Insoluble Pectin Research Articles

Dry fruit as source of fungal contaminants or functional compounds?

Abstract This study evaluated the role of dry fruits as a source of fungal contaminants or functional compounds. Dry apple, apricot, candied fruits, prune, and white and black raisin were evaluated regarding patulin and ergosterol content, centesimal composition, pH, acidity, pectin, and phenolic profile. The ergosterol was detected in 38% of the samples and patulin (PAT) in 89%, the apricot samples stood out most by contaminant level. Apricot, candied fruit, and prunes presented moisture values beyond the other dry fruits. The pH ranged from 3.8 to 4.6; acidity from 0.1 to 1.0%; sugar content from 1.7 to 5.5%; and levels of soluble and insoluble pectin from 1.6 to 5.1% and 10.9% to 27.3%, respectively. The apples showed a higher content of free phenolic compounds (6.6 mg of gallic acid/g) with a predominance of gallic and protocatechuic acids. Pearson's correlation showed a significant positive correlation between patulin and ergosterol content (0.99) and soluble pectin (0.78); a significant negative relation between total sugars (-0.66) and free phenolic compounds (-0.63). Fungal contamination and the occurrence of PAT show that this mycotoxin is present and, therefore, the evaluation of fungal toxins in dry fruits is recommended before claiming them to be a source of functional compounds.

Purification and Thermodynamic Characteristics of an Exo-Polygalacturonase from Trichoderma Pseudokoningii

Polygalacturonases (PGs) are necessary to degrade the insoluble viscous pectin components during the clarification process of fruit juice and are produced by some plants and various microbes, such as bacteria, yeasts and fungi. In this study, an exo-polygalacturonase (exo-PGP4a) was purified from T. Pseudokoningii using DEAE-Sepharose and Sephacryl S-200 columns. We show that the enzyme produced in this study by solid-state fermentation of citrus Orange peel was purified 20-fold with 12.8% recovery. The apparent molecular mass of the enzyme was determined to be 25 kDa using gel filtration and SDS-PAGE. The optimum temperature and pH of the exo-PGP4a were 45and#176;C and 6, respectively. The exo-PGP4a showed half-lives of 50.95 and 21.32 min at 55 and 75and#176;C, respectively. The activation energy for denaturation (Ea*) was 42.596 kJ/mol. The Km value of the enzyme for PGA hydrolysis was 2 mg/ml, and the Vmax was 3.27 and#181;mol min-1 mg-1. Several metal cations, such as Cu2+and Zn2+, were found to enhance the enzymatic activity of the exo-PGP4a, while Pb2+, Ca2+, Ni2+, Cd2+, Co2+ and Hg2+ ions were found to be inhibitory. In this study, we suggest the exo-polygalacturonase has potential role of the clarification of Orange, Apple, Grape, and Peach juices in the food industry.

Purification and Thermodynamic Characteristics of an Exo-Polygalacturonase from Trichoderma Pseudokoningii

Polygalacturonases (PGs) are necessary to degrade the insoluble viscous pectin components during the clarification process of fruit juice and are produced by some plants and various microbes, such as bacteria, yeasts and fungi. In this study, an exo-polygalacturonase (exo-PGP4a) was purified from T. Pseudokoningii using DEAE-Sepharose and Sephacryl S-200 columns. We show that the enzyme produced in this study by solid-state fermentation of citrus Orange peel was purified 20-fold with 12.8% recovery. The apparent molecular mass of the enzyme was determined to be 25 kDa using gel filtration and SDS-PAGE. The optimum temperature and pH of the exo-PGP4a were 45and#176;C and 6, respectively. The exo-PGP4a showed half-lives of 50.95 and 21.32 min at 55 and 75and#176;C, respectively. The activation energy for denaturation (Ea*) was 42.596 kJ/mol. The Km value of the enzyme for PGA hydrolysis was 2 mg/ml, and the Vmax was 3.27 and#181;mol min-1 mg-1. Several metal cations, such as Cu2+and Zn2+, were found to enhance the enzymatic activity of the exo-PGP4a, while Pb2+, Ca2+, Ni2+, Cd2+, Co2+ and Hg2+ ions were found to be inhibitory. In this study, we suggest the exo-polygalacturonase has potential role of the clarification of Orange, Apple, Grape, and Peach juices in the food industry.

