Morphology, profile and role of chelate-soluble pectin on tomato properties during ripening

Postharvest ripening-induced modification of cell wall polysaccharide affects plum phenolic bioavailability

The mechanisms by which cell wall polysaccharides regulate phenolic release are essential to human health. Scanning electron microscopy (SEM), surface area and porosimetry analyzer, high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM) indicated that compared to fresh plums, postharvest ripening reduced chain linearity in the homogalacturonan region of pectins and the degree of branching of RG-I; pectin and hemicellulose underwent solubilization and depolymerization by cell wall-degrading enzymes; and the specific surface area of cellulose was reduced by 19.5 %-26.8 %, with aggregation of cellulose occurring. In addition, confocal laser scanning microscopy (CLSM), polyphenol adsorption experiments, and in vitro gastrointestinal digestion experiments showed that the cell wall modifications under postharvest ripening process induced phenolics release and increased the bioaccessibility of plums: compared to the fresh plums, the equilibrium adsorption capacity of the cell wall of late postharvest ripened plums was reduced by 42.6 % (for epicatechin) and 27.4 % (for chlorogenic acid), and the bioaccessibility index of postharvest plum phenolics was increased by 11.2 %-23.9 %. These findings indicate cell wall modification under postharvest ripening process induces phenolic release and improves plum phenolic bioavailability.

Genes related to cell wall metabolisms are targeted by miRNAs in immature tomato fruits under drought stress

The metabolism of tomato fruits changes when plants experience drought stress. In this study, we investigated changes in microRNA (miRNA) abundance and detected 32 miRNAs whose expression changes in fruit. The candidate target genes for each miRNA were predicted from the differentially expressed genes identified by transcriptome analysis at the same fruit maturation stage. The predicted targeted genes were related to cell wall metabolisms, response to pathogens, and plant hormones. Among these, we focused on cell wall metabolism-related genes and performed a dual luciferase assay to assess the targeting of their mRNAs by their predicted miRNA. As a result, sly-miR10532 and sly-miR7981e suppress the expression of mRNAs of galacturonosyltransferase-10 like encoding the main enzyme of pectin biosynthesis, while sly-miR171b-5p targets β-1,3-glucosidase mRNAs involved in glucan degradation. These results will allow the systematic characterization of miRNA and their target genes in the tomato fruit under drought stress conditions.

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.

Rethinking the impact of RG-I mainly from fruits and vegetables on dietary health

Rhamnogalacturonan I (RG-I) pectin is composed of backbone of repeating disaccharide units →2)-α-L-Rhap-(1→4)-α-D-GalpA-(1→ and neutral sugar side-chains mainly consisting of arabinose and galactose having variable types of linkages. However, since traditional pectin extraction methods damages the RG-I structure, the characteristics and health effects of RG-I remains unclear. Recently, many studies have focused on RG-I, which is often more active than the homogalacturonan (HG) portion of pectic polysaccharides. In food products, RG-I is common to fruits and vegetables and possesses many health benefits. This timely and comprehensive review describes the many different facets of RG-I, including its dietary sources, history, metabolism and potential functionalities, all of which have been compiled to establish a platform for taking full advantage of the functional value of RG-I pectin.

Dynamic Changes in Health-Promoting Properties and Eating Quality During Off-Vine Ripening of Tomatoes

Tomato (Solanum lycopersicon L.) fruit is rich in various nutrients, vitamins and health-promoting molecules. Fresh tomatoes are an important part of the Mediterranean gastronomy, and their consumption is thought to contribute substantially to the reduced incidence of some chronic diseases in the Mediterranean populations in comparison with those of other world areas. Unfortunately, tomato fruit is highly perishable, resulting in important economic losses and posing a challenge to storage, logistic and supply management. This review summarizes the current knowledge on some important health-promoting and eating quality traits of tomato fruits after harvest and highlights the existence of substantial cultivar-to-cultivar variation in the postharvest evolution of the considered traits according to maturity stage at harvest and in response to postharvest manipulations. It also suggests the need for adapting postharvest procedures to the characteristics of each particular genotype to preserve the optimal quality of the fresh product.

