Sodium Carbonate-soluble Pectin Research Articles

Ultrasound modification of pectin and the mechanism of its interaction with cyanidin-3-O-glucoside

The present study investigated water-soluble pectin (WSP), chelating pectin (CSP), sodium carbonate-soluble pectin (NSP), and cyanidin-3-O-glucoside (C3G). Various ultrasonic treatments (688, 1376, 2064, 2431, and 3437 W/cm2, 10 min) were used to modify the three types of pectin, and the structural changes in pectin and the interaction mechanisms between pectin and cyanidin were analysed. The experimental results indicated that ultrasonic (US) modification reduced the molecular weight and degree of methylation (DE) of pectin. The DE values of WSP and CSP decreased by 24.51% and 80.12%, respectively. US modification disrupted the branched structure of pectin and reduces the ratio of rhamnose/galacturonic acid, which caused an increase in the linearity of pectin. US modification enhanced the interaction between the three pectins and anthocyanins, and the US condition of 2064 W/cm2 for 10 min increased the binding rate by 15.71%–46.18%. NSP had the largest binding rate, and US modification had the greatest improvement in WSP binding rate. After US modification, the particle size of the pectin-cyanidin complex decreased, and the zeta potential increased. After heat treatment, the residual mass percentage of the pectin-C3G complex increased, which suggested that the encapsulation of C3G in pectin improved thermal stability. Therefore, US treatment is a versatile processing tool that reduces the DE of pectin and enhances its linearity, which offers a promising approach to promoting pectin-C3G complexes.

Layer by layer application of chitosan and carboxymethyl cellulose coatings delays ripening of mango fruit by suppressing cell wall polysaccharides disassembly

Mango is a climacteric fruit that ripens quickly after harvest due to its climacteric nature. Edible coatings have been reported to delay the ripening of various harvested fruit. The efficacy of the applied edible coatings could be improved by using in combination as a layer-by-layer (LBL) approach. So, the influence of LBL application of chitosan (CH) and carboxymethyl cellulose (CMC) was studied on mangoes during postharvest storage at 15 °C for 20 days. Mangoes were coated with monolayers of CH (1 % w/v) and CMC (1 % w/v) as well as LBL application of CH and CMC and were compared with control. The treatment of mangoes with CH and CMC-based LBL treatment resulted in lower decay percentage and weight loss along with higher total chlorophyll pigments and suppressed total carotenoid accumulation. The LBL application of CH and CMC showed lower activity of chlorophyll degrading such as chlorophyllase (CPS), pheophytinase (Phe), Mg-dechalatase (MGD) and chlorophyll degrading peroxidase (Chl-POD) enzymes as well as reduced changes in b*, a* and L* along with a suppressed increase in ethylene (EP) and CO2 production (CPR) rates having higher antioxidant such as catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and superoxide dismutase (SOD) enzymes activity. In addition, mangoes coated with LBL treatment of CH and CMC exhibited lower water-soluble pectin (WSP) and higher protopectin (PP) having higher concentrations of chelate soluble (CSP) and sodium carbonate-soluble pectin (SCP). Similarly, LBL-coated mangoes showed significantly higher hemicellulose (HCLS) and cellulose (CLS) contents in contrast with control. It was observed that mangoes coated with CH and CMC-based LBL coating exhibited higher flesh firmness and showed suppressed cellulase (CS), pectin methylesterase (PME), polygalacturonase (PG) and β-galactosidase (β-Gal) enzymes activity. The concentrations of total soluble solids and ripening index were markedly lower and titratable acidity was higher in the LBL-based coating treatment in comparison with control. In conclusion, LBL treatment based on CH and CMC coatings could be used for the delay of ripening and softening of harvested mangoes.

