3.2. Low moisture foods
Regarding the process of almond roasting in oil, after the 2001
outbreak in Canada, a minimum P-value of 4D of Salmonella spp. was
recommended for almond producers in California: a process exposing
almonds to oil at 126.7 °C for 1.6 min is sufficient, although commercially
2.0 min is applied (this treatment achieves 5D in Salmonella
numbers) (TERP, 2007). These temperature/time conditions are much
more severe than ‘normal’ pasteurization processes because of higher
thermal resistance in nuts and similar commodities such as cocoa
beans and peanut butter, which are very low in water content (low
aW). It is known that microorganisms including Salmonella are much
more resistant to heat in low water-activity foods: D71ºC in chocolate
decreased from 20 h to 4 h after adding 2% water (Barrile & Cone,
1970); Salmonella spp. survivors were registered after roasting cocoa
beans at 130 °C for 5 min (Peñaloza-Izurieta, Krapf, Diep, Benz, &
Gantenbein-Demarchi, 2008); Ma et al. (2009) reported that 90 °C for
less than 30 min was not sufficient for reducing by 5 log CFU/g of
Salmonella in peanut butter; 26 min at 90 °C only reduced Salmonella
by 1D in dark chocolate (Krapf & Gantenbein-Demarchi, 2010). To
overcome this problem, the use of moist air (5 to 90% RH) convection
heating was successfully applied to raw almonds for their pasteurization
by Jeong, Marks, and Orta-Ramirez (2009). The surface
moisture status of the almonds rather than RH of the air, was the
most important factor in ensuring effective pasteurization.