Changes in pectin characteristics during the ripening of jujube fruit

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.

Effect of pasteurization processing and storage conditions on softening of acidified chili pepper: Pectin and it related enzymes

The softening of acidified chili peppers induced by processing and storage has become a major challenge for the food industry. This study aims to explore the impact of pasteurization techniques, thermal processing (TP), high-pressure processing (HPP), addition of sodium metabisulfite (SMS), and storage conditions (25 °C, 37 °C, and 42 °C for 30 days) on the texture-related properties of acidified chili pepper. The results showed that the textural properties of samples were destructed by TP (the hardness of samples decreased by 19.43 %) but were less affected by HPP and SMS. Compared with processing, storage temperature had a more dominant impact on texture and pectin characteristics. With increased storage temperature, water-solubilized pectin fraction content increased (increased by 160.99 %, 136.74 %, and 13.01 % in TP, HPP, and SMS-stored groups, respectively), but sodium carbonate-solubilized pectin fraction content decreased (decreased by 29.84 %, 26.81 %, and 8.60 % in TP-, HPP-, and SMS-stored groups, respectively), especially in TP-stored groups. Multivariate data analysis showed that softening was more closely related to pectin conversion induced by acid hydrolysis and pectinase depolymerization. This finding offers new perspectives for the production of acidified chili pepper.

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.

Transcriptome profiling of genes associated with fruit firmness in the melon variety 'Baogua' (Cucumis melo ssp. agrestis Jeffrey)

Fruit firmness is an important trait of melons due to its effect on fresh fruit consumption, storage, and transport. However, information on the expression of genes influencing the fruit firmness of 'Baogua' (BG) melon (Cucumis melo ssp. agrestis Jeffrey) remains rare. This study aimed to identify the key genes associated with the firmness of BG fruit sampled at 14 and 28 days after pollination (dap) via transcriptome sequencing. A total of 1113 up-regulated and 2224 down-regulated differentially expressed genes (DEGs) were identified. The main Gene Ontology terms assigned to the DEGs were phosphotransferase activity, alcohol group as acceptor, protein phosphorylation, and protein kinase activity. The enriched KEGG pathways involving the DEGs were starch and sucrose metabolism, diterpenoid biosynthesis, plant hormone signal transduction, and MAPK signaling pathway-plant. In addition, qRT-PCR verified that four GAL genes, namely, CmGAL1-4, were differentially expressed at 0, 7, 14, 21, and 28 dap. Our data revealed that CmGAL1 expression was highest at 21 dap. However, the expression levels of CmGAL2-4 were highest at 14 dap. The sequence of CmGAL1 was similar to the sequences of homologs from melon and cucumber. Subcellular localization analysis revealed CmGAL1 was located in the cell membrane and cytoplasm. Our findings implied that fruit development at 14 dap, which is a key time-point, varies considerably from fruit development at 28 dap. Our present study provides new information on the genes associated with BG fruit firmness and help improve the storage and transport of BG fruit prior to processing.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01131-5.

Effect of hydrothermal-calcium chloride treatment on pectin characteristics and related quality in green peppers during storage

Effects of hydrothermal (HT)-calcium chloride (CaCl₂) treatment on pectin characteristics and related quality in green peppers during storage were assessed. The results showed that the changes of physicochemical quality in all green peppers were similar during storage. Weight loss percentage increased, firmness, the content of free water and bound water decreased during storage. Water-soluble pectin (WSP) notably increased, but sodium carbonate-soluble pectin (SSP) and chelate-soluble pectin (CSP) decreased. Galacturonic acid (GalUA), rhamnose (Rha), galactose (Gal), and arabinose (Ara) were the crucial compositions in the backbone and branched chains of pectin in green peppers. Rha and Gal increased, but Ara decreased in pectin after storage. The changes in the ratio of Rha/GalUA, Ara/Gal, and (Gal + Ara)/Rha represented that the backbone and branched chains of pectin in green peppers depolymerized to some extent after storage. Comparing with other green peppers, HT-CaCl₂ treated green peppers posed lower weight loss percentage and WSP content, higher firmness, the content of free water, bound water, SSP, and CSP during storage. Otherwise, most pectin compositions in HT-CaCl₂ treated green peppers showed high molar ratio after storage. Hence, HT-CaCl₂ treatment was an effective way to retain pectin characteristics and related quality of green peppers, and further inhibited the softening of green peppers during storage.

Heat shock treatment maintains the quality attributes of postharvest jujube fruits and delays their senescence process during cold storage

The effects of heat shock (HT), 1-methylcyclopropene (1-MCP), or their combination (HT + 1-MCP) on the quality of fresh jujube fruits during cold storage were studied. Among them, HT showed the best preservation effect on jujube fruits, which was more effective than others in inhibiting the increase of red index, decay incidence, and weight loss and delaying the decrease of firmness, soluble solids content (SSC), titratable acidity (TA), and ascorbic acid (AsA) content. Besides, it could delay the degradation rate of the cell wall to maintain the integrity of cell membrane, and keep the high activity of active oxygen scavenging enzymes. During cold storage, malondialdehyde (MDA) content and relative electrolyte leakage (REL) of the HT group were significantly lower than those of the control group, 1-MCP, and HT + 1-MCP group (p < .05), while superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were significantly higher than those of other groups (p < .05). It was concluded that the postharvest HT treatment could effectively delay the senescence and decay of jujube fruits. PRACTICAL APPLICATIONS: Jujube fruits have high nutritional value used for food and medicine. However, they are not tolerant to storage after harvest, resulting in high economic losses. Therefore, it is of great significance to find a suitable method to maintain the quality of jujube fruits. Our results revealed the effect of HT, 1-MCP, and their combination on the quality maintenance of jujube fruits, and found that HT could effectively maintain the quality of them, which could be used as an effective method for keeping jujube fruits fresh.

Research advances in bioactive components and health benefits of jujube (Ziziphus jujuba Mill.) fruit

Jujube (Ziziphus jujuba Mill.), a highly nutritious and functional fruit, is reported to have various health benefits and has been extensively planted worldwide, especially in China. Many studies have shown that bioactive components derived from jujube fruit have significant nutritional and potential biological effects. In this paper, the latest progress in research on major bioactive compounds obtained from jujube is reviewed, and the potential biological functions of jujube fruit resources are discussed. As a dietary supplement, jujube fruit is well recognized as a healthy food which contains a variety of bioactive substances, such as polysaccharides, polyphenols, amino acids, nucleotides, fatty acids, dietary fiber, alkaloids, and other nutrients. These nutrients and non-nutritive phytochemicals obtained from jujube fruit have physiological functions including anticancer, antioxidant, anti-inflammatory, anti-hyperlipidemic, anti-hyperglycemic, immunoregulatory, neuroprotective, sedative, and antiviral functions. Of note is that new constituents, including alkaloids, dietary fiber, and other bioactive substances, as well as the antiviral, hypoglycemic, lipid-lowering, and neuroprotective effects of jujube fruit, are systematically reviewed here for the first time. Meanwhile, problems affecting the exploitation of jujube fruit resources are discussed and further research directions proposed. Therefore, this review provides a useful bibliography for the future development of jujube-based products and the utilization of jujube nutritional components in functional foods.

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.

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.