Prototype of innovative minimally processed fresh oysters (Crassostrea gigas) treated with cold atmospheric pressure plasma

Oysters are abundantly harvested shellfish and are highly perishable due to their high water activity, neutral pH and chemical composition. Deterioration can be caused by enzymatic autolysis, oxidation and microbial growth of the natural spoilage microbiota. Refrigeration is used to limit the risk associated with potentially pathogenic microorganisms and to delay changes in freshness, undesirable odour, off-flavour and texture. However, maintaining low temperature throughout the supply chain can be difficult, making additional preservation measures desirable. Post-harvest treatments based on coatings, electrolyzed or ozonated water, rapid chilling, irradiation, hydrostatic highpressure processing, and vacuum or modified atmosphere packaging (MAP) have been investigated as additional measures to reduce the levels of pathogens and spoilage in oysters. Among the non-thermal intervention strategies, not extensively studied for fish products but considered promising for maintaining food quality and safety, cold atmospheric pressure plasma (CAP) has received increasing attention in recent years. Plasma, the “fourth state of matter,” is a neutral gas containing various species such as electrons, ions, reactive atoms, free radicals, neutral molecules, and photons in a metastable state with a roughly zero net electrical charge. If enough energy is added to a gas or gas mixture, it generates a plasma that produces a wide range of unique species, including reactive oxygen and nitrogen species (ROS and RNS) and UV radiation. These reactive species play a crucial role in microbial inactivation by damaging microbial DNA and causing oxidative damage to cell envelopes and membranes. The CAP configuration and processing conditions must be optimized to maintain nutritional and quality characteristics, depending on the food matrix composition and chemicalphysical properties. Plasma technology is a smart, green, non-thermal technology with relative advantages in extending the shelf-life of various foods, with limited side effects on quality parameters thanks to the low treatment temperature. The aim of the present research was to develop a prototype of fresh oysters treated post-harvest with CAP. The setup of protocols and identification of the best performing conditions were based on a preliminary screening by modulating different processing variables such as the feeding gas (argon or atmospheric air), the main reactive species generated during the treatments (ozone or NOx), and the processing time. The effects of the different conditions were checked by evaluating the reduction of the natural spoilage microbiota and retention of nutritional and quality features of the treated products. The selected conditions were then assessed through shelf-life tests by combining CAP treatments with two different MAP conditions.