Effect of Chitosan Coating with Different Molecular Weights on the Storage Quality of Postharvest Passion Fruit (Passiflora edulis Sims)

To study the preservation effect of chitosan coating with different molecular weights on postharvest passion fruit, the "Qinmi No.9" was coated with chitosan of molecular weights of 30, 50, 100, 150 and 200 kDa (1.5%, w/v) to determine the quality of passion fruit during storage. The results showed that chitosan coating with different molecular weights was able to delay the shrinkage and yellowing, reduce the weight loss rate and inhibit the decay of passion fruit. Moreover, chitosan with a larger molecular weight was more conducive to delaying the ripening and senescence of passion fruit, as well as reducing shrinkage, and decay. At the end of storage, the weight loss of fruits coated with 200 kDa chitosan was nearly 10% less than that coated with 30 kDa chitosan, and the fruits coated with 150 and 200 kDa chitosan did not decay. The lower molecular weight (30 and 50 kDa) and higher molecular weight (150 kDa) chitosan were more effective in inhibiting weight loss, total soluble solids and soluble sugar metabolism, and maintaining titratable acid, flavonoid and total phenol contents of fruit during storage. The chitosan with 150 kDa had the best effect in maintaining the vitamin C content, which was 1.12 times higher than the control group at the end of storage. In conclusion, chitosan with different molecular weights was effective to delay senescence, slow down water loss and shrink of passion fruit and maintain the quality, chitosan with 150 kDa was more suitable to maintain the quality of postharvest passion fruit

Dynamics and control of active sites in hierarchically nanostructured cobalt phosphide/chalcogenide-based electrocatalysts for water splitting

The rational design of efficient electrocatalysts for industrial water splitting is essential to generate sustainable hydrogen fuel. However, a comprehensive understanding of the complex catalytic mechanisms under harsh reaction conditions remains a major challenge. We apply a self-templated strategy to introduce hierarchically nanostructured “all-surface” Fe-doped cobalt phosphide nanoboxes (Co@CoFe–P NBs) as alternative electrocatalysts for industrial-scale applications. Operando Raman spectroscopy and X-ray absorption spectroscopy (XAS) experiments were carried out to track the dynamics of their structural reconstruction and the real catalytically active intermediates during water splitting. Our operando analyses reveal that partial Fe substitution in cobalt phosphides promotes a structural reconstruction into P–Co–O–Fe–P configurations with low-valence metal centers (M0/M+) during the hydrogen evolution reaction (HER). Results from density functional theory (DFT) demonstrate that these in situ reconstructed configurations significantly enhance the HER performance by lowering the energy barrier for water dissociation and by facilitating the adsorption/desorption of HER intermediates (H*). The competitive activity in the oxygen evolution reaction (OER) arises from the transformation of the reconstructed P–Co–O–Fe–P configurations into oxygen-bridged, high-valence CoIV–O–FeIV moieties as true active intermediates. In sharp contrast, the formation of such CoIII/IV–O–FeIII/IV moieties in Co–FeOOH is hindered under the same conditions, which outlines the key advantages of phosphide-based electrocatalysts. Ex situ studies of the as-synthesized reference cobalt sulfides (Co–S), Fe doped cobalt selenides (Co@CoFe–Se), and Fe doped cobalt tellurides (Co@CoFe–Te) further corroborate the observed structural transformations. These insights are vital to systematically exploit the intrinsic catalytic mechanisms of non-oxide, low-cost, and robust overall water splitting electrocatalysts for future energy conversion and storage

Effects of pure oxygen and reduced oxygen modified atmosphere packaging on the quality and microbial characteristics of fresh-cut pineapple

Introduction. Modified atmosphere packaging (MAP) is a preservation technique currently used by the fresh-cut fruit industry. Fruit quality may vary according to the concentration of oxygen (O2) in the packaging. However, there is no published research on the effects of a pure O2 modified atmosphere in the packaging of fresh-cut pineapple. There are also no comparative studies of the differences between pure O2 and conventional low O2 MAP on the quality of fresh-cut pineapple. Materials and methods. Pineapple slices were sealed with a tray sealer using a polyethylene (PE) / polypropylene (PP) composite film and one of the following atmosphere treatments: (4% O2 + 5% CO2), (100% O2), and ambient air (control). We evaluated the effects on quality and microbial spoilage of fresh-cut pineapple. Results and discussion. Both modified atmosphere treatments delayed decreases in firmness, soluble solid contents (SSC), reducing sugar, and ascorbic acid. Pineapple slices packaged in pure O2 contained lower amounts of sugar and ascorbic acid and displayed more browning than the slices in the low O2 concentration. Additionally, both modified atmosphere treatments strongly delayed the growth of microorganisms. Aerobic bacteria, yeast and mold levels in pineapple slices packaged in pure O2 were higher than those packaged with the low O2 atmosphere during long-term storage. Conclusion. Modified atmosphere packaging using low O2 concentration (4% O2 + 5% CO2) was better able to maintain the quality of fresh-cut pineapple than packaging with pure O2 atmosphere

