Jurgen G. Schwarz

Prevalence and antimicrobial resistance of Salmonella recovered from processed poultry.

This study was conducted to determine the prevalence and antimicrobial resistance of Salmonella isolates recovered from processed poultry. Four hundred eighty pre- and postchill whole broiler chicken carcasses were collected from a poultry processing plant between July 2004 and June 2005. Water samples also were collected at the entrance and exit of the chiller. After preenrichment, carcass and water samples were analyzed for the presence of Salmonella using the automated BAX system followed by traditional culture methods. The proportions of pre- and postchill carcasses that were positive for Salmonella were 88.4 and 84.1%, respectively. Ninety-two percent of water samples collected at the entrance of the chiller were positive for Salmonella, but all exit samples were negative. There was no significant difference in the prevalence of Salmonella between pre- and postchill carcasses (P > 0.05). Salmonella isolates recovered were serotyped and tested for susceptibility to antimicrobials. Thirteen serotypes were identified; the most common were Salmonella Kentucky (59.5%) and Salmonella Typhimurium (17.8%). Three hundred thirty-nine (79.8%) of the isolates were resistant to at least one antimicrobial, and 53.4% were resistant to three or more antimicrobials. Resistance was most often observed to tetracycline (73.4% of isolates), ampicillin (52.9%), amoxicillin-clavulanic acid (52%), ceftiofur (51.7%), streptomycin (35.2%), and sulfisoxazole (21.8%). These results indicate the high prevalence of Salmonella contamination in whole broiler carcasses, and a large number of these Salmonella isolates were resistant to commonly used antimicrobials.

Expanded bed adsorption for recovery of patatin from crude potato juice

An expanded bed adsorption process was used to isolate patatin possessing esterase activity, from a crude juice of potato tubers. Patatin is the major storage protein of potato tubers and is released in ample amounts in the processing effluent during starch milling. We employed mixed mode affinity resins, where the binding depends primarily on the pH, and is almost independent of the ionic strength. From a library of mixed mode chemistries involving both charged and hydrophobic functions, we screened for ligands with binding specificity for patatin. The dynamic binding capacity of two high density (1.45–1.5 g ml-1) patatin-binding agarose-glass resins in response to change of linear velocity (85–230 cm h-1) was tested in packed (25 ml) and expanded (250 ml) column modes. The column operation included a loading step at low expansion; H/Ho~1.2. Adsorption from crude juice at pH 7.5, retained patatins up to a breakthrough level of 50%. The eluate fraction at pH 3.5, now effectively stripped from the pigments, provided a 2.5-fold enzyme enrichment and produced 4 g protein per cycle. Column productivity was 122 kAU L-1 h-1. The study, using potato juice as model feedstock, demonstrated the feasibility of expanded bed-recovery of potentially valuable proteins from plant biomass.

Optimizing pectin extraction from sunflower heads by alkaline washing

Abstract De-seeded sunflower heads (Helianthus annuus L. var. Cargill) with 15–25% pectin can be a valuable source of pectin. Most pigments in heads are water soluble and are strongly associated with the pectin extract. Pretreatment with a hot water-washing process was used prior to pectin extraction to improve pectin quality by removing pigments. Unfortunately pretreatment resulted in increased pectin loss. To optimize pectin extraction, various combinations of pH, time, temperature, and solid:solvent ratio were used. The Response Surface Methodology (RSM) was used to analyze the data set. The experiments of washing ground sunflower heads were performed in the washing medium at pH 6·0–8·0 for 15–55 min at 5–25°C at solvent:solid ratios of 35:1 to 15:1 (v/w). The alkaline washing treatment at pH 7·5 for 25 min at a solvent: solid ratio of 28:1 at 16°C removed more than 48% pigment, but had little effect on pectin loss (less than 3·2%). The pectin extracted had good gelling capacity.

Evaluation of Hot Water and Electron Beam Irradiation for Reducing Fusarium Infection in Malting Barley

The use of Fusarium-infected barley for malting may lead to mycotoxin production and decreased product quality. Physical methods for the treatment of Fusarium-infected barley may prevent these safety and quality defects and allow the use of otherwise good quality barley. Hot water and electron beam irradiation were evaluated for their effectiveness in reducing Fusarium infection while maintaining germinative energy in barley samples. Hot-water treatments involved temperatures of 45, 50. 55, and 60 degrees C and treatment times of 0, 1, 5, 10, and 15 min. Electron beam irradiation involved doses ranging from 0 to 11.4 kGy. Treatment with water at 45 degrees C for 15 min resulted in a reduction in Fusarium infection from 32 to 1% after 15 min, with only a very slight reduction in germination. Treatment with water at 50 degrees C for 1 min resulted in a reduction in Fusarium infection from 32 to 2%, and no effect on germination was observed for up to 5 min of treatment. At higher water temperatures. Fusarium infection was essentially eliminated, but germination was also severely reduced. Electron beam irradiation of Fusarium-infected barley reduced Fusarium infection at doses of >4 kGy, and a slight increase in germination for dry samples was observed with doses of 6 to 8 kGy. Doses of >10 kGy significantly decreased germination. Physical methods may have potential for the treatment of Fusarium-infected malting barley.

