Effects of calcium and pectin methylesterase on quality attributes and pectin morphology of jujube fruit under vacuum impregnation during storage

Vacuum impregnation: Effect on food quality, application and use of novel techniques for improving its efficiency

Vacuum Impregnation (VI) act as promising method for rapidly introducing specific concentration solutions into food matrices using a hydrodynamic mechanism and deformation phenomenon to attain a product with specific tailored functional quality characteristics. VI facilitates rapid introduction of specific solutions into the food matrices. This technique allows efficient incorporation of bioactive compounds and nutritional components, meeting the rising consumer demand for functional foods. Furthermore, VI when combined with non-thermal techniques, opens up new avenues for preserving higher quality attributes and enhancing antimicrobial effects. The unique ability of VI to rapidly infuse specific solutions into food matrices, combined with the advantages of non-thermal processes, addresses the growing consumer demand for products enriched with bioactive ingredients. Hence, the present review aims to explore the potential impact of VI, coupled with novel techniques, on food quality, its practical applications, and the enhancement of process efficiency for large-scale industrial production.

Application of atomic force microscopy in the characterization of fruits and vegetables and associated substances toward improvement in quality, preservation, and processing: nanoscale structure and mechanics perspectives

Fruits and vegetables are essential horticultural crops for humans. The quality of fruits and vegetables is critical in determining their nutritional value and edibility, which are decisive to their commercial value. Besides, it is also important to understand the changes in key substances involved in the preservation and processing of fruits and vegetables. Atomic force microscopy (AFM), a powerful technique for investigating biological surfaces, has been widely used to characterize the quality of fruits and vegetables and the substances involved in their preservation and processing from the perspective of nanoscale structure and mechanics. This review summarizes the applications of AFM to investigate the texture, appearance, and nutrients of fruits and vegetables based on structural imaging and force measurements. Additionally, the review highlights the application of AFM in characterizing the morphological and mechanical properties of nanomaterials involved in preserving and processing fruits and vegetables, including films and coatings for preservation, bioactive compounds for processing purposes, nanofiltration membrane for concentration, and nanoencapsulation for delivery of bioactive compounds. Furthermore, the strengths and weaknesses of AFM for characterizing the quality of fruits and vegetables and the substances involved in their preservation and processing are examined, followed by a discussion on the prospects of AFM in this field.

Alleviation of the degradation of cell wall pectin contributes to the maintenance of integrity of papaya (Carica papaya L.) fruit tissue during abnormal chilling injury behavior

Papaya (Carica papaya L.) is highly susceptible to chilling injury (CI), which primarily causes surface pitting, black scald, susceptibility to fungal infection, and the breakdown of tissue. It developed rapidly at 6 °C but was significantly suppressed at 1 °C, which indicated that the papaya tissue was more solid at a lower temperature. This rare phenomenon is considered to be abnormal CI behavior. The maintenance of fruit tissue integrity during abnormal CI behavior may be related to modifications of the cell wall pectin. The modifications of cell wall pectin were studied during storage at 1 and 6 °C. Storage at 1 °C alleviated the progression of CI and inhibited the degradation of pectin components and cell wall structure of papaya fruit. The increase in water-soluble pectin and the solubilization of cyclohexanediamine tetraacetic acid- (CDTA-) and sodium carbonate (Na2CO3)-soluble pectin was limited at 1 °C. Storage at this temperature limited the detachment of linear backbone chains and minimized the degradation of branching and reticular structure in the pectin molecules. Storage at this temperature also delayed the decrease in the size of pectin backbone and helped to prevent the loss of neutral sugars from the pectin side chains. Thus, alleviation of the degradation of cell wall pectin contributes to the structural integrity of the cell wall and thus helps the maintenance of the tissue integrity of papaya at 1 °C.

