Category Archives: Technology

Research – Anti‐listeria activity and shelf life extension effects of Lactobacillus along with garlic extract in ground beef

Wiley Online

The current study investigates the effect of Lactobacillus reuteri and Lactobacillus plantarum combined with water extract of garlic on microbial growth, chemical changes, and sensory attributes in ground beef samples at refrigeration condition (+4°C) up to 12 days of storage. in vitro study revealed that garlic extract combined with L. reuteri or L. plantarum caused 2.13 and 2.57 log reduction in the Listeria monocytogenes count, respectively. Combination of L. plantarum and 1% garlic extract significantly (p < .05) reduced aerobic mesophilic bacteria (1.64 log cycle) and L. monocytogenes (1.44 log cycle) counts in ground beef. Lipid oxidation was also significantly (p < .05) lower in samples treated with L. plantarum plus garlic extract (1%). Furthermore, higher sensory scores were received by samples treated with Lactobacillus plus garlic extract. In conclusion, the combination of L. plantarum and garlic extract was found to be suitable to use in ground beef by controlling the L. monocytogenes growth and increasing its shelf life.

Practical Applications

Garlic extract not only has an antimicrobial activity but also has a stimulatory effect on the Lactobacillus spp. growth. On the other hand, some Lactobacillus strains can inhibit pathogenic bacteria. Then, the combination of Lactobacillus and garlic extract may be used to produce new bio‐preserved and functional meat products. The current study indicated the potential of Lactobacillus combined with garlic extract to control microbial and chemical changes in ground beef. The combination of Lactobacillus plantarum and garlic extract significantly (p < .05) reduced Listeria monocytogenes counts and lipid oxidation rates and improved the sensory scores in ground beef.

Research – Fate of Spoilage and Pathogenic Microorganisms in Acidified Cold-Filled Hot Pepper Sauces

Journal of Food Protection


Consumption of spicy foods and hot sauces is currently a popular trend worldwide. Shelf-stable acidified sauces are commonly hot-filled to ensure commercial sterility, but cold-fill-hold processes might also be suitable if microbial safety and stability are ensured. For this study, model acidified hot pepper sauces were developed and characterized. The effects of sauce pH and of two different organic acids on the survival of Pichia manshurica and Lactobacillus curvatus isolated from contaminated commercial hot sauces and on pathogenic Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes were assessed. Full factorial designs with three levels for pH (3.2, 3.5, and 3.9) and two for organic acid (citric and acetic) were used to determine the effects of these factors and their interactions on the survival of the microorganisms. Commercially sterile sauces were independently inoculated and kept at ambient temperature. Microbial counts were determined at different sampling times, depending on the treatment evaluated. Sauces acidified to pH 3.2 with citric or acetic acid were inoculated with cocktails of five strains or serotypes of the three pertinent pathogens, and inactivation curves were determined. Trials were performed in triplicate. A greater than 5-log reduction of P. manshurica and L. curvatus was achieved in less than 6 h in sauces adjusted to pH 3.2 with acetic acid. Greater than 5-log reductions of pathogenic bacteria were achieved 0.5 h after inoculation in sauces acidified to pH 3.2 with acetic acid. In contrast, at least 48 h was required to guarantee the same inactivation for the most tolerant pathogen when citric acid was used. Thus, a cold-fill-hold process may be a suitable alternative for acidified hot pepper sauces. Based on survival of the microorganisms evaluated in this study, microbial safety and stability can be achieved by adjusting the pH to 3.2 or less by the addition of acetic acid.

  • pH and acidifier influence safety and stability of cold-filled acidified sauces.

  • Safe and stable cold-filled sauces were obtained at pH 3.2 with acetic acid.

  • Results help establish science-based conditions for cold-filled products.

Research – Validation of a High-Throughput Sausage Casing Model for the Assessment of Bacterial Inactivation Affected by Salt Concentration, pH, and Temperature

Journal of Food Protection


Previous studies have shown the efficacy of high concentrations of salt as the main preservative against vegetative bacteria present on natural sausage casings. These studies were limited in the number of variables and the interactions between these variables that were assessed. To remedy this situation, a MicroCasing high-throughput model was developed and validated to study the inactivation kinetics of various combinations of parameters (salt concentration, pH, and temperature) on eight bacterial isolates of Salmonella enterica, Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes over a prolonged period. A Weibullian power model was the best fit to show the trends in sensitivity of each bacterial isolate to salt, pH, and temperature over time. The inactivation kinetics generated with this novel approach could serve as a predictive model for the required salting period for casings. The actual bacterial contamination of the product can vary with the respective production step during processing from animal intestine into sausage casings (initial level, ∼105 CFU/g; level after salting, <102 CFU/g). Subsequent selection and grading of these casings will require complete removal of all salt, and upon completion of this production step, the casings will be resalted. By determining the actual contamination level before the salting process, the minimum storage period in salt can be calculated and potentially optimized by adjusting the pH and temperature. As a result, a standard holding period of at least 30 days may no longer be necessary to produce salted natural casings in accordance with validated quality and food safety criteria.

