Effect of production system and inhibitory potential of aroma volatiles on polyphenol oxidase and peroxidase activity in tomatoes

Physiological response and drought resistance evaluation of Gleditsia sinensis seedlings under drought-rehydration state

G. sinensis is a crucial tree species in China, possessing important economic and ecological value, and having a wide geographical distribution. G. sinensis seedlings is highly vulnerable to the drought-rehydration-drought cycle during their growth, and there is a lack of quantitative and systematic research on the physiological mechanisms of drought resistance and rehydration in G. sinensis. There is also a lack of good drought-resistant families and reliable methods for evaluating drought resistance, which severely hinders the selection and promotion of drought-resistant G. sinensis families and the industry's development. Therefore, this study selection 58 families seedlings of G. sinensis to drought stress and rehydration using an artificial simulated water control method in potted seedlings. The aim was to compare the effects of different levels of drought and rehydration on the growth and physiological indices of seedlings from different families. Identification of drought-resistant families and dependable drought related indices and techniques, the explanation of divergence in drought stress effects on various drought-resistant seedlings and the mechanisms underpinning growth and physiological responses, and the provision of theoretical reference for G. sinensis drought-resistant variety selection and cultivation. The Drought Resistance Index (DRI) served as the primary indicator, supplemented by growth, leaf morphology, and photosynthetic physiological indicators, to thoroughly assess and identify five distinct drought tolerant taxa while also selecting five representative families. Soluble protein (SP), proline (Pro), and malondialdehyde (MDA) contents, as well as the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) in seedlings from the five families, increased as the degree of drought intensified. The highest values were appeared during periods of severe drought, and gradually decreased after subsequent rehydration. Principal component analysis (PCA) revealed MDA and soluble sugars (SS) as the primary predictors of drought and rehydration response in G. sinensis seedlings respectively. Changes in osmoregulatory substance content and increased antioxidant enzyme activity may be crucial for responding to drought tolerance mechanisms. Leaf morphological indicators, seedling height, soil plant analysis development (SPAD) value, photosynthetic indicators, and MDA are dependable parameters for assessing the drought tolerance of G. sinensis seedlings. When assessing the drought-resistance of seedlings using physiological indicators such as photosynthesis, a comprehensive analysis should incorporate multiple indicators and methods. This evaluation approach could serve as a reference for screening exceptional drought-resistant families of G. sinensis.

Formulation of a Stable Oil-in-Water Microemulsion of Torreya grandis cv. Merrillii Aril Essential Oil and Its Application in Loquat Fruit Preservation

Loquat is a nutrient-rich fruit with juicy and sweet pulp, but it is vulnerable to rot and deterioration without proper postharvest preservation measures. This study aimed to improve the postharvest quality of loquat by developing a microemulsion system based on an essential oil extracted from the Torreya grandis cv. Merrillii aril (TaEO), which has antimicrobial and antioxidant properties. An optimal TaEO microemulsion (TaEO-ME) was formulated, using a mixture of Tween-40 and Tween-80 as the surfactant, 1-butanol as the co-surfactant, and TaEO as the oil phase, with mass ratios of 9:1, 3:1, and 6:1, respectively. Two TaEO-ME formulations with 60% and 70% water contents were stable for 180 days at room temperature, with a mean droplet size below 12 nm and polydispersity index less than 0.24. They also exhibited higher stability and enhanced biological activities compared to free TaEO. Loquat fruit treated with TaEO-ME displayed a reduced decay index and lower membrane lipid peroxidation after 15 days of storage at 15 °C, as indicated by the lower malondialdehyde content and higher peroxidase activity. Moreover, the TaEO-ME treatment preserved the nutrient quality by maintaining the total phenolic compounds and ascorbic acid content. Our findings suggested that TaEO-ME can be used as a substitute for chemical preservatives to keep fruits fresh.

