Verónica Alhelí Ochoa-Jiménez

Soursop (Annona muricata L.) is a climacteric tropical fruit belonging to the Annonaceae family, widely cultivated in tropical and subtropical regions due to its economic importance, nutritional value, and abundance of bioactive compounds. Its pulp is highly appreciated for fresh consumption and food processing; however, its high respiration rate and ethylene production accelerate ripening, resulting in rapid quality deterioration and a short postharvest shelf life. During ripening, soursop fruit undergoes physiological, biochemical, and molecular changes associated with organic acid metabolism, in which citrate synthase (CS) and malate dehydrogenase (MDH) play key roles within the tricarboxylic acid cycle. However, the transcriptional dynamics of genes associated with the tricarboxylic acid cycle during postharvest storage of tropical fruits remains poorly characterized. This study aimed to identify in silico genes encoding CS and MDH and to evaluate changes in physicochemical traits, enzymatic activity, and the expression of selected CS and MDH genes during postharvest storage of soursop (A. muricata) GUANAY-1 fruit. Fruits were stored at 26 ± 1 °C and evaluated on days 1, 2, 3, 4, and 5. Titratable acidity, pH, total soluble solids, CS activity, MDH activity, and the expression of selected CS and MDH genes were analyzed. Physicochemical analysis showed that the major changes in acidity, TSS, and pH occurred on day 3. In silico analysis identified 16 CS genes and 47 MDH genes in soursop, whereas transcriptome analysis identified four CS genes and three MDH genes with differential expression, designated as CS1, CS2, CS3, CS4, MDH1, MDH2, and MDH3, respectively. The Neighbor-Joining analysis grouped the CS sequences into two clusters and the MDH sequences into three clusters. Differential expression analysis revealed that CS1, CS2, CS3, CS4, MDH1, MDH2, and MDH3 were upregulated on day 3 relative to day 0 of postharvest storage. Functional enrichment analysis indicated that these genes were mainly associated with cellular respiration and the tricarboxylic acid cycle. The highest CS activity was recorded on day 3, coinciding with the maximum expression of CS1, CS2, and CS4. In contrast, MDH activity peaked on day 2, whereas MDH1 and MDH2 reached their highest expression on day 3. Correlation analysis showed positive associations between CS2 and CS4 expression and both TSS and titratable acidity. Overall, these results demonstrate temporal changes in physicochemical traits, CS and MDH enzymatic activities, and the expression of selected CS and MDH genes during postharvest storage of GUANAY-1 soursop fruit.

Soursop fruit (Annona muricata L.) exhibits a rapid loss of firmness during postharvest ripening, mainly attributed to pectin depolymerization and cell wall restructuring. Among the enzymes involved, rhamnogalacturonan lyase (RGL), belonging to the PF06045 protein family, contributes to the degradation of rhamnogalacturonan I (RG-I), a key structural component of pectin. However, the regulatory mechanisms and transcriptional dynamics of RGL genes in tropical fruits remain poorly characterized. This study aimed to evaluate RGL in three soursop varieties (GUANAY-1, GUANAY-2, and GUANAY-3) during postharvest ripening through integrative bioinformatic, transcriptional, and enzymatic analyses. Bioinformatic analysis identified five soursop genes containing the PF06045 domain, designated RGL1–RGL5, which were grouped into three phylogenetic clusters. Differential expression analysis revealed that RGL1, RGL2, and RGL3 were differentially expressed, while functional enrichment analysis indicated that these genes are mainly associated with lyase activity and cell wall polysaccharide disassembly. Quantitative polymerase chain reaction (qPCR) revealed variety-dependent transcriptional patterns. RGL2 showed expression peaks on day 5 in GUANAY-1 and GUANAY-3 and on day 7 in GUANAY-2, while RGL3 reached its maximum expression on day 5 in all varieties. Enzymatic activity also varied among varieties, showing concordance with RGL2 and RGL3 expression in GUANAY-1, a delayed maximum in GUANAY-2, and a progressive decline in GUANAY-3. Principal component analysis explained 87.2% of the total variation, with enzymatic activity contributing mainly to PC1 and RGL2 and RGL3 expression to PC2. Overall, these results demonstrate differential regulation of RGL among soursop varieties and confirm its central role in RG-I degradation during postharvest fruit softening.