Fractionation and characterization of sodium carbonate-soluble fractions of cell wall pectic polysaccharides involved in the rapid mealiness of 'Hongjiangjun' apple fruit

Apple flesh tends to turn mealy and textural deterioration commonly occurs during storage. The comparative investigation of three sub-fractions separated from sodium carbonate-soluble pectin (SSP) of 'Hongjiangjun' apples between crisp and mealy stages was performed to unveil the textural alterations related to mealiness. In situ immunofluorescence labelling showed that galactans declined in parenchyma cell walls during the fruit mealiness. FTIR analysis, monosaccharide compositions and structural polymers configurated that loss of rhammogalacturonan-I (RG-I) from SSP sub-fragments (SC0.0-P and S-M0.0-P) might be closely involved in the mealiness. The NMR spectroscopy revealed that loss of the substituted galactans from α-Rhap residues repeat unit in SC0.0-P constituting RG-I in crisp stage that subsequently converted to S-M0.0-P in mealy stage might be closely associated with the modifications of pectin in cell walls during mealiness. These findings provided novel evidence for understanding the underlying modifications of SSP polymers during the mealiness of 'Hongjiangjun' apples.

Modulating pectin structure and enhancing texture of frozen yellow peaches: The impact of low-temperature blanching

High-temperature blanching (HTB) is the primary process that causes texture softening in frozen yellow peaches. The implementation of low-temperature blanching reduced pectin methyl esterification, increased pectin cross-linking, and mitigated pectin depolymerization during the subsequent HTB, leading to the superior texture of frozen yellow peaches with enhanced water holding capacity, higher fracture stress, and initial modulus. However, adding 2 % calcium lactate (w/v) during low-temperature blanching did not further improve the texture of frozen yellow peaches. Instead, it softened the texture by reducing Na2CO3-soluble pectin (NSP) and increasing water-soluble pectin (WSP) content. This study provided a theoretical basis for applying low-temperature blanching to improve the texture of frozen yellow peaches.

Quality Changes and Fungal Microbiota Dynamics in Stored Jujube Fruits: Insights from High-Throughput Sequencing for Food Preservation

Postharvest rot is an urgent problem affecting the storage of winter jujube. Therefore, the development of new technologies for efficient and safe preservation is very important. This study aimed to elucidate the fungal microbiota found on the epidermis of jujube during the storage period using high-throughput sequencing, as well as to monitor the changes in quality indexes throughout this period. Through internal transcribed spacer (ITS) sequencing, we identified two phyla (Basidiomycota and Ascomycota) and six genera (Cryptococcus, Bulleromyces, Sporidiobolus, Alternaria, Pseudozyma, and Sporobolomyces), which potentially contribute to the spoilage and deterioration of jujube, referred to as "core fungal taxa". A high correlation was further found between preservation indices (including decay rate, firmness, and total soluble solids) and the growth of multiple core fungi over time. These findings will provide insights and a theoretical basis for further research on preservation techniques related to biological control during date fruit storage.

Recent advances in vacuum impregnation of fruits and vegetables processing: A concise review

Vacuum impregnation (VI) is a novel, non-thermal treatment that aims to modify the composition of food material by partially removing water and air and impregnating it with physiologically active compounds without affecting the structural integrity of food matrix. Application of VI accelerates the mass transfer processes, which leads to few changes in food composition and improves dehydration. Large volumes in intracellular spaces of fruit and vegetable tissues make it suitable to introduce different agents like nutrients, cryoprotectants, browning inhibitors, enzymes, and chemicals; enhancing texture profile and inhibiting tissue softening, or compounds lowering water activity and pH. water activity Thus, the VI may help to achieve new product quality associated with physicochemical features and sensory attributes. This review highlights the evolution and mechanism of VI technique, major factors affecting VI of fruits and vegetables and their responses to processing, and industrial relevance. Vacuum impregnation consists ability to revolutionize various aspects of food processing and preservation. VI serves as a versatile tool that enhances the quality, shelf life, and nutritional content of processed fruits and vegetables. It offers unique advantages of altering product composition by introducing desired compounds while preserving structural integrity. VI improves mass transfer processes, reduces water content, enhances the absorption of nutrients, antioxidants, and preservatives. This technology finds application in producing fortified foods, extending shelf life, and creating innovative products with improved sensory attributes. VI's ability to efficiently impregnate substances into porous materials, combined with its energy-saving potential and compatibility with other processing methods, makes it a valuable tool in the food industry. As consumers demand healthier and long-lasting products, VI emerges as a promising solution for meeting market demands.

