Jinru Chen

Role of curli fimbriae in mediating the cells of enterohaemorrhagic Escherichia coli to attach to abiotic surfaces

Aims:u2002 The objectives of this study were to evaluate the role of curli in assisting the cells of enterohaemorrhagic Escherichia coli (EHEC) in attaching to abiotic surfaces and to determine the influence of cell‐surface contact time on the efficiency of the attachment.

Antibacterial Activities of Blueberry and Muscadine Phenolic Extracts

Phenolics are one category of phyto-antimicrobials that refer to the antimicrobial substances extracted from plant sources. This study was undertaken to determine the influence of blueberry and muscadine phenolic extracts on the growths of 2 important foodborne bacterial pathogens, Salmonella Enteritidis and Listeria monocytogenes. Cells of S. Enteritidis (n = 4) or L. monocytogenes (n = 4) strains were inoculated (3 log CFU/mL) into tryptic soy broth (TSB) supplemented with 46.25 ppm of muscadine phenolics and 24 ppm of blueberry phenolics, respectively. The inoculated and un-inoculated broth with or without the supplemented phenolics were incubated at 37 °C for 24 h. Samples were drawn periodically, and cell populations of Salmonella and Listeria were determined on tryptic soy agar (TSA). It was observed that Salmonella was relatively more susceptible than Listeria to the phenolic extracts used in the study. The growth of Salmonella was significantly inhibited in all samples at all sampling points except for the sample that was supplemented with muscadine water extract and drawn at the 24-h sampling point. Blueberry phenolics were relatively more effective than muscadine phenolic extracts in inhibiting the growth of Salmonella. One tested strain of Listeria was more susceptible to ethanol than water phenolic extracts. The study revealed the potentials and limitations of using blueberry and muscadine phenolics to control the growths of selected Salmonella and Listeria strains.

Evaluation of Liquid Smoke Treated Ready-to-Eat (RTE) Meat Products for Control of Listeria innocua M1

Liquid smoke fractions (S1, S2, S3, and S4) were applied on ready-to-eat (RTE) meat products to control the growth of inoculated Listeria innocua M1. Turkey rolls and roast beef products were dipped in liquid smoke, surface inoculated with L. innocua M1 (10(2) CFU/25 cm(2) RTE meat surface), vacuum packaged, and stored at 4 degrees C. Section 8.5 of USDAs detection and isolation procedure for L. monocytogenes was employed in conjunction with a Micro-ID system for L. innocua M1 identification (ID). Products treated with smoke fractions S1, S2, and S3 were negative for L. innocua M1 at 2 and 4 wk during incubation at 4 degrees C. Products treated with S4 were positive for L. innocua M1 immediately following inoculation and after storage for 2 and 4 wk. Smoke fractions S1, S2, and S3 exhibited pH values lower than 4.6, acidity values higher than 1.5%, and carbonyl concentrations higher than 110 mg/mL. All liquid smoke fractions contained similar phenol concentrations (0.3 to 0.6 mg/mL), suggesting that phenols may have a limited role in the bactericidal effects of liquid smoke fractions against specific microorganisms.

Survival of Lactobacillus rhamnosus GG as Influenced by Storage Conditions and Product Matrixes

Mortality resulting from diarrhea especially that occurs in children younger than 5 y of age ranks 3rd among all deaths caused by infectious diseases worldwide. Probiotics such as Lactobacillus rhamnosus GG are clinically shown to effectively reduce the incidence of diarrhea in children. A food substrate is one of the major factors regulating the colonization of microorganisms in human gastrointestinal tracts. Peanut butter is a nutritious, low-moisture food that could be a carrier for probiotics. In this study, we observed the influence of storage conditions and product matrixes on the survival of L. rhamnosus GG. Cells of L. rhamnosus GG were inoculated into full fat or reduced fat peanut butter at 10(7) CFU/g. Inoculated peanut butter was stored at 4, 25, or 37 °C for 48 wk. Samples were drawn periodically to determine the populations of L. rhamnosus GG. Results showed that there was no significant decrease in the viable counts of L. rhamnosus GG in products stored 4 °C. The survivability of L. rhamnosus GG decreased with increasing storage temperature and time. Product matrixes did not significantly affect the survival of L. rhamnosus GG except at 37 °C. Populations of L. rhamnosus GG were preserved at >6 logs in products stored at 4 °C for 48 wk and at 25 °C for 23 to 27 wk. At 37 °C, the 6-log level could not be maintained for even 6 wk. The results suggest that peanut butter stored at 4 and 25 °C could serve as vehicles to deliver probiotics.

