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Don L. Zink, Ph.D.Center for Food Science and Applied Nutrition

U.S. Food & Drug Administration

The Changing Science of Peanut Butter

A Brief History of Peanut Butter• The ancient Inca Indians were known to

have made peanuts into a paste as early as 950 B.C.

• Dr. John Harvey Kellogg patented a “Process of Preparing Nut Meal” in 1895 using peanuts. He served peanut butter to patients in his Battle Creek Sanitarium.

A Brief History of Peanut Butter

• Ambrose Straub patented a peanut butter making machine in 1903.

• Public introduction of peanut butter into mainstream U.S. society occurred in 1904 at the St. Louis Worlds Fair

• By 1914, many companies were making peanut butter and by 1928 smooth peanut butter was sold under the Peter Pan brand name and in 1932, crunchy style peanut butter appeared under the Skippy brand.

A Brief History of Salmonella

• Coincidentally, Salmonella was discovered in the modern world at about the same time as peanut butter.

• In 1885, Theobald Smith discovered Salmonella and named the organism after Dr. Daniel Salmon, who was the administrator of the USDA research program studying hog cholera.

• At this time, there was no known connection between peanuts, peanut butter and Salmonella.

Recent Salmonella outbreaks linked to Peanuts and Peanut Butter

Year Product implicated Salmonella Serovar Country

1996 Peanut butter S. Mbandaka Australia

1996 Peanut-flavored maize snack S. Agona Multiple a

2001 Peanuts S. Stanley, S. Newport Multiple b

2006-07 Peanut butter S. Tennessee US

2008-09 Peanut butter, peanut butter-containing products

S. Typhimurium US, Canada c

a Including UK, US, and Israel.b Including Australia, Canada, and UK.c One case was reported in Canada.

Data adapted from Scott et al., 2009

Salmonella Infectious DoseYear Serovar No.

(cfu/g)Vehicle a Source of

contaminationNo. of illness

casesCountry

1973 – 1974

S. Eastbourne 2.5 ChocolateBalls

Cocoa beans 200 US, Canada

1982 S. Napoli 2-23 ChocolateBars

ContaminatedWater(postulated)

272 England, Wales

1985 –1986

S. Nima 0.04-0.24 Chocolatecoins

Unknown ? Canada

1987 S. Typhimurium ≤1 Chocolate AvianContamination(postulated)

349 Norway, Finland

2001 –2002

S. Oranienburg 1.1–2.8 Chocolate(two brands)

Unknown 439 Germany andother EuropeanCountries

2006 –2007

S. Tennessee 0.1 - 1 Peanut Butter Plant environment 628 US

a In each outbreak, the identified vehicles was traced to a single manufacturer.

Data adapted from Scott et al., 2009

Characteristics of Salmonella in Foods

• Growth in foods– Temperature: from 5.2°C to 46.2°C– pH: from 3.8 to 9.5– Aw: from 0.94 to >0.99

• Heat resistance in foods– Wide strain-to-strain variation– Dependent on pH, Aw, and food matrix

• Freezing is not effective in eliminating Salmonella from foods

• Salmonella survive long periods of dehydration

Heat Resistance of Salmonella*

• Effects of pH– S. Typhimurium – D126 = 6.1 min in poultry

scald water at pH 7.6

– S. Typhimurium – D126 = 34.5 min in poultry scald water at pH 5.9

– S. Typhimurium – D126 = 2.5 min in poultry scald water at pH 8.5

– S. Typhimurium – D126 = 0.175 min in poultry scald water at pH 10.0

* D value temperatures are in °F

Heat Resistance of SalmonellaSalmonella Serovar Heating Medium Water

ActivityTemperature

(°F)

D-value

(min)

S. Typhimurium Chocolate Syrup 0.83 150 3.2

S. Typhimurium Salt solution 0.42 248° 8.9

S. Typhimurium Salt solution 0.31 248° 10.6

S. Weltevreden Wheat flour 0.36 – 0.40 167 – 171 80

S. Weltevreden Wheat flour 0.25 – 0.30 167 – 171 150

S. Typhimurium Milk Chocolate ? 160 396

S. Typhimurium Milk Chocolate ? 194 78

Data adapted from Scott et al., 2009

Challenges with Salmonella

• Heat resistance at low water activity– The ability to destroy Salmonella on nuts

during roasting is dependent on the moisture status at the surface of the nut, not the humidity of the bulk air

• Variability among strains of Salmonella– The strains of S. Tennessee involved in the

recent outbreaks are more heat resistant that other typical strains of Salmonella

Thermal Inactivation of Salmonella

Data from Li Ma et al., 2009. J. Food Protect. 72:1596 – 1601.

Practical Impact of Peanut Butter Contamination Incidents

• The peanut butter contamination implicated a wide range of low moisture foods– Bakery products, baked pet treats– Chocolate products– Nut products

• The vast majority of affected food processors were not familiar with Salmonella and did not understand their own heating processes on a functional level– Lack of data on actual product time-temperature profiles

• Some regulators did not understand the heat resistance of Salmonella at low water activities– Some gave guidance from the Food Code on safe cooking

temperatures

Future Research Needs

• More research is needed on Salmonella heat resistance in foods– Research findings need to be converted into

user-friendly tools that can be used to evaluate cooking processes

– Small and medium size processors need more training and education about food processing

• Improved designs are needed for dry nut roasting equipment