Post-harvest ripening affects drying behavior, antioxidant capacity and flavor release of peach via alteration of cell wall polysaccharides content and nanostructures, water distribution and status

Effect of post-harvest ripening on cell wall polysaccharides nanostructures, water status, physiochemical properties of peaches and drying behavior under hot air-infrared drying was evaluated. Results showed that the content of water soluble pectins (WSP) increased by 94 %, while the contents of chelate-soluble pectins (CSP), Na₂CO₃-soluble pectins (NSP) and hemicelluloses (HE) decreased during post-harvest ripening by 60 %, 43 %, and 61 %, respectively. The drying time increased from 3.5 to 5.5 h when the post-harvest time increased from 0 to 6 days. Atomic force microscope analysis showed that depolymerization of hemicelluloses and pectin occurred during post-harvest ripening. Time Domain -NMR observations indicated that reorganization of cell wall polysaccharides nanostructure changed water spatial distribution and cell internal structure, facilitated moisture migration, and affected antioxidant capacity of peaches during drying. This leads to the redistribution of flavor substances (heptanal, n-nonanal dimer and n-nonanal monomer). The current work elucidates the effect of post-harvest ripening on the physiochemical properties and drying behavior of peaches.

Behavior of enzymes under high pressure in food processing: mechanisms, applications, and developments

High pressure processing (HPP) offers the benefits of safety, uniformity, energy-efficient, and low waste, which is widely applied for microbial inactivation and shelf-life extension for foods. Over the past forty years, HPP has been extensively researched in the food industry, enabling the inactivation or activation of different enzymes in future food by altering their molecular structure and active site conformation. Such activation or inactivation of enzymes effectively hinders the spoilage of food and the production of beneficial substances, which is crucial for improving food quality. This paper reviews the mechanism in which high pressure affects the stability and activity of enzymes, concludes the roles of key enzymes in the future food processed using high pressure technologies. Moreover, we discuss the application of modified enzymes based on high pressure, providing insights into the future direction of enzyme evolution under complex food processing conditions (e.g. high temperature, high pressure, high shear, and multiple elements). Finally, we conclude with prospects of high pressure technology and research directions in the future. Although HPP has shown positive effects in improving the future food quality, there is still a pressing need to develop new and effective combined processing methods, upgrade processing modes, and promote sustainable lifestyles.

Emerging Postharvest Technologies to Enhance the Shelf-Life of Fruit and Vegetables: An Overview

Quality losses in fresh produce throughout the postharvest phase are often due to the inappropriate use of preservation technologies. In the last few decades, besides the traditional approaches, advanced postharvest physical and chemical treatments (active packaging, dipping, vacuum impregnation, conventional heating, pulsed electric field, high hydrostatic pressure, and cold plasma) and biocontrol techniques have been implemented to preserve the nutritional value and safety of fresh produce. The application of these methodologies after harvesting is useful when addressing quality loss due to the long duration when transporting products to distant markets. Among the emerging technologies and contactless and non-destructive techniques for quality monitoring (image analysis, electronic noses, and near-infrared spectroscopy) present numerous advantages over the traditional, destructive methods. The present review paper has grouped original studies within the topic of advanced postharvest technologies, to preserve quality and reduce losses and waste in fresh produce. Moreover, the effectiveness and advantages of some contactless and non-destructive methodologies for monitoring the quality of fruit and vegetables will also be discussed and compared to the traditional methods.

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage

INTRODUCTION

Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant.

OBJECTIVES

This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness.

METHODS

The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca²⁺ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit.

RESULTS

The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0°C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca²⁺ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals.

CONCLUSION

PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca²⁺ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Composition and environmental interpretation of the weed communities in the main planting base of jujube (Ziziphus jujuba Mill. cv. 'LingwuChangzao'), Ningxia province of China

Background

Ziziphus jujuba Mill. cv. 'LingwuChangzao' is a traditional jujube cultivar in northwest China. It is of great significance to explore the weed community composition and environmental characterization for the ecological control and comprehensive management of weeds in jujube orchards. In this article, a total of 37 species were recorded in 40 sample plots (1 m × 1 m). Moreover, fourteen environmental indicators to characterize the spatial locations, climate and soil nutrient characteristics of the plant communities were adopted.

Methodology

Through the two-way indicator species analysis (TWINSPAN) quantity classification and canonical correspondence analysis (CCA) ranking methods, the types of weed communities in the main planting base of jujube 'LingwuChangzao' and the main environmental factors affecting the change and distribution of weed types were analyzed.