Survival and Growth of Listeria monocytogenes in Broth as a Function of Temperature, pH, and Potassium Lactate and Sodium Diacetate Concentrations

The objective of this study was to determine the antimicrobial effect of a combination of potassium lactate and sodium diacetate (0, 1.8, 3, and 4.5%; PURASAL P Opti. Form 4, 60% solution) on the survival and growth of Listeria monocytogenes Scott A in pH-adjusted broth (5.5, 6.0, 6.5, and 7.0) stored at 4, 10, 17, 24, 30, and 37 degrees C. Appropriate dilutions of broth were enumerated by spiral plating on tryptose agar and counted with an automated colony counter. Growth data were iteratively fit, using nonlinear regression analysis to a three-phase linear model, using GraphPad PRISM. At pH 5.5, the combination of lactate-diacetate fully inhibited (P < 0.001) the growth of L. monocytogenes at all four levels and six temperatures. At pH 6.0, addition of 1.8% lactate-diacetate reduced (P < 0.001) the specific growth rate of L. monocytogenes and increased lag time; however, 3 and 4.5% completely inhibited the growth at the six temperatures studied. Efficacy of the lactate-diacetate mixture was decreased as pH increased and incubation temperature increased. Thus, at pH 6.5, at least 3% was required to retard (P < 0.001) the growth of L. monocytogenes in broth. There was a limited effect of the lactate-diacetate level on the specific growth rate of the pathogen at pH 7.0. However, 1.8 and 3% significantly lengthened the lag time at 4 and 10 degrees C. These results suggest that 1.8% of lactate-diacetate mixture can be used as a substantial hurdle to the growth of L. monocytogenes when refrigerated temperatures are maintained for products with pH less than 6.5.

Comparison of Automated BAX PCR and Standard Culture Methods for Detection of Listeria monocytogenes in Blue Crabmeat (Callinectus sapidus) and Blue Crab Processing Plants

This study compared the automated BAX PCR with the standard culture method (SCM) to detect Listeria monocytogenes in blue crab processing plants. Raw crabs, crabmeat, and environmental sponge samples were collected monthly from seven processing plants during the plant operating season, May through November 2006. For detection of L. monocytogenes in raw crabs and crabmeat, enrichment was performed in Listeria enrichment broth, whereas for environmental samples, demi-Fraser broth was used, and then plating on both Oxford agar and L. monocytogenes plating medium was done. Enriched samples were also analyzed by BAX PCR. A total of 960 samples were examined; 59 were positive by BAX PCR and 43 by SCM. Overall, there was no significant difference (P ≤ 0.05) between the methods for detecting the presence of L. monocytogenes in samples collected from crab processing plants. Twenty-two and 18 raw crab samples were positive for L. monocytogenes by SCM and BAX PCR, respectively. Twenty and 32 environmental samples were positive for L. monocytogenes by SCM and BAX PCR, respectively, whereas only one and nine finished products were positive. The sensitivities of BAX PCR for detecting L. monocytogenes in raw crabs, crabmeat, and environmental samples were 59.1, 100, and 60%, respectively. The results of this study indicate that BAX PCR is as sensitive as SCM for detecting L. monocytogenes in crabmeat, but more sensitive than SCM for detecting this bacterium in raw crabs and environmental samples.

Comparison of continuous and batch processes for pectin extraction from sunflower heads

Abstract Sunflower heads are a promising commercial source of low-methoxyl pectin. Although previously reported research was based on a batch extraction process, examples of continuous, countercurrent processes are found with other commodities (beet sugar, vegetable oil). The two types of processes were compared using ground, washed, and dried sunflower heads with 0.75% sodium hexametaphosphate (SHMP) extractant. Under the conditions of pH 2–3.5 at liquid-to-solid (L/S) ratio 32, and L/S ratio 30–45 at pH 3.23, the maximum pectin recovery was similar for the two processes. However, the continuous process maintained maximal recovery over a wide range of pH and L/S ratio. Pectin productivity, which is the rate of pectin extraction per working volume, was much higher in the continuous process than the batch process. At pH 2.5 and L/S ratio 32, it was more than 100% higher. Consequently, the continuous process achieved adequate pectin recovery with less solvent and can be conducted with smaller-size equipment than the batch.

Effect of countercurrent ethanol washing on sunflower pectin quality

Development of efficient ethanol washing technology to remove acid and ash in precipitated sunflower pectin gels is highly desirable in industrial production. A seven-stage, countercurrent washing process was developed in which the ethanol was neutralized between each stage. Ethanol from the final stage could be recovered by standard distillation methods and used again. This process significantly reduced the quantity of ethanol used, compared to a batch washing process using fresh ethanol for each washing step. The composition, color, and gelling characteristics of pectin washed by this countercurrent process were determined and compared with those of a pectin obtained by a batch washing process using fresh ethanol for each washing step and with commercial citrus pectin. The pectin gels were of good quality.