Galacturonic Acid Content Research Articles

Effects of supplementation of sea buckthorn press cake on mycelium growth and polysaccharides of Inonotus obliquus in submerged cultivation.

Investigation of the influence of cultivation time and sea buckthorn press cake (Hippophaë rhamnoides) dosage on mycelium yield of Inonotus obliquus in submerged cultivation and on the yield, monomer composition, and macromolecular properties of the exopolysaccharides (EPS) from culture media and intracellular polysaccharides (IPS) extracted from mycelia. Supplementation at 5gl-1 combined with cultivation time of 250h granted highest yield increase in mycelia (by 122%). The supplementation reduced extraction yield and decreased the molecular weight of the main IPS population. The supplementation increased production and molecular weight of EPS. The relative content of arabinose and rhamnose in EPS positively correlated with dosage of the press cake. The press cake supplementation increased the content of galacturonic acid in IPS, but not in EPS. Sea buckthorn press cake is a food industry fibrous side stream with high oil content. It increases the cultivation yield of Inonotus obliquus mycelium and influences the produced polysaccharides. Mycelium is a resource of bioactive polysaccharides, attracting the interest of nutraceutical companies. Sea buckthorn press cake is a promising supplement for increasing mycelium production. The utilization of this agricultural side stream would therefore favour circular economy.

Semi-Pilot scale extraction of pectin from orange peel waste and evaluating its quantitative and qualitative features

Background and objective: Pectin as a natural polysaccharide possesses a wide spectrum of functional properties. It can act as a thickener, gelling agent, stabilizer, emulsifier, cation-binding agent, etc. These properties make pectin as a biopolymer valuable especially for medicine and food production. All of the pectin needed in food, medicine and cosmetic industries is supplied abroad while there is a good potential for production of this valuable substance from waste of beverage industries. In addition, the production of the pectin is simple and low cost and its added value is high. Pectin production was done only in laboratory scale and has not been industrialized. Therefore, the aim of this research was to optimize the pectin extraction from orange juice waste in the laboratory scale and then, scaling up to semi- pilot extraction. Designing and constructing the production line of Semi-pilot scale extraction of pectin from orange peel was done for the first time in Iran, to can finally, evaluate the possibility of industrialization and localization of the pectin. Materials and methods: In the first, the effect of pH (1.5-3), time of extraction (1-4 h) and S/L ratio (1:10- 1:30 g/mL) were optimized singularly and then, semi-pilot production of pectin at the optimized condition, which was obtained at the laboratory scale, was done. Two filtration methods (filter press and centrifuge) were used to to separate impurities. The yield, DE and galacturonic acid content of the extracted pectins in the semi- pilot scale were compared to the laboratory one. Results: The results indicated that all the parameters had significant effect (p≤0.05) on the yield of the extracted pectin. Increasing the pH from 1.5 to 2 increased the yield and the highest yield was obtained at pH of 2 (14.87 g/100 g d.m.) and by increasing pH from 2 to 3, the yield was decreased (6.65 g/100 g d.m). Increasing the time of extraction up to 3 h, enhaned the yield significantly but then, it was remain constant. By increasing the S/L ratio from 1:10 to 1:15, the yield was increased from 16.55 to 18.84 g/100 g d.m. and after that the yield was decreased. Designing the pectin production line was done and semi- pilot extraction was done at the optimized conditions (pH of 2, S/L ratio of 1:15 and time of 3 h). The yield of extracted pectin in the semi- pilot scale (which filter press employed instead of centrifuge) was more than that obtained at the laboratory scale althogh its galacturonic acid content was lower than that obtained at semi- pilot scale. When centrifuge was employed, the extracted pectin at the semi- pilot scale was comparable with laboratory one, indicating its high purity. Conclusion: Results indicated that the yield and quality properties of the pectin extracted at the semi-pilot extraction, which centrifuge was employed (instead of filter press), were similar to the pectin extracted at the laboratory scale and therefore, producting the pectin with high yield and quality at the semi-pilot scale is possible.