Physicochemical quality maintenance and bioactive compounds enhancement of Thai guava fruit cv. ‘Kim Ju’ by using combinative hot water and methyl jasmonate immersion

Postharvest life of Thai guava fruits is limited due to skin damage and physicochemical changes during cold storage. Both methyl jasmonate (MeJA) and heat treatments are potential approaches maintaining postharvest quality of fruits. Thus, the aim of this work was to investigate the effects of hot water and MeJA immersion on physicochemical quality of ‘Kim Ju’ guava fruit during storage at 12 ± 1 °C for 18 d. The fruit were immersed in hot water at 40 °C for 30 min (H), 0.1 mM MeJA for 10 min (0.1 mM MeJA) or H followed by 0.1 mM MeJA (H + 0.1 mM MeJA) and untreated fruit were used as control. The determined parameters were visual appearance, colour, texture, pectin substances, antioxidant activities, bioactive compounds and antioxidant enzymes activities. The results showed that H + 0.1 mM MeJA treatment maintained visual appearance and colour as compared to 0.1 mM MeJA, H or control treatment, consequently. The treatment of H + 0.1 mM MeJA retarded softening according to the inhibition of soluble pectin increase and insoluble pectin decrease. The treatment enhanced the both antioxidant and free radical scavenging activities as compared to control. These were accompanied with the increments of bioactive compounds such as ascorbic acid, total phenols, flavonoids and peroxidase activity and the retardation of catalase activity decrease. In conclusion, the H + 0.1 mM MeJA treatment could maintain postharvest qualities involving visual appearance and texture and enhanced nutritional value of guava fruit during cold storage.

Water resistance and mechanical properties of low methoxy-pectin nanocomposite film responses to interactions of Ca2+ ions and glycerol concentrations as crosslinking agents

To achieve a low methoxy-pectin nanocomposite film with maximum resistance to water and acceptable mechanical properties, the interactions of different glycerol concentrations and Ca2+ ions in both steps of crosslinking on the swelling degree (SD) and mechanical properties of prepared films were investigated using response surface methodology (RSM). Accordingly, quadratic second-order models were fitted to the SD and tensile strength responses; while the cubic model demonstrated a good relation between independent variables and elongation at break respectively. As a compromise between water resistance and mechanical properties of the prepared films, the use of 0.5% Ca2+, 0.75% Gly1 and 7.5% Gly2 is suggested as the optimum condition. Generally, crosslinking of pectin polymer with Ca2+ cations in the second step along with incorporation of nanocellulose into pectin film led to the formation of more flexible and completely water insoluble pectin nanocomposite film in comparison to the other polymers crosslinked with Ca2+ cations.

Integrated transcriptomic-metabolomic analysis reveals cellular responses of harvested strawberry fruit subjected to short-term exposure to high levels of carbon dioxide

