Rainbow trout belongs to the Salmonidae and is one of the main fish species farmed in Iran. The demand for rainbow trout in Iran and other country markets has grown significantly over the past decade and this is due to its desirable characteristics (aroma, taste, white flesh) and nutritional value. Fish and fishery products have been identified as nutritional sources because of their high protein content. However, seafood shelf-life is limited by microbial and biochemical changes which causes substantial problems in distribution. Microorganisms including molds, yeasts and bacteria are known to be responsible for putrefaction and development of poor marketing appearance as well as toxic substances in fish that are objectionable by consumers. Oxidative rancidity is another important aspect that leads to quality deterioration in food and it is a major cause of quality deterioration in muscle foods during processing and storage. Fish products are more susceptible to lipid oxidation than other muscle foods due to their high level of polyunsaturated fatty acids and the low content of antioxidants. The susceptibility of fish tissue to oxidation is dependent not only on the amount of total lipids but also on the composition of fatty acids and their location in fish muscle tissue. Lipid oxidation in fish begins in
the intracellular phospholipid fractions of muscle cell membranes. Oxidative deterioration is therefore a problem in both lean and fatty fish species, leading to the development of undesirable flavors and odors that limit the shelf life of fish products and their utilization in convenience seafood-based products. Chemical reactions and activities of the fish's own enzymes are commonly responsible for the initial loss of fish freshness. In addition, the metabolic activities of microorganisms are included in the whole spectrum of spoilage. The intrinsic quality of seafood makes it more susceptible to food-borne hazards. To fulfill consumers' demand for fresh products with extended shelf life, many studies have been performed using various preservation strategies to prolong the shelf life of fresh foods including fishery products to ensure product safety and quality. Generally, different food preservation techniques have been used to enhance microbial safety and increase the shelf life of fish and shellfish, including chemical preservation, freezing, smoking and salting. Plant materials are the most efficient natural antimicrobial and antioxidant agents and have long been used to preserve food. Aromatic plants, such as ajwain and shallot, have been used as spices and condiments in foods in the past. In the last decade, numerous researchers have evaluated the application of these plants as natural sources of antimicrobial and antioxidant compounds. These species, therefore, can play an important role as natural preservative to be applied in food industry.