Microbial and enzymatic changes in cigar tobacco leaves during air-curing and fermentation

Metabolic enzyme activity and microbial composition of the air-curing and fermentation processes determine the quality of cigar tobacco leaves (CTLs). In this study, we reveal the evolution of the dominant microorganisms and microbial community structure at different stages of the air-curing and fermentation processes of CTLs. The results showed that the changes in metabolic enzymes occurred mainly during the air-curing phase, with polyphenol oxidase (PPO) being the most active at the browning phase. Pseudomonas, Bacteroides, Vibrio, Monographella, Bipolaris, and Aspergillus were the key microorganisms in the air-curing and fermentation processes. Principal coordinate analysis revealed significant separation of microbial communities between the air-curing and fermentation phases. Redundancy analysis showed that bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota were correlated with enzyme activity and temperature and humidity. Bacteria mainly act in sugar metabolism, lipid metabolism, and amino acid metabolism, while fungi mainly degrade lignin, cellulose, and pectin through saprophytic action. Spearman correlation network analysis showed that Firmicutes, Proteobacteria, and Actinobacteria were the key bacterial taxa, while Dothideomycetes, Sordariomycetes, and Eurotiomycetes were the key fungal taxa. This research provides the basis for improving the quality of cigars by improving the air-curing and fermentation processes. KEY POINTS: • Changes in POD and PPO activity control the color change of CTLs at the air-curing stage. • Monographella, Aspergillus, Pseudomonas, and Vibrio play an important role in air-curing and fermentation. • Environmental temperature and humidity mainly affect the fermentation process, whereas bacteria such as Proteobacteria, Firmicutes, Bacteroidota, and Acidobacteriota and fungi such as Ascomycota and Basidiomycota are associated with enzyme activity and temperature and humidity.

Behavior of enzymes under high pressure in food processing: mechanisms, applications, and developments

High pressure processing (HPP) offers the benefits of safety, uniformity, energy-efficient, and low waste, which is widely applied for microbial inactivation and shelf-life extension for foods. Over the past forty years, HPP has been extensively researched in the food industry, enabling the inactivation or activation of different enzymes in future food by altering their molecular structure and active site conformation. Such activation or inactivation of enzymes effectively hinders the spoilage of food and the production of beneficial substances, which is crucial for improving food quality. This paper reviews the mechanism in which high pressure affects the stability and activity of enzymes, concludes the roles of key enzymes in the future food processed using high pressure technologies. Moreover, we discuss the application of modified enzymes based on high pressure, providing insights into the future direction of enzyme evolution under complex food processing conditions (e.g. high temperature, high pressure, high shear, and multiple elements). Finally, we conclude with prospects of high pressure technology and research directions in the future. Although HPP has shown positive effects in improving the future food quality, there is still a pressing need to develop new and effective combined processing methods, upgrade processing modes, and promote sustainable lifestyles.

Recent Advances of Polyphenol Oxidases in Plants

Polyphenol oxidase (PPO) is present in most higher plants, but also in animals and fungi. PPO in plants had been summarized several years ago. However, recent advances in studies of PPO in plants are lacking. This review concludes new researches on PPO distribution, structure, molecular weights, optimal temperature, pH, and substrates. And, the transformation of PPO from latent to active state was also discussed. This state shift is a vital reason for elevating PPO activity, but the activation mechanism in plants has not been elucidated. PPO has an important role in plant stress resistance and physiological metabolism. However, the enzymatic browning reaction induced by PPO is a major problem in the production, processing, and storage of fruits and vegetables. Meanwhile, we summarized various new methods that had been invented to decrease enzymatic browning by inhibiting PPO activity. In addition, our manuscript included information on several important biological functions and the transcriptional regulation of PPO in plants. Furthermore, we also prospect some future research areas of PPO and hope they will be useful for future research in plants.

