Effect of aqueous and ethanolic extracts of Trigonella foenum-graecum seed on the quality of Cyprinus carpio fillet inoculated with Staphylococcus aureus

Introduction: Carp, as one of the freshwater fish species, has been one of the most widely cultured species all over the world due to its fast growth rate, easy cultivation, high feed efficiency ratio as well as high nutritional value. Spoilage is the degradation of food such that the food becomes unfit for human consumption. Among the various foods, fresh fish are highly perishable. Fish spoilage can be caused by a number of means, autolytic enzymatic, lipid oxidation and microbial which results in numerous undesirable metabolites being produced in the food that cause unwanted flavors and odors. Staphylococcus aureus is an opportunistic pathogen and is responsible for a wide range of human infections and food poisoning. In recent years, despite the use of antibiotics, diseases and deaths from food-borne diseases have increased due to the emergence of antibiotic resistant strains. As a result, the use of alternative methods to prevent the growth of microorganisms and limit the increase in their resistance seems necessary. Using plant extracts that inhibit their growth can be effective and safe alternatives to fight pathogens, especially those associated with food-borne diseases. Trigonella foenum-graecum (fenugreek) is an important medicinal plant and its leaves and seeds have been used in various illnesses. This plant is widely distributed throughout the world and mainly found on the Asia. Fenugreek seeds contain active ingredients such as flavonoids, fiber, amino acids, hepatoprotective protection against free radicals, and protection against breast and colon cancer. Therefore, the aim of the present study was to investigate the effect of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed on growth of Staphylococcus aureus inoculated (10
³
CFU/g) in Cyprinus carpio fillet during storage in refrigerator (4˚C).
Material and methods: The fresh Common carp (Cyprrinus carpio) with average weight of 900 ± 50 g and average length of 30 cm were purchased from market (Zabol, South east of Iran) and transported in isothermal iceboxes to the fish product processing laboratory at University of Zabol. The fish were cleaned and filleted manually using a sterile scalp. Maximum acceptable concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed on the organoleptic properties of fillets was determined according to hedonic method. Fillet samples were randomly inoculated with Staphylococcus aureus (10
³
CFU/g) and then aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed were added to fillets according to: Treatement 1 (Ethanolic extract 1%), Treatement 2 (Aqueous extract 1%), Treatement 3 (Ethanolic extract 2.5%), Treatement 4 (Aqueous extract 2.5%), Treatement 5 (Ethanolic extract 4%), Treatement 6 (Aqueous extract 4%) and control (not treated with of Trigonella foenum-graecum (fenugreek) seed extract). Fish fillets individually packed in polyethylene packs and then stored in refrigerator (4˚C) for subsequent quality assessment. Chemical (pH, thiobarbituric acid (TBA) and total volatile basic nitrogen (TVB-N)) and microbial parameters (Staphylococcus aureus count, total viable counts (TVC) and psychrophilic viable count (PTC)) were measured at 0, 72, 144, 216 and 288 hours. All experiments were carried out in triplicate and the results are reported as the mean and standard deviation of these measurements. Data were analyzed using a one-way analysis of variance (ANOVA) with SPSS version 22 software. When differences were significant (P<0.05), the mean values were evaluated by Duncan's Multiple Range Test. Kruskal-Wallis test was used to sensory evaluation.
Results and discussion: In this study, the sensory evaluation was carried out to determine the maximum add concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed that had no negative effects on the sensory properties of common carp fillet. The results of sensory analysis showed that the overall acceptability of fillets containing 2.5% of aqueous and ethanolic extracts had better organoleptic properties. The growth rate of Staphylococcus aureus was significantly different between treatments and control during the experiment (without of the first 24 hours). All concentrations of extract were effective on the growth of Staphylococcus aureus inoculated in Cyprinus carpio fillet during storage. The Staphylococcus aureus count decreased with increasing the concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed during storage but the Staphylococcus aureus count increased in control. After 216 hours, the growth of Staphylococcus aureus was stopped in treatments containing high concentration extract. The 4% concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed were inhibited the Staphylococcus aureus growth after 216 and 288 hours respectively. The lowest number of TVC and PTC were observed in the fillet containing 4% of ethanolic extract of Trigonella foenum-graecum (fenugreek) seed. The shelf life of the control fillets was 216 hours while the treatments of 5 and 6 (4% concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed) were acceptable level after 288 hours. The TBA and TVB-N values of fillets gradually increased during storage but this increase was lower in treatments containing extract. The fillet containing 4% of ethanolic extract of Trigonella foenum-graecum (fenugreek) seed has lowest TBA and TVB-N values at the end of storage. Increasing the shelf life of fillets containing Trigonella foenum-graecum (fenugreek) seed extract can be due to the antibacterial and antioxidant properties of this plant seed.Trigonella foenum-graecum (fenugreek) seed extract is rich in polyphenolic flavonoids, which has antioxidant activity and can protect cellular structures from oxidative damage.
Conclusion: Aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed have been investigated as natural antimicrobial agents for food preservation. Based on the present study, the aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed improved the organoleptic properties and decreased the TBA and TVB-N values after treatment. High concentration of aqueous and ethanolic extracts of Trigonella foenum-graecum (fenugreek) seed greatly enhanced the shelf life of Cyprinus carpio fillets inoculated with Staphylococcus aureus during refrigerated storage. However, our results showed that ethanolic extract have more antibacterial properties than the aqueous extract and was more effective in slowing down the growth of bacteria. Thus, the use of ethanolic extract of Trigonella foenum-graecum (fenugreek) seed at concentration of 4% is recommended for increase the shelflife of Cyprinus carpio fillet during storage in refrigerator (4˚C).