Location: Fruit and Tree Nut Research
2024 Annual Report
Objectives
Determine factors and approaches that impact pecan safety, quality, and marketability of pecans. This includes developing new and improved pecan processing technologies, such as pasteurization and cracking/shelling, for improved storage and safety, while maintaining nutmeat quality and nutrition.
Approach
Developing novel nut shelling and associated processing techniques to minimize physical nutmeat damage, contamination, and loss of quality postharvest; and improving understanding of pre-harvest and postharvest environmental factors that impact pecan color, texture, oil quality, and phytochemical content to identify conditions that maximize duration of quality. To better understand food safety risks associated with pecans, the project will address factors that influence the survival and persistence of foodborne pathogens and identify effective mitigation strategies while maintaining nut quality. In order to maximize marketability, the project will explore means to cost-effectively increase intact pecan meat extraction by modifying parametrized process variables on existing processing equipment.
Progress Report
ARS researchers at Byron, Georgia determined the food safety needs of the pecan shelling industry by performing an industry needs assessment. Over half of pecan shellers had a food safety plan in place (56.5%; 13/23) and treated in-shell pecans with hot water or steam (56.5%; 13/23), but these practices tended to be associated with operation size. A majority of the shellers conditioned in-shell pecans in water but the time varied between <1 hr. (50.0%, 8/16), 1-2 hrs. (6.3%; 1/16), 3-4 hrs. (12.5%; 2/16), and >4 hrs. (31.2%; 5/16). Of the shellers that condition in-shell pecans, 58.8% (10/17) reported using a sanitizer in the conditioning water. Chlorine-based sanitizers (chlorine dioxide, sodium hypochlorite, and calcium hypochlorite) were the most commonly used in conditioning water.
ARS researchers at Byron, Georgia evaluated the use of pulsed ultraviolet light (PUVL) to inactivate E. coli and Salmonella on pecan halves (kernels) while maintaining shelf life and quality. A maximum reduction of Salmonella by 3.43 log CFU/pecan was achieved when pecan halves were treated with pulsed light for 40 s at 13.36 cm distance from the light source without affecting its quality attributes such as color, texture, moisture, water activity, and peroxide values.
We determined effective concentrations of peracetic (peroxyacetic) acid (PAA) and effectiveness compared to chlorine to reduce contamination levels and prevent cross-contamination of Salmonella during in-shell pecan washing and conditioning. Both PAA concentrations 30 and 90 ppm, were effective at reducing Salmonella levels by 3.4±0.9 and 4.2±0.5 log CFU/g respectively on in-shell pecans after 60 minutes. There was an observed cross-contamination of 4 logs onto the uninoculated pecans in water with no PAA after 60 minutes, with the 90 ppm PAA concentration being as effective at preventing cross-contamination as chlorine treatments.
Scientists compared the effectiveness of hot water, lactic acid, and chlorine on the reduction of Shiga toxin-producing E. coli (STEC) on in-shell pecans and prevent cross-contamination during washing and conditioning. Hot water was most effective at reducing STEC levels on the surface of in-shell pecans compared to washes with lactic acid and chlorine. While lactic acid and chlorine washes didn’t have the same STEC reductions, they were as effective as hot water in preventing cross-contamination and limiting STEC levels in the water.
We investigated the use of atmospheric cold plasma as a potential treatment to reduce E. coli and Salmonella levels on pecan halves and evaluate the hurdle effect of cold plasma and PUVL to inactivate foodborne pathogens. Distance and time were determined to be significant factors that influenced the reduction of Salmonella on pecan kernels using cold plasma. A maximum 1.2 log CFU/g Salmonella reduction was observed for pecans treated for 10 seconds at 4 cm. A combination of pulsed light (7 cm, 12 s) and cold plasma (4.5 cm, 9 s, 900 Hz) reduced E. coli population by 3.9 log CFU/pecan, significantly higher compared to the reduction achieved with individual treatments.
ARS researchers at Byron, Georgia investigated various organic acids (lactic, citric) and essential oil (clove bud oil) as sanitizing solutions to decontaminate in-shell pecans contaminated with Salmonella. Among the tested organic acids, lactic acid demonstrated the highest efficacy in reducing Salmonella on inshell pecans, resulting in a 2.18 log reduction when pecans were dipped in the solution for 10 min. Similarly, clove bud oil (0.2%) reduced Salmonella by 2.69 log CFU/pecan under the same treatment conditions. Research is ongoing to explore the combined effects of clove bud oil with various acids.
We evaluated the physiochemical and microbial quality of pecan float systems and optimization of sanitizer effectiveness in these systems. Preliminary results show that maintaining chlorine levels (~150-200 ppm) in the float system will assist in limiting total plate counts and coliform levels on pecans that have passed through the system. Minimum chlorine levels to prevent pathogen cross-contamination will be assessed in the lab.
ARS researchers at Byron, Georgia selected physical and engineering properties of seven varieties of inshell pecans (Desirables, Whiddon, Caddo, Stuart, Elliott, Oconee, and Pawnee) were determined. The properties determined were length, width, thickness, arithmetic mean diameter, geometric mean diameter, surface area, mass, volume, bulk density, unit density, angle of repose, texture, moisture content, water activity, color, and thermal properties (thermal conductivity, thermal diffusivity, resistivity, and specific heat). These data are useful for design and development of equipment for handling, transportation, processing, and storage of inshell pecans.
