Assessing the Effects of Cold Atmospheric Plasma on the Natural Microbiota and Quality of Pork during Storage

Authores: Yelyzaveta K. Oliinychenko, Sotirios I. Ekonomou, Brijesh K. Tiwari and Alexandros Ch. Stratakos

Date: 26 March 2024

First published: https://www.mdpi.com/2304-8158/13/7/1015

Abstract

The study investigated the effects of cold atmospheric plasma (CAP) on the shelf life of pork stored at 4°C. The CAP treatment was conducted using piezoelectric direct discharge technology. Various treatment durations of 0, 3, 6, and 9 minutes were tested on pork samples to assess their impact on the natural microbiota and meat quality.

Content

Background

The meat industry is facing significant challenges due to the increasing global demand, affecting safety, quality, economics, and environmental impact. Pork is the most consumed red meat worldwide, and its demand has been steadily rising in recent years. New processing methods in meat production have proven to be effective strategies for extending shelf life and reducing food waste.

Pork spoilage primarily begins on the surface and is influenced by various factors such as initial microbial load, storage conditions, and processing methods. Pork processors employ various disinfection methods, including thermal processing and disinfectants, to reduce microbial contamination. However, current methods have been found to be limited in effectiveness and may compromise product quality. Therefore, the introduction of new processing technologies for pork is urgently needed to improve efficiency without compromising quality.

Investigation

Currently, cold atmospheric plasma (CAP) is being researched as a technology for surface disinfection in meat processing, known for its antibacterial properties, economic feasibility, and environmental compatibility.

In this study, a PDD generator was used to generate cold non-equilibrium plasma using air. CAP contains significant amounts of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which cause direct damage to bacterial cells. Microorganisms are influenced by the electric field as well as ROS (such as hydroxyl radicals, superoxide radicals, singlet oxygen, and hydrogen peroxide) and RNS (such as nitrogen oxide, nitrogen dioxide, nitrogen oxide dimer, and peroxynitrite). These disruptions of cellular homeostasis and resulting ion imbalance ultimately lead to cell death.

Experimental Setup

Three separate batches of pork loins were purchased from the same supplier with identical expiration dates and immediately stored at a temperature of 4°C. Initially, a pre-screening was conducted to exclude pork loin pieces of inferior quality. Subsequently, the chops were precisely cut into square pieces weighing 10 g each under sterile conditions. All experiments were conducted in triplicate, with two technical replicates each.

Treatment with cold atmospheric plasma (CAP)

The CAP treatment was conducted using a piezoelectric CAP generator with direct discharge (PiezoBrush PZ3, Relyon Plasma, Regensburg, Germany). This generator operated with an input voltage of 12 V, a frequency of 50 kHz, and atmospheric air as the gas source, which was driven by a fan to transfer the excited species and chemical radicals onto the surface of the sample. The generator was positioned 10 mm away from the surface of the samples.

Before the CAP treatment, each sample was carefully placed in a labeled, sterile Petri dish. Various treatment durations (0, 1, 3, 6, and 9 minutes) were applied. Both treated and untreated samples were packed into 15 × 15 cm bags and sealed with a deep chamber vacuum sealer. The vacuum-sealed samples were then stored at 4°C and analyzed at predefined intervals (0, 2, 4, 6, and 8 days) during refrigerated storage.

Impact of CAP Treatment on Spoilage Microbiota in Pork During Storage

The present study introduces a detailed approach to evaluating the effects of CAP treatment on pork, focusing on changes in the natural microbiota and overall meat quality. Total viable counts (TVC) and Enterobacteriaceae values in CAP-treated (1, 3, 6, and 9 minutes) and untreated (0 minutes) pork samples were analyzed on different storage days and depicted in Figures 1 and 2.

TVC concentrations were most significantly reduced immediately after CAP treatment for 3, 6, and 9 minutes compared to untreated samples. A 1-minute CAP treatment showed no significant influence on TVC concentration compared to untreated samples (Figure 1, p > 0.05). Concentrations of Enterobacteriaceae were reduced below the detection limit (1.0 log CFU/g) when CAP was applied for at least 3 minutes. Samples treated for 6 and 9 minutes exhibited significantly lower TVC and Enterobacteriaceae values throughout the storage period (Figure 2, p

Conclusion

The study investigated the effectiveness of CAP treatment in reducing potentially spoilage-causing microorganisms in vacuum-packed pork stored at 4°C. CAP resulted in a significant reduction in TVC, Enterobacteriaceae, and Pseudomonas spp. concentrations, thus extending the microbiological shelf life of pork.

Although no significant changes were observed in pH, tenderness, or L* color values, changes in a* and b* color parameters, as well as increased lipid oxidation values, were noted with longer CAP treatments at the end of the storage period. These findings demonstrate the potential of CAP for sustainable extension of the microbiological shelf life of pork.

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