Results

The weed communities within the study area were divided into 15 types by the TWINSPAN classification. There were significant differences in soil factors to the species diversity indices of the weed communities, the diversity of weed communities was negatively correlated with available potassium, whereas positively correlated with soil water content. The CCA results showed that community structure and spatial distribution of weed communities were affected by soil water content, total potassium, soil organic carbon, total phosphorus, total nitrogen. Our results can be used as a reference for orchard weed management and provide a theoretical basis for weed invasion control and creating a higher biodiversity in arable land under the background of environmental change.

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 (M_w ) decreased, while WSP content and sodium chelate-soluble pectin (CSP) M_w 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 M_w , Rha content, CSP M_w , 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, M_w 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.

Yeast as carrier for drug delivery and vaccine construction

Yeast has been employed as an effective derived drug carrier as a unicellular microorganism. Many research works have been devoted to the encapsulation of nucleic acid compounds, insoluble small molecule drugs, small molecules, liposomes, polymers, and various nanoparticles in yeast for the treatment of disease. Recombinant yeast-based vaccine carriers (WYV) have played a major role in the development of vaccines. Herein, the latest reports on the application of yeast carriers and the development of related research are summarized, a conceptual description of gastrointestinal absorption of yeast carriers, as well as the various package forms of different drug molecules and nanoparticles in yeast carriers are introduced. In addition, the advantages and development of recombinant yeast vaccine carriers for the disease, veterinary and aquaculture applications are discussed. Moreover, the current challenges and future directions of yeast carriers are proposed.

Comparison of calcium and ultrasonic treatment on fruit firmness, pectin composition and cell wall-related enzymes of postharvest apricot during storage

This study was conducted to examine the effects of calcium treatment (2%, 20 min) and ultrasonic treatment (400 W, 20 min) on postharvest apricot fruit during storage. The results showed that after calcium and ultrasonic treatment, compared with the control, the firmness of apricot fruit increased by 41.53% and 3.83% at 16 d, but juice yield and water-soluble pectin (WSP) content decreased by 8.26% and 3.55%, 28.57% and 4.08%, respectively. Both calcium and ultrasonic treatment were more effective in reducing polygalacturonase (PG), β-Galactosidase (β-Gal), pectin methylesterase (PME), polyphenol oxidase (PPO) and peroxidase (POD) activity. Moreover, fruit firmness was significantly negatively correlated with juice yield, WSP and PPO, and positively correlated with PG and β-Gal, PPO and POD. In contrast, calcium treatment was more effective than ultrasonic treatment in delaying postharvest softening of apricot.

Green alternative methods for pretreatment of whole jujube before the drying process

BACKGROUND

Jujube contains a waxy cuticle that acts as a barrier against fungal pathogens, prevents nutrition damage and leakage due to mechanical damage, and maintains water content. Chemical treatment before drying is the most commonly used method for whole jujube. Although chemical pretreatment can effectively enhance drying kinetics, it can lead to the loss of soluble nutrients and cause food safety issues due to chemical residues. Therefore, this study aimed to explore the effect of various pretreatments (cold plasma, cold plasma activated water, ultrasonics, thermosonication, and blanching) on the drying process and quality properties of whole jujube so as to find effective green alternatives to chemical pretreatment.

RESULTS

The application of chemical, cold plasma, and thermosonication significantly altered the surface morphology of jujube by etching larger cracks and holes, which can facilitate the transfer of moisture, thereby improving the drying rate and the effective diffusivity. Chemical, cold plasma, and thermosonication pretreatment reduced drying time by 18%, 12%, and 7% respectively, thereby increasing the content of total phenolics by 13%, 12%, and 6% respectively, and enhancing antioxidant capacity (ferric reducing antioxidant power) by 13%, 11%, and 3% respectively. In addition, chemical and cold plasma pretreatment reduced the generation of 5-hydroxymethylfurfural by 25% and 15% respectively.

CONCLUSION

Cold plasma is a promising green alternative method to chemical pretreatment for drying processes of whole jujube. © 2021 Society of Chemical Industry.

