Search

This study investigated the inactivation mechanism of Aspergillus flavusconidia by high hydrostatic pressure (HHP). Activity counts, scanning electron microscopic (SEM) analysis, and sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) were used to study the effects of the HHP treatment on the morphology and protein composition of A. flavusspores. The results showed that that a 3-min-lasting 600 MPa treatment could completely abolish 107colony-forming units/mL of live fungi. Furthermore, we also observed that lower spore viability corresponded to a higher Propidium Iodide absorption rate. The SEM images revealed that HHP disrupted the spore morphology and resulted in pore formation that led to the release of intracellular molecules, such as nucleic acids and proteins. The nucleic acid and protein concentration in the spore suspension increased in parallel with the increasing treatment pressure. The SDS-PAGE analysis showed that there were differences in the protein bands between the HHP-treated and untreated A. flavusspores, as the HHP treatment caused partial protein degradation and extracellular release. Therefore, the results of this study proved that high pressure could induce a morphological disruption in the internal and external cellular structures and degrade intracellular and extracellular proteins leading to an inactive state in A. flavus.

The effects of high hydrostatic pressure (HHP) treatments on histamine-forming bacteria (HFB) Morganella morganiiand Photobacterium phosphoreumin phosphate buffer and tuna meat slurry were investigated using viability counting and scanning electron microscopy. The first-order model fits the destruction kinetics of high pressure on M. morganiiand P. phosphoreumduring the pressure hold period. The D-values of M. morganii(200 to 600 MPa) and P. phosphoreum(100 to 400 MPa) in phosphate buffer ranged from 16.4 to 0.08 min and 26.4 to 0.19 min, respectively, whereas those in tuna meat slurry ranged from 51.0 to 0.09 min and 71.6 to 0.19 min, respectively. M. morganiihad higher D-values than P. phosphoreumat the same pressure, indicating it was more resistant to HHP treatment. HFB had a higher D-value in tuna meat slurry compared with that in phosphate buffer, indicating that the HFB were more resistant to pressure in tuna meat slurry. The Zp values (pressure range that results in a 10-fold change in D-value) of M. morganiiand P. phosphoreumwere 162 and 140 MPa in phosphate buffer and 153 and 105 MPa in tuna meat slurry, respectively. Damage to the cell wall and cell membrane by HHP treatments can be observed by scanning electron microscopy. To our knowledge, this is the first report to demonstrate that HHP can be applied to inactivate the HFB M. morganiiand P. phosphoreumby inducing morphological changes in the cells.

High hydrostatic pressure processing (HPP) is a non-thermal pasteurization technology which has already been applied in the food industries. Besides maintaining the food safety and quality, HPP also has potential applications in the enhancement of the health benefits of food products. This study examines the current progress of research on the use of HPP in the development of health foods. Through HPP, the nutritional value of food products can be enhanced or retained, including promotes the biosynthesis of γ-aminobutyric acid (GABA) in the food materials, retains immunoglobulin components in dairy products, increases resistant starch content in cereals, and reduces the glycemic index of fruit and vegetable products, which facilitates better control of blood glucose levels and decreases calorie intake. HPP can also be utilized as a hurdle technology in combination with existing processing technologies for the development of low-sodium food products and the maintenance of microbial safety, thereby lowering the risk of triggering cardiovascular disease. Additionally, HPP can be used to enhance the diversity of probiotic food products. Appropriate sporogenous probiotics can be screened and added to various high-pressure processed food products as a certain bacterial count is still retained in the products after HPP. As HPP causes physical damage to the structures of food products, it can also be used as a synergistic extraction technology to enhance the extraction efficiency of functional components, thereby reducing extraction time. By applying HPP in the extraction of functional components from food waste, the production costs of such components can be effectively reduced. This study provides a summary of the mechanisms by which HPP enhances the health benefits of food products and the current progress of relevant research. HPP possesses huge potential in the development of novel health foods and may provide an abundance of benefits to human health in the future.