The research team acquired a 14” pecan sheller from Modern Electronics and Equipment™ (ME&E) and made modifications to facilitate better experimentation. These modifications included replacing the sheet metal siding with acrylic to observe the interior during operation and replacing the funnel output with a three-section partitioned output to compare performance. The team also connected the paddle-shaft and drum to independent motors with variable frequency drives (VFDs) for RPM control and fitted the intake end with actuators to control the tilt angle. RPM tracking was implemented, along with a feed rate control system incorporating a vibrating plate and bucket elevator.
A JC (circumferential cracking) Cracker from ME&E was enhanced with displacement sensors, rotary encoders, smart servos, and new impactor plate inserts. A control system was implemented utilizing PLC for contacting plate frequency and servo actuators for impacting plate displacement. A custom bracket was installed for the servo motor on the gate to eliminate play and enable precise control of gate angles, enhancing overall machine accuracy and performance. Modifications to a Meyer Cracker (end-to-end- cracking) included adjustable height options, manual control for the preload spring, a smart servo actuator for the displacement screw setting, VFD control for motor speed, and individual CAD designs for the impactor profile. New springs with varying spring stiffness were acquired, and plexiglass was added for observation.
The team conducted experiments to optimize pecan processing. Shelling experiments included an Air-Dry Experiment to determine moisture loss between cracking and shelling, establishing the need for same-day processing, and a Steady State Experiment that revealed the sheller likely reaches steady state within one minute. Half-Yield Experiments, involving a full-factorial Design of Experiments (DoE), studied the relationship between sheller parameters, moisture, and pecan variety to maximize half-yield.
Cracking experiments focused on the JC Cracker and Meyer Cracker in a full-factorial DoE. JC experiments explored variables such as contact plate frequency, throughput, and impactor plate positioning. Experiments with the Meyer examined spring stiffness, motor speed, and impactor profile. Shimadzu and Solenoid experiments were also conducted, analyzing displacement settings and torsional forces for cracking efficiency.
Moisture conditioning experiments involved cold bath and hot bath methods, optimizing moisture absorption recipes for different pecan varieties, and maintaining water temperatures. Preliminary agitation experiments showed no significant absorption, leading to further review and adjustment of the technique.
In the area of Industry 4.0 and imaging, the team developed an IIoT architecture for data collection and analysis, built machine learning tools to model process variables, and created a PostgreSQL database for data storage and visualization using Grafana. Additionally, they developed imaging software to detect and measure pecan cracks with accuracy, along with an imaging rig for data collection.
ARS researchers at Byron, Georgia developed imaging algorithm to classify and measure crack parameters for use in cracker machine parameter adjustment. This automated system is the first of its kind on the market by taking a full 360-degree image of the pecan and measures the different types of crack appearances and their geometry. This data is used to make a determination on the appropriateness of the crack with respect to the cracker used.
Accomplishments
1. Determined the potential contamination of E. coli and Salmonella during pecan harvesting. ARS scientists at Byron, Georgia evaluated the potential for the cross-contamination potential of Salmonella and E. coli from orchard soil onto pecans during harvesting. The results provide insight into the impact that microbial levels and potential weather conditions have on contamination of foodborne pathogens. This indicates that foodborne pathogen contamination can occur during harvest and that controls should be implemented to reduce potential microbial levels.
2. Evaluated the use of Pulsed UV light as a control strategy for Salmonella contamination on pecan halves. Fort Valley State University scientists, in collaboration with ARS scientists at Byron, Georgia evaluated the potential of pulsed UV light as a mitigation strategy to reduce Salmonella levels on pecan halves. Pulsed UV light was found to be effective at reducing Salmonella on pecan halves when treated from the light source. There were no adverse effects on pecan color, texture, moisture, water activity, and peroxide values. These results show that the use of Pulsed UV light can be utilized as a potential treatment on pecan halves to reduce pathogen levels.
3. Developed of software to detect and classify cracks on pecan shells. University of Georgia scientists in cooperation with USDA-ARS Byron, Georgia developed a unique software program for detecting and measuring pecan cracks using advanced image processing techniques, achieving over 90% accuracy in crack detection and classification This automated system is the first of its kind on the market by taking a full 360-degree image of the pecan and measures the different types of crack appearances and their geometry. This data is used to make a determination on the appropriateness of the crack with respect to the cracker used.
Review Publications
Gyawali, R., Degala, H.L., Biswal, A.K., Bardsley, C.A., Mahapatra, A.K. 2024. Effects of Intense Pulsed Light on Inactivation of Salmonella Typhimurium and Quality Characteristics of Pecan Halves. LWT - Food Science and Technology. https://doi.org/10.1016/j.lwt.2024.116344.
Pabst, C.R., Kharel, K., De, J., Bardsley, C.A., Bertoldi, B., Schneider, K. 2024. Evaluating the efficacy of peroxyacetic acid in preventing salmonella cross-contamination on tomatoes in a model flume system. Heliyon. 10(10). Article e31521. https://doi.org/10.1016/j.heliyon.2024.e31521.
Gyawali, R., Mahapatra, A.K., Bardsley, C.A., Niemira, B.A. 2024. Improving microbial safety and quality of nuts using nonthermal technologies. Trends in Food Science and Technology. 81(1). https://doi.org/10.1016/j.jfp.2023.100201.