Increased weight loss and internal air space, degraded starch and pectin combined to cause pulp mealiness in ‘Oregon Spur Ⅱ’ apples during ambient storage

Pulp mealiness is a common phenomenon in ‘Delicious’ apples during ambient storage, but the underlying mechanism remains poorly understood. In the present study, fruit physiological and quality parameters, the volume of internal air space and the degree of mealiness as well as cell wall-degrading enzyme activities and pectin material content were measured in ‘Oregon Spur Ⅱ’ apple fruit during ambient storage. The results showed that the peaks of respiration rate and ethylene production of ‘Oregon Spur Ⅱ’ fruit occurred at 5 d and 10 d of storage, respectively, during which the starch and malic acid contents and firmness decreased significantly, while the fruit weight loss, the volume of internal air space and the degree of mealiness increased rapidly. Meanwhile, the activities of pectin methylesterase (PME) and pectin lyase (PL) showed a unimodal change during storage, whereas the activity of polygalacturonase (PG) decreased, and the activities of α-L-arabinofuranosidase (α-AFase) and β-galactosidase (β-Gase) as well as the contents of water-soluble pectin (WSP), chelator-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP) increased with increasing storage time. Correlation analysis showed that α-AFase, β-Gase, WSP, CSP, weight loss, the volume the air space, firmness, starch, and malic acid were significantly correlated with the degree of pulp mealiness (|r|>0.9). In conclusion, increased weight loss and internal air space, degraded starch and pectin combined to cause pulp mealiness in ‘Oregon Spur Ⅱ’ apples during ambient storage.

Pectin-interactions and the digestive stability of anthocyanins in thermal and non-thermal processed strawberry pulp.

This study investigated the digestive stability of anthocyanins (ACNs) and their interaction with three pectin fractions-water-soluble pectin (WSP), cyclohexanetrans-1,2-diamine tetra-acetic acid-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP)-in strawberry pulp processed by pasteurization (PS), ultrasound (US), electron beam (EB) irradiation, and high pressure (HP). Compared with the control group, the ACNs content increased to the highest level (312.89mg/mL), but the retention rate of ACNs in the simulated intestine decreased significantly after US treatment. The monosaccharide compositions indicated that the WSP and CSP possessed more homogalacturonan (HG) domains than the NSP, which contains more rhamngalacturonan-I (RG-I) domains. The microstructure of US-treated pectin was damaged and fragmented. Comprehensive analysis showed that the retention rate of ACNs was closely related to the pectin structure, primarily reflected by the degree of linearity and the integrity of structure. These results revealed the structure-activity relationship between ACNs and pectin during pulp processing.

Ripening induced degradation of pectin and cellulose affects the medium-and short-wave infrared drying characteristics of mulberry

Mulberries were categorized into five stages of ripening (D1–D5, 0.905–1.055 g/cm3) based on their density, and their physicochemical properties, tissue structure, cell wall polysaccharide properties, and drying characteristics were investigated. As mulberry ripening progressed, the TSS and water-soluble pectin content rapidly increased, while the contents of TA, hardness, chelate-, sodium carbonate-soluble pectin, hemicellulose, and cellulose decreased gradually. Pectin nanostructure and monosaccharide composition indicated that both the main and side chains of pectin undergo depolymerization. Medium- and short-wave infrared drying time initially decreased and then increased during mulberry ripening, with D4 fruits exhibiting the shortest drying time. Compared with D4 fruits, the collapse of cell structure in D5 fruits prolongs their drying time. The results demonstrate that ripeness significantly affects mulberry drying characteristics, which is related to changes in cell structure and pectin properties. Utilizing mulberry density to determine ripeness and grading is an effective approach to achieving optimal drying.

Cold shock precooling improves the firmness of chili pepper during postharvest storage and the molecular mechanisms related to pectin.

This research was conducted to explore the influence of cold shock on the firmness, a quality marker in chili pepper during 0-21 d storage and determine mechanism by cold shock impacted pectin. Chili peppers were exposed to cold shock precooling (0±2°C water/ice mixture) for 0-, 30-, 90- and 150-min, respectively. Results showed that cold shock alleviated loss of firmness throughout storage. Firmness was positively associated with sodium carbonate-soluble pectin content (r=0.44), methylation degree of CDTA-soluble pectin (r=0.82) and water-soluble pectin (WSP, r=0.87), but negatively associated with WSP content (r=-0.76), and the activities of β-galactosidase (r=-0.72) and pectinlyase (r=-0.74). Cold shock for 90min was determined to be optimal. This study confirms the applicability of cold shock precooling to maintain firmness and thereby to extend the shelf life of chili pepper.