Extraction, characterization and spontaneous gelation mechanism of pectin from Nicandra physaloides (Linn.) Gaertn seeds

Nicandra physaloides (Linn.) Gaertn seeds (NPGS) could be manually scrubbed to obtain water-soluble pectin, which forms gel at room temperature without additives. The extraction, characterization and spontaneous gelation (SG) mechanism of the pectin were studied. The results showed that the pectin was located on the surface of NPGS and easily to be dissolved. Chemically, the pectin was low methoxy pectin with esterification degree of 46.93%, Gal-A content of 65.80%, and average molar weight of 631.15 kDa. The SG occurred at the pectin concentration of 1.5%, it can be destroyed by urea and SDS, however, EDTA cannot. In addition, KCl and NaCl induced the gelation of 1.0% pectin solution and the ions of K, Mg, Ca and Na were detected in the pectin. Hydrogen bonding, electrostatic and hydrophobic interaction contributed to the SG. This study could promote the commercial applications of the pectin in the field of edible colloids and cosmetics.

Effect of calcium chloride and 1-methylcyclopropene combined treatment on pectin degradation and textural changes of Eureka lemon during postharvest storage

During post-harvest storage, the cell wall properties are closely associated with the physical, chemical, and biological properties of the fruit. The degradation of pectin in the cell walls and middle lamella is critical to these properties. The effects of calcium chloride (CaCl₂) and 1-methylcyclopropene (1-MCP) combined treatment on the pectin degradation, texture, and peel color of Eureka lemon were investigated during post-harvest storage. The in-situ light microscope analysis, rapid method, and FTIR test were used to investigate the spatial distribution, the pectin content, and its degradation. The results showed a reduction in pectin degradation, by 42 d the CaCl₂ and 1-MCP combined treated fruits presented a 36.7% pectin content loss which was lower than the control which was 48.3%. The treated fruits significantly exhibited enhanced textural properties, delayed weight loss, higher total acids, and improvement of other physicochemical properties in comparison to the control. The treatment deaccelerated the fruit peel color change from green to yellow and also had a better visual appearance on the final day. Overall, the results suggest that the control treatment for pectin degradation can reduce the fruit texture decline and peel color change and maintain a good visual appearance. The influence of pectin degradation on the texture and physicochemical properties of lemon provides a theoretical basis for fruit storage optimization, quality control, and shelf-life extension.

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Combined CaCl₂ and 1-MCP treatment delayed lemon postharvest degeneration.

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Treatment suppressed pectin degradation and improved the visual appearance.

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Treatment greatly delayed softening, reduce decay rate, and extended the shelf life.

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Methylesterified pectin was localized and visualized by qualitative microscopic analysis.

Inhibitory Effects of CaCl2 and Pectin Methylesterase on Fruit Softening of Raspberry during Cold Storage

Quality of raspberry fruit experiences a rapid decline after harvest due to its vulnerable texture and high moisture content. Application of calcium chloride (CaCl2) combined with pectin methylesterase (PME) is efficient in delaying fruit softening. In this study, the effects of exogenous CaCl2 alone or in combination with PME on the structure of the cell wall, the molecular properties of pectin, and the amount of free water of raspberry during postharvest storage were investigated. The results showed that CaCl2 combined with PME treatment could maintain fruit firmness and inhibit weight loss. The treatment of CaCl2+PME maintained the cell wall structure via sustaining middle lamella integrity and reducing the activities of cell wall-degrading enzymes, such as polygalacturonase, pectin methylesterase, β-galactosidase, α-L-arabinofuranosidase, and β-xylosidase. In addition, CaCl2+PME treatment could effectively increase the content of chelate-soluble pectin (CSP) and develop a cross-linked structure between Ca2+ and CSP. Moreover, CaCl2+PME treatment was of benefit in maintaining free water content. CaCl2 in combination with PME treatment could be a promising method for inhibiting softening and maintaining the quality of postharvest raspberry during cold storage.

Expression profiling of endo-xylanases during ripening of strawberry cultivars with contrasting softening rates. Influence of postharvest and hormonal treatments

BACKGROUND

Softening is one of the main features that determine fruit quality during strawberry (Fragaria x ananassa, Duch.) ripening and storage. Being closely related to textural changes, the molecular and biochemical bases underlying strawberry cell-wall metabolism is a matter of interest. Here we investigated the abundance of transcripts encoding putative strawberry endo-xylanases in plant tissues, during fruit ripening and under postharvest and hormonal treatments. Total xylanase activity and expression of related genes in strawberry varieties with contrasting firmness were analyzed.