Postharvest Monitoring of Tomato Ripening Using the Dynamic Laser Speckle

The dynamic laser speckle (biospeckle) method was tested as a potential tool for the assessment and monitoring of the maturity stage of tomatoes. Two tomato cultivars—Admiro and Starbuck—were tested. The process of climacteric maturation of tomatoes was monitored during a shelf life storage experiment. The biospeckle phenomena were captured using 640 nm and 830 nm laser light wavelength, and analysed using two activity descriptors based on biospeckle pattern decorrelation—C4 and ε. The well-established optical parameters of tomatoes skin were used as a reference method (luminosity, a*/b*, chroma). Both methods were tested with respect to their prediction capabilities of the maturity and destructive indicators of tomatoes—firmness, chlorophyll and carotenoids content. The statistical significance of the tested relationships were investigated by means of linear regression models. The climacteric maturation of tomato fruit was associated with an increase in biospckle activity. Compared to the 830 nm laser wavelength the biospeckle activity measured at 640 nm enabled more accurate predictions of firmness, chlorophyll and carotenoids content. At 640 nm laser wavelength both activity descriptors (C4 and ε) provided similar results, while at 830 nm the ε showed slightly better performance. The linear regression models showed that biospeckle activity descriptors had a higher correlation with chlorophyll and carotenoids content than the a*/b* ratio and luminosity. The results for chroma were comparable with the results for both biospeckle activity indicators. The biospeckle method showed very good results in terms of maturation monitoring and the prediction of the maturity indices of tomatoes, proving the possibility of practical implementation of this method for the determination of the maturity stage of tomatoes.

Fruit softening and pectin disassembly: an overview of nanostructural pectin modifications assessed by atomic force microscopy

BACKGROUND

One of the main factors that reduce fruit quality and lead to economically important losses is oversoftening. Textural changes during fruit ripening are mainly due to the dissolution of the middle lamella, the reduction of cell-to-cell adhesion and the weakening of parenchyma cell walls as a result of the action of cell wall modifying enzymes. Pectins, major components of fruit cell walls, are extensively modified during ripening. These changes include solubilization, depolymerization and the loss of neutral side chains. Recent evidence in strawberry and apple, fruits with a soft or crisp texture at ripening, suggests that pectin disassembly is a key factor in textural changes. In both these fruits, softening was reduced as result of antisense downregulation of polygalacturonase genes. Changes in pectic polymer size, composition and structure have traditionally been studied by conventional techniques, most of them relying on bulk analysis of a population of polysaccharides, and studies focusing on modifications at the nanostructural level are scarce. Atomic force microscopy (AFM) allows the study of individual polymers at high magnification and with minimal sample preparation; however, AFM has rarely been employed to analyse pectin disassembly during fruit ripening.

SCOPE

In this review, the main features of the pectin disassembly process during fruit ripening are first discussed, and then the nanostructural characterization of fruit pectins by AFM and its relationship with texture and postharvest fruit shelf life is reviewed. In general, fruit pectins are visualized under AFM as linear chains, a few of which show long branches, and aggregates. Number- and weight-average values obtained from these images are in good agreement with chromatographic analyses. Most AFM studies indicate reductions in the length of individual pectin chains and the frequency of aggregates as the fruits ripen. Pectins extracted with sodium carbonate, supposedly located within the primary cell wall, are the most affected.

Ultrasound assisted immersion freezing of broccoli (Brassica oleracea L. var. botrytis L.)

OBJECTIVE

The aim of this study was to research the ultrasound-assisted freezing (UAF) of broccoli.

METHODS

CaCl2 solution was used as freezing medium. The comparative advantage of using UAF over normal freezing on the freezing time, cell-wall bound calcium to total calcium ratio, textural properties, color, drip loss and L-ascorbic acid contents was evaluated.

RESULTS

The application of UAF at selected acoustic intensity with a range of 0.250-0.412 W/cm(2) decreased the freezing time and the loss of cell-wall bound calcium content. Compared to normal freezing, the values of textural properties, color, L-ascorbic acid content were better preserved and the drip loss was significantly minimized by the application of UAF. However, when outside that range of acoustic intensity, the quality of the ultrasound-assisted frozen broccoli was inferior compared to that of the normally frozen samples.

CONCLUSIONS

Selected the appropriate acoustic intensity was very important for the application of UAF.

Advances in research on structural characterisation of agricultural products using atomic force microscopy

Atomic force microscopy (AFM) has many unique features compared with other conventional microscopies, such as high magnification with high resolution, minimal sample preparation, acquiring 2D and 3D images at the same time, observing ongoing processes directly, the possibility of manipulating macromolecules, etc. As a nanotechnology tool, AFM has been used to investigate the nanostructure of materials in many fields. This mini-review focuses mainly on its latest application to characterise the macromolecular nanostructure and surface topography of agricultural products. First the fundamentals of AFM are briefly explained. Then the macromolecular nanostructure information on agricultural products from AFM images is introduced by exploring the structure-function relationship in three aspects: agricultural product processing, agricultural product ripening and storage, and genetic and environmental factors. The surface topography characterisation of agricultural products using AFM is also discussed. The results reveal that AFM could be a powerful nanotechnology tool to acquire a deeper understanding of the mechanisms of structure and quality variations of agricultural products, which could be instructive in improving processing and storage technologies, and AFM is also helpful to reveal the essential nature of a product at nanoscale.