Exogenous melatonin mitigates chilling injury in zucchini fruit by enhancing antioxidant system activity, promoting endogenous proline and GABA accumulation, and preserving cell wall stability

Zucchini fruit are sensitive to chilling injury (CI) during postharvest low temperature storage which makes their cold stored life short. In this work, zucchini fruit were treated with melatonin (200 µmol L−1) and stored at 5 ºC for 15 d. The pre-storage melatonin treatment reduced weight loss (6.51%) and suppressed symptoms of CI (1.5 Score) along with lower malondialdehyde (MDA), relative ion leakage (RIL), superoxide anion and hydrogen peroxide (H2O2) in contrast with control. The treated zucchini exhibited higher L* (51.89) and lower a* (−10.17) and b* (29.15) values of exocarp in comparison with control. Melatonin treated zucchini showed enhanced γ-aminobutyric acid (GABA) concentration due to higher glutamate content and stimulated glutamate decarboxylase (GAD) and suppressed γ-aminobutyric acid transaminase (GABA-T) activities. In addition, melatonin application increased proline accumulation owing to stimulation of Δ-1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine δ-aminotransferase (OAT) enzymes and reduced proline dehydrogenase (ProDH) activity as compared with control. The activity of antioxidative such as ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) enzymes remained higher in melatonin treated zucchini. The fruit treated with melatonin exhibited reduced water soluble pectin (WSPN) along with higher sodium carbonate soluble pectin (SCSP), protopectin (PRPN), chelate soluble pectin (CSPN), cellulose (CLS) and hemicellulose (HLS) in comparison with control. The exogenous melatonin suppressed the activities of polygalacturonase (PG), β-galactosidase (β-Gal), cellulase (CX), and pectin methylesterase (PME) along with higher firmness. In conclusion, exogenous melatonin at 200 µmol L−1 concentration could be used for zucchini fruit CI mitigation under cold storage.

1-methylcyclopropene treatment improves chilling tolerance by regulating IAA biosynthesis, auxin signaling transduction and cell wall degradation in peach fruit

Chilling injury (CI) is a major issue in peach fruit during cold storage, which can be alleviated by 1-methylcyclopropene (1-MCP) treatment. Previous works have focused on ethylene regualtion. Recently, auxin signals were found to play vital roles in both 1-MCP-regulated fruit ripening and cold resistance. However, the information regarding the relationship between auxin metabolism and 1-MCP-induced cold tolerance was still limited, especially in cold-sensitive fruit. To investigate the underlying mechanisms, we performed transcriptome analysis and found that 1-MCP treatment significantly regulated several metabolic pathways, including auxin signaling, cell wall pectin degradation, and indole pyruvate metabolism. This regulation contribute to the development of cold resistance by maintaining cell wall structural integrity through delaying the increase of water-soluble pectin (WSP) and the decrease of CDTA-soluble pectin (CSP) and sodium carbonate-soluble pectin (NSP). Accordingly, 1-MCP treatment reduced the activities of polygalacturonase (PG), pectin methylesterase (PME) and pectin lyase (PEL), and down-regulated the expressions of PpPG1, PpPG2, PpPME1, PpPME2, PpPEL1 and PpPEL2. Moreover, the treatment decreased indole-3-acetic acid (IAA) biosynthesis via the indole pyruvate pathway, which led to the attenuation of the auxin signaling pathway through down-regulation of auxin response factors (PpARF1), auxin-responsive genes (PpAUX/IAA1, PpSAUR1 and PpGH3–1), and auxin receptor proteins (PpTIR1) expressions. Our results suggested 1-MCP treatment improved chilling tolerance by regulating IAA biosynthesis, auxin signaling transduction and cell wall degradation, and provided new insight into the mechanisms of 1-MCP-induced cold resistance in postharvest peach fruit.

Effect of the pectin contents and nanostructure on the stem straightness of two Paeonia lactiflora cultivars.

Herbaceous peony (Paeonia lactiflora Pall.) is an ancient ornamental crop and, in recent decades, an emerging popular cut flower. Straight stems are a vital criterion for cut herbaceous peony selection, while many cultivars bend as the plant develops. Pectin helps maintain the mechanical strength of the cell wall. However, little is known about its role in the stem bending of herbaceous peony. Two herbaceous peony cultivars with contrasting stem morphologies ('Dong Fang Shao Nv', upright; 'Lan Tian Piao Xiang', bending gradually) at five developmental stages were used as materials to investigate the effects of pectin content and nanostructure on straightness using the carbazole colorimetric method and atomic force microscopy observations. The contents of water-soluble pectin (WSP), CDTA-soluble pectin (CSP), and sodium carbonate-soluble pectin (SSP) differed significantly between the two cultivars, and the contents and angle of the flower and branch showed correlations. For the pectin nanostructure, WSP showed agglomerates and long chains, with a higher proportion of broad agglomerates at the later stages of the bending cultivar than the upright cultivar. CSP showed branched chains, and the proportion of broad chains was higher in the upright cultivar at later stages, while CSP shape changed from agglomerates to chains in the bending cultivar. SSP mainly consisted of short linear main chains, and side chains in the upright stem were stacked, and the bent cultivar had more broad and short chains. It can be concluded that the contents, nanometric shape, and size of the three kinds of pectin are highly likely to affect herbaceous peony stem straightness. This study provides a theoretical basis for the role of pectin in the production and breeding of herbaceous peony cut flowers.

