Insight into the molecular mechanism of phosphine toxicity provided by functional analysis of cytochrome b5 fatty acid desaturase and dihydrolipoamide dehydrogenase in the red flour beetle, Tribolium castaneum.

Phosphine is the dominant chemical used in postharvest pest control. Widespread and highly frequent use of phosphine has been selected for pest insects, including Tribolium castaneum, which is highly resistant. Lipid peroxidation and reactive oxygen species (ROS) are two major factors determining phosphine toxicity; however, the mechanisms of production of these two factors in phosphine toxicity are still unknown. Here, we first determined the time course of phosphine-induced lipid peroxidation and ROS production in T. castaneum. Our results showed that lipid peroxidation occurs before ROS in the process of phosphine toxicity, and fumigated beetles with higher resistance levels were associated with weaker activity on lipid peroxidation and ROS. A significant decline in lipid peroxidation was observed in fumigated individuals after knockdown of cytochrome b5 fatty acid desaturase (Cyt-b5-r) via RNA interference (RNAi), indicating that Cyt-b5-r is critical for triggering phosphine-induced lipid peroxidation. Moreover, significant decreases in both ROS and mortality were detected in fumigated T. castaneum adults fed melatonin for 7 days, an inhibitor of lipid peroxidation. Cyt-b5-r RNAi also inhibited ROS production and mortality in phosphine-treated beetles. Meanwhile, a significant decrease in ROS production (68.4%) was detected in dihydrolipoamide dehydrogenase (DLD) knockdown individuals with phenotypes susceptible to phosphine, suggesting that lipid peroxidation initiates ROS with the expression of DLD. However, a significant increase in ROS (122.1%) was detected in the DLD knockdown beetles with strongly resistant phenotypes, indicating that the DLD-involved pathway may not be the only mechanism of ROS generation in phosphine toxicity and the existence of a moonlighting role in downregulating ROS in strongly resistant T. castaneum.

Effect of fermented blueberry on the oxidative stability and volatile molecule profiles of emulsion-type sausage during refrigerated storage.

OBJECTIVE: The aim of this work was to assess the effect of fermented blueberry (2%, 4% and 6%) on the oxidative stability and volatile molecule profiles of emulsion-type sausage stored at 4 °C for 28 days. METHODS: The antioxidant activity of fermented blueberry (FB) was determined through radical-scavenging activity of 2, 2-diphenyl-1-picrylhydrazyl radical scavenging activity (DPPH) and hydroxyl radicals. Four formulations of sausage treatments with different FB levels (0, 2, 4, 6%) were prepared, then peroxide value (POVs), thiobarbituric acid-reactive substances (TBARS) values, protein carbonyls and thiol groups were measured. The aroma profiles of sausages for each treatments were also determined. RESULTS: The IC50 value indicated that FB had greater scavenging ability than ascorbic acid against DPPH and hydroxyl radicals. Sausages with FB significantly retarded increases in POVs and TBARS, as well as in the content of protein carbonyls during all storage days (p < 0.05). Particularly, 4% and 6% FB-treated sausages had better oxidation inhibition effects. However, FB accelerated the reduction in thiol groupss (p < 0.05). Additionally, FB inhibits the excessive formation of aldehyde compounds; for example, hexanal decreased from 58.25% to 19.41%, which may cause rancid flavors. FB also created 6 alcohols (i.e., 2-methyl-1-propanol, 3-methyl-1-butanol and phenylethyl alcohol), 5 ester compounds (i.e., ethyl acetate, ethyl lactate and ethyl hexanoate) and 3-hydroxy-2-butanone in the sausages that contribute to sausage flavors. The principal component analysis (PCA) showed that the aroma profiles of sausages with and without FB are easily identified. CONCLUSION: The addition of FB could significantly recduce the lipid and protein oxidation and improve oxidative stability for storage. Also, adding FB could inhibit rancid flavors and contribute to sausage flavors.

Insight into the Mechanism of Porcine Myofibrillar Protein Gel Properties Modulated by κ-Carrageenan.

