Pulsed Light (PL) Treatments on Almond Kernels: Salmonella enteritidis Inactivation Kinetics and Infrared Thermography Insights

Abstract

Extending the shelf-life and ensuring microbiological safety of food products while preserving the nutritional properties are key aspects that must be addressed. Heat processing of food matrices has been the golden standard during the last decades, while certain non-thermal processing options have recently gained ground. In the present study, experimental pulsed light (PL) surface inactivation treatments of Salmonella enteritidis on almonds kernels are performed. The PL system is set to test different operative conditions, namely power (1000, 1250, and 1500 W) and frequency (1.8, 3.0, and 100.0 Hz) at different treatment times (from 5 to 250 s), which result in applied fluence doses in the 0–100 J·cm−2 range. Additionally, temperature measurements are collected at each operative condition on the almond surface (using infrared (IR) thermography) and at the superficial layer of the almond (1-mm depth using a thermocouple). The observed PL inactivation kinetics are then modelled using four different models. The best goodness-of-fit is found for the two-parameter Weibull model (R2 > 0.98 and RMSE < 0.33 for all cases). The maximum achieved log-CFU reductions are 6.02 for the 1.8-Hz system, 4.69 for the 3.0-Hz system, and 3.66 for 100.0-Hz system. The offset between the collected temperature readings by the two sensors is contrasted against the inactivation rate (following the two-parameter Weibull model). It was found that the highest inactivation rate corresponds approximately to the point where the infrared camera detects a slowdown in the surface heating. Graphical Abstract

Salmonella spp. in low water activity food: Occurrence, survival mechanisms, and thermoresistance

“…A capacitor is responsible for accumulating electrical energy and releasing it in the form of inert gases (Mahendran et al, 2019; Liu et al, 2021). This technology has brought good results in reducing Salmonella populations in chia seeds (Reyes‐Jurado et al, 2019), dried parsley (Dittrich et al, 2021), almonds (Oner, 2017; Harguindeguy & Gómez‐Camacho, 2021), and Enterococcus faecium ( Salmonella Surrogate) in nonfat dry milk, wheat flour, and egg white powder (Chen et al, 2019).…”

Impact of Non-Thermal Technologies on the Quality of Nuts: A Review

“…This fact, together with the high temperature reached (115 °C), the 58.5% water loss and the circumstance that the efficacy of PL is lower in solid matrixes than in liquid ones led to the conclusion that PL was not appropriate for the treatment of almonds due to its low effectiveness and significant negative impact on almond quality. When used to inactivate Salmonella enteritidis , Oner [ 61 ] reported a 4.1 log reduction and Harguindeguy and Gómez-Camacho [ 62 ] reported a 6 log reduction after application of <50 J/cm 2 , but no effects on almond quality were studied. Finally, Liu et al [ 63 ] used a 1 min immersion in water as a previous step before subjecting almonds to PL to avoid the detrimental effect of excessive heating on dried almonds observed in their preliminary tests.…”

Effect of Pulsed Light on Quality of Shelled Walnuts

“…The efficacy of PL to inactivate microorganisms on food surfaces has been successfully tested in a wide variety of foods, including nuts such as almond kernels [4] and shelled walnuts [5].…”