Pectin degradation in ripening and wounded fruits

Drought-induced cell wall degradation in the base of pedicel is associated with accelerated cotton square shedding

Drought significantly impacts cotton square (flower buds with bracts) shedding, directly affecting yield. To address the internal physiological mechanisms of drought affecting cotton square shedding, a polyethylene glycol-simulated drought study was conducted with Dexiamian 1 and Yuzaomian 9110 to investigate cell wall degradation changes in the base of pedicel where the detachment of cotton square takes place, and its relationship with cotton square shedding. Results revealed significant decreases in cellulose, hemicellulose, and pectin contents in the base of square pedicel, leading to cell wall degradation and consequent square shedding. Furthermore, drought stress exacerbated the hydrolysis of cellulose and pectin in the base of pedicel, although not hemicellulose, resulting in more noticeable alterations in the morphology and structure of the base of pedicel, such as more significant degradation in the epidermis, cortex, and phloem. Regarding the cellulose hydrolysis, drought mainly increased the expression of genes β-glucosidase (GhBG1) and endoglucanase (GhEG1), and the activity of β-glucosidase and endoglucanase in the base of pedicel, promoting the conversion of cellulose to cellobiose, and eventually glucose. Regarding the pectin hydrolysis, drought significantly enhanced the expression of the gene pectin methylase (GhPE1), thereby accelerating pectin hydrolysis to generate polygalacturonic acid. Additionally, drought increased the expression of genes pectin lyase (GhPL1) and polygalacturonase (GhPG1), as well as the activity of pectin lyase, which further accelerated the hydrolysis of polygalacturonic acid into galacturonic acid. These findings suggest that drought mainly promotes cellulose and pectin hydrolysis in the base of pedicel, hastening cell wall degradation and final cotton square shedding.

Modification and application of highly active alkaline pectin lyase

Alkaline pectate lyase has developmental prospects in the textile, pulp, paper, and food industries. In this study, we selected BacPelA, the pectin lyase with the highest expression activity from Bacillus clausii, modified and expressed in Escherichia coli BL21(DE3). Through fragment replacement, the catalytic activity of the enzyme was significantly improved. The optimum pH and temperature of the modified pectin lyase (PGLA-rep4) were 11.0 and 70 °C, respectively. It also exhibited a superior ability to cleave methylated pectin. The enzyme activity of PGLA-rep4, measured at 235 nm with 0.2% apple pectin as the substrate, was 554.0 U/mL, and the specific enzyme activity after purification using a nickel column was 822.9 U/mg. After approximately 20 ns of molecular dynamics simulation, the structure of the pectin lyase PGLA-rep4 tended to be stable. The root mean square fluctuation (RMSF) values at the key catalytically active site, LYS168, were higher than those of the wildtype PGLA. In addition, PGLA-rep4 was relatively stable in the presence of metal ions. PGLA-rep4 has good enzymatic properties and activities and maintains a high pH and temperature. This study provides a successful strategy for enhancing the catalytic activity of PGLA-rep4, making it the ultimate candidate for degumming and various uses in the pulp, paper, and textile industries.

Effect of slicing and storage temperatures on biochemical aspects of membrane integrity in two different genotypes of tomato

BACKGROUND

Fresh-cut vegetables are subjected to multiple stressing agents including: (i) slicing, which induces cellular decompartmentalization; (ii) low refrigeration temperatures, responsible for chilling injury in the most sensitive products (e.g. tomatoes), and (iii) storage time because tissue senescence and aging can occur and reduce the shelf-life. In tomato slices, one of the most important issues is the membrane, which is responsible for several disorders related to the alteration of physiological processes, including ethylene biosynthesis.

