Characterization of an acidic pectin methylesterase from Paenibacillus xylanexedens and its application in fruit processing

Effect of microbial biostimulants on the antioxidant profile, antioxidant capacity and activity of enzymes influencing the quality level of raspberries (Rubus idaeus L.)

The influence of four microbial biostimulants containing various strains of Bacillus subtilis and/or Paenibacillus sp. on the quality of raspberries cv. Delniwa, Poemat, and Enrosadira cultivated in two consecutive seasons was investigated. The biostimulants influenced the antioxidant level, antioxidant capacity, phenolic acids and flavonoids profiles, enzymatic activity, and the degree of methylation and acetylation of the pectin in the raspberry fruits. The biostimulants had the greatest effect on the antioxidant content (16% - 20% increase) and capacity in the Delniwa raspberry fruits from the first season. A positive correlation was found between the activity of the β-galactosidase enzyme and ferric reducing power. In the second season, a decrease in the activity of pectin esterase and α-L-arabinofuranosidase and an increase in the degree of methylation of pectin were noted. Our results suggest that the changes in raspberry quality were related to the type of biostimulant applied.

Genome-based analyses to learn from and about Paenibacillus sonchi genomovar Riograndensis SBR5T

Paenibacillus sonchi genomovar Riograndensis SBR5T is a plant growth-promoting rhizobacterium (PGPR) isolated in the Brazilian state of Rio Grande do Sul from the rhizosphere of Triticum aestivum. It fixes nitrogen, produces siderophores as well as the phytohormone indole-3-acetic acid, solubilizes phosphate and displays antagonist activity against Listeria monocytogenes and Pectobacterium carotovorum. Comprehensive omics analysis and the development of genetic tools are key to characterizing and engineering such non-model microorganisms. Therefore, the complete genome of SBR5T was sequenced, and shown to encode 6,705 proteins, 87 tRNAs, and 27 rRNAs and it enabled a landscape transcriptome analysis that unveiled conserved transcriptional and translational patterns and characterized operon structures and riboswitches. The pangenome of P. sonchi species is open with a stable core pangenome. At the same time, the analysis of genes coding for nitrogenases revealed that the trait of nitrogen fixation is sparse within the Paenibacillaceae family and the presence of Fe-only nitrogenase in the P. sonchi group was exclusive to SBR5T. The development of genetic tools for SBR5T enabled genetic transformation, plasmid construction for constitutive and inducible gene expression, and gene repression using the CRISPRi system. Altogether, the work with P. sonchi can guide the study of non-model bacteria with economic potential.

Agroindustrial and food processing residues valorization for solid-state fermentation processes: A case for optimizing the co-production of hydrolytic enzymes

In the pursuit of sustainability, managing agro-industrial and food processing residues (AFR) efficiently is crucial. This study proposes a systematic approach to convert AFR into valuable products via solid-state fermentation (SSF). Using fungal enzyme production as a case study, this adaptable methodology suits any SSF bioprocess. Initially, AFR's physicochemical properties were evaluated to assess their feasible use as carbon sources and solid matrices for SSF. Then, five strains were screened for their capability to produce enzymes (Xylanase, X; pectinase, P; cellulase, C). Apple pomace (AP) and brewery spent grain (BSG) with Aspergillus sp. (strain G5) were selected. Subsequent steps involved a two-phase statistical approach, identifying critical factors and optimizing them. Process conditions were screened using a Plackett-Burman design, narrowing critical variables to three (BSG/AP, pH, humidity). Response Surface Methodology (Central Composite Design) further optimized these factors for co-synthesis of X, P, and C. The humidity had the most significant effect on the three responses. The optimum conditions depended on each enzyme and were further validated to maximize either X, P or C. The obtained extracts were used for pectin extraction from orange peels. The extract containing primarily xylanase (X = 582.39, P = 22.86, C = 26.10 U mL-1) showed major pectin yield recovery (12.33 ± 0.53%) and it was obtained using the optimal settings of BSG/AP (81/19), humidity (50.40%), and pH (4.58). The findings will enable adjusting process conditions to obtain enzymatic cocktails with a tailored composition for specific applications.

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage

INTRODUCTION

Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant.

OBJECTIVES

This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness.

METHODS

The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca²⁺ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit.

RESULTS

The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0°C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca²⁺ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals.

CONCLUSION

PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca²⁺ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Constitutive and extracellular expression of pectin methylesterase from Pectobacterium chrysanthemi in Pichia pastoris

Pectin methylesterase (PME) which is widely used in the cosmetic, food and pharmaceutical industries catalyses the hydrolysis of the methyl ester of pectin to yield methanol and free carboxyl groups. This study was performed to produce active pectin methylesterase (PME) extracellularly from Pectobacterium chrysanthemi in Pichia pastoris. Firstly, pGKBα was constructed for the secretion of heterologous protein. After it was cloned in Escherichia coli cells and the sequence was affirmed, PME gene was inserted into pGKBα. So, pGKBα-PME carried the PME gene in correct position was cloned in E. coli cells. Then, P. pastoris X-33 cells were transformed with linearized pGKBα-PME and six transformants were cultivated for recombinant PME production. It was observed that one of them had a high-capacity secretion of active PME. The molecular mass of extracellular PME enzyme was found to be about 59 kDa. The PME enzyme from P. chrysanthemi was produced by P. pastoris for the first time in this study. This recombinant enzyme might be produced in a large scale and also purified from the culture medium. Then, the purified enzyme might be used for clarification and increasing yield of juice in food industrial applications.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03291-3.