This study examined the feasibility of utilizing high-pressure processing (HPP) with enzymatic impregnation to soften vegetables. Freeze–thaw (FT) processing was used as a positive control to compare the hardness, physicochemical characteristics, and cell microstructure of vegetables. Carrot and broccoli samples were subjected to 200 MPa of pressure for 15 min and then impregnated using a Viscozyme L enzyme solution. Compared with the hardness of fresh samples, the hardness of the carrot and broccoli samples that underwent HPP and enzymatic impregnation decreased by 84.6% and 95.5%, respectively, and the hardness of the carrot and broccoli samples that underwent FT processed decreased by 73.6% and 91.3%, respectively. In particular, HPP with enzymatic impregnation reduced the content of insoluble dietary fibers (18%), increased the content of soluble dietary fibers (3%), and considerably increased the concentration of carotene (1.9 times) and isothiocyanate (4.5 times) in carrots and broccoli, respectively. Scanning electron microscopy reveals that HPP physically damaged the intercellular compartments of the vegetables, thereby increasing the impregnation of enzymes. In addition, the level of HPP and the holding time increased, and the amount of vegetable residue and the degree of moisture retention substantially decreased, indicating a negative correlation between damage and hardness. Moreover, HPP pretreatment require a short processing time then FT, which promoted the penetration of enzymes and the internal microstructural biodegradation of vegetables, and it also helped these vegetables release more soluble nutrients. Overall, HPP can be used with enzymatic impregnation to obtain texture-modified vegetables for older consumers with mastication difficulties.

AbstractPsoralea corylifoliaseeds contain many bioactive compounds commonly used in traditional Chinese medicine. In this study, the antibacterial activity and possible mechanism of P. corylifoliaseed ethanol extract (PCEE) against foodborne pathogens were investigated. Both methicillin-resistant Staphylococcus aureus(MRSA) and Listeria monocytogeneshad similar minimum inhibitory concentrations and minimum bactericidal concentrations of PCEE at 50 and 100 μg/mL, respectively. Furthermore, elevated OD260, protein concentration, and electric conductivity indicated irreversible damage to the cytoplasmic membranes of PCEE-treated cells. Indeed, the treated cells displayed disrupted membranes, incomplete and deformed shapes, and rupture as visualized by scanning electron microscopy. Multidrug-resistance efflux pump gene expression was also analyzed by quantitative reverse transcription PCR. Although the mdrL, mdrT, and ldegenes of L. monocytogenesand the mepAgene of MRSA were upregulated, there was no significant difference that indicated an attempt by the efflux pumps to discharge PCEE. MRSA norAexpression and abcAexpression were significantly downregulated (p< 0.05). A possible mechanism for PCEE may be to cause an energy depletion, either by inhibiting adenosine triphosphate binding or by disturbing the proton gradient, resulting in membrane damage.

A 2-year study was performed at two ready-to-eat tilapia sashimi processing plants (A and B) to identify possible routes of contamination with Listeria monocytogenesduring processing. Samples were collected from the aquaculture environments, transportation tanks, processing plants, and final products. Seventy-nine L. monocytogenesisolates were found in the processing environments and final products; 3.96% (50 of 1,264 samples) and 3.86% (29 of 752 samples) of the samples from plants A and B, respectively, were positive for L. monocytogenes. No L. monocytogeneswas detected in the aquaculture environments or transportation tanks. The predominant L. monocytogenesserotypes were 1/2b (55.70%) and 4b (37.97%); serotypes 3b and 4e were detected at much lower percentages. At both plants, most processing sections were contaminated with L. monocytogenesbefore the start of processing, which indicated that the cleaning and sanitizing methods did not achieve adequate pathogen removal. Eleven seropulsotypes were revealed by pulsed-field gel electrophoresis and serotyping. Analysis of seropulsotype distribution revealed that the contamination was disseminated by the processing work; the same seropulsotypes were repeatedly found along the work flow line and in the final products. Specific seropulsotypes were persistently found during different sampling periods, which suggests that the sanitation procedures or equipment used at these plants were inadequate. Plant staff should improve the sanitation procedures and equipment to reduce the risk of L. monocytogenescross-contamination and ensure the safety of ready-to-eat tilapia products.

AbstractThe aim of this work was to investigate the mechanisms underlying the inactivation of Listeria monocytogenesin raw milk under high hydrostatic pressure (HHP). The results showed that a 450-MPa treatment for 5 min could completely eliminate 108colony-forming units/mL of viable bacteria, as indicted by increased uptake of propidium iodide. Morphological damage to the cell wall, cell membrane, and cytoplasmic components by HHP treatments was observed on scanning and transmission electron micrographs. The protein bands on sodium dodecyl sulfate–polyacrylamide gel electrophoresis gels differed between HHP-treated and untreated L. monocytogenes, in that HHP decreased the protein content and caused partial protein degradation. Therefore, our results indicate that HHP inactivates L. monocytogenesby causing morphological changes in the internal and external cellular structures, as well as through membrane damage, cell wall rupture, and membrane protein degradation.

A 15-month-old boy presenting with hand, foot and mouth disease died of myocarditis and intractable shock caused by coxsackievirus A16 infection. It is apparent that coxsackievirus A16 infection is not always a benign infection.