Drying and inactivation of enterococcus faecium in raw almonds by sequential infrared and hot air drying

Authors: VENKITASAMY, CHANDRASEKAR - University Of California, Davis; ZHU, CAIPING - Shaanxi Normal University; Brandl, Maria; NIEDERHOLZER, FRANZ - University Of California - Cooperative Extension Service; ZHANG, RUIHONG - University Of California, Davis; McHugh, Tara; Pan, Zhongli

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/2018
Publication Date: 4/30/2018
Citation: Venkitasamy, C., Zhu, C., Brandl, M., Niederholzer, F.J., Zhang, R., Mchugh, T.H., Pan, Z. 2018. Drying and inactivation of enterococcus faecium in raw almonds by sequential infrared and hot air drying. LWT - Food Science and Technology. 95(2018):123-128. https://doi.org/10.1016/j.lwt.2018.04.095.
DOI: https://doi.org/10.1016/j.lwt.2018.04.095

Interpretive Summary: Contamination of almonds with Salmonella enterica (S. enterica) is a major safety concern in almond production, and may occur prior to processing. The harvest practice of shaking and drying almonds for 1-2 weeks on the ground increases the risk of contamination with enteric pathogens. Rain during the harvest season may cause complete loss of the crop due to increased contamination risk and lack of adequate drying technology. The objective of this study was to develop a sequential infrared and hot air (SIRHA) drying method for whole almonds to perform simultaneous drying and decontamination of almonds. The wet almonds with hull and shell were dried in the SIRHA dryer using different time-combinations of infrared (IR) radiation and hot air (HA) to determine the optimum drying conditions. Almonds with their hulls were inoculated with Enterococcus faecium, a surrogate for Salmonella enterica, which has caused major recalls and outbreaks due to contaminated almonds. Inoculated whole almonds were dried to evaluate the decontamination efficacy of the SIRHA method. The SIRHA drying (IR drying at 70oC for 1 h and followed by a 2 h HA drying) reduced the moisture content of almonds to 7% in 3 h, with a saving of 2 h (40%) of drying time compared with HA drying alone. The population sizes of E. faecium showed the largest size reductions of 4.69±0.71, 1.82±0.39, 1.52±0.31 log CFU/nut on hulls, shells and kernels, respectively, after SIRHA drying combined with tempering (T) (2 h IR with 2 h T and 1 h HA). The peroxide value (PV) and free fatty acids (FFA) content of almond oil samples from all drying treatments were well within the accepted level for the almond industry. Our results suggested that the high decontamination efficacy of IR-based technologies on the hulls is valuable to the industry as a first approach to improve the microbial safety of almonds while providing a time- and energy-saving means to dry a crop that exceeds normal moisture content. Additional sanitization during processing may be required to further decontaminate the almond shells and kernels.

Technical Abstract: The harvest practice of shaking and drying almonds for 1-2 weeks on the ground increases the risk of contamination with enteric pathogens. Rain during the harvest season may cause complete loss of the crop due to increased contamination risk and lack of adequate drying technology. The objectives of this study were to develop a sequential infrared and hot air (SIRHA) drying method for whole almonds and evaluate its effectiveness to perform simultaneous drying and decontamination of almonds. The wet almonds with hull and shell were dried in the SIRHA dryer using different time-combinations of infrared (IR) radiation and hot air (HA) to determine the optimum drying conditions. Almonds with their hulls were inoculated with Enterococcus faecium, a surrogate for Salmonella enterica, which has caused major recalls and outbreaks due to contaminated almonds. Inoculated whole almonds were dried to evaluate the decontamination efficacy of the SIRHA method. The SIRHA drying (IR drying at 70oC for 1 h and followed by a 2 h HA drying) reduced the moisture content of almonds to 7% in 3 h, with a saving of 2 h (40%) of drying time compared with HA drying alone. The population sizes of E. faecium showed the largest size reductions of 4.69±0.71, 1.82±0.39, 1.52±0.31 log CFU/nut on hulls, shells and kernels, respectively, after SIRHA drying combined with tempering (T) (2 h IR with 2 h T and 1 h HA). The peroxide value (PV) and free fatty acids (FFA) content of almond oil samples from all drying treatments were well within the accepted level for the almond industry. Our results suggested that SIRHA drying could be used for drying rain-impacted wet whole almonds, but additional sanitization may be required to further decontaminate the shells and kernels.