Inactivation of microorganisms in milk and apple cider treated with ultrasound.

Nonthermal technologies are emerging as promising alternatives to heat treatment for food processing. Ultrasound, defined as sound waves with a frequency greater than 20 kHz, has proven bactericidal effects, especially when combined with other microbial-reduction strategies such as mild heating. In this study, ultrasound treatment (sonifier probe at 20 kHz, 100% power level, 150 W acoustic power, 118 W/cm2 acoustic intensity) with or without the effect of mild heat (57 degrees C) was effective at reducing microbial levels in raw milk, Listeria monocytogenes levels inoculated in ultrahigh-temperature milk, and Escherichia coli O157:H7 in apple cider.

Comparison of growth kinetics for healthy and heat-injured Listeria monocytogenes in eight enrichment broths.

Detection of Listeria in food products is often limited by performance of enrichment media used to support growth of Listeria to detectable levels. In this study, growth curves were generated using healthy and heat-injured Listeria monocytogenes strain F5069 in three nonselective and five selective enrichment broths. Nonselective enrichment media included the current Food and Drug Administration Bacteriological Analytical Manual Listeria enrichment broth base (BAM), Listeria repair broth (LRB), and Trypticase soy broth.

Increased Detection of Acid-Injured Escherichia coli O157:H7 in Autoclaved Apple Cider by Using Nonselective Repair on Trypticase Soy Agar .

Three different acid-resistant strains of Escherichia coli O157:H7 were inoculated individually and as a cocktail into sterile apple cider (pH 3.2) at a level of approximately 10 cells per ml and incubated at 2°C. Samples were plated on Trypticase soy agar (TSA), violet red bile agar (VRBA), sorbitol MacConkey agar (SMA), and Petrifilm E.

Comparison of Methods for Determining Coliform and Escherichia coli Levels in Apple Cider .

The main objective of this research was to determine the easiest and most reliable media for enumerating coliform bacteria and Escherichia coli levels in apple cider. During the autumn of 1994 a total of 59 apple cider samples were collected directly from 12 cider producers and were assessed for bacterial levels and pH. Plate count agar was used to determine heterotrophic bacteria levels.