RESULTS

FaXynA and FaXynC mRNA abundance was significantly higher than FaXynB in each plant tissue studied. Higher total xylanase activity was detected at the end of the ripening of the softer cultivar ('Toyonoka') in comparison with the firmer one ('Camarosa'), correlating with the abundance of FaXynA and FaXynC transcripts. Postharvest 1-methylcyclopropene treatment up-regulated FaXynA and FaXynC expressions. FaXynC mRNA abundance decreased with heat treatment but the opposite was observed for FaXynA. Calcium chloride treatment down-regulated FaXynA and FaXynC expression. Both genes responded differently to plant growth regulators' exposure. FaXynC expression was down-regulated by auxins and gibberellins treatment and up-regulated by abscisic acid. FaXynA was up-regulated by auxins, while no changes in mRNA levels were evident by abscisic acid and gibberellins treatment. Ethephon exposure did not change FaXynA and FaXynC expressions.

CONCLUSION

New knowledge about the presence of xylanases in ripening strawberry fruit and their response to postharvest and hormonal treatments is provided. Our findings suggest a role for endo-xylanases in hemicelluloses depolymerization and possibly in strawberry fruit softening. © 2020 Society of Chemical Industry.

Changes in pectin characteristics of jujube fruits cv "Dongzao" and "Jinsixiaozao" during cold storage

Softening is one of the main factors affecting market value and consumer preferences for jujubes, and it was closely related to the modification and depolymerization of pectin. Changes in characteristics of three pectins (water-soluble pectin (WSP), sodium carbonate-soluble pectin (SSP) and chelate-soluble pectin (CSP)), including their contents, degree of methylesterification (DM), neutral sugar compositions, the molecular weight (M_w ) distributions and nanostructures, from two jujube fruits cv Dongzao (DZ) and Jinsixiaozao (JS) during cold storage were assessed. The results showed that variation in pectin characteristics during cold storage was similar between DZ and JS. The reduction of firmness corresponded to a conversion of water-insoluble pectin to WSP during cold storage. DM of WSP presented an increase trend in the late storage. Rhamnose (Rha), arabinose (Ara) and glucose (Glc) were the crucial compositions in three pectins, and most neutral sugar compositions in three pectins first increased and then decreased during cold storage. Changes in the ratio of (galactose (Gal)+Ara)/Rha and Ara/Gal represented that the branch chains of rhamnogalacturonan-I in three pectins depolymerized after storage. The high M_w in WSP and SSP of jujubes were solubilized and extensively depolymerized into pectin with lower M_w after storage. AFM images showed an increase in short chains and branch structures of three pectins after storage. Overall, three pectins in DZ and JS depolymerized and solubilized during cold storage. WSP and SSP were more contributed to the softening of jujubes compared to CSP, and they played the critical role for regulating the softening of jujube fruits during cold storage. PRACTICAL APPLICATION: Softening is one of the main factors affecting market value and consumer preferences for jujubes, and it was closely related to the modification and depolymerization of pectin. Changes in characteristics of three pectins (WSP, SSP, CSP), including their contents, degree of methylesterification, neutral sugar compositions, the molecular weight distributions and nanostructures, from two jujube fruits cv Dongzao (DZ) and Jinsixiaozao (JS) during cold storage were assessed. Three pectins in DZ and JS depolymerized and solubilized during cold storage. WSP and SSP were more contributed to the softening of jujubes compared to CSP, and they played the critical role for regulating the softening of jujube fruits during cold storage. This study would elucidate the mechanism of jujube softening and help to regulate the postharvest quality during cold storage.

Comparative transcriptomic analysis of cantaloupe melon under cold storage with ozone treatment

Ozone treatment was found to delay the postharvest cantaloupe melon decay and improve its intrinsic quality during the cold storage. The transcriptomes of cantaloupe peel and pulp in response to ozone treatment were investigated to reveal the mechanisms using a high-throughput RNA sequencing approach. Results showed that 570 and 313 differentially expressed genes were identified in peel and pulp, respectively. According to these identified genes, the gene ontology and pathway enrichment analysis indicated that the ozone treatment could maintain the firmness of the cantaloupe by changing pectin metabolites and reduction of the ethylene production by regulating relevant genes especially in the peel. The total flavonoid content changes in peel and pulp related to the regulation of phenylalanine ammonia lyase, 4-coumarate-CoA ligase and P450 family genes which further leading to the inhibition of phenylalanine metabolic pathway in peel but promotion of secondary metabolism in pulp. The qRT-PCR results were in accordance with our RNA sequencing results which validated the conclusions. The present study for the first time reveals the mechanism of cantaloupe in response to ozone treatment at a transcriptome level which is of importance for cantaloupe storage.

