Metabolomic Analysis, Combined with Enzymatic and Transcriptome Assays, to Reveal the Browning Resistance Mechanism of Fresh-Cut Eggplant

Physiological, biochemical, and transcriptomic alterations in Castor (Ricinus communis L.) under polyethylene glycol-induced oxidative stress

BACKGROUND

Castor is an important industrial raw material. Drought-induced oxidative stress leads to slow growth and decreased yields in castor. However, the mechanisms of drought-induced oxidative stress in castor remain unclear. Therefore, in this study, physiological, biochemical, and RNA-seq analyses were conducted on the roots of castor plants under PEG-6000 stress for 3 d and 7 d followed by 4 d of hydration.

RESULTS

The photosynthetic rate of castor leaves was inhibited under PEG-6000 stress for 3 and 7 d. Biochemical analysis of castor roots stressed for 3 d and 7 d, and rehydrated for 4 d revealed that the activities of APX and CAT were highest after only 3 d of stress, whereas the activities of POD, GR, and SOD peaked after 7 d of stress. RNA-seq analysis revealed 2926, 1507, and 111 differentially expressed genes (DEGs) in the roots of castor plants under PEG-6000 stress for 3 d and 7 d and after 4 d of rehydration, respectively. GO analysis of the DEGs indicated significant enrichment in antioxidant activity. Furthermore, KEGG enrichment analysis of the DEGs revealed significantly enriched metabolic pathways, including glutathione metabolism, fatty acid metabolism, and plant hormone signal transduction. WGCNA identified the core genes PP2C39 and GA2ox4 in the navajowhite1 module, which was upregulated under PEG-6000 stress. On the basis of these results, we propose a model for the response to drought-induced oxidative stress in castor.

CONCLUSIONS

This study provides valuable antioxidant gene resources, deepening our understanding of antioxidant regulation and paving the way for further molecular breeding of castor plants.

Determination of o-quinones in foods by a derivative strategy combined with UHPLC-MS/MS

As primary polyphenol oxidant products, the occurrence of o-quinone is greatly responsible for quality deterioration in wine, including browning and aroma loss. The high reactivity of o-quinone causes huge difficulty in its determination. Herein, a derivative strategy combined with UHPLC-MS/MS analysis was established with chlorogenic acid quinone (CQAQ) and 4-methylcatechol quinone (4MCQ) as model compounds. Method validation demonstrated its efficiency for two analytes (R2 > 0.99, accuracy 98.71-106.39 %, RSD of precision 0.46-6.11 %, recovery 85.83-99.37 %). This approach was successfully applied to detect CQAQ and 4MCQ, suggesting its applicability in food analysis. CQAQ in coffee was much more than 4MCQ and with the deepening of baking degree, CQAQ decreased and 4MCQ increased. The amounts of CQAQ in various vegetables were markedly different, seemingly consistent with their respective browning degrees in practical production. This study developed an accurate and robust analytical approach for o-quinones, providing technical support for their further investigation in foods.

Combination of Sodium Nitroprusside and Controlled Atmosphere Maintains Postharvest Quality of Chestnuts through Enhancement of Antioxidant Capacity

The purpose of this study was to clarify the effect of CA (controlled atmosphere, 2-3% O2 + 3% CO2) and NO (nitric oxide, generated by 0.4 nM sodium nitroprusside), alone or combined (CA + NO), on the physio-chemical properties, enzyme activities and antioxidant capacities of chestnuts during storage at 0 °C for 180 d. Compared with control (CT), CA and CA+NO both improved the storage quality of the samples, but only CA resulted in more ethanol production. Moreover, these improvements were further enhanced and ethanol synthesis was inhibited by the addition of NO. A spectrometer was used to assess the production of phenolic content (TPC) and activities of phenylalanine ammonia-lyase (PAL), superoxide dismutas (SOD), peroxidase (POD), catalase (CAT) and polyphenol oxidase (PPO) as influenced by CA or CA+NO treatments. Higher TPC, PAL, SOD, POD, CAT, and lower PPO were observed in CA alone, and more so in the combination with NO group. The increased antioxidant production and enhanced antioxidant activities contributed to scavenging reactive oxygen species (ROS) and reducing malondialdehyde (MDA). This study unveiled the correlations and differences between the effects of CA and CA+NO on storage quality, providing valuable insights into postharvest preservation and suggesting that the combination (CA+NO) was more beneficial for quality maintenance in chestnuts.

