Analyses of microstructure and cell wall polysaccharides of flesh tissues provide insights into cultivar difference in mealy patterns developed in apple fruit

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.

Investigation of the formation of furfural compounds in apple products treated with pasteurization and high pressure processing

The thermal treatment carried out in the processing of apple products is very likely to induce Maillard reaction to produce furfurals, which have raised toxicological concerns. This study aimed to elucidate the formation of furfural compounds in apple products treated with pasteurization and high pressure processing (HPP). The method for simultaneous determination of five furfural compounds including 5-hydroxymethyl-2-furfural (5-HMF), furfural (F), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF), 2-acetylfuran (FMC), and 5-Methyl-2-furfural (MF) using high performance liquid chromatography equipped with diode array detector (HPLC-DAD) was successfully developed and validated. All five furfurals exhibited an increasing trend after the pasteurization treatment of apple clear juice, cloudy juice, and puree. 5-HMF, F, FMC, and MF were increased significantly during the precooking of apple puree. Whereas there was no significant change in the furfurals formation after apple products treated with high pressure processing (HPP) with 300 MPa and 15 min. Based on the variation of the fructose, glucose and sucrose detected in apple products after thermal treatment, it revealed that the saccharides and thermal treatment have great effect on the furfural compounds formation. The commercial fruit juice samples with different treatments and fruit puree samples treated with pasteurization were also analyzed. Five furfurals were detected more frequently in the fruit juice samples treated with pasteurization or ultra-high temperature instantaneous sterilization (UHT) than those treated with HPP. 5-HMF and FMC were detected in all fruit puree samples treated with pasteurization, followed by F, MF, and HDMF with the detection rate of 79.31 %, 72.41 %, and 51.72 %. The results could provide a reference for risk assessment of furfural compounds and dietary guidance of fruit products for human, especially for infants and young children. Moreover, moderate HPP treatment with 300 MPa and 15 min would be a worthwhile alternative processing technology in the fruit juice and puree production to reduce the formation of furfural compounds.

Boron-mediated amelioration of copper toxicity in Citrus sinensis seedlings involved reduced concentrations of copper in leaves and roots and their cell walls rather than increased copper fractions in their cell walls

Little information is available on how boron (B) supplementation affects plant cell wall (CW) remodeling under copper (Cu) excess. 'Xuegan' (Citrus sinensis) seedlings were submitted to 0.5 or 350 µM Cu × 2.5 or 25 µM B for 24 weeks. Thereafter, we determined the concentrations of CW materials (CWMs) and CW components (CWCs), the degree of pectin methylation (DPM), and the pectin methylesterase (PME) activities and PME gene expression levels in leaves and roots, as well as the Cu concentrations in leaves and roots and their CWMs (CWCs). Additionally, we analyzed the Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectra of leaf and root CWMs. Our findings suggested that adding B reduced the impairment of Cu excess to CWs by reducing the Cu concentrations in leaves and roots and their CWMs and maintaining the stability of CWs, thereby improving leaf and root growth. Cu excess increased the Cu fractions in leaf and root pectin by decreasing DPM due to increased PME activities, thereby contributing to citrus Cu tolerance. FTIR and XRD indicated that the functional groups of the CW pectin, hemicellulose, cellulose, and lignin could bind and immobilize Cu, thereby reducing Cu cytotoxicity in leaves and roots.

Characterizing the impact of species/strain-specific Lactiplantibacillus plantarum with community assembly and metabolic regulation in pickled Suancai

To investigate the colonization and impact of the specific Lactiplantibacillus plantarum strains, four isolated strains were applied in pickled Suancai which is a traditional pickled mustard (Brassica juncea). Results showed that strain-8 with the highest lactic acid bacteria (LAB) counts and acetic acid (p < 0.05). There were 11.42 % ∼ 32.35 % differential volatile compounds detected, although nitriles, esters, and acids were predominant. L. plantarum disturbed the microbial community, in which the microbial composition of strain-11 was most similar to the naturally fermented sample. Amino acids, carbohydrate metabolism, and metabolism of cofactors and vitamins were the main functional classes because of the similar dominant microbes (Lactiplantibacillus and Levilactobacillus). The functional units were separated based on NMDS analysis, in which bacterial chemotaxis, amino acid-related units, biotin metabolism, fatty acid biosynthesis, and citrate cycle were significantly different calculated by metagenomeSeq and Benjamin-Hochberg methods (p < 0.05). The contents of most flavor compounds were consistent with their corresponding enzymes. In particular, glucosinolates metabolites were different and significantly related to the myrosinase and metabolic preference of LAB. Therefore, this study revealed the impact mechanism of the specific L. plantarum strains and provided a perspective for developing microbial resources to improve the flavor diversity of fermented vegetables.