Harvested strawberry (Fragaria × ananassa) fruit has a short shelf life due to rapid postharvest metabolism, quick softening, mechanical damage, and fungal decay. To improve the storability of strawberry fruit, we subjected harvested fruit to short-term exposure to 30% carbon dioxide (CO2) and used transcriptomic and metabolomic analyses to identify the cellular responses induced by this treatment. Fruit was stored at 10 °C for 10 d after a 3-h exposure to 30% CO2 (treatment) or ambient air (control) at 25 °C, respectively. The CO2 treatment reduced fruit decay and softening compared to the control throughout the 10-d storage period. Transcriptomic analyses revealed that expression levels of genes encoding cell wall-degrading enzymes (expansin, pectinesterase, and β-xylosidase) decreased in response to the CO2 treatment. Within 1 d after the CO2 treatment, the expression levels of genes encoding heat-shock proteins significantly increased. Metabolite profiling revealed that glucose, quinic acid, and succinic acid increased in responses to the CO2 treatment at 1 d. Transmission electron microscopy showed that disintegration of the middle lamella in the cell wall was inhibited by the CO2 treatment. Polyuronide (insoluble pectin) content in cell walls was 30% higher, on average, in the treated fruit than those in the control fruit during the 10-d storage period. These results indicate that a short-term treatment with 30% CO2 reduces the degradation of pectin in the cell wall by reducing the activity of cell wall-degrading enzymes and induces abiotic stress-response genes in harvested strawberry fruit. Our results improve our understanding of the molecular mechanisms behind CO2-responsive genes in strawberry fruit and provide insight into ways to improve the postharvest quality of strawberries.

Mechanisms of carrot texture alteration induced by pure effect of high pressure processing

Abstract The pure effect of high pressure processing (HPP) (400–1200 MPa/2 min) on carrot (Daucus carota L.) texture was investigated with minor influence of adiabatic heating. For carrot hardness and chewiness, 400 MPa result in respective loss of 71.0%, 73.8%, but no further loss was observed as pressure increased. Cohesiveness and resilience were observed to recover as pressure above 1000 MPa. Mechanisms exploration from cellular microstructure showed that carrot cells evolved from orderliness at atmospheric pressure to corrugation, elongation, collapse but partially compaction at 400, 800 and 1200 MPa, respectively, accompanied with movement of cytoplasmic content to intercellular spaces. Principal component analysis (PCA) highlighted the characteristic biochemical responses of HPP-treated carrots with pronounced ion leakage (>70%), hydrogen peroxide accumulation (>128.0%, 800–1200 MPa) and enhanced pectinmethylesterase (PME) activity (>135.2%, 400–1000 MPa). Moreover, molecular weight analysis of pectin polysaccharides showed that HPP triggered pectin depolymerisation, solubilisation of water insoluble pectin and fraction interconversion. Overall, carrot texture is interactively influenced by pressure-induced modifications on cell morphology, membrane integrity and pectin properties. Industrial relevance Application of HPP in industrial scale is rising. As an essential factor highly linked with freshness, texture alteration during processing is an industrial-concerned issue. This work provides information on textural alteration under a wide pressure range (400–1200 MPa). The reported pressure thresholds triggering different cellular responses of carrot tissue therefore added new theoretical basis for the industrial optimisation of high pressure conditions. The temperature control strategy used could be potentially applied in food industry with the substituted food-friendly pressure transmitting medium, as well as other areas requiring strict temperature control, for instance high pressure extraction.

The solubility of primary plant cell wall polysaccharides in LiCl-DMSO

In order to understand the architecture of the primary plant cell wall, knowledge on its polysaccharides and their interactions is of importance. In this study, further architectural insight was obtained by sequential LiCl-DMSO and buffer extractions after planetary ball milling. After milling, up to 50% of all polysaccharides in the Chelating agent Unextractable Solids (ChUS) from carrot, tomato and strawberry solubilised in LiCl-DMSO without loss of structural information. Approximately 30% of all pectin was LiCl-DMSO insoluble but solubilised in the subsequent buffer extraction, and these populations had higher HG:RG-I ratios than LiCl-DMSO soluble populations. The degree of methyl-esterification (DM) of pure pectins highly determined its solubility in LiCl-DMSO. However, solubility of cell wall pectin was governed by more factors since both soluble and insoluble pectin were substantially methyl-esterified and acetylated. Digestion of LiCl-DMSO soluble and insoluble fractions by pectinases confirmed the presence of acetylated HG-regions for carrot and strawberry pectin.

