1. IntroductionRainbow trout (Oncor

1. Introduction
Rainbow trout (Oncorhynchus mykiss) 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 (Oraei, Motalebi, Hoseini, & Javan, 2010). 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 (Omojowo & Sogbesan, 2003). 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 (Pezeshk, Rezaei, & Hosseini, 2011). 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 (Wang, 2009). 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 (Sallam, Ahmed, Elgazzar, & Eldaly, 2007). 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 (Sallam et al., 2007). 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 (Oraei et al., 2010). Plant materials are the most efficient natural antimicrobial and antioxidant agents and have long been used to preserve food (Sharifi-Rad, Hoseini-Alfatemi, Sharifi-Rad, & Teixeira da Silva, 2014). 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 (Mnayer et al., 2014). These species, therefore, can play an important role as natural preservative to be applied in food industry.
Ajwain (Trachyspermum ammi (L.) Sprague, syn. Carum copticum (L.) Link, Seidemann, 2005) from the Apiaceae family exhibits several biological effects including analgesic, anti-inflammatory, anxiolytic and antispasmodic activities. Its seed has been widely consumed as a food flavoring agent and spice. Moreover, the seeds have several therapeutic effects and have been used for treatments of indigestion, flatulence, colic, diarrhea, and dyspepsia. Total essential oil of ajwain has large amounts of carvacrol or thymol. These phenolic compounds are expressed to be either bactericidal or bacteriostatic agents depending on the concentration (Zarshenas, Moein, Mohammadi Samani, & Petramfar, 2014).
Shallot (Allium ascalonicum L.) from the Alliaceae family is widely cultivated in Asian countries. It constitutes important ingredients in many Asian and European diets and is known for its medicinal properties. This plant has antimicrobial and antioxidant activities (Mnayer et al., 2014) and contains two main classes of antioxidant and antimicrobial components: sulfur-containing compounds (allyl trisulfide, allyl-cysteine and diallyl sulfide) and flavonoids (quercetins and flavones) (Brewer, 2011).
Despite the above mentioned facts, the application of ajwain seed and shallot fruits extract as natural preservatives have not been studied in depth in food product especially fish products that was coated and fried. Thus, the objective of the present study was to evaluate the effects of ajwain seed and shallot fruit extract as antioxidant and antimicrobial compounds on extending the shelf life of semi-fried coated rainbow trout (O. mykiss) fish fillet products and the associated quality changes in the products during ea storage trial at 4 ± 1 C.