Bench scale batch steam explosion of Florida red and white grapefruit juice processing residues

Florida juice processors amassed 51,000 metric tons of grapefruit juice processing residues (GFPR) in the 2018-19 season. GFPR contain valuable compounds such as pectic hydrocolloids, peel oil, sugars, phenolics and flavonoids that are ultimately lost or destroyed when they are converted to low value animal feed and molasses. If these compounds could be isolated from GFPR rather than destroyed, they could be converted to high value products. In this work, red and white GFPR were subjected to steam explosion in a batch system at 130, 150 and 170°C and 1, 2, 4 and 8 min holding time to identify the conditions for maximum recovery of pectic hydrocolloids, peel oil, sugars, phenolics and flavonoids. Steam explosion at 170°C and an 8 min hold time resulted in the recovery of 56-85% of total available glucose and fructose and the volatilization of 68-98% of the available peel oil. Of the phenolics and flavonoids analyzed, 61-62% could be extracted using steam explosion. Maximum recovery of pectic hydrocolloids, estimated by galacturonic acid content, was 1.6446 g • 100 g−1 for red GFPR at 130°C – 8 min and 1.557 g • 100 g−1 for white GFPR at 150°C – 2 min.

Characterization of tissue‐specific differences in cell wall pectic polysaccharides of carrot root

This study investigated the physicochemical characteristics of CWPs from epidermis, cortex, and stele of carrot. The CWPs extracted from cortex contained the highest content of galacturonic acid (GalA), as well as the highest degree of methylation. Compared to Na2CO3 extractable fraction (NEF) and water extractable fraction (WEF), chelator extractable fraction (CEF) contained higher GalA content, and it was identified with more linear homogalacturonan (HG). The highest amounts of Gal, Ara, and Rha were obtained in NEF extracted from cortex, suggesting that abundant side chains attached to pectic backbone of NEF and formed “hairy region.” In addition, gentle changes of the molar mass along with tissue zones were observed in different pectic fractions. However, the molar mass of NEF was always higher than WEF regardless of the tissues. According to FTIR, the configurations of all CWPs were similar and exhibited typical structural properties of pectic polymers. Practical applications Cell wall pectic polysaccharides (CWPs) are important macromolecules which highly correlated with food products qualities. The CWPs extracted from epidermis, cortex, and stele of carrot root were prepared and their physicochemical characteristics were evaluated. Detailed characteristics of tissue-specific differences in CWPs of carrot root could provide more fundamental information for carrot-related food processing.

Effects of pH and temperature on the structure, rheological and gel-forming properties of sugar beet pectins

Sugar beet pectin (SBP) was modified by alkaline at both 25 °C and 3 °C to produce gel-type pectins. The structure, rheological and gelation properties of series modified SBPs were then assessed. The results showed that low temperature effectively inhibited the β-elimination of SBP during alkali treatment, and the average molecular weight (Mw) and galacturonic acid (GalA) content of the resulting SBP were much higher than that of the alkali-treated SBP at 25 °C. Due to the low degree of methylation (DM) (≦ 21.2) and degree of acetylation (DA) (≦ 14.6), SBP treated under pH 11 and 12 at 3 °C could successfully form stable elastic gels, and these gels were further confirmed to be frequency-independent through rheological analysis. The SEM and TG/DTG results showed that the corresponding gel of SBP treated under pH 12 at 3 °C for 120 min had the most uniform micro-network structure and the best thermal stability. This work for the first time demonstrated the effect of a wide pH range on the chemical structure, rheological and physical gelation properties of SBP, especially under alkaline conditions at a low temperature (3 °C). Findings from this work suggest that alkali treatment at low-temperature allows SBP to have the potential to become a gel-type commercial pectin.

Effects of different extraction methods on structural and physicochemical properties of pectins from finger citron pomace

The functionality and property of pectin are correlated with its structure which is affected by the extraction method used. In this study, three different methods of extracting pectin, the microwave-assisted extraction (MAE), the ultrasonic-assisted extraction (UAE) and the conventional heating extraction (CHE), were used at three different temperatures with both an acid and alkali extraction solution. It was found that temperature mainly influenced pectin yield, while pectin structures and physicochemical properties were affected by the pH condition and extraction technology. The alkali-extraction with MAE and UAE at short time promoted the yield of low-ester pectin. Monosaccharide composition analysis showed a high galacturonic acid (GalA) content in the pectin derived from MAE and UAE. The high viscosity and desirable viscoelastic properties of the acid-MAE pectin were due to its large molecular weight and particle size. The results contribute to our understanding of the association among pectin extraction, structure and properties.

