Drying and decontamination of raw pistachios with sequential infrared drying, tempering and hot air drying

- Sequential IR heating, tempering and hot air drying (SIRHA) achieved inactivation of Enterococcus faecium in pistachios.
- Enterococcus faecium was used as a surrogate for Salmonella enterica.
- SIRHA sequential treatments reduced the required drying time compared with current hot air drying.
- The quality of SIRHA-dried pistachios was within the standard range based on oil quality.

Pistachio nuts have been associated with outbreaks of foodborne disease and the industry has been impacted by numerous product recalls due to contamination with Salmonella enterica. The current hot air drying of pistachios has low energy efficiency and drying rates, and also does not guarantee the microbial safety of products. In the study described herein, dehulled and water-sorted pistachios with a moisture content (MC) of 38.14% (wet basis) were dried in a sequential infrared and hot air (SIRHA) drier to < 9% MC. The decontamination efficacy was assessed by inoculating pistachios with Enterococcus faecium, a surrogate of Salmonella enterica used for quality control in the almond industry. Drying with IR alone saved 105 min (34.4%) of drying time compared with hot air drying. SIRHA drying of pistachios for 2 h with infrared (IR) heat followed by tempering at a product temperature of 70 °C for 2 h and then by hot air drying shortened the drying time by 40 min (9.1%) compared with drying by hot air only. This SIRHA method also reduced the E. faecium cell population by 6.1-log CFU/g kernel and 5.41-log CFU/g shell of pistachios. The free fatty acid contents of SIRHA dried pistachios were on par with that of hot air dried samples. Despite significant differences in peroxide values (PV) of pistachio kernels dried with the SIRHA method compared with hot air drying at 70 °C, the PV were within the permissible limit of 5 Meq/kg for edible oils. Our findings demonstrate the efficacy of SIRHA drying in achieving simultaneous drying and decontamination of pistachios.