RESULTS

Electrolyte leakage and the content of thiobarbituric acid reactive substances in sliced tomatoes increased over time at two storage temperatures (4 °C and 15 °C) compared with intact fruit for the commercial variety (cultivar) Jama used as reference. However, in the tomato Italian landrace Canestrino, electrolyte leakage in sliced fruits increased after 120 h of storage compared to intact tomatoes, while the thiobarbituric acid reactive substance content increased rapidly over time at both storage temperatures. In the packages, higher ethylene content and carbon dioxide concentrations were detected in sliced tomatoes compared with intact fruits for both genotypes. In the most sensitive genotype for slicing (Jama), phospholipase C activity increased in tomato slices after 24 h of storage, but phospholipase D reached a higher value only at 168 h after processing at 4 °C of storage.

CONCLUSIONS

The results evidence that the main damage in slices of full ripe tomatoes is more related to cutting, rather than chilling injury due to storage temperatures, with differences related to the genotype. Slicing enhanced membrane catabolism, ethylene production, and enzyme activity of phospholipases with a significant genotype effect. © 2021 Society of Chemical Industry.

Suppression of N-glycan processing enzymes by deoxynojirimycin in tomato (Solanum lycopersicum) fruit

The present study investigated the potential of a small molecule inhibitor, 1-deoxynojirimycin (DNJ), to extend the shelf life of tomatoes. The optimum concentration of DNJ and the proper ripening stage for treatment were standardized using response surface methodology, following a central composite design. The concentration of DNJ used for the analysis was 0.15 mM, and 0.30 mM and the ripening stages of the tomato fruit analysed were immature green, mature green, breaker, ripen and over-ripen. Analysis of the influence of the DNJ treatment of the fruit using quadratic multiple regression models considering the factors colour, texture, and free sugars revealed significant responses. A DNJ concentration of 0.30 mM and fruit-ripening stage of mature green was found to be optimal for the treatment. DNJ-treatment maintained fruit firmness throughout ripening with a significant reduction in reducing sugar formation. Enzyme activity of the N-glycan processing enzymes involved in cell wall softening, α-mannosidase and β-d-N-acetylhexosaminidase revealed a significant reduction in their activity by 2 and 3.5-fold, respectively. Down-regulation of expression of important ripening-related and softening process-associated genes, aminocyclopropane carboxylic synthase-4, aminocyclopropane carboxylic oxidase, polygalacturonase and pectin methylesterases at 4, 5, 6 and 5-fold, respectively, was also observed. The present results showed that the treatment of mature green tomato fruit with DNJ at a concentration of 0.30 mM can delay the ripening of the tomato fruit by inhibiting cell wall and N-glycan processing enzymes.

Trends and advances in edible biopolymer coating for tropical fruit: A review

Nowadays, many of the tropical fruits have been commercialized worldwide due to increasing demand. In 2018, global tropical fruit has reached an unprecedented peak of 7.1 million tonnes. As such, a lot of large scale farming has been initiated to cultivate the fruit for commercialization. The nature of tropical fruit is perishable make the fruit easily undergo post-harvest losses especially when the fruit travels in a long distance for distribution. Losses of tropical fruit is estimated around 18-28% after harvesting. Then, the losses will continually develop during the trading process. Applying fruit coating on the fruit can minimize substantial privation. This article compendiously reviews the needs of coating and discuss different types of coating materials. The efficiency of different coating materials; polysaccharide, protein, lipid and composite based coating on tropical fruit is highlighted. There are various types of coating available for major fruit such as banana, mango, pineapple and avocado that can effectively extend the post-harvest life, minimize water loss, reduce chilling injuries and fight against post-harvest disease. Coating from minor fruit such as durian, rambutan, passion-fruit and mangosteen are still limited especially made from lipid and protein coating. In choosing the most appropriate coating for tropical, the nature of fruit needs to be understood. In addition, the chemistry of coating components and techniques of application is important in modulating the fruit quality.

