The effects of edible coating of basil seed gum and caraway essential oil on microbial and chemical characteristics of Silver carp fillets

Introduction : Consumption of seafood has increased during recent years as consumers have become more aware of its nutritional benefits and of the health concerns associated with other meat products such as chicken and beef . Fish is a more perishable product than other muscle foods and its freshness degrades after death due to various biochemical reactions (e.g. changes in protein and lipid content, and the formation of biogenic amines and hypoxanthine ) and microbiological spoilage ( Matak et al., 2015 ). Spoilage of fish results from changes brought about by biological reactions such as oxidation of lipids , the activities of the fish muscular enzymes and the metabolic activities of microorganisms ( Bagheri et al., 2016 ). Nowadays , to maintain the safety and quality of foods , long-term storage of the product and prevent the spread of foodborne diseases , the use of anti-microbial substances in food products has developed a lot ( Appendini and Hotchkiss, 2002) . Using anti-oxidant and anti-microbial preservatives in meat and meat products is very common to prevent the lipid oxidation and spoilage and increased the shelf life and quality of products ( Rashidaie et al., 2019 ) . The use of chemical preservatives in food is harmful to the health of consumers and leads to the occurrence of dangerous diseases such as types of cancers , on the other hand with the increase in environmental warnings , much attention has been paid to the use of biodegradable and environmentally friendly packaging films under the title of edible films and coating , thus food industry manufacturers and researchers are looking for the use of natural preservatives to increase the shelf life and maintain the quality of foods( Joerger, 2007 ) . Natural anti-microbials from different sources are used to preserve food from spoilage and pathogenic microorganisms . Many plants have been considered as the source of natural anti-oxidants due to their effective compounds such as polyphenolic compounds , flavonoids , tannins and phenolic acids . In addition to the anti-oxidant properties, these compounds also have anti-microbial, anti-cancer, and anti-mutagenic properties ( Rashidaie et al.,2019 ) . Hypophthalmichthys molitrix is widely used in Freshwater fish breeding systems around the world, due to its fast growth, stress resistance and high nutritional value ( Khorrami et al., 2013 ) . In Iran , in recent years, the breeding rate of this species has been on the rise . Microbial contamination and physicochemical reactions have an effective role in reducing the edible quality of various types of fish and edible coating based on natural compounds can increase the shelf life of the products ( Arshad and Batool, 2017 ) . This research was conducted to investigate the effect of the edible coating of basil seed gum and various concentrations of caraway essential oil on the microbial and chemical characteristics of Hypophthalmichthys molitrix fillet during storage in the refrigerator temperature . The benefits of basil seed gum compared to other polysaccharides are its hydrophilic, bio compatible and cost effective properties ( Khazaeia et al.,2014 ). Basil has a high amount of phenolic compounds and as a result it's anti-oxidative properties is high . It also has antimicrobial effects ( Phuong et al.,2010 ) . Cuminaldehyde, γ-Terpinene and p-cymene are among the effective compounds in caraway essential oil which have antifungal, antibacterial and antioxidant effects (AL-Jabri and Hossain,2014), moreover It has anti-allergic effects, reduces blood cholesterol and strengthens the body’s immune system ( Brody et al., 2008 ).
Material and methods : In this study the control sample (fish fillet without coating) and treatments coated with 5% basil seed gum and 0.25, 0.5 and 1% caraway essential oil where evaluated . The basil seeds were carefully cleaned removing dusts, stones and chaffs. The gum extraction conditions were as follows : 70 °C temperature, pH =7, 20-minute soaking time and a water to seed ratio of 65:1. The Caraway essential oil was obtained by hydro-distillation of the seeds during 3 hours using a Clevenger-type apparatus. During 15 days of the storage in the refrigerator and at intervals of 3days microbial tests, including the psychrotrophic and total bacterial count, and physicochemical tests, including measuring the amount of pH , Thiobarbituric acid (TBA ) and total volatile basic nitrogen (TVB-N ) were performed . The thiobarbituric acid reactive substances test is a method to investigate secondary oxidative products especially in polyunsaturated fatty acids such as malonaldehydes . The TVB-N value is one of the most widely used indicators of seafood deterioration . It is a general term which includes the calculation of three methyl amine ( produced by spoilage bacteria ), dimethyl amine ( produced by autolytic enzymes during chilled preservation ) , ammonia (produced by the deamination of amino acids and nucleotide catabolizes ) as well as other volatile basic nitrogenous compounds correlated with seafood spoilage ( Erikson et al., 2011) . All the tests were carried out in triplicates and the results were expressed as mean values and standard deviation. The analysis of variance was applied to the data and the means were compared by Duncan’s test using SPSS statistical software .
Results and discussion : Increasing the concentration of caraway essential oil in the edible coating the fish fillets during 15 days of the storage in the refrigerator had the positive effect on the reduction of psychrotrophic bacteria and total microbial count, so that by increasing the concentration of caraway essential oil the microbial load decreased and this difference was statistically significant (P<0.05 ). In addition, the amount of pH , Thiobarbituric acid and total volatile basic nitrogen in the coated samples were significantly more favorable than the control sample. During the storage of treatments in the refrigerator, the pH level increased . There was no significant difference between the pH of the control sample and the other treatments until the Sixth Day . On days 9 and 12, the pH of control sample was significantly higher than the treatments containing 0.5% and 1% essential oil . On the 15th day, the minimum and maximum pH values were evaluated in the treatment containing 1% essential oil and the control sample, respectively, while the difference in the investigated factor was significant in all the samples ( P<0.05 ) . The amount of TBA increased in all treatments during the storage period in the refrigerator. In the days of 3-15 , the TBA value in the control sample was significantly more than other treatments . On days 6 to 15, in treatments with more caraway essential oil , the TBA value was significantly less than in other treatments . The highest and lowest amount of TBA was determined in the control sample and treatment containing 1 % caraway essential oil, respectively . TVB-N index mainly represents the quality of fish and the expression presence of nitrogen compounds from destruction molecules such as proteins and nucleic acids by proteolytic bacteria . In all samples , the amount of TVB-N increased during the storage period in the refrigerator. On days 0 and 3, there was no statistically significant difference in the amount of total volatile basic nitrogen in the samples . From the Sixth Day, the amount of TVB-N in the control sample was significantly higher than the coated samples . The increase in the amount of TVB-N during the storage period can be related to the activity of bacteria and internal enzymes that accelerate the spoilage process and the accumulation of trimethylamine , dimethylamine , ammonia and other nitrogenous bases . The use of essential oil in the coating of fish fillets was effective in reducing the total amount of volatile basic nitrogen , compared to the control sample .
Conclusion : The results of this research showed that the use of an edible coating of basil seed gum and caraway essential oil reduces the intensity of bacterial activity in fish fillet samples and increases its shelf life in the refrigerator . The speed of quality reduction in treatments was significantly lower than in the control sample . The use of an edible coating of basil seed gum and 1% caraway essential oil improved the microbial and chemical characteristics and increased the shell life of fish fillets for 12 days in the refrigerator . Considering the disadvantages of chemical preservatives for consumers and to increase the shelf life of fish, it is recommended to use edible coating of basil seed gum and caraway essential oil .