Genetic diversity is essential for the conservation and genetic improvement of perennial fruit crops such as soursop (Annona muricata L.), an economically important species in tropical and subtropical regions. However, information on the genetic variability of soursop across different producing regions remains limited. In this study, we evaluated the genetic diversity and population structure of soursop accessions from two geographically distant producing regions: the Pacific–Occident region of Mexico (R1) and Valle del Cauca, Colombia (R2). A total of 11 accessions, collected from seven orchards in R1 and four orchards in R2, were analyzed using three simple sequence repeat (SSR) markers (LMCH36, LMCH43, and LMCH79) and three sequence-related amplified polymorphism (SRAP) marker combinations (me3+em1, me3+em15, and me4+em15). SSR analysis revealed limited polymorphism, as markers LMCH36 and LMCH79 were monomorphic across all accessions. In contrast, the LMCH43 marker showed polymorphic behavior in the Nuevo Urecho, Tecomán 1, and Coquimatlán accessions, allowing the identification of allelic variation and the discrimination between homozygous and heterozygous individuals. SRAP markers exhibited a high level of polymorphism in all evaluated accessions, demonstrating greater efficiency for detecting genetic diversity in A. muricata. The percentage of polymorphic loci ranged from 25.45% to 56.38% in R1 and from 74.55% to 86.46% in R2, with the highest diversity detected using the SRAP combinations me3+em1, me3+em15, and me4+em15. Analysis of molecular variance indicated that most genetic variation was distributed within accessions (82% in R1 and 97% in R2), rather than among accessions. Cluster analysis, principal coordinate analysis, and Bayesian population structure consistently separated the accessions into two main genetic populations corresponding to their geographic origin, with additional sub-structuring within the Mexican region. Overall, Colombian accessions showed higher genetic diversity than Mexican accessions. These results highlight the utility of SRAP markers and the SSR marker LMCH43 for genetic studies in soursop providing valuable information for the conservation of genetic resources and the development of future breeding and genetic improvement programs, particularly in Mexico.

The dragon fruit (Selenicereus sp.) peel is a viable plant source for the extraction of polysaccharides such as pectin, the demand for which has increased significantly in the food and pharmaceutical industries. In Nayarit, Mexico, the Queen Purple variety of dragon fruit (Selenicereus cf. guatemalensis) is commonly cultivated. The peel is typically discarded, while only the pulp is utilized for direct consumption or processed into derivative products. The objective of this study was to characterize the properties of pectin extracted from the peel of dragon fruit (Selenicereus cf. guatemalensis ‘Queen Purple’). The yield, molecular weight, anhydrouronic acid content, betalain content, antioxidant capacity, and phenolic compounds were determined using gravimetric, volumetric, spectrophotometric, and colorimetric techniques, among others. Furthermore, the functional groups and degree of esterification of the pectin were identified using Fourier-transform infrared spectroscopy. The pectin presented a yield of 12.8%, esterification degree of 49.85%, molecular weight of 645 kDa, anhydrouronic acid, phenolic acid and betalain content of 98.27%, 195.7 mg EAG/100 gDW and 4.26 mg/100 gDW respectively and an antioxidant capacity of 149.6, 192.76 and 20.5 mg EAA/100 gDW by the DPPH, ABTS and FRAP methods respectively, classified as high-purity, low-methoxyl, intermediate-molecular-weight, with an important betalain content and antioxidant capacity. Based on these findings, the extracted pectin complies with the Food and Agriculture Organization specifications and shows promise as a functional ingredient in the food industry.