The purpose of this study is to explain the mechanism of porcine myofibrillar protein gel properties modulated by κ-carrageenan. The textural properties results showed that the stress at fracture of the composite gel with 0.4% κ-carrageenan had the highest value (91.33 g), which suggested that the 0.4% κ-carrageenan addition was the limitation. The strain at fracture was significantly reduced with κ-carrageenan addition. The composite gel with 0.4% κ-carrageenan had the lowest proportion of T22 (7.85%) and the shortest T21 relaxation time (252.81 ms). The paraffin section showed that the phase separation behavior of the composite gel transformed from single-phase behavior to dispersed phase behavior to bi-continuous phase behavior, and the ratio of CG/MP phase area significantly increased from 0.06 to 1.73. The SEM showed that the three-dimensional network of myofibrillar protein transformed from a loose structure to a compact structure to an unaggregated structure with κ-carrageenan addition. The myofibrillar protein network of the treatment with 0.4% κ-carrageenan had the highest DF value (1.7858) and lowest lacunary value (0.452). The principal component analysis was performed on the data of microstructure and textural properties, and the results showed that the dispersed phase behavior and moisture stabilization promoted the aggregation of myofibrillar protein and the composite gel had better water holding capacity and textural properties, while bi-continuous phase behavior hindered the aggregation of myofibrillar protein and the composite gel had worse water holding capacity and textural properties.

Effect of Malondialdehyde-Induced Oxidation Modification on Physicochemical Changes and Gel Characteristics of Duck Myofibrillar Proteins.

This paper focuses on the effect of malondialdehyde-induced oxidative modification (MiOM) on the gel properties of duck myofibrillar proteins (DMPs). DMPs were first prepared and treated with oxidative modification at different concentrations of malondialdehyde (0, 0.5, 2.5, 5.0, and 10.0 mmol/L). The physicochemical changes (carbonyl content and free thiol content) and gel properties (gel whiteness, gel strength, water holding capacity, rheological properties, and microstructural properties) were then investigated. The results showed that the content of protein carbonyl content increased with increasing MDA oxidation (p < 0.05), while the free thiol content decreased significantly (p < 0.05). Meanwhile, there was a significant decrease in gel whiteness; the gel strength and water-holding capacity of protein gels increased significantly under a low oxidation concentration of MDA (0−5 mmol/L); however, the gel strength decreased under a high oxidation concentration (10 mmol/L) compared with other groups (0.5−5 mmol/L). The storage modulus and loss modulus of oxidized DMPs also increased with increasing concentrations at a low concentration of MDA (0−5 mmol/L); moreover, microstructural analysis confirmed that the gels oxidized at low concentrations (0.5−5 mmol/L) were more compact and homogeneous in terms of pore size compared to the high concentration or blank group. In conclusion, moderate oxidation of malondialdehyde was beneficial to improve the gel properties of duck; however, excessive oxidation was detrimental to the formation of dense structured gels.

The effect of water-insoluble dietary fiber from star anise on water retention of minced meat gels.

The mechanism of star anise dietary fiber (SADF) in improving the water-holding capacity (WHC) of meat batter during chilled storage was investigated. In the 0-day storage group, the cooking loss (CL) decreased from 11.93% to 9.38% with the increased content of SADF, indicating that the physical filling of SADF could improve the WHC of cooked meat batter. After 7 days of chilled storage, the CL of meat batter without SADF increased from 11.93% to 17.65%, while the addition of SADF significantly reduced the CL, especially 2% SADF showing the lowest CL. Additionally, adding SADF could significantly improve the color stability and increase the hardness of cooked meat batter. According to the results of TBARS and carbonyls, SADF significantly inhibited lipid oxidation and alleviated oxidative damage of protein, resulting in an increase in the level of ß-sheet, which was confirmed by the result of FT-IR. Therefore, the water mobility of meat batter was restricted, which was confirmed by the T2 relaxation time. In general, the water retention of meat batter during chilled storage was improved via antioxidant and physical filling of SADF.

Insight into the mechanism of myofibrillar protein gel influenced by konjac glucomannan: Moisture stability and phase separation behavior.