Differences in the dietary fiber content of fruits and their by-products quantified by conventional and integrated AOAC official methodologies

Accurate determination of total dietary fiber (DF) and its soluble (SDF) and insoluble (IDF) fractions is relevant for food analysis research and nutritional labelling. AOAC integrated DF methodology (AOAC 2011.25, IM) has procedure differences compared to the traditionally used AOAC method (991.43, TM), resulting in different DF quantification. However, IM has been mostly performed for cereal-based products and its application in sources such as fruit products needs to be studied. The aim of this study was to compare the DF content obtained by TM with that achieved using IM in pulps and peels of banana (Musa paradisiaca), mamey sapote (Pouteria sapota), mango (Mangifera indica), Meyer lemon (Citrus meyeri), orange (Citrus sinensis), prickly pear (Opuntia ficus-indica), tamarind (Tamarindus indica), and watermelon (Citrullus lanatus). Samples containing high starch (banana and its peel, mamey sapote and mango pulp) showed higher IDF values when IM was used. Differences were observed when pectinaceous fruits (orange, Meyer lemon, mango and prickly pear) were assayed, since soluble and insoluble pectins are underestimated by TM. Fruits with a high content of non-digestible oligosaccharides showed higher SDF values when assayed by IM. The use of IM in fruits and their by-products provides relevant information about DF fractions and reduces DF underestimations typically observed when assayed by TM.

SALICYLIC ACID IMMERSION MAINTAINS PHYSIOCHEMICAL QUALITY AND ENHANCES BIOACTIVE COMPOUNDS IN ‘KIMJU’ GUAVA FRUIT DURING COLD STORAGE

The aims of this work were to investigate the effect of salicylic acid (SA) immersion on the physicochemical quality maintenance and biologically active compounds enhancement of ’Kimju’ guava. The fruit were immersed in water (control) and 2 mM SA solution and stored at 12 ± 1 ºC, 90±2% RH. The observed factors were pigments, total sugars, total soluble solids (TSS), total acidity (TA), firmness and pectin components, bioactive compounds such as ascorbic acid (AsA), total phenols (TP), total flavonoids (TF) and the activities of antioxidant enzymes including peroxidase (POD) and catalase (CAT). The total chlorophylls chlorophyll a and b contents of the treated fruit were higher than those of the control. The SA immersion did not affect the total carotenoids concentration and TSS whilst it delayed the increase in total sugars and lowered TA content. The fruit softening was delayed by the SA immersion due to the control of soluble pectin increase and insoluble pectin decrease. The antioxidant activity and the concentrations of AsA, TP and TF were enhanced by the SA immersion. The SA immersion also stimulated POD activity but did not induced CAT activity. In conclusion, 2.0 mM SA immersion is an effective postharvest treatment maintaining quality and improving nutritional values of ‘Kimju’ guava.

Identification and Quantification of Intracoordination Water in Insoluble Pectinates Cu<sup>2+</sup> and Pb<sup>2+</sup>

By derivatography in insoluble pectins Cu2+ (РCu2+) and Pb2+ (РPb2+), the presence of “a high-temperature component” (150°C- 165°C) is established. During potentiometric alkalimetric titration of РCu2+ and РPb2+, endpoints are established at рН accordingly 4.87 and 4.95, proving acid properties of PM. Obtained data show the presence of water in the internal sphere of PM. Considering the loss of this water and the known ratio of metal cations and monomers of pectin (L-), the simplest formulas of pectins are established: [Cu(L-)2(H2O)2], [Pb(L-)2(H2O)4].

Patterns of flesh reddening, translucency, ethylene production and storability of ‘Friar’ plum fruit harvested at three maturity stages as affected by the storage temperature

