Don L. Zink, Ph.D.

1
The Changing Science of Peanut Butter

• Don L. Zink, Ph.D.
• Center for Food Science and Applied Nutrition
• U.S. Food Drug Administration

2
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.

3
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.

4
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.

5
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
6
Salmonella Infectious Dose
Year Serovar No. (cfu/g) Vehicle a Source of contamination No. of illness cases Country
1973 1974 S. Eastbourne 2.5 Chocolate Balls Cocoa beans 200 US, Canada
1982 S. Napoli 2-23 Chocolate Bars Contaminated Water (postulated) 272 England, Wales
1985 1986 S. Nima 0.04-0.24 Chocolate coins Unknown ? Canada
1987 S. Typhimurium 1 Chocolate Avian Contamination (postulated) 349 Norway, Finland
2001 2002 S. Oranienburg 1.12.8 Chocolate (two brands) Unknown 439 Germany and other European Countries
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
7
Characteristics of Salmonella in Foods

• Growth in foods
• Temperature from 5.2C to 46.2C
• pH from 3.8 to 9.5
• Aw from 0.94 to gt0.99
• 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

8
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
9
Heat Resistance of Salmonella
Salmonella Serovar Heating Medium Water Activity Temperature (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
10
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

11
Thermal Inactivation of Salmonella
Data from Li Ma et al., 2009. J. Food Protect.
721596 1601.
12
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

13
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