  • A new model system was developed for analysis of bacterial inactivation kinetics in foods.

  • The novel model allows determination of product-specific bacterial inactivation over time.

  • Effects of time, temperature, pH, and salt on casing preservation can be clarified with the model.

  • Prediction of inactivation parameters allows casing production to meet HACCP criteria.

Research – Microbiological Testing Results of Boneless and Ground Beef Purchased for the U.S. National School Lunch Program, School Years 2015 to 2018

Journal of Food Protection


The Agricultural Marketing Service (AMS) purchases beef for the National School Lunch Program and other federal nutrition assistance programs. For beef that will be delivered to food service facilities raw, each ca. 900-kg lot of boneless beef raw material and each ca. 4,500-kg sublot of resultant ground beef is tested for standard plate count (SPC) organisms, coliforms, Escherichia coli, Salmonella, and E. coli O157:H7. In addition, 1 of every 10 lots of boneless beef, randomly selected, is tested for E. coli O26, O45, O103, O111, O121, and O145. For beef that will be cooked using a validated lethality step at a federally inspected establishment before delivery, each lot of boneless beef and each sublot of ground beef is tested for SPC organisms, coliforms, and E. coli only. Any lot or sublot exceeding predefined critical limits (CLs) of 100,000 CFU g−1 for SPC organisms, 1,000 CFU g−1 for coliforms, or 500 CFU g−1 for E. coli or for beef containing Salmonella or any of previously mentioned E. coli serotypes is rejected for purchase. For school years 2015 through 2018 (July 2014 through June 2018), 220,497,254 kg of boneless beef and 189,347,318 kg of ground beef were produced for AMS. For boneless beef, 133 (0.06%), 164 (0.07%), and 106 (0.04%) of 240,488 lots exceeded CLs for SPC organisms, coliforms, and E. coli, respectively; 2,038 (1.30%) and 116 (0.07%) of 156,671 lots were positive for Salmonella and E. coli O157:H7, respectively; and 59 (0.36%) of 16,515 lots were positive for non-O157 Shiga toxin–producing E. coli. For ground beef, 46 (0.10%), 27 (0.06%), and 19 (0.04%) of 45,769 sublots exceeded CLs for SPC organisms, coliforms, and E. coli, respectively; and 329 (1.40%) and 18 (0.08%) of 23,475 sublots were positive for Salmonella and E. coli O157:H7, respectively. All lots and sublots found to exceed indicator organism CLs or to contain pathogens were identified, rejected for purchase, and diverted from federal nutrition assistance programs.

  • AMS purchases beef for the National School Lunch Program.

  • Less than 0.10% of beef samples exceeded indicator organism critical limits.

  • Salmonella was found in 1.4% and E. coli O157:H7 was found in 0.08% of samples.

  • Indicator critical limit exceedance was weakly associated with pathogen presence.

  • Beef with excessive indicator organisms or containing pathogens was rejected for purchase.

Research -Antibacterial Interactions of Colloid Nanosilver with Eugenol and Food Ingredients

Journal of Food Protection


This study was conducted to investigate antibacterial properties of the colloidal silver nanoparticles (SNPs) and eugenol, alone and in combination, on Staphylococcus aureus and Salmonella Typhimurium and their interactions with food constituents (fat, protein, and carbohydrate). We examined antibacterial activities of SNPs and eugenol in Luria-Bertani (LB) broth and 1.5 and 3% fat ultrahigh-temperature (UHT) milk. MICs of eugenol and SNPs (particle size of 31.3 nm) were also investigated in the presence of sunflower oil, meat extract, and starch at concentrations of 2, 5, and 10% to examine the interactions between food constituents and antimicrobial agents. MICs and MBCs of eugenol and SNPs for both bacteria were at 2,500 and 25 μg/mL, respectively. Combinations of the two substances had additive and synergistic effects on Salmonella Typhimurium and S. aureus, respectively. Both compounds had bactericidal activity. In food matrices, results indicated that eugenol only in sunflower oil at 5 and 10% concentrations had significant antibacterial activity. A similar result was achieved for SNPs with 10% meat extract. In LB broth, eugenol at 2,500 and 5,000 μg/mL achieved 6-log reductions in the microbial population of both bacteria after 3 h, while SNPs achieved the same effect after 9 h. In UHT milk with 1.5% fat, eugenol at 5,000 μg/mL and SNPs at 25 μg/mL achieved 6-log reductions in bacterial populations after 24 h. Thus, the antimicrobial activity of both eugenol and SNPs depended on the medium in which the experiment was conducted, and the combination of both antimicrobial agents increased the antimicrobial effect.

