Deciphering the Mechanism by Which Carbon Dioxide Extends the Shelf Life of Raw Milk: A Microbiomics- and Metabolomics-Based Approach

Microbial community succession in raw milk determines its quality and storage period. In this study, carbon dioxide (CO2) at 2000 ppm was used to treat raw milk to investigate the mechanism of extending the shelf life of raw milk by CO2 treatment from the viewpoint of microbial colonies and metabolites. The results showed that the shelf life of CO2-treated raw milk was extended to 16 days at 4 °C, while that of the control raw milk was only 6 days. Microbiomics analysis identified 221 amplicon sequence variants (ASVs) in raw milk, and the alpha diversity of microbial communities increased (p < 0.05) with the extension of storage time. Among them, Pseudomonas, Actinobacteria and Serratia were the major microbial genera responsible for the deterioration of raw milk, with a percentage of 85.7%. A combined metagenomics and metabolomics analysis revealed that microorganisms altered the levels of metabolites, such as pyruvic acid, glutamic acid, 5'-cmp, arginine, 2-propenoic acid and phenylalanine, in the raw milk through metabolic activities, such as ABC transporters, pyrimidine metabolism, arginine and proline metabolism and phenylalanine metabolism, and reduced the shelf life of raw milk. CO2 treatment prolonged the shelf life of raw milk by inhibiting the growth of Gram-negative aerobic bacteria, such as Acinetobacter guillouiae, Pseudomonas fluorescens, Serratia liquefaciens and Pseudomonas simiae.

Footprint analysis of CO2 in microbial community succession of raw milk and assessment of its quality

With the growing production of raw milk, interest has been increasing in its quality control. CO2, as a cold processing additive, has been studied to extend the cold storage period and improve the quality of raw milk. However, it is yet uncertain how representative microbial species and biomarkers can succeed one another at distinct critical periods during refrigeration. Therefore, the effects of CO2 treatment on the succession footprint of the microbial community and changes in quality during the period of raw milk chilling were examined by 16S rRNA analysis combined with electronic nose, and electronic tongue techniques. The results indicated that, the refrigeration time was shown to be prolonged by CO2 in a concentration-dependent way. And CO2 treatment was linked to substantial variations in beta and alpha diversity as well as the relative abundances of various microbial taxa (p < 0.01). The dominant bacterial phylum Proteobacteria was replaced with Firmicutes, while the major bacterial genera Acinetobacter and Pseudomonas were replaced with lactic acid bacteria (LAB), including Leuconostoc, Lactococcus, and Lactobacillus. From the perspective of biomarkers enriched in CO2-treated sample, almost all of them belong to LAB, no introduction of harmful toxins has been found. The assessment of the quality of raw milk revealed that CO2 improved the quality of raw milk by lowering the acidity and the rate of protein and fat breakdown, and improved the flavor by reducing the generation of volatiles, and increasing umami, richness, milk flavor and sweetness, but reducing sourness. These findings offer a new theoretical foundation for the industrial use of CO2 in raw milk.

Efficacy of a postharvest treatment aiming at eradication of all developmental stages of Tecia solanivora in ware potatoes

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver a scientific opinion on the efficacy of a postharvest treatment aiming to eradicate all developmental stages of Guatemalan potato tuber moth Tecia solanivora (Lepidoptera: Gelechiidae) in ware potatoes. The Panel evaluated the scientific publication describing the elevated CO₂ treatment, which was defined as: 10-day exposure to 30% CO₂, 20% O₂ and 50% N₂ in controlled atmosphere at 17°C on the variety Negra Yema de Huevo (Papas Antiguas de Canarias, PDO potatoes, Solanum chaucha). In the scientific publication, the treatment was applied under semi-commercial and commercial conditions on artificially and field-infested tubers. The effect of the pest developmental stage on the treatment efficacy was investigated with artificial infestation of potato tubers with eggs, neonate and second instar larvae. Pupae and adults were placed in separate containers during the treatment. However, the third and fourth larval instars were not investigated. Further limitations were the sample size in the experiments, the mortality rate in the control group and the unknown level of infestation of the naturally infested potato tubers. It was not possible to evaluate the degree of pest freedom due to incomplete data on the conditions of production, i.e. the infestation level in the field. The Panel was able to conclude that although no surviving insects were observed in the performed experiments, the statistical evaluation of the presented results from the commercial trial indicate that it cannot be excluded that insects would survive the treatment. For example, based on the data provided the 95% confidence interval of the survival rate for eggs was: 0%-0.453%.

Wet-CO2 Pretreatment Process for Reducing Residual Lithium in High-Nickel Layered Oxides for Lithium-Ion Batteries

As the push for inexpensive vehicle electrification grows, high-energy-density cathodes for lithium-ion batteries, such as high-nickel layered oxides, have received a great deal of attention in both industry and academia. These materials, however, suffer from severe residual lithium formation, which causes slurry gelation during electrode fabrication and gas evolution during cycling. Herein, a novel cobalt hydroxide coating method on wet-CO₂ gas-treated LiNi_0.91Mn_0.03Co_0.06O₂ (Co-CO₂-NMC91) is presented. Notably, the wet-CO₂ treatment prior to a dry cobalt hydroxide coating plays a critical role in improving the coating uniformity and ultimately decreases the effective residual lithium content. Furthermore, full cells of Co-CO₂-NMC91 exhibit excellent capacity retention of 91% after 200 cycles. This study highlights how a wet-CO₂ treatment can be used to improve a typical dry coating and provides new insights toward the development of cathodes for high-energy-density LIBs without severe slurry gelation or gas evolution.

CO2-Oxidized Ti3C2Tx-MXenes Components for Lithium-Sulfur Batteries: Suppressing the Shuttle Phenomenon through Physical and Chemical Adsorption

Lithium-sulfur (Li-S) batteries are one of the main challenges facing Li-ion technology because the insulating nature of sulfur and the shuttle phenomenon of dissolved lithium polysulfides (LPSs) in liquid electrolytes result in critical problems, including low Coulombic efficiency, loss of active material, and rapid capacity decay. Here, we oxidized delaminated transition metal carbides (MXenes) using CO₂ (Oxi-d-MXenes) and used them as both cathode electrode with sulfur and modified separator coated onto the glass fiber without a conductive material and binder to suppress the diffusion of LPSs. Oxi-d-MXenes annealed at 900 °C using CO₂ gas formed perfectly converted rutile-TiO₂ nanocrystalline particles on their two-dimensional sheets. Li-S batteries fabricated with the Oxi-d-MXenes cathode and the Oxi-d-MXenes-modified separator exhibited high Coulombic efficiency (nearly 99%) and retained a capacity of about 900 mAh g^-1 after 300 cycles at a current density of 1C. These results were attributed to the chemical and physical adsorption between the Oxi-d-MXenes and the LPSs. Our results imply that Oxi-d-MXenes prepared by the CO₂ treatment exhibit physical and electrochemical properties that enhance the performance of Li-S batteries.