Nisin and ε-polylysine combined treatment enhances quality of fresh-cut jackfruit at refrigerated storage

This study investigated the effects of nisin combined with ε-polylysine on microorganisms and the refrigerated quality of fresh-cut jackfruit. After being treated with distilled water (control), nisin (0.5 g/L), ε-polylysine (0.5 g/L), and the combination of nisin (0.1 g/L) and ε-polylysine (0.4 g/L), microporous modified atmosphere packaging (MMAP) was carried out and stored at 10 ± 1°C for 8 days. The microorganisms and physicochemical indexes were measured every 2 days during storage. The results indicated that combined treatment (0.1 g/L nisin, 0.4 g/L ε-polylysine) had the best preservation on fresh-cut jackfruit. Compared with the control, combined treatment inhibited microbial growth (total bacterial count, mold and yeast), reduced the weight loss rate, respiratory intensity, polyphenol oxidase and peroxidase activities, and maintained higher sugar acid content, firmness, and color. Furthermore, it preserved higher levels of antioxidant compounds, reduced the accumulation of malondialdehyde and hydrogen peroxide, thereby reducing oxidative damage and maintaining high nutritional and sensory qualities. As a safe application of natural preservatives, nisin combined with ε-polylysine treatment has great application potential in the fresh-cut jackfruit industry.

Unraveling crop enzymatic browning through integrated omics

Enzymatic browning reactions, triggered by oxidative stress, significantly compromise the quality of harvested crops during postharvest handling. This has profound implications for the agricultural industry. Recent advances have employed a systematic, multi-omics approach to developing anti-browning treatments, thereby enhancing our understanding of the resistance mechanisms in harvested crops. This review illuminates the current multi-omics strategies, including transcriptomic, proteomic, and metabolomic methods, to elucidate the molecular mechanisms underlying browning. These strategies are pivotal for identifying potential metabolic markers or pathways that could mitigate browning in postharvest systems.

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

Transcriptomics and metabolomics provide insight into the anti-browning mechanism of selenium in freshly cut apples

Enzymatic browning has a considerable negative impact on the acceptability and marketability of freshly cut apples. However, the molecular mechanism by which selenium (Se) positively affects freshly cut apples in this regard is not yet clear. In this study, 0.75 kg/plant of Se-enriched organic fertilizer was applied to "Fuji" apple trees during the young fruit stage (M₅, May 25), the early fruit enlargement stage (M₆, June 25), and the fruit enlargement stage (M₇, July 25), respectively. The same amount of Se-free organic fertilizer was applied as a control. Herein, the regulatory mechanism by which exogenous Se exerts its anti-browning effect in freshly cut apples was investigated. The results showed that the M₇ treatment applied in Se-reinforced apples could remarkably inhibit their browning at 1 h after being freshly cut. Additionally, the expression of polyphenol oxidase (PPO) and peroxidase (POD) genes treated with exogenous Se was significantly reduced compared to controls. Moreover, the lipoxygenase (LOX) and phospholipase D (PLD) genes, which are involved in membrane lipid oxidation, were expressed at higher levels in the control. The gene expression levels of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and ascorbate peroxidase (APX) were upregulated in the different exogenous Se treatment groups. Similarly, the main metabolites measured during the browning process were phenols and lipids; thus, it could be speculated that the mechanism by which exogenous Se produces its anti-browning effect may be by reducing phenolase activity, improving the antioxidant capacity of the fruits, and alleviating membrane lipid peroxidation. In summary, this study provides evidence regarding and insight into the response mechanism employed by exogenous Se to inhibit browning in freshly cut apples.

