Study On Nutrition And Flavor Components Of Three Kinds Of Sea Crabs

Sea crabs are popular for its delicious taste and high nutritional value. Recently, overfishing of Portunus trituberculatus which is a representative of crabs with high economic value leads to the decline of its annual production, however, crab with relative low economic value but rich natural resources such as Ovalipes punctatus and Japenese stone crab are still under-development. In this study, differences of nutrition and flavor compositon between Ovalipes punctatus, Japenese stone crab and Portunus trituberculatus were analyzed in order to providing theoretical data for improving the utilization and processing techniques of low economic value crabs.Initially, nutrients of three kinds of sea crabs were analyzed. The results showed that Ovalipes punctatus had the highest amino essential acids index value(149), followed with Portunus trituberculatus(137), while the ratio of branched chain amino acid/aromatic amino acid in three kinds of sea crabs shared the same correlation. Except for Ovalipes punctatus, the percentages of polyunsaturated fatty acids in other two kinds of sea crabs were above50%, while EPA and DHA account for90%. Ovalipes punctatus had the highest percentage of polyunsaturated fatty acids and its incidence of coronary heart disease, atherogenic(AI) and thrombogenic(TI) indices were the lowest. All crabs were rich in elements (e.g. Cu, Ca and Zn), and the mineral content of Ovalipes punctatus and Japenese stone were slightly lower than Portunus trituberculatus. All the results indicated that Ovalipes punctatus and Japenese stone crab had high nutritional value.Secondly, non-volatile flavor substances of three kinds of sea crabs were studied and their taste impacts were evaluated by taste active value(TAV). The resluts suggested that argine, histidine, glycien, glutamic acid and alanine were of high TAV(greater than one) in three kinds of sea crabs. Glycine betaine, oxidation thrimethylamine and inorganic ions, K+, Na+and Cl-had important contribution to taste of sea crabs. The taste profile characteristics of Portunus trituberculatus were IMP, AMP and lactic acid, while both of Japenese stone crab and Ovalipes punctatus were GMP and AMP. The equivalent umami concentration(EUC) of Portunus trituberculatus was the highest(15.45gMSG/100g), followed by Japenese stone crab(10.33gMSG/100g). Sensory evalution showed that lactic acid, glutamic acid and IMP with particularly high content in Portunus trituberculatus might made the taste superior to that of the other two kinds of sea crabs.A combination sampling method of SPME and SDE was applied to study volatiles of three kinds of sea crabs completely. The single factor experiment and orthogonal test were designed to optimize the condition of headspace solid-phase microextraction(SPME) and steam distillation extraction(SDE). The optimum conditions of SPME were as follows:CAR/DVB,4g sample, extraction temperature of65℃, extraction time of40min, desorption time of4min, and addition of NaCl of0.16g. The optimum conditions of SDE were as below:ether dosage of50ml, ratio of material and liquid of1:4, and distillation time of180min.Volatiles of three kinds of sea crabs were analyzed by GC-MS. Meanwhile, volatiles were identified by a combination of mass spectrometry and retention indices. A total of83kinds of volatiles were identified, and aldehydes, alcohols, aromatic, esters and ketones were the main flavor substance. The study of main fragrance compounds of three sea crabs was statistically interpteted by a combination data-processing method including principal component analysis(PCA) and relative aroma activity value(ROAV). The following15kinds of compounds were main fragrance compounds of Portunus trituberculatus, including octanal, nonanal, decanal, heptanal, hexanal,2-acetyl thiazole, etc; Japenese stone crab had16kinds of main fragrance compounds, including octanal, nonanal, decanal. phenylacetaldehyde,2-kwai olefinic aldehyde,2-kwai ketone, etc; Ovalipes punctatus had12kinds of main fragrance compounds, including octanal, nonanal, decanal,3-methyl butyl aldehyde, dibutyl phthalate,3-kwai ketone, etc. Among them, octanal, nonanal, decanal, heptanal, hexanal,2-acetyl thiazole and undecanal were common main aroma substances in three kinds of sea crab.