Effects of Cinnamon Essential Oil on Oxidative Damage and Outer Membrane Protein Genes of Salmonella enteritidis Cells

Salmonella is an important pathogen causing food poisoning. Food safety and health are the themes of today′s society. As a class of food-borne pathogens, Salmonella enteritidis had become one of the common zoonotic pathogens. Cinnamon essential oil (CEO) had been reported as an antibacterial agent, but there are few studies on its antibacterial mechanism. This study investigated the effects of CEO on oxidative damage and outer membrane protein genes of Salmonella enteritidis cells. First, the reactive oxygen species content in bacteria treated with different concentrations of cinnamon essential oil was determined by fluorescence spectrophotometry, and the effects of superoxide dismutase (SOD), catalase (CAT) and superoxide dismutase (SOD), and catalase (CAT) and peroxidase (POD) were determined by the kit method. The activity of POD and the content of malondialdehyde (MDA) were investigated to investigate the oxidative damage of CEO to Salmonella enteritidis cells. By analyzing the effect of CEO on the Salmonella enteritidis cell membrane’s outer membrane protein gene expression, the mechanism of CEO′s action on the Salmonella enteritidis cell membrane was preliminarily discussed. The results showed that CEO treatment had an obvious oxidative damaging effect on Salmonella enteritidis. Compared with the control group, the increase in CEO concentration caused a significant increase in the bacteria ROS content. The observation technique experiment found that with the increase in CEO concentration, the number of stained cells increased, which indicated that CEO treatment would increase the ROS level in the cells, and it would also increase with the increase in CEO concentration, thus causing the oxidation of cells and damage. In addition, CEO treatment also caused the disruption of the balance of the cellular antioxidant enzymes (SOD, CAT, POD) system, resulting in an increase in the content of MDA, a membrane lipid metabolite, and increased protein carbonylation, which ultimately inhibited the growth of Salmonella enteritidis. The measurement results of cell membrane protein gene expression levels showed that the Omp genes to be detected in Salmonella enteritidis were all positive, which indicated that Salmonella enteritidis carried these four genes. Compared with the control group, the relative expressions of OmpF, OmpA and OmpX in the CEO treatment group were significantly increased (p < 0.05), which proved that the cell function was disturbed. Therefore, the toxicity of CEO to Salmonella enteritidis could be attributed to the damage of the cell membrane and the induction of oxidative stress at the same time. It was speculated that the antibacterial mechanism of CEO was the result of multiple effects. This work was expected to provide a theoretical basis for the development of new natural food preservatives and the prevention and control of Salmonella enteritidis.

Underutilized Northern plant sources and technological aspects for recovering their polyphenols

Consumers worldwide are increasingly interested in the authenticity and naturalness of products. At the same time, the food, agricultural and forest industries generate large quantities of sidestreams that are not effectively utilized. However, these raw materials are rich and inexpensive sources of bioactive compounds such as polyphenols. The exploitation of these raw materials increases income for producers and processors, while reducing transportation and waste management costs. Many Northern sidestreams and other underutilized raw materials are good sources of polyphenols. These include berry, apple, vegetable, softwood, and rapeseed sidestreams, as well as underutilized algae species. Berry sidestreams are especially good sources of various phenolic compounds. This chapter presents the properties of these raw materials, providing an overview of the techniques for refining these materials into functional polyphenol-rich ingredients. The focus is on economically and environmentally sound technologies suitable for the pre-treatment of the raw materials, the modification and recovery of the polyphenols, as well as the formulation and stabilization of the ingredients. For example, sprouting, fermentation, and enzyme technologies, as well as various traditional and novel extraction methods are discussed. Regarding the extraction technologies, this chapter focuses on safe and green technologies that do not use organic solvents. In addition, formulation and stabilization that aim to protect isolated polyphenols during storage and extend shelflife are reviewed. The formulated polyphenol-rich ingredients produced from underutilized renewable resources could be used as sustainable, active ingredients--for example, in food and nutraceutical industries.