Texture formation of dehydrated yellow peach slices pretreated by osmotic dehydration with different sugars via cell wall pectin polymers modification

In this study, texture of heat pump drying (HPD) yellow peaches pretreated by osmotic dehydration (OD) with different sugars (sucrose/Suc, isomaltooligosaccharide/IMO, glucose/Glc) were evaluated. Properties of pectin fractions, namely water soluble pectin (WSP), chelator soluble pectin (CSP) and sodium carbonate soluble pectin (NSP) from yellow peach slices were also determined. Results showed that IMO-HPD samples exhibited the highest hardness (22.218 ± 1.661 N) and chewiness (6.741 ± 0.729 N). WSP fractions from IMO-HPD samples showed the lowest degree of methylation (28.5 ± 0.5%), illustrating IMO could catalyze the demethylation of homogalacturonan in WSP. Glc-HPD samples exhibited the highest resilience (35.732 ± 2.748%), springiness (82.255 ± 3.868%), and pectin content, in which the content of WSP, CSP, and NSP fractions were 88.55, 29.60, and 55.96 mg/g AIR, respectively. Both CSP and NSP extracted from Glc-HPD samples showed the smallest molar mass, namely 4.630 ×10 5 Da and 6.639 ×10 5 Da, respectively, contributing to the breakage of the linkage between CSP and NSP and the cell wall induced by the infiltration of Glc. Correlation analysis suggested that the degradation or conversation was the pivotal cause of texture formation of OD-HPD yellow peach slices. In conclusion, the interaction between osmosis solutes and pectin could significantly affect the texture formation of OD-HPD yellow peach slices, which would provide theoretical guidance for improving the texture properties of dehydrated fruits with OD pretreatments. • Osmotic dehydration markedly hardened the texture of yellow peach slices. • Isomaltooligosaccharide catalyzed the demethoxylation of water soluble pectin. • Heat pump drying caused water-insoluble pectin shift to water-soluble pectin. • The infiltration of glucose could break the linkages between cell walls. • Strong correlation between texture formation and pectin features was explored.

Transcriptomics analysis reveals molecular mechanism of softening and cell wall polysaccharides-disassembling in peaches treated by flow microcirculation of sodium nitroprusside medium

Peach (Prunus persica L. Batsch. var. compressa Bean) is prone to softening during storage, and this leads to a marked deterioration in quality and shortened shelf life. The influences of sodium nitroprusside (SNP) atomization on softening development, cell wall ultrastructure, cell wall polysaccharides metabolism in peach fruit stored at 0 ± 0.5 °C for 60 d were explicated. SNP atomization treated fruit, when contrasted to the control, exhibited higher firmness, contents of chelate-soluble pectin (CSP), sodium carbonate-soluble pectin (SSP), cell wall materials (CWM), cellulose and hemicellulose (HC), but lower water-soluble pectin (WSP) content. SNP treatment suppressed activities of cell wall-degrading relevant enzymes, the disassembly of cell wall structure, and the decomposition of middle lamella and plasma membrane in peach fruit. The RNA sequencing results suggested that the differentially expressed genes from amino sugar metabolic process (beta-D-xylosidase, BXL), galactose metabolism (beta-galactosidase, β-Gal), pentose and glucuronate interconversions (polygalacturonase, PG), cellular carbohydrate metabolic process (xyloglucan- endotransglucosylase/hydrolase, XTH), and expansin (Exp) were associated with cell wall degradation in peaches with aerosolized water (control) or SNP treatments. Based on these results, the delayed softening of peaches with SNP atomization was ascribed to cell wall polysaccharides degradation regulated by gene expression levels and enzymes.