Operando spectroscopic monitoring of metal chalcogenides for overall water splitting: New views of active species and sites

Metal-based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X-ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure-activity relationships of low-crystalline cobalt sulfide (L-CoS) catalysts toward overall water splitting. The operando results for L-CoS catalyzing alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S-Co-Co-S moieties as the true catalytic active species. In comparison, during the acidic HER, L-CoS undergoes reversible redox changes of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co-S-Co configurations. Further operando characterizations highlight the crucial formation of high-valent Co4+ species in L-CoS for the alkaline oxygen evolution reaction (OER), and generation of such active species was found to be far more facile than in crystalline Co3O4 and Co-LDH references. These insights offer a clear picture of the complexity of active species and site formation under different media, and demonstrate how their restructurings exert influence on the catalytic activity

Sulfinate and carbene co-catalyzed Rauhut-Currier reaction for enantioselective access to azepino[1,2-a]indoles

A carbene and sulfinate co-catalyzed intermolecular Rauhut-Currier reaction between enals and nitrovinyl indoles is disclosed. The carbene catalyst activates the enal and the sulfinate co-catalyst activates the nitrovinyl indole. Both activation processes are realized via the formation of covalent bonds between the catalysts and substrates to generate catalyst-bound intermediates. The dual catalytic reaction affords azepino[1,2-a]indole products with excellent stereoselectivity. Our study demonstrates the unique involvement of sulfinate as an effective nucleophilic catalyst in activating electron-deficient alkenes for asymmetric reactions. This dual catalytic approach should also encourage future explorations of both sulfinate and carbene catalysts for new reactions.NRF (Natl Research Foundation, S’pore)ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)Accepted versio

Effects of Hydrogen Sulfide on Storage Quality of Postharvest Banana Fruits (Musa ABB Pisang Awak)

Effects of different concentrations of hydrogen sulfide (H2S) on the quality of postharvest banana fruits (Musa ABB Pisang Awak) were studied. Pisang Awak bananas fruits were treated with H2S released by 0.3, 0.6 and 0.9 mmol/L NaHS solution respectively, and the firmness, color, weight loss rate, browning index, soluble solids (TSS), titratable acid (TA), respiration rate and ethylene production rate were observed and measured regularly during storage. The results showed that H2S treatment significantly delayed the increase of epidermis yellowing and pulp browning index of postharvest Pisang Awak bananas, slowed down the increase of fruit softening and weight loss rate, and inhibited the increase of TSS content and TA content to some extent. Besides, there was no significant difference among the 3 groups treated with different concentrations of TSS (P>0.05), and the effect of 0.6 mmol/L NaHS treatment group was more significant. At the same time, NaHS treatment significantly inhibited the increase of respiration and ethylene production rate (P0.05). Generally speaking, different concentrations of NaHS could delay the ripening and senescence of postharvest Pisang Awak bananas, and the fresh-keeping effect of 0.6 mmol/L NaHS treatment was the most obvious

Regulation of Embden–Meyerhof–Parnas (EMP) Pathway and Tricarboxylic Acid (TCA) Cycle Concerning Aberrant Chilling Injury Behavior in Postharvest Papaya (<i>Carica papaya</i> L.)

