Possible inhibitory effect of microbial transglutaminase on the formation of biogenic amines during Trappist cheese ripening.

Trappist cheese (semi-hard, rennet-coagulated cheese with round eyes) was manufactured and matured for 4 weeks at 12 ± 1°C, 85% relative humidity (RH). The effect of microbial transglutaminase (MTGase) was followed by measuring the levels of free amino acids (FAAs) and biogenic amines (BAs) every 2 weeks during 4 weeks of cheese ripening. Results show that MTGase can decrease the cadaverine production by 30%, but only at the initial stage of ripening. Application of MTGase results in 49% less putrescine, 12% less tyramine production at the end of 4 weeks ripening time, and can decrease histamine levels by 8% after 2 weeks of ripening time in the examined semi-hard cheese type.

Hygiene assessments of school kitchens based on the microbiological status of served food.

BACKGROUND: According to European trends, more children eat at school canteens than ever before, therefore food safety and quality have become increasingly significant in recent years. Nevertheless, there are large differences in food safety levels in different school canteens. We hypothesize that the microbial status of the served meal represents on the general hygiene of the kitchen. Our research examines whether mesophilic aerobic bacteria measured in served food are connected with the level of hygiene in the catering unit, and whether this indicator can be used as a criterion for assessing school kitchens. METHODS: Meal samples were collected from six school kitchens, and mesophilic aerobic bacterial count was measured. Samples were collected on five different days, so each kitchen was monitored five times. Two meals per visit were collected: a soup and a main course. RESULTS: Out of the 60 samples, 26 were good (CFU/g < 103), 24 were acceptable (CFU/g: 103–105), and in 10 samples, the microbial count was found to be above the limit (CFU/g > 105). Statistical calculations revealed that microbial contamination of served meals was influenced neither by the supplier nor by the type of meal (soup or main course). However, the level of hygiene in the serving kitchen significantly affects the microbial status of meals. CONCLUSIONS: Based on the results, a qualification system can be developed using the mesophilic aerobic bacterial count measurable in the served meal to assess hygiene. By regular determination of mesophilic aerobic bacterial count and the presence of Enterobacteriaceae, the food safety of a catering unit can be quantitatively evaluated.

Rapid in-house detection method of Campylobacter spp. from food by redox potential monitoring combined with real-time PCR.

The rapid detection of Campylobacter spp. is of utmost importance for the reduction of infections in humans by contaminated food products. The standard culturing method (ISO 10272-1:2006) involves a high time and labour demand. In this paper, we present a method that reduces the detection time of Campylobacter spp. to or below one third as compared to the ISO method, at a reduced cost per test. We used redox potential change of enrichment cultures (Bolton broth with Bolton selective supplement) for reliably selecting Campylobacter-contaminated raw milk and broiler meat samples. Identification of Campylobacter spp. in the contaminated samples was done by real-time PCR method. Culturing time to conclusive redox monitoring varied between 6 and 24 h for positive samples, depending on the contamination rate, in contrast to 136 h with the standard culturing process. However, now the Campylobacter-negative majority of food samples will not need to be tested by real-time PCR because redox potential monitoring can identify them in the selective enrichment phase. This method could be potentially used as a faster alternative to the current standard ISO 10272-1:2006, for nonregulatory monitoring purposes.

In vitro study on the effect of doxycycline on the microbial activity of soil determined by redox-potential measuring system.

The potential effect of doxycycline on the microbial activity was investigated in three types of soil. Soil samples were spiked with doxycycline, incubated at 25°C and tested at 0, 2, 4 and 6 days after treatment. The microbiological activity of the soil was characterized by the viable count determined by plate pouring and by the time necessary to reach a defined rate of the redox-potential decrease termed as time to detection (TTD).The viable count of the samples was not changed during the storage. The TTD values, however exhibited a significant increase in the 0.2-1.6 mg/kg doxycycline concentration range compared to the untreated samples indicating concentration-dependent inhibitory effect on microbial activity. The potency of the effect was different in the 3 soil types. To describe the combined effect of the doxycycline concentration and time on the biological activity of one type of soil a mathematical model was constructed and applied.The change of microbial metabolic rate could be measured also without (detectable) change of microbial count when the traditional microbiological methods are not applicable. The applied new redox potential measurement-based method is a simple and useful procedure for the examination of microbial activity of soil and its potential inhibition by antibiotics.

Rapid detection of Listeria monocytogenes in raw milk and soft cheese by a redox potential measurement based method combined with real-time PCR.

The incidence of outbreaks of foodborne listeriosis has indicated the need for a reliable and rapid detection of the microbe in different foodstuffs. A method combining redox potential measurement and real-time polymerase chain reaction (PCR) was developed to detect Listeria monocytogenes in artificially contaminated raw milk and soft cheese. Food samples of 25 g or 25 ml were homogenised in 225 ml of Listeria Enrichment Broth (LEB) with Oxford supplement, and the redox potential measurement technique was applied. For Listeria species the measuring time was maximum 34 h. The absence of L. monocytogenes could reliably be proven by the redox potential measurement method, but Listeria innocua and Bacillus subtilis could not be differentiated from L. monocytogenes on the basis of the redox curves. The presence of L. monocytogenes had to be confirmed by real-time PCR. The combination of these two methods proved to detect < 10 cfu/g of L. monocytogenes in a cost- and time-effective manner. This method can potentially be used as an alternative to the standard nutrient method for the rapid detection of L. monocytogenes in food.