Mengshi Lin

Bio: Mengshi Lin is an academic researcher from University of Missouri. The author has contributed to research in topics: Surface-enhanced Raman spectroscopy & Silver nanoparticle. The author has an hindex of 44, co-authored 153 publications receiving 6367 citations. Previous affiliations of Mengshi Lin include Washington State University & Fujian Agriculture and Forestry University.

Antibacterial activities of zinc oxide nanoparticles against Escherichia coli O157:H7.

Abstract: Aims: To investigate antibacterial activities of zinc oxide nanoparticles (ZnO NP) and their mode of action against an important foodborne pathogen, Escherichia coli O157:H7. Methods and Results: ZnO NP with sizes of 70 nm and concentrations of 0, 3, 6 and 12 mmol l−1 and NP-free solutions were used in antimicrobial tests against E. coli O157:H7. ZnO NP showed increasing inhibitory effects on the growth of E. coli O157:H7 as the concentrations of ZnO NP increased. A complete inhibition of microbial growth was achieved at the concentration level of 12 mmol l−1 or higher. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy were used to characterize the changes of morphology and cellular compositions of bacterial cells treated with ZnO NP and study the mode of action of ZnO NP against E. coli O157:H7. The intensity of lipid and protein bands in the Raman spectra of bacterial cells increased after exposure to ZnO NP, while no significant changes in nucleic acid bands were observed. Conclusions: ZnO NP were found to have antibacterial activity against E. coli O157:H7. The inhibitory effects increase as the concentration of ZnO NP increased. Results indicate that ZnO NP may distort and damage bacterial cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. Significance and Impact of the Study: These results suggest that ZnO NP could potentially be used as an effective antibacterial agent to protect agricultural and food safety.

Detection of melamine in gluten, chicken feed, and processed foods using surface enhanced Raman spectroscopy and HPLC.

Abstract: Melamine, a nitrogen-rich chemical, was implicated in pet and human food recalls in 2007, which caused enormous economic losses to the food industry. In this study, melamine concentration in wheat gluten, chicken feed, and processed foods (that is, cake and noodle) was measured by surface enhanced Raman spectroscopy (SERS) in combination with SERS-active substrates. SERS was able to rapidly detect 0.1% melamine in wheat gluten, 0.05% in chicken feed, 0.05% in cakes, and 0.07% in noodle, respectively. A partial least squares (PLS) model was established for the quantification of melamine in foods by SERS: R= 0.90, RMSEP = 0.33. In addition, SERS results were verified by HPLC analysis based on a simplified FDA method. Compared with HPLC, the SERS method is much faster and simpler, requires minimum sample preparation, but still yields satisfactory qualitative and quantitative results. These results demonstrate that it is an applicable approach to use SERS to screen foods, eliminate presumptive negative samples of melamine contamination from the sample population, and then verify presumptive positive samples using HPLC protocols. Combining these 2 methods could provide a more rapid and cost-effective way for monitoring melamine contamination in increasingly large numbers of imported foods and feed products.

Application of Mid-infrared and Raman Spectroscopy to the Study of Bacteria

Abstract: Infrared spectroscopy and Raman spectroscopy provide complementary technologies for rapid and precise detection of microorganisms and are emerging methods in food analysis. It is possible to use either of these techniques to differentiate and quantify microorganisms in relatively simple matrices such as liquid media and simple solutions with determinations taking less than an hour. Vibrational spectroscopy, unlike other techniques used in microbiology, is a relatively simple method for studying structural changes occurring within a microbial cell following environmental stress and applications of food processing treatments. Vibrational spectroscopy provides a wide range of biochemical properties about bacteria in a single spectrum, most importantly characteristics of the cell membrane. These techniques are especially useful for studying properties of bacterial biofilms on contact surfaces, the presence and viability of bacterial vegetative cells and spores, the type and degree of bacterial injury, and assessment of antibiotic susceptibility. Future trends in food analysis will involve combining vibrational spectroscopy with microscopy, mass spectroscopy, or DNA-based methods to comprehensively study bacterial stress. Further advances in selectivity, sensitivity, and improved chemometric methods, along with reduction in the cost of instrumentation, may lead to the development of field-ready and real-time analytical systems.

