Effect Of Green Tea Polyphenols On The Quality Of Carp (Cyprinus Carpio L.) And Catfish (Clarias Gariepinus) During Storage

Fish is a very important foodstuff, due to its high protein content and nutritional value. It is also a greatly perishable product, especially in hot climates and tropical areas where cold preservation techniques are often missing and quality losses can occur very rapidly after catch. Addition of antioxidants during storage or processing can be used to inhibit lipid oxidation, protein denaturation and microbial and insect infestation. However, questions regarding the safety of synthetic antioxidants together with consumer's preference have led to increased interest and research on natural antioxidants. Consumers favor natural antioxidants, which may have a positive effect on human health.In this study, the total phenolics contents, antioxidant capacities of green tea were assessed by the total phenolics assay, the 2,2-diphenyl-1-picrylhydrazyl (DPPH·) scavenging (RSA) method and the reducing power assay. For extraction of green tea polyphenol (GTP) and Malian black tea polyphenol (MBTP), different extraction solvents were used to identify the best extraction solvent. The effect of different extraction parameters on the extraction yield was also observed. Ethanol was the solvent of choice and the total polyphenol extraction yield when using 80% ethanol solution was respectively 126.58±2.58 (mg/g) for GT and 96.2±1.25 (mg/g) for MBT. These were significantly higher (P < 0.05) than 80% methanol 98.48±0.7 mg/g, 64.25±1.08 mg/g and 45.42±0.72 mg/g, 31.3±0.53 mg/g for hot water extraction methods.The stronger antioxidant capacity of tea polyphenol (TP) is due to the presence of phenolic compounds, such as catechins in its composition. The catechin content in green tea solution was 21.39% and 8.22% for MBT. GTP showed greater RSA 68.45% on the stable DPPH~·free radically when compared with the extract of MBTP 62.13% which contained the lowest amount of polyphenolics and VC 28.28%.For refrigerated carp (Cyprinids carpio L.) and catfish (Clarias gariepinus), the antioxidant activities of crude GTP, physico-chemical, sensory and microbiological changes were investigated.Each fish was trimmed to remove scales, head, fins, tail, viscera, bones, visible fat, and skin, and treated with different concentrations of GTP 0.01%, 0.03%, 0.05% and 0.01% of vitamin C (VC) respectively. Control muscle sample (CK) did not contain any antioxidant. Physico-chemical, sensory and microbiological changes were evaluated over a course of 9 days and using a 3-days periodical interval analysis. Carp minced fillet containing 0.03% GTP showed the best characteristics (p<0.05) in relation to oxidative stability, protein denaturation, microbial growth and sensory evaluation. For catfish, 0.05% GTP concentration was more effective in delaying lipid oxidation and biochemical characteristics, when compared with the control CK and others treated samples except microbiological changes where 0.03%GTP inhibition effect was greater than 0.05%GTP treatment sample. However, minced fillet treated with 0.01% VC was less effective than 0.01% GTP treated sample in reducing lipid oxidation. When compared the effect of GTP on carp and catfish. The inhibition activity on the carp fillet was higher than that of catfish for all parameters except microbiological change during refrigerated storage because Catfish contained relatively high fat percentages than carp, which generally favour oxidation susceptibility.The fatty fish is not only rich in lipids susceptible to oxidation but it contains also pro-oxidant substances in significant quantities. These substances are prooxidative transition metals, heme proteins and enzymes (lipoxygenases, cyclo-oxygenase). They are present in muscle and induce lipid oxidationThe effect of adding laboratory extracted crude green tea polyphenol GTP1, commercial crude green tea polyphenol GTP2 and VC respectively on the susceptibility of dried carp and catfish quality changes during ambient storage was also investigated. Fish fillets were treated with different concentrations of GTP1 and GTP2 respectively: 1% NaCl plus 0.01%GTP; 1% NaCl plus 0.03%GTP and 1% NaCl plus 0.01% of VC before drying process. Control muscle sample (CK) contained only 1% NaCl (without GTP). Samples were oven dried for 5-day at 45℃. The quality change was evaluated over a course of 4 weeks for pH, volatile basis nitrogen (VBN), peroxide value (POV), thiobarbituric acid reactive substances (TBARS), free fatty acid (FFA), fatty acid (FA) and sensory change. The results indicated that the most effective antioxidant was GTP and there were no significant differences (P < 0.01) between GTP1 and GTP2. 0.03% of GTP2 and GTP1 inhibition values were significant higher (P < 0.05) when compared with VC, CK and 0.01% of GTP1 and GTP2. The lower inhibition effect of CK and VC treatment samples may be due to the pro-oxidant effect of NaCl. CK was prepared only with added NaCl, and salting is known to increase the pro-oxidant activity of iron in myofibrillar foods, and VC can also act as a pro-oxidant even in the absence of transition metal ions.Like the refrigerated storage, the quality parameters for dried carp fillet were also better than those of catfish and the water loose during drying process were between 81% from the beginning of drying process to 8% at the end for carp and 69% for catfish from the beginning to 10% at the end of the process.The study of both refrigerated and dried carp and catfish suggests that GTP is a good natural antioxidant. The antioxidant activity of GTP is due to the presence of polyphenolic compounds in its composition. The most frequent are catechins and the most important of the catechins are epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC). EGCG is thought to be the main active ingredient and primarily responsible for the green tea effect. EGCG possesses two triphenolic groups in its structure, which are reported to be important for its stronger activity.After drying process, the percent of fatty acid (PUFA) decreased for both carp and catfish. The difference between raw and dried carp and catfish polyunsaturated fatty acid amount may be due that during the drying process, polyunsaturated fatty acids have been oxidize because the presence of a high proportion of PUFA in fish lipids makes them particularly susceptible to peroxidative damage. Chemical breakdown of protein, fat and water contents contribute to quick spoilage of fish. Storage period should be kept to a minimum with adequate storage conditions provided so as to prevent deteriorative changes occurring through oxidative damage and microbial spoilage.One important factor has been noticed during the storage period in the changes of pH values for refrigerated and dried fish. The pH increased during refrigeration storage but decreased during ambient storage of dried fish. The difference might be due that PUFA witch are responsible to lipid oxidation, values decreased during drying process when compare their values to the raw fish. Their proteolysis may have produced nitrogenous compounds witch may caused the decrease of pH values for the first week of dried fish storage. The further decrease of pH is due to the fact that carbohydrates of dried fish were fermented to acid.In summary, this study demonstrated that GTP improves carp and catfish fillet quality during storage by preventing lipid oxidation, inhibiting protein denaturation and bacterial growth. In food industry, it can be used as alternatives to the synthetic antioxidants because use of these types of antioxidants is controlled nonetheless due to their carcinogenic potential.