The effect and mechanism of myofibrillar protein (MP) gelation influenced by konjac glucomannan (KG) addition were studied. The KG addition significantly improved gel strength and water holding capability (WHC) of MP-KG composite gel, but it had additive limitation at 1.0%. The SEM showed that KG (<1.0%) reduced the appearance of moisture channels and promoted the formation of an integral MP gel network. Raman spectroscopy showed that KG addition (<1.0%) promoted the protein unfolding and the interaction of hydrophobic groups during thermal processing. However, the KG (>1.0%) would form continuous viscous hydrogel and interpenetrate with the MP solution, which hindered the interaction of hydrophobic groups during thermal process, and the MP formed a loose and degraded final structure. Hence, MP gels produced with the addition of KG underwent a transformation from a loose structure to a compact structure to an unaggregated structure, which was influenced by moisture stability and phase separation behavior.

The effects of three polysaccharides on the gelation properties of myofibrillar protein: Phase behaviour and moisture stability.

The effects of three polysaccharides on the textural properties and microstructure of myofibrillar protein (MP) gels were studied. The gel strength and rheological properties of composite MP gels were significantly improved with insoluble dietary fibre (DF) and modified starch (MS) addition, while konjac glucomannan (KG) had limited effects at 1% addition. The SEM images indicated that moisture extrusion formed moisture channels and deteriorated the aggregation of MP gel networks during the thermal process. The polysaccharides stabilized moisture and reduced the appearance of moisture channels in the gel network, thereby promoting the formation of compact and integral gel networks. The MP-polysaccharide mixture is a thermally incompatible system and presented two main forms after the thermal process: 1) the "trapped" structure and 2) the "interpenetrated" structure. In the "trapped" structure, the MP was the dominant structure of the composite gel network. In the "interpenetrated" structure, the continuous polysaccharide hydrogel substantially hindered the aggregation of MP gel networks. Principal component analysis showed that the phase behaviour and moisture stability of polysaccharides significantly influenced the textural quality and microstructure of composite MP gelation. The study indicated that polysaccharides that contribute to moisture stability and form a "trapped structure" (phase behaviour) are ideal fat replacements for improving composite gel properties, especially DF.

Insight into the mechanism of physicochemical influence by three polysaccharides on myofibrillar protein gelation.

In this study, the effect and mechanism of myofibrillar protein (MP) gelation influenced by the hydration characteristic of three polysaccharides were studied through puncture test, paraffin section, SEM and Raman spectroscopy. The gel strength and water holding capability reflect that MP gelation only significantly improves until modified starch (MS) addition beyond 1.0%. The MS granule improves MP gel property through simply physical swelling effect. At gelatinization temperature, MS absorbs the moisture nearby to compress the MP three-dimensional networks, but the swelling effect is limited. The insoluble dietary fiber (IDF) improves MP gelation property through moisture stability. The IDF addition could lessen the appearance of moisture channel in MP gel networks and promote the interaction of hydrophobic groups. The MP gelation with 2.0% IDF addition has the highest gel strength (279 g) and water holding capability (91.87%). The konjac glucomannan (KG) (>1.0%) could degrade gel property of MP gelation through interpenetrate structure, because the KG hydrogel hinders the aggregation of the MP gel networks. In conclusion, the IDF, which has strong water-holding capability at room temperature and distribute individually, is the best polysaccharides-based fat replacement in low-fat restructured products.

The effects of insoluble dietary fiber on myofibrillar protein gelation: Microstructure and molecular conformations.

The effects of insoluble dietary fiber (IDF) on heat-induced gelation properties, such as microstructural changes and the molecular conformation of myofibrillar proteins (MP), were analyzed by image analyses and Raman spectroscopy. Scanning electron microscopy revealed that pure MP gelation contained a loose and dispersed network with interconnected water channels. With IDF addition, the lacunarity and the particle size of water pores both significantly decreased (P < 0.05) and fractal dimension significantly increased (P < 0.05), which indicated the formation of a homogenous and compact three-dimensional network. Through Raman spectra, IDF addition resulted in modification of amide I and III regions, by a significant decrease in α-helix content, accompanied by an increase of ß-sheets, ß-turns, and random coil content (P < 0.05); the intensity of CU+005CH stretching vibrations bending vibrations bands were significantly decreased (P < 0.05). Principal component analyses showed significant correlations between textual property, microstructure and molecular conformations. Cluster analyses indicated IDF improved the functionality of MP gel by 1): IDF stable the moisture phase 2) "concentrated" MP promoted structural integrity and compact gelation.