Flesh reddening and translucency are two predominant physiological disorders of ‘Friar’ plum (Prunus salicina Lindl.) during cold storage. In order to investigate the occurrence of these disorders, the fruit were harvested at early-, mid- and late-maturity stages and stored at 0, 2, 5, 15 or 25°C, 85–95% relative humidity. Three concomitant patterns for flesh reddening, translucency and abnormal softening (melting) of ‘Friar’ plums were evident: rapid increases in these disorders at 5 and 15°C, a delayed/suppressed of these disorders at 0 and 2°C, and normal ripening at 25°C, irrespective of fruit maturity stage. Three similar temperature-mediated patterns of anthocyanin accumulation related to flesh reddening, pectin solubilization related to translucency, and decline in firmness related to abnormal softening were observed. Three patterns of ethylene production were also identified: early and dramatically high ethylene production at 5 and 15°C, suppressed ethylene production at 0 and 2°C, and almost no ethylene production at 25°C. These results suggest that ethylene may be involved in the onset and development of flesh disorders of ‘Friar’ plums during cold storage. Respiration greatly increased, water-soluble pectin content increased early during storage and remained high, and insoluble pectin (i.e., protopectin) decreased, in plums held at 5 and 15°C. Overall, the biochemical and physiological behavior of plums were greatly affected by storage at 5 and 15°C compared with 0, 2 and 25°C, and late-maturity plums were more susceptible to storage disorders.

The stiffening of the cell walls observed during physiological softening of pears.

Main conclusionThe Young’s modulus of the primary cell walls of pears decreases linearly during the pre-harvest on-tree maturation and increases during postharvest storage, and does not correlate with firmness of fruit.The determination of mechanical properties of cell walls is indispensable for understanding the mechanism of physiological softening and deterioration of quality of fruits during postharvest storage. The Young’s modulus of the primary cell walls from pear fruit (Pyrus communis L., cultivars ‘Conference’ and ‘Xenia’) during pre-harvest maturation and postharvest storage in an ambient atmosphere at 2 °C followed by shelf life was studied using atomic force microscopy (AFM). The results were related to the firmness of fruits, galacturonic acid content in water, chelator, sodium carbonate and insoluble pectin fractions, polygalacturonase and pectin methylesterase activities. The Young’s modulus of the primary cell walls decreased linearly during the last month of pre-harvest maturation from 3.2 ± 1.8 to 1.1 ± 0.7 MPa for ‘Conference’ and from 1.9 ± 1.2 to 0.2 ± 0.1 MPa for ‘Xenia’ which correlated with linear firmness decrease. During postharvest storage the cell wall Young’s modulus increased while firmness continued to decrease. Correlation analysis for the entire period of the experiment showed a lack of straightforward relation between the Young’s modulus of primary cell walls and fruit firmness. The Young’s modulus of cell walls correlated negatively either with galacturonic acid content in sodium carbonate soluble pectin (‘Conference’) or with insoluble pectin fractions (‘Xenia’) and positively with polygalacturonase activity. It was therefore evidenced that covalently linked pectins play the key role for the stiffness of fruit cell walls. Based on the obtained results, the model explaining the fruit transition from firm and crispy to soft and mealy was proposed.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-015-2423-0) contains supplementary material, which is available to authorized users.

Soluble fiber on energy metabolism of ruminants

Much of the energy produced by ruminant animals in a breeding environment is derived from the fermentation of soluble and structural carbohydrates, which are converted by microbial fermentation into metabolic products that can be allocated to the synthesis of meat, milk, wool and work. In this context the study´s objective is to review the importance of soluble fiber in the ruminants´ energetic metabolism and show the main differences in comparison to other fibers. The soluble fibers are pectins, beta-glucans, gums, mucilages and some hemicelluloses, and the insoluble fibers are cellulose, lignin, hemicelluloses and insoluble pectins. Pectin is the only component of the cell wall which is completely and rapidly fermentable therefore it is not in contrast to hemicelluloses one of the lignified substance of the matrix. Researchers when testing two types of corn kernels processing (flaked or coarsely grounded) and its replacement by 50% citrus pulp pelleted in Holstein cows fed with corn silage, observed that the partial inclusion of citrus pulp used in the diet did not affect the intake of DM and organic material and the digestibility of starch and crude protein. However, the apparent digestibility of NDF and ADF were higher, causing a beneficial effect on the performance of dairy cows. Where animals fed with soluble fiber showed higher weight gain and better feed conversion. In general the by-products with high pectin concentration have great potential for use in ruminant´s diets due to their high energetic density. Besides that they have a favourable type of fermentation without lactic acid production, helping maintaining a favourable rumen environment; however such introduction in the diet of ruminants must be done carefully, in order not to lose the initial economic goals and animal welfare allied to a good production.

