Abstract
This study validated a typical commercial donut frying process as an effective kill-step against a 7-serovar Salmonella cocktail (Newport, Typhimurium, Senftenberg, Tennessee, and three dry food isolates) when contamination was introduced through inoculated flour. The bread and pastry flour mix (3:1) was inoculated with the Salmonella cocktail, and subsequently dried back to original preinoculation moisture content, achieving a Salmonella population of 7.6 log CFU/g. Inoculated flour was used to prepare a typical commercial donut batter, which was fried using 375°F (190.6°C) oil temperature. No viable Salmonella was detected using an enrichment plating protocol in the donuts after 2 min of frying, resulting in >7-log reduction in Salmonella population. The internal donut temperature increased from ∼30°C to ∼119°C at the end of 2 min of frying. The water activities of the donut crumb and crust after 2 min of frying, followed by 30 min of ambient air cooling, were 0.944 and 0.852, respectively. The donut pH after ambient-air cooling was 5.51. The D- and z-values of the Salmonella cocktail in donut dough were determined using thermal-death-time disks and temperature-controlled water baths. The D-values of the cocktail were 8.6, 2.9, and 2.1 min at 55°C, 58°C, and 61°C, respectively, whereas the z-value was 10°C. This study validated that >7-log reduction could be achieved if donuts are fried for at least 2 min in the oil at 190.6°C, and calculated D- and z-values present the heat resistance of Salmonella in donut dough at the start of the frying processes. However, results from this study should not be extrapolated when donut composition and frying parameters are changed significantly.
Highlights
This study validated a typical commercial donut frying process as an effective kill-step against a 7-serovar Salmonella cocktail (Newport, Typhimurium, Senftenberg, Tennessee, and three dry food isolates) when contamination was introduced through inoculated flour
Contamination of raw ingredients used in processed foods can occur, and pathogens such as Salmonella and Shiga toxin-producing Escherichia coli can be introduced into bakery products through a wide range of ingredients such as egg, milk products, flour, chocolate, coconut, peanut butter, fruit, spices, and yeast (Ahmad et al, 2000; Akins, 2014)
The donuts were fried in soybean oil at 190.6°C for 2 min followed by 30 min of ambient air cooling (F+C), with product sampling at 1 and 2 min of frying and at F + C to enumerate the surviving Salmonella population
Summary
Contamination of raw ingredients used in processed foods can occur, and pathogens such as Salmonella and Shiga toxin-producing Escherichia coli can be introduced into bakery products through a wide range of ingredients such as egg, milk products, flour, chocolate, coconut, peanut butter, fruit, spices, and yeast (Ahmad et al, 2000; Akins, 2014). Baking, cooking, roasting, frying, and boiling are generally considered effective kill-steps in controlling potential foodborne pathogens in food products, formal scientific evidence or validation of most of these processes for the inactivation of foodborne pathogens in bakery products has not been thoroughly investigated (Channaiah et al, 2016). According to the FSMA, food processors must validate all preventive controls that are process steps and critical for food safety based on the scientific evidences (FDA, 2015). Food manufacturers in the United States or those exporting to the United States need such validation documentation to support their food safety programs under the requirements of FSMA (FDA, 2015)
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