Introduction Soursop (Annona muricata L.) is a crop with medicinal properties and numerous bioactive compounds. Ripening is a complex process that regulates fruit quality and changes in metabolite content, such as flavonoids, polyphenols, and organic acids. Objectives This study aimed to analyze the phenolic profiling of soursop fruit ripening. Methods The metabolic changes in different days of storage of soursop fruits were investigated using a semi-metabolomic approach based on ultra-performance liquid chromatography coupled to electrospray ionization quadrupole-time of flight mass spectrometry (UPLC-ESI-QTOF-MS). Further, multivariate analysis such as supervised partial least squares discriminant analysis (PLS-DA) was conducted to identify differential metabolites. Results A total of 68 metabolites were identified in soursop fruit during postharvest storage. A higher number of metabolites were identified in the Day zero (D0) compared to the Day one (D1), Day three (D3), and Day five (D5), belonging to flavonoids, other polyphenols, phenolic acids, and organic acids. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the pathways of flavone and flavonol biosynthesis, flavonoid biosynthesis, and biosynthesis of secondary metabolites were mostly enriched. Additionally, we included all the compounds and their postharvest storage in the public Phenolics profile database. Conclusions Here, we show that the stage of ripening has a significant effect on the phenolic content, highlighting the point of cut (D0) and the onset of senescence (D5). The findings of this study provide new insights into the soursop fruit quality and may contribute to the identification of metabolic markers for its storage.

The banano (Musa x paradisiaca L.) is a tropical fruit, susceptible to infection by Colletotrichum sp. Fungicides are the most typical approach for controlling postharvest infections. Concerns regarding its negative impact on human health and the environment have prompted the quest for alternate remedies. Because of its antimicrobial activity, chitosan is an environmentally friendly alternative. This study aimed to determine the influence of chitosan on the in vitro development of Colletotrichum sp. isolated from banana fruits. Inhibition mycelial growth, spore concentration and spore germination were evaluated in three chitosan concentrations, 0.5 %, 1.0 % and 1.5 %. Optical, fluorescence, and scanning electron microscopy were used to examine the impact of chitosan on spore growth and morphology. We observed that chitosan solutions inhibited Colletotrichum species in vitro. Chitosan at 1.5 % significantly decreased the percentage of mycelial growth inhibition and spore concentration in comparison with the control. Compared to the control, a concentration of 1.5 % chitosan considerably decreased the mycelial growth and spore concentration. In addition, a complete inhibition of spore germination and a low mycelium content was observed with 1.0% and 1.5% chitosan, controlling the in vitro development of Colletotrichum sp. in banana fruits.

The rapid ripening of soursop (Annona muricata L.) fruits is owing to its high respiration rate. Several enzymes affect the fruit cell wall in this process, resulting in the depolymerization of pectin primarily in the homogalacturonan. The main group of enzymes affecting the pectin content of soursop fruits include polygalacturonase (PG), pectate lyase (PL), pectin methylesterase (PME), and PME inhibitors (PMEis). In this study, pectin-degrading enzymes were analyzed using bioinformatic tools to uncover the gaps in our knowledge of this fruit. In this context, 67 genes encoding PG, 33 PL, 58 PME, and 39 PMEi isoenzymes were found. These genes were categorized into several families based on the results of phylogenetic analysis. Regarding the analysis of gene expression, a total of 25 were identified as differentially expressed genes (DEGs) in PG, while 3, 21, and 15 were found for PL, PME, and PMEis, respectively. Likewise, functional enrichment analysis demonstrated that the DEGs are involved in the modification of the cell wall, specifically in the degradation of pectin. On the other hand, gene co-expression networks revealed that the genes PG32 and PG35 affect the expression of PGs, as well as PL19 of the PL family, PME20, PME32, and PME35 of the PME family, and PMEi04 of the PMEi family. This suggests that they have a significant impact on the softening of soursop fruits.

Fungi decay is the most crucial factor leading to postharvest fruit losses. The objective was to test the effect of a bacterium exudate over the growth of Alternaria alternata infecting tomato fruit. The biochemical tests catalase, oxidase, motility-indole-ornithine, triple sugar iron, nitrification test, growth at 45°C and 60°C, Gram staining, and sequencing of 16S ribosomal gene, were performed in the bacterium. Tomato fruit in the red ripe stage was either untreated, infected with spores of A. alternata (IN), infected and treated with the exudate of bacterium growing in either Luria-Bertani broth (LB+BE+IN) or potato dextrose broth (PDB+BE+IN). The damage index (DI) was measured for 23 days at 25 °C in the tomatoes. The bacterium was identified as a Bacillus licheniformis strain and found to excrete an active chitinase isoform. Potent inhibition of the fungi growth in vitro was recorded, and DI was lower in the LB+BE+IN treatment compared to the IN treatment. We concluded that the exudate can control the growth of A. alternata infecting tomato fruit without adversely affecting fruit quality.