title: Survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on inoculated almonds and pistachios stored at -19, 4, and 24° C.
abstract: The survival of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes was determined on almonds and pistachios held at typical storage temperatures. Almond kernels and inshell pistachios were inoculated with four- to six-strain cocktails of nalidixic acid-resistant  Salmonella, E. coli O157:H7, or L. monocytogenes at 6 log CFU/g and then dried for 72 h. After drying, inoculated nuts were stored at -19, 4, or 24°C for up to 12 months. During the initial drying period after inoculation, levels of all pathogens declined by 1 to -log  CFU/g on both almonds and pistachios. During storage, moisture content (4.8%) and water activity (0.4) of the almonds and pistachios were consistent at -19°C; increased slowly to 6% and 0.6, respectively, at 4°C; and fluctuated from 4 to 5% and 0.3 to 0.5 at 24°C, respectively.  Every 1 or 2 months, levels of each pathogen were enumerated by plating; samples were enriched when levels fell below the limit of detection. No reduction in population level was observed at -19 or 4°C for either pathogen, with the exception of E. coli O157:H7-inoculated  almonds stored at 4°C (decline of 0.09 log CFU/g/month). At 24°C, initial rates of decline were 0.20, 0.60, and 0.71 log CFU/g/month on almonds and 0.15, 0.35, and 0.86 log CFU/g/month on pistachios for Salmonella, E. coli O157:H7, and L. monocytogenes, respectively,  but distinct tailing of the survival curves was noted for both E. coli O157:H7 and L. monocytogenes.
authors.affiliation: Department of Food Science and Technology, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
authors.forename: Martha A
authors.initials: MA
authors.lastname: Kimber
authors.forename: Harbir
authors.initials: H
authors.lastname: Kaur
authors.forename: Luxin
authors.initials: L
authors.lastname: Wang
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Danyluk
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Harris
mesh_terms: D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000254:growth & development*; D005511:Food Handling; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D008089:Listeria monocytogenes / Q000254:growth & development*; D050296:Microbial Viability; D027927:Pistacia / Q000382:microbiology*; D027861:Prunus / Q000382:microbiology*; D012475:Salmonella / Q000254:growth & development*; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water