Physiological and metabolic analysis of winter jujube after postharvest treatment with calcium chloride and a composite film

BACKGROUND

Ziziphus jujuba Miller cv. Dongzao is extremely susceptible to reddening, browning, nutritional loss, and perishability after harvest. In this study, we evaluated the mechanisms of calcium chloride and chitosan/nano-silica composite film treatments on the quality, especially in reddening, by physiological and metabolomic assays.

RESULTS

The treatment delayed the decline of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and chalcone isomerase (CHI) activities. Meanwhile, the treated groups retarded the increases in anthocyanin and quercetin contents by inhibiting the gene expressions of flavonol synthase (ZjFLS), dihydroflavonol 4-reductase (ZjDFR), and anthocyanidin synthase (ZjANS), while promoting leucoanthocyanidin reductase (ZjLAR) expression, which leads to retardation of fruit reddening. Anthocyanins were found to be responsible for post-harvest winter jujube reddening through principal component analysis. Results from the technique for order preference by similarity to an ideal solution indicated that the treated group delayed the decline of the quality of 'Dongzao' and extended its shelf life.

CONCLUSION

The treatment induced the heightening of flavonoids metabolism. They enhanced the nutritional value and the ability to resist stress by delaying the decline of PAL, CHS, and CHI activities. Meanwhile, the treated groups retarded the increase in anthocyanin and quercetin contents by inhibiting the gene expressions of ZjFLS, ZjDFR, and ZjANS and promoting ZjLAR expression, which leads to retardation of fruit reddening. Anthocyanins are responsible for post-harvest winter jujube reddening. Coating treatment effectively delayed the decline of winter jujube quality. © 2020 Society of Chemical Industry.

Atomic force microscopy in food preservation research: New insights to overcome spoilage issues

A higher level of food safety is required due to the fast-growing human population along with the increased awareness of healthy lifestyles. Currently, a large percentage of food is spoiled during storage and processing due to enzymes and microbial activity, causing huge economic losses to both producers and consumers. Atomic force microscopy (AFM), as a powerful scanning probe microscopy, has been successfully and widely used in food preservation research. This technique allows a non-invasive examination of food products, providing high-resolution images of surface structure and individual polymers as well as the physical properties and adhesion of single molecules. In this paper, detailed applications of AFM in food preservation are reviewed. AFM has been used to provide comprehensive information in food preservation by evaluating the spoilage with its related structure modification. By utilizing AFM imaging and force measurement function, the main mechanisms involved in the loss of food quality and preservation technologies development can be further elucidated. It is also capable of exploring the activities of enzymes and microbes in influencing the quality of food products during storage. AFM provides comprehensive solutions to overcome spoilage issues with its versatile functions and high-throughput outcomes. Further research and development of this novel technique in order to solve integrated problems in food preservation are necessary.

Structural characteristic of a sulfated polysaccharide from Gracilaria Lemaneiformis and its lipid metabolism regulation effect

A sulfated polysaccharide extracted from Gracilaria lemaneiformis (GLP) with a prominent effect in regulating lipid metabolism was isolated. The molecular weight was 31.5 kDa and it was composed mainly of galactose, glucose and xylose. Fourier-transform infrared (FT-IR) spectrum and nuclear magnetic resonance (NMR) analysis suggested that GLP was composed of the following repeating unit: [3-β-Gal-4(OSO3)-1→4-α-3,6-anhydrogal-2(OSO3)-1→]. GLP could significantly decrease serum total cholesterol, triglyceride and free fatty acid levels and lower alanine aminotransferase and aspartate aminotransferase activities in high-fat-diet mice. Additionally, GLP could keep the body weight and attenuate accumulation of fat surrounding the liver and epididymis induced by high-fat diet. Results of RT-PCR indicated that GLP might regulate lipid metabolism and accelerate free fatty acid oxidation by up-regulating the expression of the PPARα, ACS and CPT1a gene. The present study suggests that GLP may be potentially useful for regulating lipid metabolism.

