Category Archives: Clostridium sporogenes

Research – Levels and types of microbial contaminants in different plant-based ingredients used in dairy alternatives

Posted on August 3, 2024 by | 1 comment

Science Direct

Abstract

In this study levels and types of microbial contaminants were investigated in 88 different plant-based ingredients including many that are used to manufacture dairy alternatives. Studied ingredients encompassed samples of pulses (pea, faba bean, chickpea, and mung bean), cereals/pseudocereals (oat, rice, amaranth and quinoa) and drupes (coconut, almond and cashew). The microbial analysis included: i) total viable count (TVC), ii) total aerobic mesophilic spore count (TMS), iii) heat resistant aerobic thermophilic spore count (HRTS), iv) anaerobic sulfite reducing Clostridium spore count (SRCS), and v) Bacillus cereus spore count (BCES). Microorganisms isolated from the counting plates with the highest sample dilutions were identified using 16S rRNA and MALDI-TOF MS analyses.

Many of the investigated ingredients showed a high proportion of spores as part of their total aerobic mesophilic counts. In 63 % of the samples, the difference between TVC and TMS counts was 1 Log10 unit or less. This was particularly the case for the majority of pea isolates and concentrates, faba bean isolates, oat kernels and flakes, and for single samples of chickpea isolate, almond, amaranth, rice, quinoa, and coconut flours. Concentrations of TVC ranged between <1.0 and 5.3 Log10 CFU/g in different samples, and TMS varied between <1.0 and 4.1 Log10 CFU/g. Levels of HTRS, BCES and SRCS were generally low, typically around or below the LOD of 1.0 Log10 CFU/g.

In total, 845 individual bacterial colonies were isolated belonging to 33 different genera. Bacillus licheniformis and B. cereus group strains were most frequently detected among Bacillus isolates, and these species originated primarily from pea and oat samples. Geobacillus stearothermophilus was the main species encountered as part of the HRTS. Among the Clostridium isolates, Clostridum sporogenes/tepidum were predominant species, which were mostly found in pea and almond samples. Strains with potential to cause foodborne infection or intoxication were typed using the PCR-based method for toxin genes detection. In the B. cereus group, 9 % of isolates contained the ces gene, 28 % contained hbl, 42 % cytK, and 69 % were positive for the nhe gene. Absence of the boNT-A and -B genes was confirmed for all isolated C. sporogenes/tepidum strains. Nearly all (98 %) B. licheniformis isolates were positive for the lchAA gene.

Insight into the occurrence of microbial contaminants in plant-based ingredients, combined with knowledge of their key inactivation and growth characteristics, can be used for the microbial risk assessment and effective design of plant-based food processing conditions and formulations to ensure food safety and prevent spoilage.

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Posted in Bacillus cereus, bacterial contamination, Clostridium, Clostridium sporogenes, Contaminated water, cross contamination, food contamination, Food Microbiology Research, Malditof, Mesophilic Aerobes, microbial contamination, Research

Research – Exploring Propolis as a Sustainable Bio-Preservative Agent to Control Foodborne Pathogens in Vacuum-Packed Cooked Ham

Posted on May 4, 2024 by | Leave a comment

MDPI

Abstract

The search for natural food additives makes propolis an exciting alternative due to its known antimicrobial activity. This work aims to investigate propolis’ behaviour as a nitrite substitute ingredient in cooked ham (a ready-to-eat product) when confronted with pathogenic microorganisms of food interest. The microbial evolution of Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, and Clostridium sporogenes inoculated at known doses was examined in different batches of cooked ham. The design of a challenge test according to their shelf life (45 days), pH values, and water activity allowed the determination of the mesophilic aerobic flora, psychotropic, and acid lactic bacteria viability. The test was completed with an organoleptic analysis of the samples, considering possible alterations in colour and texture. The cooked ham formulation containing propolis instead of nitrites limited the potential growth (δ < 0.5 log10) of all the inoculated microorganisms until day 45, except for L. monocytogenes, which in turn exhibited a bacteriostatic effect between day 7 and 30 of the storage time. The sensory analysis revealed the consumer’s acceptance of cooked ham batches including propolis as a natural additive. These findings suggest the functionality of propolis as a promising alternative to artificial preservatives for ensuring food safety and reducing the proliferation risk of foodborne pathogens in ready-to-eat products.

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Posted in Bacillus, Bacillus cereus, Bio-Preservative, Clostridium, Clostridium botulinum, Clostridium sporogenes, Food Microbiology Research, Food Pathogen, Pathogen, pathogenic, Propolis, psychrotrophic bacteria, Research, Staphylococcus aureus

Research – Controlling Clostridium sporogenes spoilage of “requeijão cremoso” processed cheese: Modelling the growth/no-growth probability as a function of pH, sodium chloride and nisin

Posted on March 17, 2024 by | Leave a comment

Science Direct

Abstract

Predictive models were developed to assess the growth response of Clostridium sporogenes in “requeijão cremoso” processed cheese, as affected by pH and sodium chloride and nisin concentrations. A complete factorial design was performed using different formulations: pH (5.2, 5.6, and 6.0), sodium chloride (0.5, 0.75, 1.0, 1.25, and 1.5%), and nisin (0.0, 5.0, 7.5, 10.0 and 12.5 mg/kg), totalizing 75 conditions. Packs with 150g of “requeijão cremoso” were inoculated with 103 spores/g following storage at 10 °C for up to 60 days. The counts of C. sporogenes were performed on day zero and at the end of storage after a heat shock (80 °C for 12 min). The formulations that allowed an increase in the population >1 log CFU/g were assigned the value of 1 (growth), and the formulations in which the increase was <l log CFU/g were assigned 0 (no growth). Overall, the growth of C. sporogenes was affected by pH, salt concentration and nisin, e.g. at pH 5.2 the growth/no growth limit is 1.25% salt and no nisin, at pH 5.6 this limit is reduced to 0.75% salt, while at pH 6.0 only the effect of pH was sufficient to inhibit C. sporogenes even in the absence of salt and nisin. All isolated parameters and their combinations significantly affected spore germination, indicating that the model generated significantly contributes to the optimization of the processing and mitigation of the microbiological spoilage of “requeijão cremoso” processed cheese by Clostridia.

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Posted in Clostridium, Clostridium sporogenes, Food Microbiology Research, Food Technology, Research, Technology