Composition, Physicochemical Features, and Covalent Gelling Properties of Ferulated Pectin Extracted from Three Sugar Beet (Beta vulgaris L.) Cultivars Grown under Desertic Conditions

Sugar beet is a potential source of pectin, competitive with traditional sources, that has recently acquired great relevance for its interesting covalent gelling and applications in food and biomedical industries. Pectins from three Sugar beet (Beta vulgaris L.) commercial cultivars (Cadet, Coronado large, and SV MEI) were grown under irrigated desertic conditions and the influence of cultivar, on pectin yield, composition, physicochemical and gelling characteristics was investigated. The composition and chemical properties of pectin from the three cultivars were in general, statistically different, especially in the Syngenta Cadet cultivar, presenting higher protein (10.3%), neutral sugars (21.6%), galacturonic acid (55%) and ferulic acid (5.5 mg/g) content, which are important parameters for gel formation. All pectins gelled via oxidative coupling and the main ferulic acid dimers found were 8-5′ and 8-O-4′. Pectin from Cadet cultivar formed gels with higher hardness (6.65 N) and adhesiveness (12.2 N) values than the other two varieties. The results indicate that pectin composition is affected by the sugar beet cultivars reported herein, especially in ferulic acid content, which confer the covalent gelling capability. Sugar beet cultivars grown under desert conditions could be a source of gelling ferulated pectins for the food industry, as valuable as those obtained in temperate conditions.

Valorization of unripe papaya for pectin recovery by conventional extraction and compressed fluids

The aim of the study was to establish a green protocol for pectin extraction from unripe papaya flour (UPF), comparing conventional acid hydrolysis (CONV) and compressed fluid extraction techniques, including Pressurized Hot Water Extraction (PHWE) and Enhanced Solvent Extraction (ESE). Highest pectin yields were achieved with ESE (216 ± 10.8 mg g−1) when CO2+H2O (20:80) + citric acid (0.05 mol L−1) was applied (40 MPa/80 °C/60 min/300–710 µm), similar to that obtained by CONV (202 ± 49.5 mg g−1) and PHWE (208.0 ± 9.4 mg g−1) using oxalic acid. UPF pectin presented an average galacturonic acid (GalA) content of 73% (w/w) and degree of esterification (DE) of 57.8%, and it was composed predominantly of galactose, glucose and rhamnose. This pectic substance has been shown to contain two main types of pectic chains: rhamnogalacturonan-I (RG-I, average 58%) proportionally higher than homogalacturonan (HG, average 28%). Compressed fluid extraction techniques allowed obtaining high quality pectin with similar composition to other commercial products.

Maintaining the firmness of minimally processed papaya using pectin methylesterase and calcium lactate

The objective of this work was to evaluate the effect of vacuum infusion of pectin methylesterase (PME) and calcium lactate (C6H10CaO6) in maintaining the firmness of minimally processed papaya, in order to maintain the quality and cellular integrity of the fruit. After minimal processing, the treatments used were: fruit without infusion (control), with H2O infusion, with PME infusion, with C6H10CaO6 infusion and with PME+C6H10CaO6 infusion. At zero times, four and eight days of storage, analyzes of total galacturonic acid, methanol, cell integrity, vitamin C, pH, acidity, soluble solids, damage, freshness and contamination were performed. Papaya treated with the PME+calcium combination showed an increase in firmness (5.8 N) on the eighth day of storage, differing from the control treatment (1.3 N), reporting the least leakage of electrolytes. On the fourth day, the fruit treated with PME+C6H10CaO6 showed the highest content of galacturonic acid and on the eighth day the highest content of methanol, indicating an effective action of the enzyme PME and calcium in this period. The PME+C6H10CaO6 treatment was effective in maintaining and improving the quality of papaya while preserving freshness, soluble solids content, acidity and pH throughout storage.

Extraction and characterization of high methoxyl pectin from Citrus maxima peels using different organic acids

The objective of this study was to determine the effects of citric acid, acetic acid and lactic acid on extraction yield, chemical structure and antioxidant capacities of high methoxyl pectins extracted from peels of different pomelo varieties. The pectins were extracted by mixing freeze-dried pomelo peels with organic acids (pH 3.0) at a ratio of 1:30 (w/v). The results indicate that extraction yields of pectin extracted using citric acid was the highest (6.5–9.0%), followed by that using acetic acid (6.2–8.2%) and lactic acid (6.1–8.0%). All extracted pectins were categorized as high methoxyl pectins with degrees of esterification of 51.1–62.7%. Galacturonic acid content of the extracted pectin using citric acid (76.5–85.0%) was significantly higher than that using acetic acid (65.1–68.2%) and lactic acid (60.4–65.8%). The antioxidant capacity of the pectins using citric acid and lactic acid was significantly higher than that using acetic acid. FT-IR results show that structures of the extracted pectins from peels of different pomelo varieties were different. As a result, the pure high methoxyl pectin could be produced from pomelo peel by-products under organic solvent extraction, a potential "green" extraction technique.

