Determination of volatile nitrosamines in grilled lamb and vegetables using comprehensive gas chromatography – Nitrogen chemiluminescence detection

The grilling of meat may generate dangerous levels of mutagenic and carcinogenic nitrosamines (NAs). Meat and vegetable samples underwent a two-step solid-phase extraction before analysis by comprehensive gas chromatography with a nitrogen chemiluminescence detection system (GCxGC-NCD). The GCxGC-NCD method showed high selectivity, sensitivity and equimolarity in its response to six specific NAs. NA contamination of charcoal-grilled lamb at various stages of cooking and with various fat contents and also charcoal-grilled vegetables were investigated. The grilling of lamb on unready charcoal resulted in the formation of considerable quantities of NAs. Grilling lamb on properly prepared, ready charcoal resulted in an increase in total concentrations of six NAs from 0 to 4.51 μg kg⁻¹ over a period of 16 min. Increasing the fat content of the grilled lamb from 5% to 20% caused a modest increase in total concentrations of the six investigated NAs from 4.51 to 5.30 μg kg⁻¹.     

Effects of modified atmosphere and vacuum packaging on microbiological and chemical properties of rainbow trout (Oncorynchus mykiss) fillets

Microbial (psychrotrophic, mesophilic aerobic bacteria and Enterobacteriacae counts), and chemical analysis [pH, total volatile bases nitrogen (TVB-N), lipid oxidation (Thiobarbituric acid reactive substance, TBARS)] of rainbow trout (Oncorynchus mykiss) fillets in air (control), vacuum and modified atmosphere packaging (MAP) with various gas mixtures conditions at 4+/-1 degrees C were determined. The gas mixtures evaluated were 100% CO2, 2.5% O2+7.5% N2+90% CO2 and 30% O2+30% N2+40% CO2. Psychrotrophic bacteria count was above 1 x 10(7) cfu/g on the 12th day in 100% CO2. However; mesophilic bacteria count was below 1 x 10(6) cfu/g at the end of the 14-day storage period. Enterobacteriaceae count was significantly lower in samples packaged with MAP. Lipid oxidation increased rapidly after 6 days of storage in the samples containing 30% O2. While minimum TBARS values were recorded in fillets containing 100% CO2 and vacuumed fillets, the lowest TVB-N values were obtained in fillets with 100% CO2.     

Investigating hydrophobicity and the effect of exopolysaccharide on aggregation properties of dairy propionibacteria isolated from Turkish homemade cheeses

Propionic acid bacteria have been used widely as starter cultures. However, their potential as probiotics has received little attention. The ability to auto- and coaggregate is a desirable property for probiotics in health-promoting foods. Therefore, in the current study, we assessed the effect of exopolysaccharides produced by dairy propionibacteria strains on the aggregative and hydrophobicity properties. All propionibacteria strains tested showed auto- and coaggregation ability with Escherichia coli ATCC 11229, but the results were strain specific and dependent on exopolysaccharides production and incubation conditions. In addition, propionibacteria strains tested were determined to be highly hydrophilic. Our results indicate that the ability to autoaggregate, together with cell-surface hydrophobicity and coaggregation abilities with an E. coli strain, can be used for preliminary screening in order to identify potentially probiotic bacteria suitable for human or animal use.     

Optimal mixed convection for maximal energy recovery with vertical porous channel (solar wall)

A vertical open-ended channel filled with a porous medium, with an imposed heat flux and a heat loss coefficient on one of its walls, is studied numerically. A fan can enhance the self-driven flow, and therefore a mixed convection regime is considered. The objective is to maximize the overall energy recovery (heat transfer to the fluid minus fan power). Correlations are developed for optimal pressure drop to be imposed by the fan and maximal energy recovery, as a function of the Rayleigh number, the channel aspect ratio, and the heat loss coefficient. The optimal allocation of the total energy losses (i.e., sum of the heat loss and fan power) is shown. Potential applications include solar wall and solar chimney used for ventilation and preheating of makeup air in buildings.