Metagenomic and Metatranscriptomic Analyses of Diverse Watermelon Cultivars Reveal the Role of Fruit Associated Microbiome in Carbohydrate Metabolism and Ripening of Mature Fruits

The plant microbiome is a key determinant of plant health and productivity, and changes in the plant microbiome can alter the tolerance to biotic and abiotic stresses and the quality of end produce. Little is known about the microbial diversity and its effect on carbohydrate metabolism in ripe fruits. In this study, we aimed to understand the diversity and function of microorganisms in relation to carbohydrate metabolism of ripe watermelon fruits. We used 16S metagenomics and RNAseq metatranscriptomics for analysis of red (PI459074, Congo, and SDRose) and yellow fruit-flesh cultivars (PI227202, PI435990, and JBush) of geographically and metabolically diverse watermelon cultivars. Metagenomics data showed that Proteobacteria were abundant in SDRose and PI227202, whereas Cyanobacteria were most abundant in Congo and PI4559074. In the case of metatranscriptome data, Proteobacteria was the most abundant in all cultivars. High expression of genes linked to infectious diseases and the expression of peptidoglycan hydrolases associated to pathogenicity of eukaryotic hosts was observed in SDRose, which could have resulted in low microbial diversity in this cultivar. The presence of GH28, associated with polygalacturonase activity in JBush and SDRose could be related to cell wall modifications including de-esterification and depolymerization, and consequent loss of galacturonic acid and neutral sugars. Moreover, based on the KEGG annotation of the expressed genes, nine α-galactosidase genes involved in key processes of galactosyl oligosaccharide metabolism, such as raffinose family were identified and galactose metabolism pathway was reconstructed. Results of this study underline the links between the host and fruit-associated microbiome in carbohydrate metabolism of the ripe fruits. The cultivar difference in watermelon reflects the quantum and diversity of the microbiome, which would benefit watermelon and other plant breeders aiming at the holobiont concept to incorporate associated microbiomes in breeding programs.

Ethylene-induced overproduction of reactive oxygen species is responsible for the development of watersoaking in immature cucumber fruit

Watersoaking is an ethylene-induced disorder observed in some members of the Cucurbitaceae including cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thunb. Matsum and Nakai), and tropical pumpkin (Cucurbita moschata Duch.). Previous studies have found that immature beit-alpha cucumber (cv. Manar) exhibit watersoaking after 6d of continuous exposure to 10 μLL(-1) ethylene in air (21 kPa O(2)). The present study was designed to investigate the early dynamics of ethylene responses in immature cucumber fruit in order to provide insight into the watersoaking triggering mechanism. Changes in respiration, epidermal color, firmness, reactive oxygen species (ROS) production and electrolyte leakage were evaluated as a function of time under different ethylene concentrations and exposure duration. Ethylene concentrations exceeding 10 μLL(-1) did not accelerate changes in any of the evaluated responses. The first detectable change was a significant rise in respiration on day 2, followed by a significant rise in ROS on day 4, and significant degreening, mesocap softening, and increased electrolyte leakage on day 6; the latter responses coincident with incipient watersoaking. Varying the duration of exposure to ethylene indicated that the critical exposure time is between 2 and 4d. Notably, all deleterious responses to ethylene were suppressed under a hypoxic atmosphere. A model is proposed in which ethylene induces a sharp increase in respiration with a concomitant sharp rise in ROS, which the immature fruit is incapable of quenching. The resulting production of excess ROS leads to discoloration and membrane deterioration, leading to the release of cytoplasmic content, rapid softening, and the visual symptom of watersoaking.

Pectina: da matéria-prima ao produto final

A pectina, provavelmente a mais complexa macromolécula natural, é um heteropolissacarídeo contendo predominantemente resíduos de ácido galacturônico. Este polímero, do grupo das fibras dietéticas, é amplamente utilizado como geleificante e estabilizante na indústria de alimentos. O principal processo industrial para obtenção de pectina está baseado na solubilização da protopectina do bagaço de maçã e casca de frutos cítricos, realizada em condições levemente ácidas sob aquecimento. Estudos recentes têm reportado a extração de pectina de novas matérias-primas sob diferentes condições, com influência sobre a qualidade e sobre o rendimento do produto final, para aumentar sua qualidade reológica. Esta revisão descreve a estrutura, as fontes, as aplicações, o processo de extração industrial assim como as principais técnicas de caracterização da pectina.