, high pressure pretreatment (HP = 400 MPa, 60 °C, 15 min), HP combined with 0.5% calcium chloride soaking, and control (non‐pretreated sample). Alcohol insoluble residues (AIR) from the pretreated carrot discs were characterized in terms of degree of methoxylation (DM). The AIR samples were further subjected to fractionation into water‐soluble pectin (WSP), chelator‐soluble pectin (CSP), and sodium carbonate‐soluble pectin (NSP). Heat depolymerization patterns and β‐elimination kinetics were investigated on the different pectin fractions. Thermal texture degradation was strongly influenced by the pretreatment condition used and the processing temperature during subsequent thermal treatment. Pretreatment conditions that showed a significant reduction in DM exhibited decreased WSP content, reduced β‐elimination, and consequently superior textural characteristics. β‐elimination was markedly pronounced in the highly methoxylated WSP fractions. CSP and NSP fractions were insensitive to β‐elimination. A strong correlation (r> 0.95) between thermal texture loss of carrots and β‐elimination kinetics exists. Overall, the benefits of controlled pectinmethylesterase activity in carrot processing were pointed out.     

Effect of high pressure/high temperature processing on cell wall pectic substances in relation to firmness of carrot tissue

Thermal processing for food preservation results in undesired softening of fruits and vegetables. To explore the potential of high pressure sterilization in food processing, the effects of combined high pressure/high temperature (HP/HT) treatments on carrot pectic polysaccharides and the related textural properties were investigated and compared with that of samples thermally processed at atmospheric pressure. Disks of fresh carrot (Daucus carota var. Yukon) tissue were subjected to three different treatments (80 °C–0.1 MPa, 100 °C–0.1 MPa and 80 °C–600 MPa) for varying time intervals. Subsequently, the residual texture and microstructural changes of the carrots were evaluated. Alcohol-insoluble residues were prepared from the samples and sequentially fractionated with water, cyclohexane-trans-1,2-diamine tetra-acetic acid (CDTA) and Na₂CO₃ solutions. Thermal treatments at 0.1 MPa caused extensive tissue softening. This was marked by increased cell separation, an increase in water soluble pectin (WSP) paralleled by a decrease in chelator (CSP) and sodium carbonate (NSP) soluble pectin. HP/HT treated carrots showed minimal softening and negligible changes in intercellular adhesion. This was accompanied by a significant reduction in the degree of methyl esterification of pectin, low WSP in contrast to the high CSP and NSP fractions, minor changes in the different pectin fractions during treatment, and a substantial amount of pectin in the fractionation residue. There was a clear difference between HP/HT and thermally processed carrot pectin; HP/HT showing pronounced texture preservation.     

Structural Characterization and Antifatigue Effect In Vivo of Maca (Lepidium meyenii Walp) Polysaccharide

Maca (Lepidium meyenii Walp) polysaccharides (MP) with purity of 99.2% were obtained to investigate their structural characteristics and antifatigue effect in vivo. The physicochemical properties of MP were analyzed through high‐performance gel filtration chromatography, IR, monosaccharide composition, methylation, GC‐MS, and NMR analyses. The antifatigue effect of MP was evaluated by using a mouse weight‐loaded swimming model. MP is an acidic heteropolysaccharide with an average molecular weight (M_w) of 793.5 kDa. It is composed of D‐GalA: D‐Glc: L‐Ara: D‐Man: D‐Gal: L‐Rha = 35.07:29.98:16.98:13.01:4.21:0.75 (mol, %). The findings revealed that MP contained β‐1,3‐Galp(A), β‐1,3‐Glcp, and α‐1, 3‐Manp linked alternatingly to form a backbone (5:4:1). MP (above mid‐dosage 50 mg/kg bw/d) could effectively elongate swimming durations and accelerate average swimming speeds (within the 1st 5 min) of mice (P < 0.05) and improve the serous biochemical parameters of mice. Compared with the control model, high‐dosage (100 mg/kg bw/d) MP treatment could significantly enhance glutathione peroxidase and creatine kinase activities (P < 0.05) and decreased lactate dehydrogenase activity (P < 0.01). High‐dosage MP could significantly reduce the levels of blood urea nitrogen, lactic acid, and malondialdehyde (P < 0.05). MP is an acidic polysaccharide with a high D‐GalA content, which could be responsible for the antifatigue effect of maca.     

Sustainable production of pectin from lime peel by high hydrostatic pressure treatment

The application of high hydrostatic pressure technology for enzymatic extraction of pectin was evaluated. Cellulase and xylanase under five different combinations (cellulase/xylanase: 50/0, 50/25, 50/50, 25/50, and 0/50 U/g lime peel) at ambient pressure, 100 and 200 MPa were used to extract pectin from dried lime peel. Extraction yield, galacturonic acid (GalA) content, average molecular weight (M_w,ave), intrinsic viscosity [η]_w, and degree of esterification (DE) were compared to those parameters obtained for pectins extracted using acid and aqueous processes. Pressure level, type and concentration of enzyme significantly (p < 0.05) influenced yield and DE of pectin. Enzyme and high pressure extraction resulted in yields which were significantly (p < 0.05) higher than those using acid and aqueous extraction. Although pressure-induced enzymatic treatment improves pectin yield, it does not have any significant effect on M_w,ave and [η]_w of pectin extracts indicating the potential of high pressure treatment for enzymatic pectin production as a novel and sustainable process.     