Effects of ultrasound modification at different frequency modes on physicochemical, structural, functional, and biological properties of citrus pectin

Ultrasonic irradiation for modified pectin preparation has become a research hotspot, but the influence of ultrasonic frequency is rarely studied. Therefore, in this study, mono frequency (MFU) and simultaneous dual frequency (SDFU) ultrasounds were used to modify citrus pectin (CP), and the effects of different ultrasonic frequency modes on the physicochemical, structural, functional, and biological properties of CP were comparatively investigated. The results showed that ultrasonic irradiation at 40 kHz in the MFU mode led to a larger increment in the galacturonic acid content of CP, but greater reductions in its intrinsic viscosity, molecular weight, and degree of methoxylation than in the SDFU modes. Ultrasonic frequency had no significant influence on the main CP chain, but rather on its neutral sugar side chains. The scanning electron microscopy (SEM) results suggested that CP treated by ultrasound at 40 kHz in the MFU mode exhibited fewer aggregates or looser networks than other ultrasonic treatments. Compared with the original CP, ultrasound treatment at different frequency modes effectively enhanced the thermal stability of CP, but remarkably lowered its shear thinning fluid behavior and liquid-like property. Moreover, among ultrasonically treated CPs, the CP obtained through ultrasound at 40 kHz in MFU mode exhibited the best antioxidant activity and bile acid-binding capacity in vitro.

Environmentally Friendly Hydrothermal Processing of Melon by-Products for the Recovery of Bioactive Pectic-Oligosaccharides.

Melon by-products, that currently lack high value-added applications, could be a sustainable source of bioactive compounds such as polysaccharides and antioxidants. In this work, melon peels were extracted with water to remove free sugars, and the water-insoluble solids (WISs) were subjected to hydrothermal processing. The effect of temperature on the composition of the obtained liquors and their total phenolic content was evaluated. The selected liquors were also characterized by matrix assisted laser desorption/ionization-time of flight mass spectroscopy (MALDI-TOF MS), fourier transform infrared spectroscopy (FTIR) and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC–PAD), and its phenolic compounds were identified and quantified by high-performance liquid chromatography-diode array detector-tandem mass spectrometry (HPLC–DAD–MS/MS). In addition, the spent solids from the hydrothermal treatment were characterized and their potential use was assessed. At the optimal conditions of 140 °C (severity 2.03), the total oligosaccharide yield accounted for 15.24 g/100 g WIS, of which 10.07 g/100 g WIS were oligogalacturonides. The structural characterization confirmed the presence of partially methyl esterified oligogalacturonides with a wide range of polymerization degrees. After precipitation, 16.59 g/100 g WIS of pectin were recovered, with a galacturonic acid content of 55.41% and high linearity.

Pectin from sunflower by-product: Optimization of ultrasound-assisted extraction, characterization, and functional analysis

In the current study, sunflower by-product pectin (SFBP) was obtained using ultrasound-assisted extraction (UAE) technique. The UAE variables were successfully optimized, and the optimal condition (irradiation time 30 min, temperature 33 °C and ultrasound power 400 W) yielded 11.15%. Under this condition, SFBP was rich in low-esterified galacturonic acid content (72.94%), and had long side branches of galactan, arabinogalactan, and arabinan, with an average molecular weight of 175.353 kDa. The structural properties were characterized using FTIR, NMR, XRD spectroscopies. The thermal analysis by DSC and TGA suggested suitable thermal stability for SFBP. The solubility, water and oil holding capacities, emulsifying capacity, emulsifying stability (vs various conditions), foam capacity, foam stability, DPPH and ABTS inhibitions, and reducing power assay were measured to evaluate the potential of SFBP to be considered as a food ingredient.

Valorization of exhausted olive pomace for the production of omega-3 fatty acids by Crypthecodinium cohnii

Exhausted olive pomace (EOP) represents a potential candidate side stream to be utilized in biotechnological processes. EOP composition includes significant amounts of extractives and pectin, which are both usually discarded and are not utilized in the valorization process of the raw material. In this study, organosolv technology was optimized to remove the extractives and pectin using a Central Composite Rotatable Design. Optimal pretreatment conditions were predicted to be at 97.95 °C for 23.18 min, upon addition of 50% (v/v) EtOH in H2O, with 0.5% (w/v) of H2SO4 as catalyst. The composition analysis of liquid fraction revealed a high content of total sugars (17.58 g/L), galacturonic acid (7.05 g/L) and phenolic compounds (2.97 g/L). The liquid fraction was utilized as a carbon source by the heterotrophic marine microalgae Crypthecodinium cohnii, where it was shown to promote lipid accumulation up to 38.5% wt. of cell biomass, even without any additional detoxification step. This study is the first report that shows the use of galacturonic acid as carbon source for the growth of C. cohnii, while underpinning the use of EOP as a promising substrate for the development of zero-waste bioprocesses.