The role of fructose at a range of concentration on the texture and microstructure of freeze-dried pectin-cellulose matrix cryogel

Freeze-dried (FD) fruit and vegetable materials with a large amount of sugar are unstable. With the aim to understand the structure formation of FD products, the effects of fructose content on the texture and microstructure of FD matrix were investigated by using pectin-cellulose cryogel model. Cryogels containing fructose of 0-40% were produced using freeze-drying at three different primary drying temperatures of -40, -20, and 20°C. The resultant cryogels were characterized by texture profile analyzer, scanning electron microscope, and μCT. Results indicated that at drying temperature of -40°C, increasing fructose concentration promoted the hardness of the cryogels, and cryogels of 16% fructose obtained maximum hardness. Excessive fructose (≥20%) weakened the described hardness, while exhibiting stronger springiness and resilience. The microstructure showed that dense pores and increased wall thickness due to fructose aggregation were critical factors responsible for increased hardness. The porous structure as well as relatively large pore size were necessary for crispness, in addition, rigid pore wall with certain strength were also required. At the drying temperature of 20°C, large hetero-cavities dominated the microstructure of cryogels with 30% and 40% fructose, caused by melting inside during FD process. In this situation, lower Tm (-15.48 and -20.37°C) were responsible for cryogels' melting In conclusion, if possible, regulating fructose content and state may enable the precision texture design of FD fruit and vegetable foods.

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.

The combination treatment of chlorogenic acid and sodium alginate coating could accelerate the wound healing of pear fruit by promoting the metabolic pathway of phenylpropane

Water loss and microbial infection induced by mechanical injury are the main sources of harvested loss of fruits and vegetables. Plenty studies have shown that regulating phenylpropane-related metabolic pathways can effectively accelerate wound healing. The combination treatment of chlorogenic acid and sodium alginate coating on postharvest wound healing of pear fruit were investigated in this work. The result shows combination treatment reduced weight loss and disease index of the pears, enhanced texture of healing tissues, maintained the integrity of cell membrane system. Moreover, chlorogenic acid increased the content of total phenols and flavonoids, and ultimately leads to the accumulation of suberin poly phenolic (SPP) and lignin around wound cell wall. Activities of phenylalanine metabolism-related enzymes (PAL, C4H, 4CL, CAD, POD and PPO) in wound-healing tissue were enhanced. The contents of major substrates such as trans-cinnamic, p-coumaric, caffeic, and ferulic acids also increased. The presented results suggested that the combination treatment of chlorogenic acid and sodium alginate coating stimulated wound healing in pears by elevating the phenylpropanoid metabolism pathway, so that maintain high postharvest fruit quality.

Comparative transcriptomic analysis provides novel insights into the difference in textural alteration between mealy and crisp apple patterns