Changes in Selected Physical Property and Enzyme Activity of Rice and Barley Koji during Fermentation and Storage

UNLABELLEDnKoji are solid-state fermentation products made by inoculating steamed grains with the spores of fungi, particularly Aspergillus spp. This research was undertaken to identify the fermentation and storage conditions optimal for the production and maintenance of selected hydrolytic enzymes, such as α-amlyase and protease, in koji. Steamed rice and barley were inoculated with 2 × 10 ¹¹ Aspergillus oryzae spores per kilogram of grains and fermented for 118 h in a growth chamber at 28 to 32 °C with controlled relative humidities. Samples were drawn periodically during fermentation and storage at -20, 4, or 32 °C, and α-amylase and protease activity, mold counts, a(w), moisture contents, and pH of collected samples were determined. It was observed that the a(w), moisture contents, and pH of the koji were influenced by the duration of fermentation and temperature of storage. The α-amylase activity of both koji increased as the populations of A. oryzae increased during the exponential growth phase. The enzyme activity of barley koji was significantly higher than that of rice koji, reaching a peak activity of 211.87 or 116.57 U at 46 and 58 h, respectively, into the fermentation process. The enzyme activity in both products started to decrease once the mold culture entered the stationary growth phase. The protease activities of both koji were low and remained relatively stable during fermentation and storage. These results suggest that rice and barley koji can be used as sources of α-amylase and desired enzyme activity can be achieved by controlling the fermentation and storage conditions.nnnPRACTICAL APPLICATIONnAmylases and proteases are 2 important hydrolytic enzymes. In the food industry, these enzymes are used to break down starches and proteins while reducing the viscosity of foods. Although amylases and proteases are found in plants and animals, commercial enzymes are often produced using bacteria or molds through solid state fermentation, which is designed to use natural microbial process to produce enzymes in a controlled environment. A properly produced and maintained koji with a high hydrolytic enzyme activity can serve as an important source of the enzymes for the food industry.

Survival of Salmonella in home-style mayonnaise and acid solutions as affected by acidulant type and preservatives.

Mayonnaise made from contaminated eggs has been linked to outbreaks of Salmonella infections. This study was undertaken to determine the fate of salmonellae in home-style mayonnaise and acid solutions with or without chemical preservatives. Egg yolks were inoculated with different levels of a three-serotype (Typhimurium, Heidelberg, and Enteritidis [untypeable phage type]) mixture of Salmonella or a three-phage-type (4, 8, and 13) mixture of Salmonella Enteritidis. The inoculated yolks were used to make mayonnaise with 2, 3, or 4 teaspoons of a commercial wine vinegar or lemon juice. The mayonnaise was sampled for salmonellae over a 15-day period at 4°C, and negative samples were tested further by a three-tube most-probable-number assay. The same Salmonella mixtures were respectively inoculated into six acid solutions including wine vinegar, lemon juice, and acetic or citric solutions with or without chemical preservatives. The Salmonella populations of the Salmonella Enteritidis mixture were more persistent than those of the other Salmonella mixture in mayonnaise. Both Salmonella mixtures survived longer in mayonnaise made with vinegar than with lemon juice during storage at 4°C. In the acid solutions, however, the populations of the two Salmonella mixtures were not significantly different. The numbers of the two Salmonella mixtures in acetic or citric acid solutions with the preservatives were significantly lower than those in vinegar, lemon juice, and the solutions without the preservatives. Results suggest that Salmonella in contaminated egg yolks could survive the mayonnaise-making process. The inhibition of Salmonella by vinegar and lemon juice is due to the hurdle effect of organic acids and chemical preservatives.

Mitigating the Antimicrobial Activities of Selected Organic Acids and Commercial Sanitizers with Various Neutralizing Agents

This study was conducted to evaluate the abilities of five neutralizing agents, Dey-Engley (DE) neutralizing broth (single or double strength), morpholinepropanesulfonic acid (MOPS) buffer, phosphate-buffered saline (PBS), and sodium thiosulfate buffer, in mitigating the activities of acetic or lactic acid (2%) and an alkaline or acidic sanitizer (a manufacturer-recommended concentration) againt the cells of Shiga toxin-producing Escherichia coli (STEC; n = 9). To evaluate the possible toxicity of the neutralizing agents to the STEC cells, each STEC strain was exposed to each of the neutralizing agents at room temperature for 10 min. Neutralizing efficacy was evaluated by placing each STEC strain in a mixture of sanitizer and neutralizer under the same conditions. The neutralizing agents had no detectable toxic effect on the STEC strains. PBS was least effective for neutralizing the activity of selected organic acids and sanitizers. Single-strength DE and sodium thiosulfate neutralized the activity of both acetic and lactic acids. MOPS buffer neutralized the activity of acetic acid and lactic acid against six and five STEC strains, respectively. All neutralizing agents, except double-strength DE broth, had a limited neutralizing effect on the activity of the commercial sanitizers used in the study. The double-strength DE broth effectively neutralized the activity of the two commercial sanitizers with no detectable toxic effects on STEC cells.