Variation in Cell Wall Metabolism and Flesh Firmness of Four Apple Cultivars during Fruit Development.

Fruit ripening and softening are highly complex processes, and there is an interplay and coordination between the metabolic pathways that are involved in the biological processes. In this study, we aimed to elucidate the variation in the characters and possible causes of cell wall materials and morphological structure during apple fruits development. We studied the cell wall material (CWM), structure, cellular morphology, hydrolase activity, and the transcriptional levels of the related genes in four apple varieties 'Ruixue' and 'Ruixianghong' and their parents ('Pink Lady' and 'Fuji') during fruit development. The decrease in the contents of CWMs, sodium carbonate soluble pectin, hemicellulose, and cellulose were positively correlated with the decline in the hardness during the fruit development. In general, the activities of polygalacturonase, β-galactosidase, and cellulase enzymes increased during the late developmental period. As the fruit grew, the fruit cells of all of the cultivars gradually became larger, and the cell arrangement became more relaxed, the fruit cell walls became thinner, and the intercellular space became larger. In conclusion, the correlation analysis indicated that the up-regulation of the relative expression levels of ethylene synthesis and cell wall hydrolase genes enhanced the activity of the cell wall hydrolase, resulting in the degradation of the CWMs and the depolymerization of the cell wall structure, which affected the final firmness of the apple cultivars in the mature period.

Extraction, characterization, and antioxidant properties of cell wall polysaccharides from the pericarp of Citrus Reticulata cv. Chachiensis

The pericarp of Citrus reticulata cv. Chachiensis (PCRC) had been used as a traditional herbal medicine in southeast and eastern Asia, and it was also an important source of nutraceuticals and functional food ingredients. In the present study, the cell wall polysaccharides were sequentially extracted from PCRC using different solvents, resulting in five pectic fractions and two hemicellulose fractions, namely water-soluble pectin (WSP), hot water-soluble pectin (HWSP), chelator-soluble pectin (CSP), diluted acid-soluble pectin (HSP), sodium carbonate-soluble pectin (NSP), 1 mol/L KOH soluble hemicellulose (KSH-1) and 4 mol/L KOH soluble hemicellulose (KSH-2). The seven fractions were characterized in terms of composition, structure, thermal, rheological, and antioxidant properties. The pectin fractions were classified as high-methoxy pectin with a degree of methyl esterification (DM) between 56.89% and 62.20%. Ammonium oxalate extraction provided the CSP fraction with the highest content of galacturonic acid (75.18%) and the lowest degree of acetylation (0.03). HWSP was considered to be an aggregative of homogalacturonan (HG) and rhamnogalacturonan I (RG-I) containing side chains of galactans and arabinans. Thermal analysis indicated that HWSP had the highest thermal stability than other fractions. All fractions exhibited the characteristics of non-Newtonian fluids, with NSP showing the highest apparent viscosity. Assays for antioxidant activities suggested WSP had the highest DPPH radical scavenging activity while NSP had the highest hydroxyl radical scavenging activity. The result could be a good basis for the applications of cell wall polysaccharides, especially pectin, of PCRC in the preparation of functional food products.

Effects of electrolysed water and levulinic acid combination on microbial safety and polysaccharide nanostructure of organic strawberry

This study aimed to better understand the effects of acidic electrolysed water (AEW, 4 mg/L) and levulinic acid (LA, food grade, 2%) combination on organic strawberry over 7 days. This combined method reduced the population of strawberry’s natural microbiota by 1–2 log CFU/g and kept the level of inoculated Escherichia coli O157:H7 and Salmonella below the detection limit (2 log CFU/g) during the whole storage period. Meanwhile, AEW + LA did not affect the physicochemical qualities of strawberries significantly, maintaining most texture and biochemical attributes at an acceptable level (e.g., firmness, colour, soluble solids content and organic acid content). Atomic force microscopy further revealed that the treatment containing LA preserved the sodium carbonate soluble pectin (SSP) nanostructure best by maintaining their length and height, and slowed the breakdown of SSP chains by promoting acid-induced bonding and soluble pectin precipitation. These results demonstrated that low concentration AEW and LA combination is a promising sanitising approach for organic strawberry preservation.