THE USE OF HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY AS SCREENING TECHNIQUE FOR PECTIN AND PECTIN SUBSTANCES OF DIETARY FIBERS

The peak of the unspecified compound of quantitative analysis of organic acids in biological materials by using high-performance liquid chromatography was identified. This peak corresponded to polygalacturonic acid. A High-performance liquid chromatographic method was developed to identify and quantify of water soluble pectin fraction and insoluble pectin fraction, galacturonic acid and polygalacturonic acid. The method based on the extraction of free water soluble fraction with phosphate buffer (pH 4.8) or with 0.01 N phosphoric acid and on the acid hydrolysis of insoluble pectin fraction in presence 0.1 N HNO3. The pectin fractions were separated and determined on a C610H column using elution with 0.01 N phosphoric acids and ultraviolet detection at 210 nm. Galacturonic acid and polygalacturonic acid were used as internal standard. The calibration curves were presented for each of the standards. The determinations were performed in the linear range of 0.04÷0.17% w/v for both pectin fractions. Proposed procedure can considered as a rapid method for quantitative pectin determination in the food, food nutrition’s food, and pharmaceutical agents.

Fiber from a regular diet is directly associated with fecal short-chain fatty acid concentrations in the elderly

It has recently been suggested that fiber exerts a considerable effect on microbiota composition and on fecal short-chain fatty acid (SCFA) production, the concentration of which in the colon is important for immune regulation and for maintaining gut and overall health. To test the hypothesis that the fiber consumed in a regular diet affects fecal SCFA concentrations in the elderly, the authors investigated the association between different types of fiber intake and fecal SCFA concentrations in 32 institutionalized elderly subjects aged between 76 and 95 years. Food intake was recorded by means of a validated food frequency questionnaire. Total, soluble (pectin and hemicellulose) and insoluble (pectin, hemicellulose, Klason lignin, and cellulose) fiber was determined using Marlett Food Composition Tables. Analysis of acetic, propionic, and butyric acid concentrations was performed using gas chromatography–mass spectrometry. Potato intake was directly associated with SCFA concentrations and apple intake with propionate concentration. Of the fibers, cellulose showed an independent association with acetate and butyrate concentrations, and insoluble pectin explained a part of the variation in propionate. In conclusion, our results provide further evidence regarding the relation between diet and SCFA concentration in the elderly. The identification of an association between the regular intake of foods such as potatoes and the production of SCFAs provides an opportunity to improve public health.

Effect of heat treatment and homogenization on the rheological properties of aqueous parsnip suspensions

Parsnip (Pastinaca sativa) suspensions, at concentrations corresponding to a dilute and concentrated regime, were subjected to pasteurization, and heat treatments that favored β-elimination reactions and pectin methyl esterase activity. The different heat treatments were combined with homogenization. Physicochemical properties such as content of insoluble/soluble material and insoluble/soluble pectin were measured together with particle and rheological properties. Pectin methyl esterase activity led to a high yield of insoluble material and insoluble pectin, whereas β-elimination led to a high yield of soluble material and solubilized pectin. Homogenization after heat treatment resulted in increased solubilization of the pectin, especially after β-elimination reactions. Parsnip suspensions subjected to pectin methyl esterase activity exhibited the highest elastic modulus most likely due to the cross-linked pectin conferring rigidity to the cell walls. The content of insoluble material and the particle properties such as size and rigidity are important factor for the rheological properties of concentrated parsnip suspensions.

