Disentangling the "tip-effects" enhanced antibacterial mechanism of Ag nanoparticles.

Silver nanoparticles (Ag NPs) exhibit strong antibacterial activity and are widely used in industries such as medical, food and cosmetics. In this study, Ag nanospheres and Ag nanotriangles are selected as antibacterial agents to reveal the distinct mechanism of tip effects towards their antibacterial performance. A series of antibacterial experiments were implemented, including in situ monitoring as well as studying and determining the evolution of the inhibition zone, minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC) values, growth kinetics, bactericidal curve, bacterial morphologies and intracellular reactive oxygen species (ROS). Ag nanotriangles can eradicate E. coli and S. aureus at extremely low concentrations in comparison to Ag nanospheres, in particular under sunlight irradiation. The destroyed bacterial cell walls were examined by scanning electron microscopy. Through the investigation of ROS production, the generation efficiency of ROS is improved by the merit of sunlight irradiation thanks to the localized surface plasmon resonance (LSPR) properties of Ag NPs. However, a more significant improvement in ROS generation efficiency occurred in the presence of Ag nanotriangles contributed by the pronounced "tip effects". This study sheds light on the structure-performance relationship for the rational design of antibacterial agents.

The bioavailability, absorption, metabolism, and regulation of glucolipid metabolism disorders by quercetin and its important glycosides: A review.

Quercetin and its glycosides (QG), vitally natural flavonoid, have been popular for health benefits. However, the absorption and metabolism affect their bioavailability, and the metabolic transformation alters their biological activities. This review systematically summarizes the bioavailability and pathways for the absorption and metabolism of quercetin/QG in vivo and in vitro, the biological activities and mechanism of quercetin/QG and their metabolites in treating glucolipid metabolism are discussed. After oral administration, quercetin/QG are mainly absorbed by the intestine, undergo phase II metabolism in the small intestine and liver to form conjugates and are metabolized into small phenolic acids by intestinal microbiota. Quercetin/QG and their metabolites exert beneficial effects on regulating glucolipid metabolism disorders, including improving insulin resistance, inhibiting lipogenesis, enhancing thermogenesis, modulating intestinal microbiota, relieving oxidative stress, and attenuating inflammation. This review enhances understanding of the mechanism of quercetin/QG regulate glucolipid metabolism and provides scientific support for the development of functional foods.

Inhibitory effects and reactions of gallic acid, catechin, and procyanidin B2 with nitrosation under stomach simulating conditions.

Nitrite widely exists in meat products, and has the functions of bacteriostasis, antisepsis, and color development. However, in an acidic environment, nitrite will react with amines, and further generate nitrosamines with carcinogenic and teratogenic effects. Polyphenols have good antioxidant and nitrite-scavenging effects. This study aimed to evaluate the inhibitory effects of gallic acid, catechin, and procyanidin B2 on the nitrosation reaction under stomach simulating conditions and discuss the potential inhibitory mechanism. The nitrite scavenging rate and nitrosamine synthesis blocking rate of gallic acid, catechin, and procyanidin B2 under different reaction times and contents was determined by UV-vis spectrophotometry. The possible products of the reaction of the three polyphenols with nitrite were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS) to reveal the mechanism of inhibiting nitrification. The results showed that the scavenging rate of the three polyphenols on nitrite and the blocking rate of nitrosamine synthesis increased with the increase of the content and reaction time. The ability of the three polyphenols to inhibit nitrosation was catechin > procyanidin B2 > gallic acid. HPLC-MS analysis showed that under simulated gastric juice conditions, the three phenolics were oxidized by nitrous acid to form their semiquinone radicals as the intermediates and nitrosated derivatives, while nitrite might be converted to ˙NO. These results suggested that gallic acid, catechin, and procyanidin B2 could inhibit nitrosation reactions in an acidic environment and may be used as food additives to reduce nitrite residues and nitrosamines in food.

Study of the effect of calcium signal participating in the antioxidant mechanism of yeast under high-sugar environment.

BACKGROUND: Saccharomyces cerevisiae is susceptible to high-sugar stress in the production of bioethanol, wine and bread. Calcium signal is widely involved in various physiological and metabolic activities of cells. The present study aimed to explore the effects of Ca2+ signal on the antioxidant mechanism of yeast during high-sugar fermentation. RESULTS: Compared to yeast without available Ca2+, yeast in the high glucose with Ca2+ group had higher dry weight, higher ethanol output at 12 and 24 h and higher glycerol output at 24 and 36 h. During the whole growth process, the trehalose synthesis capacity of yeast in the high glucose with Ca2+ group was lower and intracellular reactive oxygen species content was higher compared to yeast without available Ca2+. Intracellular malondialdehyde content of yeast under high glucose with Ca2+ was significantly lower than yeast under high glucose without available Ca2+ except for 6 h. The superoxide dismutase and catalase activities of yeast and glutathione content were higher in the high glucose with Ca2+ group compared to yeast in high glucose without available Ca2+. The expression levels of SOD1, GSH1, GPX2 genes were higher for high glucose without available Ca2+ at 6 h, while yeast in the high glucose with Ca2+ group had a higher expression of antioxidant-related genes except SOD1 and CTT1 at 12 h. The expression levels of antioxidant-related genes of yeast for high glucose with Ca2+ were higher at 24 h, and those of genes except SOD1 of yeast in the high glucose with Ca2+ group were higher at 36 h. CONCLUSION: High-glucose stress limited the growth of yeast, while a moderate extracellular Ca2+ signal could improve the antioxidant capacity of yeast in a high-glucose environment by regulating protectant metabolism and enhancing the antioxidant enzyme activity and expression of antioxidant genes in a high-sugar environment. © 2024 Society of Chemical Industry.