Untargeted Metabolomics Using UHPLC-HRMS Reveals Metabolic Changes of Fresh-Cut Potato during Browning Process

Surface browning plays a major role in the quality loss of fresh-cut potatoes. Untargeted metabolomics were used to understand the metabolic changes of fresh-cut potato during the browning process. Their metabolites were profiled by ultra-high performance liquid chromatography coupled with high resolution mass spectrometry (UHPLC-HRMS). Data processing and metabolite annotation were completed by Compound Discoverer 3.3 software. Statistical analysis was applied to screen the key metabolites correlating with browning process. Fifteen key metabolites responsible for the browning process were putatively identified. Moreover, after analysis of the metabolic causes of glutamic acid, linolenic acid, glutathione, adenine, 12-OPDA and AMP, we found that the browning process of fresh-cut potatoes was related to the structural dissociation of the membrane, oxidation and reduction reaction and energy shortage. This work provides a reference for further investigation into the mechanism of browning in fresh-cut products.

Short-Term Gaseous Treatments Improve Rachis Browning in Red and White Table Grapes Stored at Low Temperature: Molecular Mechanisms Underlying Its Beneficial Effect

Short-term gaseous treatments improve rachis quality during table grape postharvest, but little is known about the mechanisms involved. In this work, we observed that the application of a 3-day CO2 treatment at 0 °C improved rachis browning of Superior Seedless and Red Globe bunches, affecting the non-enzymatic antioxidant system by reducing the total phenolic content, the antioxidant activity and the expression of different stilbene synthase genes. Lipid peroxidation levels revealed lower oxidative stress in CO2-treated rachis of both cultivars linked to the activation of the enzymatic antioxidant system. Furthermore, whereas a positive correlation was denoted between rachis browning and the accumulation of key ABA regulatory genes in Red Globe bunches, this effect was restricted to ACS1, a key synthetic ethylene gene, in Superior Seedless clusters. This work also corroborated the important role of ethylene-responsive factors in the beneficial effect of the gaseous treatment, not only in the berries but also in the rachis. Finally, the application of the gaseous treatment avoided the induction of cell wall-degrading enzyme-related genes in both cultivars, which could favor the maintenance of rachis quality. This work provides new insight into specific responses modulated by the gaseous treatment focused on mitigating rachis browning independently of the cultivar.

Determination of the Content of Phenolic Compounds and the Changes of Polyphenol Oxidase and Each Index during Browning of Phyllanthus emblica at Different Storage Temperatures

In order to further study the early browning of P. emblica marker and mechanism, it is necessary for us to measure the changes in the content of some substances to find quality markers during the browning process of P. emblica. So, we simulated the storage conditions under different temperatures, including 5°C, 25°C, and 35°C. And, the contents of some of its phenolic compounds were determined by RP-HPLC. Polyphenol oxidase (PPO) activity was determined by PPO reagent kits, and pH was determined with a pH measuring instrument, etc. The experimental results showed that 1-galloyl-glucose was the smoothest at 5°C among the three storage temperature conditions. It fluctuates and decreases in a curve at 35°C and 25°C. The content changes of gallic acid (GA) fluctuated more obviously at 35°C, and it showed a maximum value on the 7th day. The content changes of 1,3,6-tri-O-galloyl-β-D-glucose (TGG) all showed a peak on the 5th day and then showed a gradual decrease. The content changes of ellagic acid (EA) fluctuated more at 35°C. The peak of the content of rutin at both 35°C and 25°C appeared on the 3rd day, and that showed a gradually decreasing trend. The PPO activity varied more significantly at 25°C and 35°C. The browning index increased with time at both 35°C and 25°C. The complete browning of P. emblica was already observed on the 13th day. Tips for experimental results 5°C are effective in preventing browning of P. emblica. The contents of TGG, 1-galloyl-glucose, and rutin in P. emblica are greatly affected by temperature and time, and its contents had a linear relationship with time and temperature and can be used as one of the indicators of early browning, which provides a reference for the storage and transportation of fresh fruit in Chinese herbals.