Carboxymethyl cellulose coating regulates cell wall polysaccharides disassembly and delays ripening of harvested banana fruit

Banana is a perishable fruit that ripens and deteriorates quickly after harvest. In this work, we investigated the impact of a dip in carboxymethyl cellulose (CMC) at concentrations of 0.5%, 1.0% and 1.5% on the quality of harvested bananas during storage at ambient conditions of 20 ± 1 ºC for a 15-d period. It was noted that 1.5% CMC markedly delayed the occurrence of decay incidence (9%) and suppressed physiological weight loss (6%). The 1.5% CMC treatment suppressed the activities of chlorophyllase, pheophytinase, Mg-dechelatase and chlorophyll (Chl)-degrading peroxidase (POD), which ultimately delayed banana peel color changes by conserving higher total Chl contents and reducing the accumulation of carotenoids. This subsequently resulted in higher L* and a* along with a lower increase in b* values as compared with control. Banana fruit coated with 1.5% CMC exhibited delayed ethylene and respiration peaks in comparison with control. In the same way, 1.5% coating maintained higher firmness and showed higher contents of protopectin, chelate-soluble pectin, sodium carbonate soluble pectin, cellulose and hemicellulose along with lower water-soluble pectin due to reduced activities of cellulase, pectin methylesterase, polygalacturonase and β-glucosidase. In the same way, postharvest application of 1.5% CMC coating suppressed the increase in total soluble solids (TSS) and showed higher titratable acidity (TA) along with a lower ripening index (TSS/TA ratio) in flesh of banana fruit compared with control. In conclusion, 1.5% CMC application could be an appropriate coating concentration to delay the ripening and rapid softening of harvested bananas stored in ambient conditions.

High pressure processing improves the texture quality of fermented minced pepper by maintaining pectin characteristics during storage.

Texture quality affects the sensory and market acceptance of fermentation minced pepper (FMP), but it will deteriorate during storage. Thus, high pressure processing (HPP) and thermal pasteurization (TP) were used to improve the texture quality of FMP during storage. The results showed that variations in texture quality and pectin characteristics under HPP and TP treatments were similar during storage. The hardness, cell wall material (CWM) and sodium carbonate-soluble pectin (SSP) content, water-soluble pectin (WSP) molecular weight (Mw ) decreased, while WSP content and sodium chelate-soluble pectin (CSP) Mw increased after storage. HPP-treated FMP showed higher hardness (66.64-85.95 N) than that in TP-treated one (57.23-62.72 N) during storage. Rhamnose (Rha), arabinose, mannose, and glucose were the crucial compositions in three pectins, and their total molar ratios, respectively, reached 89.19% and 87.97% after HPP and TP treatment. However, the molar ratio of most monosaccharide in three pectins decreased after storage. Atomic force microscope images indicated the short chains and branch structures increased but aggregates decreased in most pectin components during storage. Pearson correlation analysis demonstrated FMP hardness was extremely (p<0.01) positively correlated with CWM and SSP content, and extremely (p<0.01) negatively correlated with WSP content. Compared to TP treatment, HPP presented higher hardness, SSP content and Mw , Rha content, CSP Mw , and lower WSP content during storage. Hence, HPP was an effective method to improve the texture quality of FMP by maintaining pectin characteristics during storage. PRACTICAL APPLICATION: Softening is one of the main factors affecting market value and consumer preferences for FMP, and it is closely related to the modification and depolymerization of pectin. Changes of texture quality and pectin properties in HPP- and TP-treated FMP during storage were assessed, including hardness, the content, monosaccharide compositions, Mw distribution, and nanostructure of WSP, SSP, and CSP. Compared to TP treatment, HPP could effectively improve the texture quality of FMP by inhibiting pectin degradation during storage. All the findings presented in this study would help to provide new insights into regulating the texture quality of FMP.

Ripening induced degradation of pectin and cellulose affects the far infrared drying kinetics of mangoes

The quality parameters of mangoes change during ripening, which has a vital impact on processing characteristics. Effects of ripening stage (four stages from the lowest to highest degree—RS-1, RS-2, RS-3, RS-4) on cell wall polysaccharides and far infrared drying kinetics of mangoes were investigated. As ripening progressed, the water-soluble pectin contents increased by 213.5%; while the chelate-, sodium carbonate-soluble pectin and hemicellulose contents decreased by 44.0%, 59.5% and 65.8%, respectively. Moreover, the molecular weight reduction confirmed the degradation of pectin. These further caused the alteration of cell wall structure and changes in water distribution. Meanwhile, the drying time of mangos with different ripeness were in the order: RS-3 > RS-4 > RS-2 > RS-1. It correlated with the degradation of cell wall polysaccharides, the destruction of cell wall and the increases in free water during ripening. The ripeness classification could effectively improve the uniformity and efficiency of fruits drying processing.