Postharvest abnormal chilling injury (CI) behavior in papaya (Carica papaya L.) fruit is a rare phenomenon that may be associated with respiratory metabolism. This study thus aimed to investigate the impacts of storage temperatures (1 and 6 °C) on the respiratory metabolism of postharvest papaya and its impact on CI development. Results demonstrated that 1 °C storage reduced the activities of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), and α-ketoglutarate dehydrogenase (α-KGDH) and regulated the expression of corresponding enzymes in the Embden–Meyerhof–Parnas (EMP) pathway and tricarboxylic acid (TCA) cycle compared with 6 °C storage, resulting in a lower respiration rate of the EMP-TCA pathway and mitigating the development of CI. Meanwhile, lower contents of nicotinamide adenine dinucleotide (hydrogen) (NAD(H)) were observed in papaya fruit stored at 1 °C. Notably, papaya fruit stored at 1 °C maintained higher activity and transcriptional levels of SDH and IDH during the whole storage period. These findings suggest that 1 °C storage reduced the respiration rate of the EMP-TCA pathway by reducing the expression level and activity of related enzymes, which is conducive to the reduction of respiration substrate consumption and finally alleviating the occurrence of CI

Stability and bioactivity evaluation of black pepper essential oil nanoemulsion

Black pepper essential oil has the same disadvantages as other plant essential oils, such as volatilization, high sensitivity to light and heat and poor water solubility, which leads to great limitations in application. This study improved the stability and antibacterial properties of black pepper essential oil (BPEO) based on a nano-emulsification process. Tween 80 was selected as the emulsifier to prepare the BPEO nanoemulsion. Gas chromatograph - mass spectrometer (GC-MS) was used to analyze the composition of BPEO, of which d-limonene was the main component (37.41%). After emulsification, black pepper nanoemulsion was obtained (droplet size was 11.8 nm). The water solubility and stability of the emulsions at 25 °C were also improved with decreasing particle size. Antimicrobial properties of plant pathogens (Colletotrichum gloeosporioides, Botryodiplodia theobromae) and foodborne pathogens (Staphylococcus aureus, Escherichia coli) were evaluated by disk diffusion and other techniques for determining minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). With 12.5 mg mL−1 MIC and 25 mg mL−1 MBC, BPEO inhibited the growth of two tested plant pathogens and two foodborne pathogens. Essential oils (EO) were encapsulated in a nanoemulsion system to enhance the bacteriostatic effect of essential oils and reduce MIC and MBC concentrations. After emulsification, the biological activity (antimicrobial and antioxidant) of the BPEO nanoemulsion was considerably improved, nano-emulsification had certain significance for the study of EOs

Effect of glycine betaine on chilling injury in relation to energy metabolism in papaya fruit during cold storage

“Zhongbai” papaya fruit were treated with 15 mmol/L glycine betaine (GB) and then refrigerated at 6°C for 40 days to study the influence of GB on chilling injury (CI) and possible mechanism associated with energy metabolism. The results exhibited that GB treatment remarkably reduced the CI severity as indicated by lower CI index during storage. GB treatment lowered electrolyte leakage and malondialdehyde content, which accounted for maintenance of membrane integrity and reduced lipid peroxidation. Moreover, GB treatment improved the energy status as revealed by increased adenosine triphosphate (ATP) level, energy charge, and activities of energy metabolism‐related enzymes including mitochondrial membrane H+‐adenosine triphosphatase (H+‐ATPase) and Ca2+‐adenosine triphosphatase (Ca2+‐ATPase), succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). The results indicate that enhanced chilling tolerance in papaya fruit by GB treatment during cold storage might be ascribed to improved energy status in association with increased activities of energy metabolism‐related enzymes

Effect of glycine betaine on chilling injury in relation to energy metabolism in papaya fruit during cold storage

“Zhongbai” papaya fruit were treated with 15 mmol/L glycine betaine (GB) and then refrigerated at 6°C for 40 days to study the influence of GB on chilling injury (CI) and possible mechanism associated with energy metabolism. The results exhibited that GB treatment remarkably reduced the CI severity as indicated by lower CI index during storage. GB treatment lowered electrolyte leakage and malondialdehyde content, which accounted for maintenance of membrane integrity and reduced lipid peroxidation. Moreover, GB treatment improved the energy status as revealed by increased adenosine triphosphate (ATP) level, energy charge, and activities of energy metabolism‐related enzymes including mitochondrial membrane H+‐adenosine triphosphatase (H+‐ATPase) and Ca2+‐adenosine triphosphatase (Ca2+‐ATPase), succinate dehydrogenase (SDH), and cytochrome C oxidase (CCO). The results indicate that enhanced chilling tolerance in papaya fruit by GB treatment during cold storage might be ascribed to improved energy status in association with increased activities of energy metabolism‐related enzymes