Papaya (Carica papaya L.) is a fleshy fruit with a rapid pulp softening during ripening. Ripening events are accompanied by gradual depolymerization of pectic polysaccharides, including homogalacturonans, rhamnogalacturonans, arabinogalactans, and their modified forms. During intermediate phases of papaya ripening, partial depolymerization of pectin to small size with decreased branching had enhanced pectin anti-cancer properties. These properties were lost with continued decomposition at later phases of ripening. Pectin extracted from intermediate phases of papaya ripening markedly decreased cell viability, induced necroptosis, and delayed culture wound closing in three types of immortalized cancer cell lines. The possible explanation for these observations is that papaya pectins extracted from the third day after harvesting have disrupted interaction between cancer cells and the extracellular matrix proteins, enhancing cell detachment and promoting apoptosis/necroptosis. The anticancer activity of papaya pectin is dependent on the presence and the branch of arabinogalactan type II (AGII) structure. These are first reports of AGII in papaya pulp and the first reports of an in vitro biological activity of papaya pectins that were modified by natural action of ripening-induced pectinolytic enzymes. Identification of the specific pectin branching structures presents a biological route to enhancing anti-cancer properties in papaya and other climacteric fruits.

Papaya (Carica papaya L.) is a fleshy fruit that presents a rapid pulp softening during ripening. However, the timeline on how papaya pectinases act in polysaccharide solubilization and the consequent modification of the cell wall fractions during ripening is still not clear. In this work, the gene expression correlations between, on one hand, 16 enzymes potentially acting during papaya cell wall disassembling and, on the other hand, the monosaccharide composition of cell wall fractions during papaya ripening were evaluated. In order to explain differences in the ripening of papaya samplings, the molecular mass distribution of polysaccharides from water-soluble and oxalate-soluble fractions (WSF and OSF, respectively), as well as the oligosaccharide profiling from the WSF fraction, were evaluated by high performance size exclusion chromatography coupled to a refractive index detector and high performance anion-exchange chromatography coupled to pulse amperometric detection analyses, respectively. Results showed that up-regulated polygalacturonase and β-galactosidase genes were positively correlated with some monosaccharide profiles. In addition, an overall increase in the retention time of high molecular weight (HMW) and low molecular weight (LMW) polysaccharides in WSF and OSF was shown. The apparent disappearance of one HMW peak of the OSF may result from the conversion of pectin that were crosslinked with calcium into more soluble forms through the action of PGs, which would increase the solubilization of polysaccharides by lowering their molecular weight. Thus, the results allowed us to propose a detailed process of papaya cell wall disassembling that would affect sensorial properties and post-harvesting losses of this commercially important fruit.

Dietary fibers have been shown to exert immune effects via interaction with pattern recognition receptors (pRR) such as toll-like receptors (tLR) and nucleotide-binding oligomerization domain (noD)like receptors. Pectin is a dietary fiber that interacts with PRR depending on its chemical structure. Papaya pectin retains different chemical structures at different ripening stages. How this influence PRR signaling is unknown. The aim of this work was to determine how ripening influences pectin structures and their ability to interact with TLR2, 3, 4, 5 and 9, and NOD1 and 2. It was evaluated the interaction of the water-soluble fractions rich in pectin extracted from unripe to ripe papayas. The pectin extracted from ripe papayas activated all the TLR and, to a lesser extent, the NOD receptors. The pectin extracted from unripe papayas also activated TLR2, 4 and 5 but inhibited the activation of TLR3 and 9. The differences in pectin structures are the higher methyl esterification and smaller galacturonan chains of pectin from ripe papayas. Our finding might lead to selection of ripening stages for tailored modulation of pRR to support or attenuate immunity. Dietary fibers (DF) commonly represent a wide variety of polysaccharides originating from fruits, vegetables, whole grains and legumes with several health benefits. Such benefits include slow gastric empty 1 and improve physical bowel function 2. Besides the physical benefits, DF can also interact directly with intestinal cells and/or the immune cells from the mucosa 3-5. It is not just the direct effects of DF on cells may trigger immune modulations 6 but also the DF fermentation in the gut 7,8. The direct interaction of DF with the intestinal cells may occur through pattern recognition receptors (PRR) 9. The PRR are germline-encoded sensors expressed in intestinal epithelial cells and gut immune cells. PRR are the key receptors responsible for the recognition of exogenous molecules by the host 5,9. Toll-like receptors (TLR) are a family of PRR that play a central role in the activation of innate immunity 10 and have been shown to be involved in DF-induced immune signaling as described below. The immune response mediated by TLR activation requires the recruitment of myeloid differentiation primary response protein 88 (MyD88) adaptor and the translocation of NF-κB to the nucleus 10. Only TLR3 NF-κB activation is not dependent on MyD88 protein which is mediated by TIR domain-containing adapter inducing IFN-β (TRIF), though 11. The interactions between wide variety of DF and TLR have been extensively studied. DF have a complex and heterogeneous structure and some DF activate TLR to different extents 12 while other DF (such as pectin) seem to block TLR signaling and attenuate intestinal inflammation 6. Nucleotide-binding oligomerization domains (NOD) have also been shown to be influenced by DF, such as β2 → 1-fructans. NOD are proteins responsible for the recognition of intracellular bacteria 10. Through this signaling via PRR, DF have been shown to mediate several ho...

While chemically and thermally modified citrus pectin (MCP) has already been studied for health benefits, it is unknown how size-fractionated oligo-and polysaccharides differentially affect cancer cell behavior. We produced thermally MCP and fractionated it by molecular size to evaluate the effect these polymers have on cancer cells. MCP30/10 (between 30 and 10kDa) had more esterified homogalacturonans (HG) and fewer rhamnogalacturonans (RG-I) than MCP and MCP30 (higher than 30kDa), while MCP10/3 (between 10 and 3kDa) showed higher amounts of type I arabinogalactans (AGI) and lower amounts of RG-I. MCP3 (smaller than 3 kDa) presented less esterified HG and the lowest amount of AGI and RG-I. Our data indicate that the enrichment of de-esterified HG oligomers and the AGI and RG-I depletions in MCP3, or the increase of AGI and loss of RGI in MCP30/10, enhance the anticancer behaviors by inhibiting migration, aggregation, and proliferation of cancer cells.