Morphological, physiochemical, and transcriptome analysis and CaEXP4 identification during pepper (Capsicum annuum L.) fruit cracking

In pepper (Capsicum annuum L.), fruit cracking is a common physical deformation that not only affects the fruit quality, but also increases the water loss rate during storage and reduces shelf-life and economic value. To comprehensively unravel the putative genes and mechanism underlying fruit cracking, the cracking-susceptible cultivar ‘L92’ was subjected to morphological, physiochemical and transcriptome analyses and an assay of postharvest water loss. The polygalacturonase, peroxidase, and cellulase activity levels and water-soluble pectin and lignin contents were significantly higher in FSC (fruit seriously cracking) fruits than in FNC (fruit without cracking) fruits. The hemicellulose and cellulose contents of FSC fruits were lower than those of FNC fruits; with non-significant differences in chelator trans-1,2-diaminocyclohexane-N,N,N0,N0-tetraacetic acid-soluble pectin and sodium carbonate-soluble pectin levels. By comparing the FSC with the FNC fruits and analyzing differentially expressed gene (DEG) profiles during the fruit cracking process, 1,574 DEGs were identified. Among them, 45 unigenes were significantly enriched in KEGG pathways related to cell wall metabolism and lignin biosynthesis. The silencing of CaEXP4 induced cells in the epidermal layer to be smaller and more neatly and tightly arranged, with a greater number of cell layers of the sub-epidermal layer compared with control fruit. Small structural modifications may lead to changes in cell wall structure and elasticity, which might have caused the fruit cracking. To the best of our knowledge, this is the first morphological, histological, physiochemical, and transcriptome analysis to show the role of CaEXP4 during cracking of pepper fruit.

Alteration of pectin metabolism in blood orange fruit (Citrus sinensis cv. Tarocco) in response to vesicle collapse

Abstract Segment drying is a severe physiological disorder of citrus fruit, and vesicles become granulated or collapsed. Aside from the hypothesis that alteration of cell wall metabolism is the main factor of citrus granulation, little is known about vesicle collapse. This study aimed to elucidate the changes in pectin metabolism during vesicle collapse in blood orange. Vesicle collapse was characterized by decreased nutrients and increased chelate- and sodium carbonate-soluble pectin and calcium content. The nanostructure of chelate-soluble pectin became complex and developed multi-branching upon collapse. The activity of pectin methylesterase increased, while that of polygalacturonase and pectate lyase decreased upon collapse. Genome-wide transcriptional analysis revealed an increasing pattern of genes encoding pectin methylesterase and other enzymes involved in pectin synthesis and demethylesterification upon collapse. Drying vesicles were characterized by increased abscisic acid content and relevant gene expression. In conclusion, we discovered alteration in pectin metabolism underlying citrus vesicle collapse, mainly promoting pectin demethylesterification, remodeling pectin structures, and further inhibiting pectin degradation, which was hypothesized to be a main factor for citrus collapse. This is the first study to disclose the potential intrinsic mechanism underlying vesicle collapse in orange fruit.

Changes in biochemical properties and pectin nanostructures of juice sacs during the granulation process of pomelo fruit (Citrus grandis)

Postharvest granulation is a severe physiological disorder in citrus fruit that may be related to pectin metabolism. This study was designed to analyze the changes in fruit quality and pectin metabolism of pomelo fruit during granulation from expansion, gelation to lignification. Fruit quality showed a decrease starting from the gelation stage. Contents of water-soluble pectin, chelate-soluble pectin, sodium carbonate-soluble pectin and calcium, and activity of pectin methylesterase increased, while polygalacturonase activity decreased upon granulation. Atomic force microscopy analysis showed that both length and width of those three types of pectin molecules increased during granulation, accompanied by the decrease of linear structure molecules of pectin and the increase of pectin polymers, and multi-branched pectin tending to form cross-linked structure. Complex network of pectin might be remodeled during granulation process that immobilized the free water in juice sacs and induced the gelation occurrence, further promoted the granulation process.