The Effect of Cultivation Method of Strawberry (Fragaria x ananassa Duch.) cv. Honeoye on Structure and Degradation Dynamics of Pectin during Cold Storage.

The high quality and long shelf life of strawberry fruit are largely dependent on the cultivation method. The goal of this experiment was to study the effect of different cultivation methods on molecular structure and rheological properties of pectin extracted from strawberry quality parameters during cold storage. Three methods of cultivation of strawberry cv. Honeoye were tested: organic cultivation on raised beds, organic cultivation with the flat-planted method and conventional cultivation with the flat-planted method. The nanostructure of pectin (AFM), its chemical structure (FT-IR) and rheological properties were studied. The fruits were also tested by size, dry matter, firmness, acidity and the content of soluble solids, anthocyanin, phenolics, vitamin C and galacturonic acid. Pectin isolated from organic strawberries was more rapidly degraded than conventional strawberry pectin, which limits the possibilities for their processing and use as gelling or stabilizing agents at 20 °C. The differences in fruit quality were particularly noticeable with respect to the anthocyanin content, which was significantly higher for organic strawberry. The organic fruit also had better sensory properties because of its lower acidity and higher soluble solid content (SSC). These and other results from this experiment showed that strawberries produced by organic farming methods had better biochemical properties compared to conventional fruit; however, pectin transformation undergone faster limits their further technological applications.

Wood forming tissue-specific expression of PdSuSy and HCHL increases holocellulose content and improves saccharification in Populus

Development of strategies to deconstruct lignocellulosic biomass in tree species is essential for biofuels and biomaterials production. We applied a wood forming tissue-specific system in a hybrid poplar to express both PdSuSy (a sucrose synthase gene from Populus deltoides × P. euramericana that has not been functionally characterized) and HCHL (the hydroxycinnamoyl-CoA hydratase-lyase gene from Pseudomonas fluorescens, which inhibits lignin polymerization in Arabidopsis). The PdSuSy-HCHL overexpression poplars correspondingly driven by the promoters of Arabidopsis AtCesA7 and AtC4H resulted in a significant increase in cellulose (> 8%), xylan (> 12%) and glucose (> 29%) content, accompanying a reduction in galacturonic acid (> 36%) content, compared to control plants. The saccharification efficiency of these overexpression poplars was dramatically increased by up to 27%, but total lignin content was unaffected. These transgenic poplars showed inhibited growth characteristics, including > 16% reduced plant height, > 10% reduced number of internodes, and > 18% reduced fresh weight after growth of 4 months, possibly due to relatively low expression of HCHL in secondary xylem. Our results demonstrate the structural complexity and interaction of the cell wall polymers in wood tissue and outline a potential method to increase biomass saccharification in woody species.

Sugar beet pectin extracted by ultrasound or conventional heating: a comparison.

The yield and quality of sugar beet pulp pectin obtained by ultrasound-assisted extraction (UAE) were compared to those obtained by conventional heating. Extraction temperature (70-90)°C, extraction time (2-4) h and pH (1-1.5) were considered as the variables for the conventional extraction while ultrasound frequency (20-60) kHz, time (10-30) min and amplitude (60-100%) were considered as the variables for UAE. The optimal conditions for maximum yield of pectin for conventionally and ultrasonically extracted pectin were determined by the central composite design and the Box Behnken design, respectively. The optimum conditions of conventional extraction were the temperature of 90°C, time of 4h and pH of 1. The optimum conditions of UAE were ultrasound frequency of 20kHz, time of 10min, and ultrasound amplitude of 96%. Extraction using the optimized conditions of conventional heating and UAE achieved the best yield of 20.75% and 20.85%, respectively. The degree of methyl esterification, ferulic acid content and molecular weight of UAE pectin were higher than conventionally extracted pectin but the content of galacturonic acid in UAE pectin was lower than that of conventionally extracted pectin. The infrared spectra of both pectins revealed the occurrence of polysaccharide component. The pectin achieved by UAE had higher lightness value than conventionally extracted pectin, confirming its application in different products partially in bright food products. The UAE pectin possessed higher viscosity than conventionally extracted pectin. The addition of UAE pectin increased all of the DSC gelatinization parameters. Overall, UAE could be a promising scalable and economical approach to obtain pectin with unique characteristics.