Caco-2 cell-based electrochemical biosensor for evaluating the antioxidant capacity of Asp-Leu-Glu-Glu isolated from dry-cured Xuanwei ham.

A cell-based electrochemical biosensor was developed to determine the antioxidant activity of Asp-Leu-Glu-Glu (DLEE) isolated from dry-cured Chinese Xuanwei ham. A platinized gold electrode (Pt NPs/GE) covered with silver nanowires (Ag NWs) was fabricated to detect H2O2 using redox signaling via cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Under optimal condition, the detection limit of the modified electrode was 0.12µM with a linear relationship from 0.2 to 2µM, which showed relatively outstanding catalytic effects towards the reduction of H2O2. Furthermore, the generation of reactive oxygen species (ROS) in the cell can be used to indirectly assess changes in intercellular oxidative stress by detecting variations in electrochemical signals. A 3D cell culture of alginate/graphene oxide (NaAlg/GO) was used to encapsulate and immobilize Caco-2 cells. Based on ROS generation and electrochemical results, we found that DLEE could effectively reduce oxidative stress level in Caco-2 cells under external stimulation. DLEE showed high antioxidant activity with a relative antioxidant capacity (RAC) rate of 88.17% at 1.5mg/mL. Finally, an efficient electrochemical biosensor was established using the active 3D Caco-2 cell platform. This system is sensitive and simple to operate with the property to evaluate the antioxidant activity of peptides by the detection of H2O2 in cell membrane. In summary, this work describes a new method for assessing antioxidant capacity of peptide DLEE using cell-based electrochemical signaling with a rapid screening pattern.

Improved gel functionality of myofibrillar proteins incorporation with sugarcane dietary fiber.

The effects of sugarcane dietary fiber (SDF) on the gelation properties of porcine myofibrillar proteins (MP) were studied to understand its mechanism of action in improving gel functionality. Rheological tests on all composite gels (MP with SDF) showed the visco-elastic nature of MP, but the G' significantly increased with contents of SDF and with particle size (P<0.05). However, the δ exhibited the opposite effect. Light microscopy suggested that SDF affected moisture distribution in the gel by drawing water from MP and homogenously embedded in gelation. It is proposed that during the heating the more concentrated MP promoted the unfolding of MP chains and facilitated the formation of ß-sheet instead of α-helices, leading to a compact and homogenous three-dimensioned network. These results indicated that the SDF changed the water distribution and resulted in the enhanced gelation which reacted to firmly bind SDF and form a synergistic interaction system.

Effects of the sugarcane dietary fiber and pre-emulsified sesame oil on low-fat meat batter physicochemical property, texture, and microstructure.

The purpose of this study was to evaluate the effects of sugarcane dietary fiber (SDF) and pre-emulsified sesame oil for pork fat replacement on batter characteristics. Replacing pork fat with SDF and pre-emulsified sesame oil significantly affected color, water- and fat-binding properties, texture, dynamic rheology, microstructure and sensory analysis. With SDF and pre-emulsified sesame oil, the batters had improved textures and gave good sensory scores. These batters containing SDF had reduced the cholesterol and fat contents. With increasing levels of SDF, the batters had higher water- and fat-binding properties, improved texture (hardness, gumminess and chewiness), dynamic rheology and a more balanced nutritional composition. However, when the level of SDF reached 3%, the pores formed by SDF in batter were too large to hinder aggregation and the hardness of batter was unacceptable, which result the allover acceptability to be unsatisfactory. The sample 2% SDF had comparable overall acceptability to the control batter.