Effects of Ca2+ signal on the activities of key enzymes and expression of related genes in yeast ethanol metabolism and mitochondrial function during high sugar fermentation.

BACKGROUND: During high sugar fermentation, yeast is mainly affected by high sugar stress in the early stage. It becomes jointly affected by high sugar and ethanol stress as ethanol accumulates during fermentation. Ca2+, as the second messenger of the cell, mediates various metabolic processes. In this study, the effects of the Ca2+ signal on the activities of key enzymes, expression of related genes of ethanol metabolism, and mitochondrial function were investigated. RESULTS: The results showed a significant increase in the activities of enzymes related to ethanol metabolism in yeast cells under a high sugar environment. Ca2+ significantly promoted the activities of enzymes related to mitochondrial respiratory metabolism and regulated the carbon flow between ethanol metabolism and the tricarboxylic acid cycle. The high sugar environment affected the expression of genes related to carbon metabolism, while the addition of Ca2+ stabilized the expression of related genes. CONCLUSION: Ca2+ signal participated in ethanol and mitochondrial metabolism and regulated the key enzymes and related gene expression to enhance the resistance of yeast to stress during high sugar fermentation. © 2024 Society of Chemical Industry.

Effect of calcium levels on structure and function of mitochondria in yeast under high glucose fermentation.

In this study, the effects of calcium levels on structure and function of mitochondria under high glucose environment were studied. In the high glucose environment, yeast growth capacity was inhibited, and intracellular reactive oxygen species (ROS) content was increased from 6 h to 12 h, while ROS content was reduced in group with 1 × 10-1 and 1 g/L CaCl2 level from 24 h to 36 h. Exogenous calcium addition had a significant effect on the elevation of intracellular Ca2+ and cytochrome C content in yeast from 6 h to 12 h; mitochondrial membrane potential decreased with the increase of CaCl2 level under high glucose levels. Mitochondrial swelling of yeast was influenced by high glucose levels and showed a regulatory dynamic change by Ca2+ levels. Isocitrate dehydrogenase activity increased in 1 × 10-3 g/L CaCl2 level from 6 h to 12 h, α-ketoglutarate dehydrogenase activity increased with an increase in CaCl2 level from 6 h to 24 h. Calcium affected the structure and function of mitochondria by regulating the intracellular signal, enzymes in tricarboxylic acid cycle, and cytochrome system of yeast under high glucose stress.

Influence of gardenia yellow on in vitro slow starch digestion and its action mechanism.

This study aimed to explore the influence of gardenia yellow on in vitro wheat starch digestion. The influence of gardenia yellow on the digestion properties of starch was determined through in vitro digestion, and its action mechanism on slow starch digestion was revealed by laser scanning confocal microscopy, enzymatic inhibition dynamics, and other means of characterization. Results showed that gardenia yellow could inhibit starch digestion, significantly increase the resistant starch and slowly digestible starch contents in starch (P < 0.05), and trigger the decrease in glycemic and hydrolysis indices. Furthermore, gardenia yellow could spontaneously bind to the catalytic sites of α-amylase and α-glucosidase, affect their secondary structures through vdW force and hydrophobic interaction, and reduce their catalytic abilities to inhibit the digestion process of wheat starch. Therefore, the interactions of gardenia yellow with starch and digestive enzymes jointly promote the slow digestion of starch.

Research on the Influences of Five Food-Borne Polyphenols on In Vitro Slow Starch Digestion and the Mechanism of Action.

Inhibiting starch digestion can effectively control postprandial blood sugar level. In this study, the in vitro digestion differences among the mixtures of five polyphenols (i.e., procyanidins [PAs], catechin [CA], tannic acid [TA], rutin [RU], and quercetin [QU]) and starch were analyzed through an in vitro simulation test of starch digestion. The interaction characteristics of these five polyphenols with α-amylase and α-glucosidase were investigated in terms of the inhibition effect, dynamics, fluorescence quenching, and circular dichroism (CD). The results revealed that the rapidly digestible starch (RDS) contents decreased, while the resistant starch (RS) contents increased. All five polyphenols inhibited the α-amylase activity through the noncompetitive approach but inhibited the α-glucosidase activity through the competitive approach. Five polyphenols combined with α-amylase spontaneously by using the hydrophobic effect. The interaction of PAs and QU with α-glucosidase were recognized as van der Waals forces and H bonding, whereas CA and TA interacted with α-glucosidase through the hydrophobic effect. All five polyphenols can cause conformational changes in enzymes.