Percorrer por autor "Kirby, Roy M."
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- Effect of heat on microorganisms isolated from freshly caught chilled scad (Trachurus trachurus)Publication . Vaz-Pires, Paulo; Gibbs, Paul; Kirby, Roy M.The effects of heat on bacteria making up part of the microFlora of the sea-Fish Trachurus trachurus were studied. From 80 bacterial isolates which were subject to primary identiFication four were selected. The bacteria were subjected to a heat stress of 55°C for 20 s both in pure and mixed suspensions, the D-values and post-stress recovery in nutrient broth were measured. Using differential plating on selective agents to identify sites of injury and recovery times, the growth parameters dissolved oxygen, redox potential and pH were measured during recovery. Bacteria presumptively identiFied as Shewanella putrefaciens and Pseudomonas putida were more sensitive to heat than other bacteria, suggesting that most heat treatments of Fish may reduce the number of these bacteria. After dissolved oxygen was used up during recovery in nutrient broth, Eh declined from positive to negative values typical of facultative bacteria showing that, after initial aerobic growth, the bacteria changed their metabolism to grow anaerobically. When dissolved oxygen reached zero, about 120 h after inoculation, the numbers of all bacteria were about 107mL−1, and corresponds to a minimum in the pH values, except for the most heat sensitive isolate (300 h after inoculation). Differential plating showed increased sensitivity to NaCl induced by heat treatments in some isolates.
- A method and medium for the electrical detection of Listeria spp. from foodPublication . Capell, Christopher J.; Kirby, Roy M.; Moss, Maurice 0.The development of a liquid medium for the detection of Listeria spp. by capacitance monitoring of food samples previously enriched in UVM 1 broth is described. Rapid growth of Listeria monocytogenes was shown to occur in liquid media with selectivity based on antibiotics found in Oxford agar. The final capacitance medium contained higher concentrations of the Oxford selective agents than Oxford agar and did not require the esculin/ferric ammonium citrate reaction to be observed. The medium relied upon the ability of Listeria spp. to induce a greater than 30% change in capacitance within 30 h. When run in parallel with the Listeria spp. test samples of a large food company, the method gave far fewer false-positive results than Fraser broth.
- A new capacitance medium for presumptive detection of Listeria spp. from cheese samplesPublication . Rodrigues, Maria José R. M.; Capell, Christopher J.; Kirby, Roy M.The paper presents a new medium and a method for the rapid presumptive detection of Listeria spp. in cheese samples by electrical capacitance changes. The Bactometer based capacitance broth (LED medium) required a 30% change in signal within 30 h to identify presumptive positive results. Of 32 cheese samples tested, 10 were found to contain Listeria spp. using a Fraser broth screening method and 12 using the LED medium and method. The LED method also gave 16 fewer (total = 1) false presumptive positive results. Results show the LED method to be superior to Fraser broth in regard to both the number of false presumptive positive and confirmed false negative results detected. The method appears to be suitable as a reliable rapid screen for the presence of Listeria spp. in cheese.
- Physical measurement of the quality of fresh scad (Trachurus trachurus) and rainbow trout (Oncorhynchus mykiss) during ice storage using the RT FreshmeterPublication . Vaz-Pires, Paulo; Araújo, Isabel; Kirby, Roy M.The RT Freshmeter was used to obtain a quality index of two Portuguese fish, scad (Trachurus trachurus) and farmed rainbow trout (Oncorhynchus mykiss). The curves obtained were comparable to those previously published using the GR Torrymeter. However variations were lower during the first phase of storage and it was observed that the curves could be divided into two distinct regions. The slope of the linear regression was higher during the first 5 days of storage, representing the first region of the curve, in both fish studied. It is proposed that the two different rates of change of the quality index obtained with the meter reflect the two predominant spoilage mechanisms, enzymic and microbiological. The RT Freshmeter measurements are compared to organoleptic changes. Preliminary results obtained with the RT Freshmeter on rainbow trout fillets without skin indicate that this instrument is not suitable for use with this product due to large variations and curve slopes close to zero.