The use of nutrient-optimizing/cost-minimizing software to develop ready-to-use therapeutic foods for malnourished pregnant women in Mali

Malnutrition affects people of all ages in many countries in the developing world. One treatment for malnutrition is the intervention involving ready-to-use therapeutic foods (RUTFs). This study developed RUTFs for pregnant women in Mali using formulation computer software and largely local, plant-based ingredients. Mali has the worlds second highest birth rate and infant mortality rate. Nutrient profiles of possible ingredients and their prices from 2004 to 2009 were entered into the software. Computer-selected ingredients included peanuts, cowpeas, and millet as well as rice or barley koji (sources of α-amylase and ingredients). Components of the six selected formulations were milled, hydrolyzed with koji α-amylase, and heated at 121°C for 15 min. The contents of protein, fat, ash, fiber, carbohydrates, amino acid, and energy of dehydrated products were determined and compared with software-predicted values. Actual and predicted values were comparable: the protein content was 1.45–2.04% higher, and ash content was 0.60–0.89% higher than the predicted values, while the fat content was 0.18–0.88% lower, the lysine content was 0.17–0.25% lower, and fiber content was 0.16% lower to 2.06% higher than the predicted values. The difference in actual and predicted energy levels were 14.8–22.2%. The amount of RUTF needed to meet the requirement of most limiting nutrients, lysine and energy, ranged from 2620 to 3002 g. The costs for producing the RUTFs were substantially lower than importing commercial RUTFs even with increased ingredient prices in Mali from 2004 to 2009.

Survival of four commercial probiotic mixtures in full fat and reduced fat peanut butter

A well-documented health benefit of probiotics is their ability to reduce the incidence of diarrhea in young, malnourished children in the developing countries. This study was undertaken to determine whether peanut butter, a nutritious, low-moisture food could be a carrier for probiotics by observing the survivability of selected probiotic mixtures in peanut butter under different storage conditions. Commercial probiotic mixtures (B, U, N and S) comprising of multiple strains of Lactobacillus, Bifidobacterium, Streptococcus and Lactococcus were inoculated into full fat or reduced fat peanut butter at 10(7)xa0CFU/g. Resulting products were stored at 4, 25 or 37xa0°C for 12 months. Populations of Lactobacillus, Bifidobacterium and Streptococcus/Lactococcus were determined periodically. The average viable cell counts of N and S were significantly lower than those of B and U (pxa0<xa00.05). In all probiotic products stored at different temperatures, Bifidobacterium had the greatest survivability, followed by Lactobacillus and Streptococcus/Lactococcus. The probiotics used in the study had different surviving patterns, and their survival was influenced by storage conditions. Fat content of peanut butter had no significant impacts on probiotic viability. Results suggest that peanut butter can be a vehicle to deliver probiotics for preventing diarrhea among malnourished children.

Lead and cadmium levels in cattle muscle and edible tissues collected from a slaughter slab in Nigeria

Contamination levels of lead (Pb) and cadmium (Cd) in muscles, liver and kidney of 50 randomly selected, freshly slaughtered cattle in Ogun State, Nigeria were assessed using an official procedure and atomic absorption spectrophotometry. Results showed that Pb and Cd were present in all of the tested samples. Mean Pb concentrations were 0.721 ± 0.180 mg kg−1, 0.809 ± 0.220 mg kg−1 and 0.908 ± 0.422 mg kg−1 in muscle, liver and kidney tissues, respectively. Mean Cd concentrations were 0.157 ± 0.049 mg kg−1, 0.172 ± 0.071 mg kg−1 and 0.197 ± 0.070 mg kg−1 in muscle, liver and kidney tissues, respectively. Pb and Cd levels in muscle versus kidney tissues and also in liver versus kidney samples were significantly different (p < 0.05). Mean Pb concentrations in all tested tissues were significantly higher than the International Standards while the mean Cd concentrations in liver and kidney samples were within the limits of these standards.