Influence of pectin structure on texture of pectin–calcium gels

A library of pectins with varying degree and pattern of methoxylation was produced by demethoxylating a parent pectin by use of NaOH or pectinmethylesterase from plant or fungal origin. Additionally, pectin was chemically depolymerised by a heat treatment. The resulting pectins were characterised in terms of degree and pattern of methoxylation (“(absolute) degree of blockiness”) and the extent of depolymerisation. Pectin–calcium gels were prepared and their texture was studied by performing compression tests. From the resulting force vs. distance curves, the modulus of elasticity under low strain and the fracture stress and strain were determined. The modulus of elasticity under low strain increased with decreasing degree of methoxylation. At very low degree of methoxylation, gels were brittle, resulting in low fracture stress. Both modulus of elasticity and fracture stress correlated more with degree of blockiness and absolute degree of blockiness as compared to degree of methoxylation. Gel strength increased with increasing Ca²⁺ or pectin concentration. Depolymerisation of pectin resulted in formation of brittle gels.Industrial relevancePectin with low degree of methoxylation can form a gel in presence of calcium. Therefore, it is widely used in the food industry. In addition, pectin-calcium interactions are of importance for the texture of fruits and vegetables, since crosslinked pectin in the cell wall provides cell-cell adhesion and mechanical strength of tissues. This research is focused on textural characteristics of pectin-calcium gels. It is shown that pectin structural properties influence texture of gels. As a result, control of pectin structure allows fine-tuning of functional properties.     

Pectin Extraction from Lemon By-Product with Acidified Date Juice: Effect of Extraction Conditions on Chemical Composition of Pectins

Mixtures of date and lemon pectins were extracted from lemon by-product with acidified date juice under different conditions of temperature, pH and time. Individual pectins from date and lemon, respectively, were also extracted using the same experimental conditions, then analysed and compared to pectin mixtures. It was found that the use of extreme conditions resulted in higher galacturonic acid content, lower degree of methylation, lower neutral sugar content, lower molecular weight and darker colour pectins. Examination of the individual neutral sugars showed that the main ones were galactose (1.6–5.4%), arabinose (1.6–4.2%) and rhamnose (0.5–0.8%). The Gal A/Rha molar ratios varied from ∼53 to ∼149. Moreover, mixture of pectin extracted at the optimal extraction conditions (84.34 °C, pH 2.8 during 3 h 34 min) had interesting properties, with a high galacturonic acid content (63.4%), low degree of methylation (∼35%) and a mass molecular weight of about 243 kg/mol.     

Firmness and Cell Wall Characteristics of Pasteurized Jalapeño Pepper Rings as Affected by Preheating and Storage

Changes in cell wall pectic substances, degree of pectin methylation, bound calcium and firmness were determined in preheated and nonpreheated fresh pack jalapeño pepper rings stored for 5 mo. Pepper rings preheated for 60 min at 50°C in a brine solution (8% NaCl and 0.2% CaCl₂, were firmer, had more nonextrctable pectins (NXP), more bound calcium, less water-soluble and chelator-soluble pectins (CSP), and less pectin methylation than nonpreheated pepper rings. The greater formation and maintenance of nonextractable pectins, which resisted acid hydrolysis during pasteurization and storage is probably an important factor in firming.     

Physicochemical and molecular analysis of cell wall metabolism between two navel oranges (Citrus sinensis) with different mastication traits

BACKGROUND: FJ72‐1 navel orange and its bud mutant FJWC exhibit differences in melting texture character which are influenced mostly by cell wall metabolism. Here we compared the contents of water soluble pectin (WSP), protopectin, total pectin (TP), cellulose, and hemicellulose, activities of polygalaturonase (PG), pectin methylesterase (PME), pectate lyases (PL), cellulase (Cel) and gene expression levels of PG, PME, PL and Cel between the two cultivars. RESULTS: The content of cellulose and hemicellulose decreased progressively during fruit ripening. At the harvest time (230 DAF), the content of cellulose and hemicellulose in FJWC were obviously higher than those in FJ72‐1; the WSP content, PG activities and its gene expression level in FJWC was lower than those in FJ72‐1. Moreover, gene expression levels of PME and Cel in FJWC were only one‐quarter of those in FJ72‐1 at 230 DAF. CONCLUSION: The present work showed that the inferior melting character of FJWC attributed to the lower WSP, higher TP or protopectins, higher cellulose and hemicellulose than those in the pulp of FJ72‐1 at harvest time. Lower expression levels of PG, PME and Cel at harvest time might be associated with the inferior melting character. Copyright © 2010 Society of Chemical Industry     

真空微波干燥过程中 南瓜果胶性质变化与质构的关系

为了明确真空微波干燥过程中脱水果蔬果胶性质变化对质构的影响,实验以南瓜为原料,采用不同微波强度进行处理,分析脱水南瓜硬脆度和微观结构,以及果胶含量、酯化度和单糖组成等性质的变化之间的关系。结果表明:微波强度为9 W/g时,南瓜获得较大的脆度和适中的硬度,孔状结构均匀。随着微波强度的升高,南瓜水溶性果胶(WSP)含量先减少后增加,螯合性果胶(CSP)含量先增加后减少。微波处理后南瓜果胶分子链断裂,分子量减小。随微波强度的升高,南瓜中不饱和半乳糖醛酸(UG)含量、果胶酯化度呈现先升高后降低的趋势,微波强度为9 W/g时,UG含量较高,达到10.54 mg/g。综合分析,真空微波干燥过程中UG含量是影响南瓜硬度的主要因素之一,酯化度和WSP含量影响其脆度和多孔结构的形成。