Development and evaluation of a dry heat treatment for inactivation of Salmonella on almonds
Date
2023
Authors
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Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Along with the increase of almond demand and production, recent outbreaks and recalls associated with Salmonella-contaminated almonds have aroused increasing concerns of their safety. As of 2007, the FDA mandated a 4-log reduction of Salmonella processing requirement for all raw almonds distributed in North America. The currently used processing methods for almond pasteurization include propylene oxide fumigation, hot water blanching, steam processing, oil roasting, and dry roasting, as recommended by the Almond Board of California. However, due to the concerns over chemical residuals and potential damage to original sensory and nutritional qualities, alternative processing technologies are needed. ☐ Almonds have a high fat content and a rich level of unsaturated fatty acids which are prone to oxidation. Thus, a dry heat treatment method along with vacuum packaging in oxygen-, moisture-, and light-impermeable mylar bags was developed in this study for pasteurization of almonds. The goal of this study was to achieve > 5-log reduction of Salmonella on almonds while preserving the original quality attributes of almonds. ☐ Different types of technologies that are currently available in the almond industry and those that have been explored in studies on the elimination or reduction of Salmonella were comprehensively reviewed in Chapter 2; potential strategies to improve the pasteurization efficiency and minimize processing damage were also discussed. ☐ In the first study, Salmonella-inoculated almonds were conditioned to four different water activity (aw) levels (0.43, 0.33, 0.23, and 0.20) and packaged by three methods (vacuum packaging in mylar bags, nonvacuum packaging in ambient-sealed glass tubes, and no packaging in petri dishes without covers) before being subjected to hot air treatment in a 73°C oven. As a result, almonds at higher aw achieved more efficient inactivation of Salmonella; vacuum packaging along with 4 h of 73°C heat treatment was able to achieve > 5 log reductions of Salmonella for almonds with initial aw of 0.43. Vacuum packaging achieved better outcomes in reducing Salmonella populations than no packaging and nonvacuum packaging. ☐ In the second study, the effects of almond aw and storage conditions (temperature and duration) were investigated on the survival and thermal resistance of Salmonella inoculated on almonds that had been packaged in mylar bags and polyethylene bags. The results indicated that both storage temperature and aw affected the survival of Salmonella. However, the resistance of Salmonella during 75°C dry heat treatment was not affected by storage temperatures or durations. Therefore, it was understood that the almond pasteurization scheme should not be affected by the age of almonds or storage conditions. ☐ In the third study, the 75°C dry heat treatments were compared with ultraviolet (UV) treatments, chemical sanitizers, and sequential treatments involving application of two or more types of treatments. The UV treatments, chemical sanitizers, and sequential treatments were not able to achieve desired Salmonella lethality without causing quality deterioration such as kernel cracking and burning marks. The dry heat treatment was identified to be a much better processing method to protect the quality of almonds. ☐ In the final study, the mild temperature of 75°C was selected to treat Salmonella-inoculated almonds at five different aw levels (0.59, 0.54, 0.43, 0.33, and 0.23). The survival data were analyzed using statistical tools for production of D values and development of a prediction model. The validation study of the predictive model indicated that the model can be used to predict processing times needed to achieve desired kill. This model is believed to be a useful tool to optimize treatment conditions and ensure that almonds are safe for consumption while still maintaining their quality properties. ☐ In summary, the vacuum packaging method in mylar bags could completely block out light and oxygen during the heat treatment, and thus, minimize oxidation of lipids and other nutrients. In addition, the vacuum packaging reserved the moisture and maintained the original aw levels of almonds throughout the treatment, and thus, did not result in increased thermal resistance of Salmonella like dry roasting. The treatment regime identified in this study can achieve > 5 log reductions of Salmonella within a much shorter timeframe compared to traditional dry heat treatment. This processing method can be adopted by the almond industry for pasteurization of almonds. The processing setup included moisture conditioning and vacuum packaging in moisture-impermeable containers (e.g., moisture-preventative liners or metal silos) can be easily scaled up and readily incorporated into the existing processing plant. Besides, the development of a predictive model for almond pasteurization is necessary to ensure the safety and quality of almonds by optimizing pasteurization conditions while also improving the efficiency and effectiveness of pasteurization operations. With the predictive model, the processor will only need to measure the aw of the product to calculate the processing time needed in achieving the desired kill, which reduce the risks of over-processing or under-processing. ☐ Overall, these studies demonstrated that dry heat treatment at moderate temperatures along with vacuum packaging in mylar bags can serve as an effective and efficient decontamination method for almond pasteurization. The major advantage of this method is the preservation of almond quality due to the mild temperature that was employed, and the much shorter time utilized compared to traditional thermal processing methods. It can be used as a potential intervention technique alone, or in combination with other processing technologies as a part of a hurdle intervention program to ensure the safety of almonds.
Description
Keywords
Almond, Dry heat, Inactivation, Pasteurization, Salmonella, Vacuum packaging