Characterization of an acidic pectin methylesterase from Paenibacillus xylanexedens and its application in fruit processing

A pectinase-producing bacterial isolate, identified as Paenibacillus xylanexedens SZ 29, was screened by using the soil dilution plate with citrus pectin and congo red. A pectin methylesterase gene (Pxpme) was cloned and expressed in Escherichia coli. The gene coded for a protein with 334 amino acids and a calculated molecular mass of 36.76 kDa. PxPME showed the highest identity of 32.4% with the characterized carbohydrate esterase family 8 pectin methylesterase from Daucus carota. The recombined PxPME showed a specific activity with 39.38 U/mg against citrus pectin with >65% methylesterification. The optimal pH and temperature for PxPME activity were 5.0 and 45 °C. Its K_m and V_max value were determined to be 1.43 mg/mL and 71.5 μmol/mg·min, respectively. Moreover, PxPME could increase the firmness of pineapple cubes by 114% when combined with CaCl₂. The acidic and mesophilic properties make PxPME a potential candidate for application in the fruit processing.

Impacts of thermal and non-thermal processing on structure and functionality of pectin in fruit- and vegetable- based products: A review

Pectin, a major polysaccharide found in the cell walls of higher plants, plays major roles in determining the physical and nutritional properties of fruit- and vegetable-based products. An in-depth understanding of the effects of processing operations on pectin structure and functionality is critical for designing better products. This review, therefore, focuses on the progress made in understanding the effects of processing on pectin structure, further on pectin functionality, consequently on product properties. The effects of processing on pectin structure are highly dependent on the processing conditions. Targeted control of pectin structure by applying various processing operations could enhance textural, rheological, nutritional properties and cloud stability of products. While it seems that optimizing product quality in terms of physical properties is counteracted by optimizing the nutritional properties. Therefore, understanding plant component biosynthesis mechanisms and processing mechanisms could be a major challenge to balance among the quality indicators of processed products.

Silver Can Induce Oxidative Stress in Parallel to Other Chemical Elicitors to Modulate the Ripening of Chili Cultivars

Two chili cultivars, i.e., cv. Bullet and cv. Tejaswini, were evaluated on postharvest related ripening characteristics with varying durations under hydrogen peroxide, putrescine and silver treatments. The reducing sugar was inversely related to the maximum values at 7 days of ripening. Silver and putrescine were the most regulatory in terms of changing of the total carbohydrate content as compared to hydrolysis of the total reducing sugar. Regarding pectin methylesterase activity, both chilies were consistent, regardless of the number of days of incubation. Still, putrescine and silver were significant contributors to variations in cv. Bullet and cv. Tejaswani. For the pigment content, lycopene and chlorophyll increased in a linear manner, although these treatments significantly varied over time. Hydrogen peroxide and putrescine were responsible for the maximum accumulation of lycopene for both the cultivars, whereas, only cv. Tejaswani displayed maximum carotenoid for putrescine. Silver for both chili varieties was the most inhibitory for lycopene and carotenoid content. Superoxide had a good impact on the accumulation of lipid peroxides, irrespective of the chili variety. The maximum accumulation of lipid peroxide was recorded at seven days of treatment. Phenolics and flavonoids were in decreasing order for both the chili varieties, progressing through the days of the study period in a similar manner. Silver was the main contributor to variations in the phenolics and flavonoid contents in cv. Tejaswani. The solubilization of total carbohydrate into reducing sugar was in an inverse relationship, with the maximum values being reached at 7 days of ripening.

Postharvest acibenzolar-S-methyl treatment maintains storage quality and retards softening of apple fruit

"Golden delicious" apples were dipped in 100 mg/L acibenzolar-S-methyl (ASM) to investigate the fruit quality and softening during 12 days of storage. Weight loss, flesh firmness, ethylene release, respiratory rate, content of total soluble solids and titratable acid, the activity of pectinase, cellulase, and β-glucosidase, and water-insoluble pectin and water-soluble pectin contents were investigated. The results demonstrated that ASM treatment inhibited ethylene release and respiratory rate, reduced titratable acidity, and enhanced total soluble solids content in apples. Moreover, application of ASM suppressed the reduction of flesh firmness, activity of pectin methylesterase, and polygalacturonase. Cellulase, β-glucosidase, and degradation of protopectin in apple fruit were also suppressed by ASM treatment during storage. In conclusion, ASM could maintain fruit quality by regulating cell wall-degrading enzymes during storage. PRACTICAL APPLICATIONS: Application of acibenzolar-S-methyl after harvest has the potential of delaying fruit softening by regulating cell wall-degrading enzymes, thus retain fruit quality.