Effect of Growth on the Thermal Resistance and Survival of Salmonella Tennessee and Oranienburg in Peanut Butter, Measured by a New Thin-Layer Thermal Death Time Device

Abstract

<jats:p>In published data the thermal destruction of Salmonella species in peanut butter deviates from pseudo–first-order kinetics. The reasons for such deviation are unknown. This study examined both the method used to measure the thermal destruction rate and the method of growth of the microorganisms to explain variations in destruction kinetics. Growth on a solid matrix results in a different physiological state that may provide greater resistance to adverse environments. In this study, Salmonella Tennessee and Oranienburg were grown for 24 h at 37°C under aerobic conditions in broth and agar media to represent planktonic and sessile cell growth, respectively. Peanut butter was held at 25°C and tested for Salmonella levels immediately after inoculation and at various time intervals up to 2 weeks. Thermal resistance was measured at 85°C by use of a newly developed thin-layer metal sample holder. Although thermal heat transfer through the metal device resulted in longer tau values than those obtained with plastic bags (32.5 ± 0.9 versus 12.4 ± 1.9 s), the bags have a relative variability of about 15% compared with about 3% in the plates, allowing improved uniformity of sample treatment. The two serovars tested in the thin-layer device showed similar overall thermal resistance levels in peanut butter regardless of growth in sessile or planktonic states. However, thermal destruction curves from sessile cultures exhibited greater linearity than those obtained from planktonic cells (P = 0.0198 and 0.0047 for Salmonella Oranienburg and Salmonella Tennessee, respectively). In addition, both Salmonella serovars showed significantly higher survival in peanut butter at 25°C when originally grown on solid media (P = 0.001) with a &amp;lt;1-log loss over 2 weeks as opposed to a 1- to 2-log loss when grown in liquid culture. Consequently, the use of cells grown on solid media may more accurately assess the survival of Salmonella at different temperatures in a low-water-activity environment such as peanut butter.</jats:p>

Survival or Growth of Inoculated Escherichia coli O157:H7 and Salmonella on Yellow Onions (Allium cepa)under Conditions Simulating Food Service and Consumer Handling and Storage

“…Salmonella cells in inocula prepared on agar plates are in a sessile form and can be significantly more desiccation tolerant than when the same strain is prepared in broth and in a planktonic state (14,24). The form of pathogens that might contribute to postharvest contamination of onion skin is unknown.…”

“…Survival of both pathogens was enhanced on onion skin when the inoculum was grown on solid medium than when cultured in broth. Culture preparation is one of the factors to consider when inoculating food products (19), and the data presented here and elsewhere (14,24) suggest that for circumstances in which desiccation may occur, collection of inoculum from agar represents a worst-case or conservative experimental approach. E. coli 0157:H7 and Salmonella populations declined on the outer skin of whole intact onions at both ambient conditions and 4°C.…”

Atımlı Işık Uygulaması ile Bademde Salmonella Enteritidis İnaktivasyonu

“…At 3800 and 3400 V, little difference in almond temperatures were observed at 16.6 and 19.1 cm; however, at lower voltage (3000 V) there existed greater differentiation between temperature with respect to distance. None of the temperatures reached just below the almond surface with up to 60 s treatment were high enough to contribute thermal inactivation of Salmonella [27,23]. Nevertheless, in other study, temperature increased to higher levels on skin sides of salmon fillets within 60 s of pulsed light treatment; 100, 86, 76°C at 3, 5, and 8 cm distances to quartz window, respectively, indicating that surface temperature may vary based on food type as well [26].…”

Inoculation Preparation Affects Survival of Salmonella enterica on Whole Black Peppercorns and Cumin Seeds Stored at Low Water Activity

“…Improved Salmonella survival under a variety of environmental conditions, including desiccation, starvation, and acidity, has been reported for cells grown on agar and cells within biofilms compared with planktonic cells (19,20). Thermal destruction curves of agar-grown cells of Salmonella serotypes Tennessee and Oranienburg were more linear than those for planktonic cells cultured in liquid; however, overall thermal resistance in the test product was similar (23). Incorporation into biofilms increases the resistance of Salmonella to a variety of adverse conditions, including heat (2), presence of antimicrobials (9,29), moderate acid conditions (45), and desiccation (1).…”