Effect of pre-treatment and freezing on the polyphenol oxidase activity and color stability of sliced peaches.

BACKGROUND: A study was conducted to determine the polyphenol oxidase (PPO) activity and changes in surface color and hydroxymethylfurfural (HMF) content in fresh and pre-frozen peach slices stored at different temperatures. In this study, fresh (F) and pre-frozen (P) peaches were subjected to one of four treatments: (i) no treatment (N); (ii) blanching in boiling (96 °C ± 4 °C) water (B); (iii) dipping in 2% l-ascorbic acid and 2% citric acid (AC); or (iv) blanching placed in boiling water, cooling and dipping in 2% ascorbic acid and 2% citric acid (BAC). Peaches from each treatment group were held at -7, -9, or - 12 °C for 21 days. RESULTS: After 21 days of storage, PPO activity and browning was greater in peaches stored at -7 °C than the PPO activity and browning of peaches stored at -9 °C and - 12 °C. Overall, lightness (L*), yellowness (b*), chroma (c*) and hue (h*) decreased while redness (a*) increased during storage. The BAC peaches had less discoloration and lower PPO activity than peach slices exposed to other treatments. Non-enzymatic browning (HMF indicator) was more pronounced for blanched peaches during storage than unblanched peaches. Pretreatment of blanched peaches with ascorbic and citric acid reduced browning during 21 days at frozen storage for peaches held at -9 °C or - 12 °C. CONCLUSION: Storage at -12 °C significantly reduced browning and HMF formation in both blanched and unblanched peach slices in comparison with -7 °C storage. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of DNA extraction methods on the real time PCR quantification of Campylobacter jejuni, Campylobacter coli, and Campylobacter lari in chicken feces and ceca contents.

Polymerase chain reaction (PCR) method was coupled with a DNA extraction to enumerate Campylobacter spp. from poultry gastrointestinal tract samples. Three experiments were conducted that included: 1) Development of a DNA standard curve related to bacterial DNA primers; 2) Design of a cell/genomic DNA extraction protocol to isolate Campylobacter spp. DNA from complex samples such as poultry feces; and 3) Comparison of PCR quantification to standard plate count methodology. The standard curve using primers for Campylobacter spp. was created for DNA extracted from environmental isolates with a linear range (R2 > 0.95) and with a high specificity for C. coli and C. jejuni recovered from poultry, swine and laboratory isolates. A 2-step extraction process of bacterial DNA from poultry feces was developed in which the cells were first concentrated using a gradient-centrifugation step followed by comparison of 4 DNA extraction methods. Two commercial DNA extraction methods (Zymo Research Quick DNA, and Invitrogen magnetic separation), a traditional phenol-chloroform DNA extraction method using proteinase K to inactivate DNAses, and an in-house isolation method for DNA extraction based on chaotropic salts were used. The middle gradient layer recovered 89% to 98% of the bacteria cells from the sample, with recovery dependent upon the Campylobacter genus. The 4 DNA extractions methods recovered 112 to 302 ug/nL of DNA. Finally, the qPCR and standard plate methods were highly correlated for enumerating Campylobacter spp. in the 2.0 to 8.0-log CFU range. Analyses of the results from this study demonstrate that the combination of the standard curve for Campylobacter spp. DNA primers, the gradient cell concentration method and DNA extraction techniques with qPCR can be used to enumerate Campylobacter spp. from poultry samples with findings similar those of traditional plate count methodology.

Detecting and correlating bacterial populations to visual color change of polydiacetylene-coated filters.

Membrane filters were coated with 10,12-pentacosadiynoic acid (PCDA) then polymerized on the filter for rapid bacterial detection and quantification. The polymerized PCDA (pPDCA)-coated filter changed color in response to Salmonella Typhimurium and Escherichia coli but not to Listeria innocua. The time required for color change of pPCDA-coated filters was determined by a visual panel. A simple linear regression model was generated to fit the observed data and was validated with goodness of fit analysis and residual analysis. The pPCDA-filter method estimated Salmonella Typhimurium populations of 8 to 3 log CFU ml-1 within 1.5-7.5 h, respectively.

