Publications and Resources
Abstract
This study investigated the efficacy of intense pulsed light (IPL) and cold atmospheric plasma (CAP) alone or in combination for inactivating Escherichia coli on pecan halves. The IPL treatments of 1 to 15 s at 4.5 to 9.5 cm and the CAP treatments of 9 to 15 s at 4.5 to 9.5 cm (100 to 900 Hz) were used. For the combination treatments, the IPL treatments were at 7 cm for 12 s and the CAP treatments were at 4.5 cm for 9 s (900 Hz). The IPL and CAP reduced E. coli population ranging from 0.12 to 2.63 and 0.44 to 1.52 log10 CFU/pecan, respectively. Time and distance significantly affected E. coli reductions for IPL and CAP treatments. The combined effect of IPL and CAP yielded significantly higher reduction (3.91 log10 CFU/pecan) compared with individual treatments with no significant effect on texture and colour of pecan halves.
Keywords: pecan, tree nut, low-moisture foods, shelf life, Escherichia coli, inactivation, cold atmospheric plasma, intense pulsed light, nonthermal processing, nut quality
Abstract
During harvest pecan nuts are at risk of contamination with foodborne pathogens from extended contact with the ground. The objective of this study was to determine the potential transfer of Escherichia coli and Salmonella from the ground to in-shell pecans during the harvesting process. Plots (2 m2) were sprayed with 1 L of a rifampicin (rif) resistant strain of either E. coli TVS 353 or an attenuated Salmonella Typhimurium inoculum at a low (∼4 log CFU/ml), mid (∼6 log CFU/ml) or high (∼8 log CFU/ml) concentrations. The following day, nuts were mechanically harvested and samples from each plot were collected at 1 min, 4 h, and 24 h. Samples were enumerated for Salmonella and E. coli on tryptic soy agar supplemented with rif. The Salmonella levels in the soil from the inoculated plots were 2.0 ± 0.3, 4.1 ± 0.1, and 6.4 ± 0.2 log CFU/g for the low, mid, and high inocula, respectively. The E. coli levels in the soil from the inoculated plots were 1.5 ± 0.4, 3.7 ± 0.3, and 5.8 ± 0.1 log CFU/g for the low, mid, and high inocula, respectively. There was a significant difference in the average daily rainfall among the three trials. Trial 3 received 23.8 ± 9.2 cm, while trials 1 and 2 received much less (0.1 ± 0.1 0.0 ± 0.0 cm, respectively). Inoculation concentration and trial were significant (P<0.05) factors that influenced the transfer of E. coli and Salmonella to pecans. For the high inoculum treatment, bacterial transfer to pecans ranged from 0.7 ± 0.3 to 4.1 ± 0.2 for E. coli and 1.3 ± 0.7 to 4.3 ± 0.4 log CFU/g for Salmonella. For the medium inoculum treatment, transfer ranged from <0.3 to 1.5 ± 0.1 for E. coli and <0.3 to 1.9 ± 0.2 log CFU/g for Salmonella. For the low treatment, transfer ranged from <0.3 to 0.4 ± 0.2 and <0.3 to 0.5 ± 0.1 log CFU/g for E. coli and Salmonella, respectively. These results show the need for implementing agricultural practices that prevent potential transfer of foodborne pathogens onto the surface of in-shell pecans during harvest.
Abstract
Tree nuts have been associated with several foodborne outbreaks and recalls in the U.S. While thermal decontamination methods can inactivate pathogens, they come with challenges of varying severity on the product quality. Thus, this study evaluated the effects of nonthermal intense pulsed light (IPL) on Salmonella Typhimurium inactivation and quality attributes of pecan halves. The level of microbial reduction increased with an increase in treatment time from 10 to 40 s and decreased with an increase in the distance (8.28–13.36 cm) from the light source. Both treatments (time and distance) were found to have a significant effect (P ≤ 0.05) on microbial reduction, whereas interaction effects (time * distance) were not significant. A 3.43 log CFU/pecan reduction in Salmonella was achieved when samples were treated at 13.36 cm for 40 s. No significant difference in the color, texture, water activity, moisture content, and peroxide value was observed between control and IPL-treated samples. We observed a decrease in most monosaccharide sugar levels compared to untreated pecans. The SEM images showed changes in bacterial cell morphology in IPL treated samples. This study demonstrated that IPL treatment could be used as a potential decontamination method for pecan halves.
Abstract
Background
Increase in foodborne illnesses associated with low-moisture foods have led to growing concern regarding the safety of nuts and nut-based products. Nonthermal techniques, antimicrobial agents, and packaging provide an alternative to thermal processing that can achieve microbial safety and preserve the quality characteristics of nuts.
Scope and approach
This review highlights the applications of various nonthermal techniques such as high pressure processing, cold plasma, ultraviolet light, pulsed light, ultrasound, and irradiation. Additionally, it covers the applications of antimicrobial agents, modified atmosphere packaging, and films and coatings. Future recommendations for enhancing the safety of nuts are also discussed based on the findings from the literature review.
Key findings and conclusions
Nuts can be a vehicle for foodborne pathogens. Over the years, several large-scale outbreaks associated with nuts and nut-based products have been implicated. Nonthermal processing techniques can be used to enhance the safety and quality of nuts while keeping loss of product quality to a minimum. With the increasing demand for nonthermal processing, energy-based technology will be a promising way to reduce microbial load without leaving toxic chemical residues. Nut preservation could also be accomplished using the hurdle approach, which combines various nonthermal methods. The resulting hurdle treatment can enhance the microbial safety and quality of nuts and nut-based products.
USDA Pecan Research is a research collaboration between the Fruit and Tree Nut Research: USDA ARS, University of Georgia College of Engineering, and Fort Valley State University.