Mealiness is a common textural deterioration of several fruit after harvest. To unravel the underlying mechanism involved in mealiness, biochemical characterization and global transcriptomic profiling were comparatively performed between mealy 'Hongjiangjun' (HJJ) and crisp 'Fuji' apples. Sensory evaluation and SEM-based microstructure observation showed that HJJ apples appeared to be mealy in only 3 d at 23 ± 1 °C, while Fuji apples did not appear to be mealy even after 28 d of storage. Textural deterioration and ethylene burst occurred more sharply in HJJ apples than in Fuji apples during storage. The results obtained from the dimensional RNA-sequencing analysis showed that a much stronger upregulation of the transcription of genes encoding polygalacturonase (PG), pectin acetylesterase (PAE), pectinesterase (PE), β-galactosidase (GAL), α-l-arabinofuranase (AF), and expansin (EXP) was observed in the pair of mealy HJJ apples vs. harvest than in the pair of Fuji apples after 28 d vs. harvest. The gene expression of ethylene responsive factor (ERF) was found to be strongly upregulated in HJJ apples compared with Fuji apples, which may mediate the regulation of downstream genes encoding cell wall-modifying enzymes. Weighted gene co-expression network analysis showed that the transcription factors MdbHLH63 and MdERF-like, and a constructure gene of MdGAL had strong connectivity with mealiness. Validation by qRT-PCR further confirmed the main findings obtained by RNA-sequencing. The occurrence of apple mealiness involves altered expression patterns of cell wall-modifying enzymes as well as MdbHLH63 and MdERF-like, which are core genes regulating the mealiness process. The above findings provide global insight into the difference in textural alteration between mealy and crisp apple patterns.

A wide diversity exists in pectin structure from thirteen apple cultivars

To emphasize that differences in pectin structure among cultivars play a crucial role in the texture and quality of fruits and vegetables, the sugar content and methyl-esterification of pectin fractions from 13 apple cultivars was studied. Cell wall polysaccharides were isolated as alcohol-insoluble solids (AIS) and subsequently extracted to yield water-soluble solids (WSS) and chelating-soluble solids (ChSS). All fractions contained significant amounts of galacturonic acid, while sugar compositions varied between cultivars. AIS and WSS pectins showed a degree of methyl-esterification (DM) > 50 %, while ChSS pectins had either a medium (~50 %) or low (<30 %) DM. Homogalacturonan as major structure was studied using enzymatic fingerprinting. Methyl-ester distribution of pectin was described by degrees of blockiness and -hydrolysis. Novel descriptive parameters were obtained by measuring the levels of methyl-esterified oligomers released by endo-PG (DB_PGme) and PL (DB_PLme). Pectin fractions differed in relative amounts of non-, moderately-, and highly methyl-esterified segments. WSS pectins were mostly lacking non-esterified GalA sequences, while ChSS pectins had medium DM and many non-methyl-esterified blocks or a low DM with many intermediate methyl-esterified GalA blocks. These findings will be of help to better understand physicochemical properties of apple and its products.

What are the determining factors controlling the juice yield of cider apple? A multimodal and multiscale investigation

Apple cider juice yield at harvest and after 15 and 30 days of storage durations was studied by analyzing the mechanical properties of fresh and plasmolyzed flesh, water distribution, cell wall polysaccharide composition and organization of the apples; in this study, the apple varieties used were Avrolles, Douce coetligne, Douce moen, Judor, Petit jaune. Juice yield mainly depended on the apple variety and the storage duration. Cellulose organization and cell wall pectin hydration were affected by ripening and are related to fruit firmness. Flesh viscoelastic mechanical properties were not general indications of juice yields. However, these properties helped distinguish the varieties according to flesh damage caused by ice crystals upon freezing. Cell encapsulation of the juice in the flesh contributed to lower yields. The apple variety and harvesting mode are recommended as a means to better control juice yield variations.

Targeting ripening regulators to develop fruit with high quality and extended shelf life

Fruit quality directly impacts fruit marketability and consumer acceptance. Breeders have focused on fruit quality traits to extend shelf life, primarily through fruit texture, but, in some cases, have neglected other qualities such as flavor and nutrition. In recent years, integrative biotechnology and consumer-minded approaches have surfaced, aiding in the development of flavorful, long-lasting fruit. Here, we discussed how specific transcription factors and hormones involved in fruit ripening can be targeted to generate high-quality fruit through traditional breeding and bioengineering. We highlight regulators that can be used to generate novel-colored fruit or biofortify fresh produce with health-promoting nutrients, such as vitamin C. Overall, we argue that addressing grower and industry needs must be balanced with consumer-based traits.

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.