Partial Characterization of Watermelon Albedo Pectin Extracted Using Citric Acid Combined with Microwave Assisted Extraction

The aim of this study was to determine the influence of microwave power and extraction time on pectin chemical characteristics of watermelon albedo using citric acid combined with Microwave Assisted Extraction (MAE) method. Microwave power variations being applied were 50% (225 W), 75% (315 W), and 100% (450 W) and the extraction times were 1 minute, 2 minutes and 3 minutes. The data obtained was statistically analysed using two-way Analysis of Variance at a significance level of 5% continued by Duncan Multiple Range Test if there was a significant difference. The results showed that the variation of power and extraction time significantly affect yield, equivalent weight, degree of methylation, galacturonic acid content, and degree of esterification. Pectin yield was ranging from 2.19% to 5.34% and equivalent weight of the pectin ranging from 441.09 mg to 1432.00 mg. Pectin from the watermelon albedo was classified as low methoxyl pectin with degree of methylation ranged from 4.82%–6.92%. Galacturonic acid content of the pectin obtained was ranging from 39.83% to 79.21%. The pectin had a degree of esterification ranging from 49.57% to 68.74% which was classified as high ester pectin.

The effects of foliar-applied manganese on major cell wall polysaccharide fractions and soluble sugar composition of cucumber leaves

Increasing evidence shows that micronutrients can induce changes in cell wall (CW) properties in plants. A detailed knowledge of these changes will contribute to understand the beneficial and detrimental impacts of trace elements on plant development and defence. In the present work, the influence of foliar spray of manganese (Mn) on the composition of CW polysaccharides and soluble sugars was investigated in cucumber leaves using spectrophotometric and chromatographic techniques. Cucumber seedlings were hydroponically cultured under controlled situations for 21 days. At the two-leaf stage, the above facade of cucumber leaves was fertilized with MnSO4 solutions at various dosages (1.8, 4.5 and 7.2 mM). Results showed that the foliar Mn spray decreased the galacturonic acid (GalA) content, while it increased the degree-of-methyl-esterification (DM) of pectin. The amounts of fucose, arabinose and galactose diminished upon Mn application. The contents of rhamnose and xylose decreased or did not change by Mn treatment. The glucose level enhanced at low concentration of Mn (1.8 mM), but it decreased at medium and high concentrations of Mn (4.5 and 7.2 mM). The increase of mannose content was significant only at medium concentration of Mn. Overall, the amount of total hemicellulose increased at 1.8 mM concentration of Mn, while a decrease was observed at 4.5 and 7.2 mM concentrations of Mn. The cellulose content decreased at low and high concentrations of Mn, although it remained unchanged at medium concentration of Mn. Generally, the total contents of CW polysaccharides increased at low concentration of Mn, but they decreased at the higher concentrations of Mn. Such changes can be important in plant resistance to environmental stresses via reduction of permeability against fungal pathogens and decrease of water loss from tissues under stresses such as drought and salinity.

Modification of apple, beet and kiwifruit cell walls by boiling in acid conditions: Common and specific responses

Cell wall (CW) degradation causes texture loss of plant-based products after processing. However, these losses differ in intensity, which could be due to cell wall structure or plant tissue internal pH conditions. To distinguish these two factors, CWs isolated from apple, beet and kiwifruit were subjected to boiling at pH 2.0, 3.5 and 6.0. Pectin depolymerization was the least pronounced at pH 3.5, while galacturonic acid contents of all CWs decreased at pH 6.0 due to the β-elimination. Pectins were solubilized, and their size decreased with increased pH during CW treatment. At pH 6.0, degrees of methylation decreased mostly in apple and beet CWs while galactose decreased more in kiwifruit CW. At pH 2.0, arabinan was lost in apple and beet CW due to acid hydrolysis. Apple CW was the most susceptible to degradation either at pH 2.0 or 6.0, while beet CW was more degraded at pH 2.0. In contrast, kiwifruit CW was the least susceptible to degradation whichever the pH. Acid hydrolysis and β-elimination appeared to be common mechanisms that cause loss of neutral sugars, often from pectin side chains, and galacturonic acid, respectively, but their effects were of different intensities. This work has a guiding significance for improving texture in the thermally canning process.