Polydiacetylene sensor interaction with food sanitizers and surfactants.

Polydiacetylene (PDA) vesicles are of interest as biosensors, particularly for pathogenic bacteria. As part of a food monitoring system, interaction with food sanitizers/surfactants was investigated. PDA vesicles were prepared by inkjet-printing, photopolymerized and characterized by dynamic light scattering (DLS) and UV/Vis spectroscopy. The optical response of PDA vesicles at various concentrations verses a fixed sanitizer/surfactant concentration was determined using a two variable factorial design. Sanitizer/surfactant response at various concentrations over time was also measured. Results indicated that only Vigilquat and TritonX-100 interacted with PDA vesicles giving visible colour change out of 8 sanitizers/surfactants tested. PDA vesicle concentration, sanitizer/surfactant concentration, and time all had a significant (P<0.0001) effect on colour change. As they are highly sensitive to the presence of Vigilquat and TritonX-100, PDA sensors could be used to detect chemical residues as well as for detection of various contaminants in the food industry.

Impact of commercial processing on the microbiology of shell eggs.

Shell egg microbiology has been studied extensively, but little information is available on how modern U.S. processing conditions impact microbial populations. As regulations are being drafted for the industry, such information can be important for determining processing steps critical to product safety. Five different shell egg surface microbial populations (aerobic bacteria, yeasts and molds, Enterobacteriaceae, Escherichia coli, and Salmonella) were monitored at 12 points along the processing line (accumulator, prewash rinse, washer 1, washer 2, sanitizer, dryer, oiler, scales, two packer head lanes, rewash entrance, and rewash exit). Three commercial facilities were each visited three times, a total of 990 eggs were sampled, and 5,220 microbiological samples were subsequently analyzed. Although variations existed in concentrations of microorganisms recovered from each plant, the patterns of fluctuation for each population were similar at each plant. On average, aerobes, yeasts and molds, Enterobacteriaceae, and E. coli prevalence were reduced by 30, 20, 50, and 30%, respectively, by the end of processing. The microbial concentrations (log CFU per milliliter) in the egg rinse collected from packer head lanes were decreased by 3.3, 1.3, 1.3, and 0.5, respectively, when compared with those of rinses collected from eggs at the accumulator. Salmonella was recovered from 0 to 48% of pooled samples in the three repetitions. Higher concentrations of Salmonella were recovered from preprocessed than from in-process or ready-to-pack eggs. These data indicate that current commercial practices decrease microbial contamination of egg shell surfaces.

Identification of Enterobacteriaceae from washed and unwashed commercial shell eggs.

To evaluate the effect of processing on the safety and quality of retail shell eggs, a storage study was conducted with unwashed and commercially washed eggs. This work demonstrated that commercial processing decreased microbial contamination of eggshells. To know which species persisted during storage on washed or unwashed eggs, Enterobacteriaceae isolates were selected and identified biochemically. For each of three replications, shell eggs were purchased from a commercial processing plant, transported back to the laboratory, and stored at 4 degrees C. Once a week for 6 weeks, 12 eggs for each treatment (washed and unwashed control) were rinsed in sterile phosphate-buffered saline. A 1-ml aliquot of each sample was plated onto violet red bile glucose agar with overlay and incubated at 37 degrees C for 24 h. Following incubation, plates were observed for colonies characteristic of the family Enterobacteriaceae. A maximum of 10 isolates per positive sample were streaked for isolation before being identified to the genus or species level using commercially available biochemical strips. Although most of the isolates from the unwashed control eggs belonged to the genera Escherichia or Enterobacter, many other genera and species were identified. These included Citrobacter, Klebsiella, Kluyvera, Pantoea, Providencia, Rahnella, Salmonella, Serratia, and Yersinia. Non-Enterobacteriaceae also recovered from the unwashed egg samples included Xanthomonas and Flavimonas. Very few washed egg samples were contaminated with any of these bacteria. These data provide useful information on the effectiveness of processing in removing microorganisms from commercial shell eggs.