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

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 while increased chelate- and sodium carbonate-soluble pectin and calcium content. The nanostructure of chelate-soluble pectin got 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 de-acetylation upon collapse. Drying vesicles were characterized by increased abscisic acid content and relevant gene expressions. In conclusion, we discovered alteration of 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 the citrus collapse. This is the first to disclose the potential intrinsic mechanism underlying vesicle collapse in orange fruit.

Zizania latifolia Cell Wall Polysaccharide Metabolism and Changes of Related Enzyme Activities during Postharvest Storage

The metabolism of polysaccharides in the Zizania latifolia cell wall helps maintain the postharvest quality during storage. Fresh Z. latifolia was stored at 4 °C and 25 °C to evaluate the hardness, cell wall polysaccharide composition, cell wall structure, active ingredients, and cell wall metabolism-related enzyme activities. The results showed that hardness declined concomitantly with an increase in water-soluble pectin content during storage, as well as with a decrease in propectin and cellulose contents. Correlation analysis showed that lower activities of cell wall-degrading enzymes, such as polygalacturonase, cellulase, and β-galactosidase in Z. latifolia stored at 4 °C, were associated with lighter fiberization and greater hardness, compared with those stored at 25 °C. Additionally, the results of infrared spectroscopy showed that texture softening may be attributed to a decrease in the degree of esterification of water-soluble polysaccharides at 25 °C compared to that at 4 °C.

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.

Green Husk of Walnuts (Juglans regia L.) from Southern Italy as a Valuable Source for the Recovery of Glucans and Pectins

Walnut green husk is an agricultural waste produced during the walnut (Juglans regia L.) harvest, that could be valued as a source of high-value compounds. In this respect, walnut green husks from two areas of Southern Italy (Montalto Uffugo and Zumpano), with different soil conditions, were investigated. Glucans and pectins were isolated from dry walnut husks by carrying out alkaline and acidic extractions, respectively, and then they were characterized by FT-IR, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The colorimetric method for the enzymatic measurement of α- and β-glucans was performed. The maximum total glucan yield was recovered from Montalto walnut husks (4.6 ± 0.2 g/100 g DM) with a β-glucan percentage (6.3 ± 0.4) higher than that calculated for Zumpano walnut husks (3.6 ± 0.5). Thermal analysis (DSC) confirmed the higher degree of crystallinity of glucans from Zumpano. The pectin content for Montalto husks was found to be 2.6 times that of Zumpano husks, and the esterification degree was more than 65%. The results suggested that J. regia L. green husks could be a source of glucans and pectins, whose content and morphological and thermal characteristics were influenced by different soil and climate conditions.

Comparative evaluation of package types in alleviating textural softening and package-swelling of Paocai during storage: Insight into microbial invasion, cell wall pectinolysis and alteration in sugar and organic acid profiles

The present study aimed to investigate the effect of initial vacuum package (VP), air package (AP) and salt-solution package (NP) on texture softening and package-swelling of Paocai by comparing the changes in physicochemical properties, pectinolysis, microstructure, microbial profile, as well as sugar and organic acid profiles during storage. Results showed that, when compared with AP and NP, with suppressive microbial invasion and less total pectinase activity, VP could retain more soluble pectin and induce more compact microstructure of Paocai, leading to higher hardness of Paocai during storage. As for package-swelling, VP mitigated gas-production in package by changing the microbial composition and metabolic patterns of sugar and organic acid in Paocai, especially targeted regulating the abundance of genus Kazachstania. This study provided a perspective for appropriate packaging technology to control the pectinase activity as well as cell-invading and gas-producing microorganisms for manufacturing fermented vegetable with better texture and non-package-swelling.

Aggregation and weak gel formation by pectic polysaccharide homogalacturonan

This study presents a novel model of homogalacturonan (HG) based on the dissipative particle dynamics (DPD). The model was applied to investigate the mechanism of self-aggregation of low-methoxylated homogalacturonan in aqueous solutions in the absence of cations. The coarse-grained model provided new insights into the structural features of HG aggregates and networks in aqueous solutions. Depending on the properties and concentration of polysaccharides, two major patterns of self-assembly were observed for HG - ellipsoidal aggregates and a continuous three-dimensional network. Simulations showed that a decrease in the degree of dissociation of HG results in a higher rate of self-aggregation, as well as facilitating the formation of larger assemblies or thicker nanofilaments depending on the type of final self-assembly. Simulations of polysaccharides of different chain lengths suggested the existence of a structural threshold for the formation of a spatial network for HG consisting of less than 35 GalA units.