  • The interactions of eugenol, nanoparticles, and food constituents were investigated.

  • Eugenol and SNP had synergistic effects on S. aureus.

  • Protein and lipids reduced the efficacy of eugenol.

  • Protein negatively impacted the activity of SNPs.

Research – Antifungal Activity of Selected Natural Preservatives against Aspergillus westerdijkiae and Penicillium verrucosum and the Interactions of These Preservatives with Food Components

Journal of Food Protection


The present study examined the influence of primary food components on the antifungal activity of the essential oil of Origanum vulgare, carvacrol, thymol, eugenol, and trans-cinnamaldehyde against Penicillium verrucosum and Aspergillus westerdijkiae. The MIC was determined in food model media enriched with proteins (1, 5, or 10%), carbohydrates (1, 4, or 6%), or oil (1, 5, or 10%). Proteins increased the antifungal activity of O. vulgare essential oil, carvacrol, thymol, and eugenol, whereas the effect of trans-cinnamaldehyde decreased with increasing protein content. The presence of carbohydrates diminished the inhibitory effect of the natural preservatives on A. westerdijkiae; for P. verrucosum, their inhibitory effect increased with carbohydrates. Only the antifungal activity of trans-cinnamaldehyde did not depend on the carbohydrate content. The presence of oil had the strongest influence. At a concentration of 1% oil, the antifungal activity decreased significantly, and at 10% oil, almost no inhibition was observed. To investigate the effect of the antifungal agents on the morphology of the target molds, they were grown on malt extract agar containing carvacrol and trans-cinnamaldehyde and were examined by scanning electron microscopy. The hyphae, conidiophores, vesicles, and phialides were severely altered and deformed, and spore formation was clearly suppressed.

  • The antifungal activity of natural preservatives is influenced by the food matrix.

  • Proteins increase the impact of O. vulgare EO, carvacrol, thymol, and eugenol.

  • Carbohydrates diminish the inhibition of natural preservatives on A. westerdijkiae.

  • In the presence of oil, natural inhibitors lose their antifungal effect.

  • Carvacrol and trans-cinnamaldehyde lead to distorted hyphae and loss of sporulation.

Research – Inactivation of Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica under High Hydrostatic Pressure: A Quantitative Analysis of Existing Literature Data

Journal of Food Protection


High hydrostatic pressure processing (HPP) is a mild preservation technique, and its use for processing foods has been widely documented in the literature. However, very few quantitative synthesis studies have been conducted to gather and analyze bacterial inactivation data to identify the mechanisms of HPP-induced bacterial inactivation. The purpose of this study was to conduct a quantitative analysis of three-decimal reduction times (t) from a large set of existing studies to determine the main influencing factors of HPP-induced inactivation of three foodborne pathogens (Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica) in various foods. Inactivation kinetics data sets from 1995 to 2017 were selected, and t values were first estimated by using the nonlinear Weibull model. Bayesian inference was then used within a metaregression analysis to build and test several models and submodels. The best model (lowest error and most parsimonious) was a hierarchical mixed-effects model including pressure intensity, temperature, study, pH, species, and strain as explicative variables and significant factors. Values for t and ZP associated with inactivation under HPP were estimated for each bacterial pathogen, with their associated variability. Interstudy variability explained most of the variability in t values. Strain variability was also important and exceeded interstudy variability for S. aureus, which prevented the development of an overall model for this pathogen. Meta-analysis is not often used in food microbiology but was a valuable quantitative tool for modeling inactivation of L. monocytogenes and Salmonella in response to HPP treatment. Results of this study could be useful for refining quantitative assessment of the effects of HPP on vegetative foodborne pathogens or for more precisely designing costly and labor-intensive experiments with foodborne pathogens.

  • A meta-analysis was performed to identify factors influencing HPP inactivation of pathogens.

  • Three-decimal reduction times following HPP were estimated from existing data.

  • Staphylococcus aureus is the most piezoresistant of the three pathogens studied.

  • These three foodborne pathogens are less HPP resistant in acidic products.