Enzymatic Liquefaction of Cell-Walls from Kent and Tommy Atkins Mango Fruits

Tab le mango varieties discarded by the export market are generally not considered suitable for processing mainly because they yield too viscous fruit purees. The objective of this study was determining if appropriate enzy mat ic treatment can overcome this barrier. Cell-wall polysaccharides fro m mesocarp and pericarp of fu lly ripe table mangoes were characterized analy zing the alcohol-insoluble residues (AIR). Content of celluloses, hemicellu loses, lignin and soluble and insoluble pectin were assessed after selective ext raction. After hydrolysis of main fractions, neutral sugars were determined by gas chromatography showing that xylose prevails (12-14 %) in the non-cellu losic fract ion of ins oluble cell walls fro m mesocarp, indicating predo minance with cellulose, of xilan-type polysaccharides in mango flesh. Water insoluble AIR (WAIR) was incubated with co mmercial preparat ions, characterized for their main enzy mat ic activit ies and comprising balanced proportion of pectinases and cellulases with other different secondary activities. At equivalent 500 µl per kilogram of puree and at 45°C, solubilisation rates of uronids and neutral sugars reach respectively 100 and 90% only when xy lanase activities were present. Then, a commercial enzy me preparation containing pectinases, cellulases and high xylanase activities was applied to native mango puree varying enzyme concentration and incubation time according to a central composite rotatable design. It was shown that percent of final suspended insoluble solids and Bostwick consistency could be considerably reduced in minutes, using a relatively lo w amount of enzyme preparation (150 µl.L -1 ). Rheological properties of mango purees can be modulated easily according to incubation time and concentration of enzymatic solution to fit the needs of food industries.

Effect of Calcium Sprays on Mechanical Strength and Cell Wall Fractions of Herbaceous Peony (Paeonia Lactiflora Pall.) Inflorescence Stems

Calcium is an essential element and imparts significant structural rigidity to the plant cell walls, which provide the main mechanical support to the entire plant. In order to increase the mechanical strength of the inflorescence stems of herbaceous peony, the stems are treated with calcium chloride. The results shows that preharvest sprays with 4% (w/v) calcium chloride three times after bud emergence are the best at strengthening “Da Fugui” peonies’ stems. Calcium sprays increased the concentrations of endogenous calcium, total pectin content as well as cell wall fractions in herbaceous peonies stems, and significantly increased the contents of them in the top segment. Correlation analysis showed that the breaking force of the top segment of peonies’ stems was positively correlated with the ratio of water insoluble pectin to water soluble pectin (R = 0.673) as well as lignin contents (R = 0.926) after calcium applications.

POSTHARVEST CONSERVATION OF CUBIU (SOLANUM SESSILIFLORUM DUNAL) FRUITS IN RESPONSE TO PASSIVE MODIFIED ATMOSPHERE ASSOCIATED WITH REFRIGERATION

Cubiu (Solanum sessiliflorum Dunal) is a fruit with high potential for being used in food industry in Manaus, Amazonas, Brazil. This work was carried out to verify the effect of modified atmosphere associated with refrigeration on postharvest conservation of cubiu fruits. Ripe fruits, except the control ones, were stored on polystyrene trays under passive modified atmosphere (polyvinyl chloride film coverage) and stored under refrigeration (7°C and ±85% relative humidity) for 16 days. Every three days they were analysed regarding weight loss, acidity, pH, soluble solids, total sugars, ascorbic acid, phenolic compounds, polyphenoloxidase activity, alcohol insoluble solids and pectin. Neither atmosphere nor storage time produced difference on most chemical compounds, but in both cases, the ascorbic acid content only lowered in the first eight days (yet the decrease was sharper in environmental atmosphere). Concentrations of phenolic compounds and polyphenoloxidase activity were higher in mesocarp tissues. Weight loss reduction in the fruit as a whole, lack of wrinkling in the surrounding area of stem insertion, and superficial darkening right in the stem insertion, were the major benefits provided by the passive modified atmosphere in the postharvest conservation of very ripe cubiu fruits stored for sixteen days under refrigeration.