Applications of nanotechnology in food packaging and food safety: Barrier materials, antimicrobials and sensors

Abstract: In this article, several applications of nanomaterials in food packaging and food safety are reviewed, including: polymer/clay nanocomposites as high barrier packaging materials, silver nanoparticles as potent antimicrobial agents, and nanosensors and nanomaterial-based assays for the detection of food-relevant analytes (gasses, small organic molecules and food-borne pathogens). In addition to covering the technical aspects of these topics, the current commercial status and understanding of health implications of these technologies are also discussed. These applications were chosen because they do not involve direct addition of nanoparticles to consumed foods, and thus are more likely to be marketed to the public in the short term.

A review on nanofluids: preparation, stability mechanisms, and applications

Abstract: Nanofluids, the fluid suspensions of nanomaterials, have shown many interesting properties, and the distinctive features offer unprecedented potential for many applications. This paper summarizes the recent progress on the study of nanofluids, such as the preparation methods, the evaluation methods for the stability of nanofluids, and the ways to enhance the stability for nanofluids, the stability mechanisms of nanofluids, and presents the broad range of current and future applications in various fields including energy and mechanical and biomedical fields. At last, the paper identifies the opportunities for future research.

Antibacterial Activity and Mechanism of Action of Zinc Oxide Nanoparticles against Campylobacter jejuni

Abstract: The antibacterial effect of zinc oxide (ZnO) nanoparticles on Campylobacter jejuni was investigated for inhibition and inactivation of cell growth. The results showed that C. jejuni was extremely sensitive to treatment with ZnO nanoparticles. The MIC of ZnO nanoparticles for C. jejuni was determined to be 0.05 to 0.025 mg/ml, which is 8- to 16-fold lower than that for Salmonella enterica serovar Enteritidis and Escherichia coli O157:H7 (0.4 mg/ml). The action of ZnO nanoparticles against C. jejuni was determined to be bactericidal, not bacteriostatic. Scanning electron microscopy examination revealed that the majority of the cells transformed from spiral shapes into coccoid forms after exposure to 0.5 mg/ml of ZnO nanoparticles for 16 h, which is consistent with the morphological changes of C. jejuni under other stress conditions. These coccoid cells were found by ethidium monoazide-quantitative PCR (EMA-qPCR) to have a certain level of membrane leakage. To address the molecular basis of ZnO nanoparticle action, a large set of genes involved in cell stress response, motility, pathogenesis, and toxin production were selected for a gene expression study. Reverse transcription-quantitative PCR (RT-qPCR) showed that in response to treatment with ZnO nanoparticles, the expression levels of two oxidative stress genes (katA and ahpC) and a general stress response gene (dnaK) were increased 52-, 7-, and 17-fold, respectively. These results suggest that the antibacterial mechanism of ZnO nanoparticles is most likely due to disruption of the cell membrane and oxidative stress in Campylobacter.

Listeria monocytogenes, a food-borne pathogen

Abstract: Listeria monocytogenes is a Gram positive, aerobic, facultative anaerobic and nonacid fast bacterium, which can cause the disease listeriosis in both human and animals. It is widely distributed thoroughout the environment and has been isolated from various plant and animal food products associated with listeriosis outbreaks. Contaminated ready-to-eat food products such as gravad and cold-smoked salmon and rainbow trout have been associated with human listeriosis in Sweden. The aim of this study was to analyse the occurrence and level of L. monocytogenes in gravad and cold-smoked salmon (Salmo salar) products packed under vacuum or modified atmosphere from retail outlets in Sweden. Isolated strains were characterized by serotyping and the diversity of the strains within and between producers were determined with PFGE (Pulsed-field gel electrophoresis). The characterized fish isolates were compared with previously characterized human strains. L. monocytogenes was isolated from 11 (three manufacturers) of 56 products analysed. This included gravad salmon products from three manufacturers and cold-smoked salmon from one manufacturer. The highest level of L. monocytogenes found was 1500 cfu/g from a cold-smoked salmon product but the level was low (<100 cfu/g) in most of the products. Serovar 1/2a was predominant, followed by 4b. Three products of gravad salmon harboured more than one serovar. PFGE typing of the 56 salmon isolates detected five Asc I types: four types were identical to human clinical strains with Asc I and one was identical and one was closely related to human clinical strains with Apa I. Isolation of identical or closely related L. monocytogenes strains from human clinical cases of listeriosis and gravad and cold-smoked salmon suggested that these kinds of products are possible sources of listeriosis in Sweden. Therefore, these products should be considered risk products for human listeriosis.