Determination and dietary intake risk assessment of 14 pesticide residues in apples of China

The presence of pesticide residues in apples raises serious health concerns. In this study, a novel, sensitive, high-performance method was developed to simultaneously analyze the residues of 14 pesticides in apples using modified QuEChERS sample pretreatment coupled with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The optimized purification procedure demonstrated satisfactory recovery and precision for all the tested pesticides. The limits of detection (LOD) and quantification (LOQ) values of 14 pesticides in the apple matrix ranged from 0.03 μg/kg to 0.3 μg/kg and 0.1 μg/kg to 1.0 μg/kg, respectively. The proposed method detected six pesticides in the apple samples collected from 20 counties in China's major apple-producing regions. Furthermore, the risk quotient (RQ, %) of the detected pesticides was evaluated by the national estimated acceptable daily intake. The RQs of six pesticides in Chinese people of different age groups were less than 100%.

Investigating sensory properties of seven watermelon varieties and factors impacting refreshing perception using quantitative descriptive analysis

Watermelon (Citrullus lanatus) is known for its refreshing quality, though its sensory attributes have never been related to its perceived refreshment. Modified quantitative descriptive analysis by a trained panel was used to examine the sensory profile of seven watermelon varieties. Eleven attributes including perceived refreshing intensity were measured on a 0-10 line scale using chemical references. Watermelon samples were evaluated with and without nose clips to control orthonasal and retronasal aroma and temperature was included as a variable to observe their effects on perceived refreshment. The dominant watermelon attributes were wateriness, refreshing, crispness, sweet, mealiness, fresh, ripe, and melon. The varieties were best differentiated by refreshing (p < 0.001), crispness (p = 0.002), sweet (p < 0.001), mealiness (p = 0.016), green (p = 0.007), and sour perception (p < 0.001). Captivation and Excursion were the most refreshing varieties. Captivation, Excursion, and Seedless varieties were less refreshing when flavor perception was inhibited; ratings ranged from 6.8 to 7.2 without nose clips and 5.9-6.0 with nose clips (p = 0.002). Refreshing was most positively driven by wateriness, followed by crispness, fresh, melon, and sweet, and negatively driven by mealiness, as indicated by partial least square regression. Samples served cold were more refreshing (ratings of 7.1 without and 6.0 with nose clips) than those served at room temperature (ratings of 4.9 without and 3.5 with nose clips), p < 0.001. This study defined the sensory profile of seven watermelon varieties and showed that flavor, texture, and temperature were responsible for the refreshing perception of watermelon for the first time.

Effect of Addition of Pectins from Jujubes (Ziziphus jujuba Mill.) on Vitamin C Production during Heterolactic Fermentation

Soluble fibers, including pectins from apple and lemon, are commonly used as prebiotic and to prepare functional foods. The present study aimed to investigate the physicochemical and functional properties of pectins extracted from jujubes (Ziziphus jujuba Mill.). Pectins were extracted from jujubes at three stages of harvesting and characterized by FTIR and SEM analyses. Whole milk inoculated with kefir grains was supplemented by 0.25 mg·mL^-1 of pectins. The pH value and vitamin C content were evaluated after 24 and 48 h of fermentation. Pectins from jujubes at the first harvesting stage (PJ1K) showed the lowest methoxylation degree. The addition of pectins enhanced the production of vitamin C during heterolactic process. This result was found to depend on jujube harvesting stage as PJ1K stimulated the growth of yeasts in kefir grains yielding to the highest amount of vitamin C (0.83 ± 0.01 µg·mL^-1) compared to other samples (0.53-0.60 µg·mL^-1) at 24 h. Lactic acid bacteria diminish pH rapidly with respect to control (4.13 ± 0.05), according to the stage of maturation, reducing its initial value by 38.3% in PJ1K. Besides being an excellent prebiotic, pectins from jujubes could be used to enrich kefir with vitamin C.