| A traditional Chinese folk says: Overnight dead crabs equals to poison. Nevertheless, the underlying reason has never been reported previously. Comparing with other studies, the innovation of this study was the crab natural death, which closed to the real life of human. Quality of Chinese Mitten Crab(Eriocheir sinensis) at different stages including alive, 0, 2, 5, 10, 15 and 24 h after death was investigated by processing characteristics(death rate, meat yield, weight loss rate), sensory evaluation, chemical and microbiological(total-volatile basic nitrogen, volatile compounds, biogenic amine), microbiological( total viable count). The objective of this study was to find characteristic indexes that could be used to identify the Chinese mitten crab from alive to the early death. Specifically, this study could provide the theory basis(this might be more applicable) for quality and safety improvement.Studies have shown that female Chinese mitten crab keep-alive time was 10 days, for male of 7 days. Female crabs mortality rates were higher than male crab in the initial storage(1-6 days). The time to reached half of the death was 3 days and 6 days for female and male crab, respectively. The weight loss rate was increased with the increased of death of time, the crab weight loss rate steeply increase to 8.08% for female and 8.85% for male after 24 h after death. The edible parts yield of Chinese mitten crab decreased as the death length increase. The belly meat yield dropped suddenly after death(p < 0.05). Crab roe yield decreased dramatically to about 8.36% and 6.18% for crab paste in 24 h after death. Crab roe yield decreased at a larger rate than crab meat after 2 h death, which suggesting the degradation rate of crab roe was greater than that of crab meat.Sensory score decreased as the increase of death time. There was a perceivable odor produced after death 10 h and opened the crab shells the odor achieved acceptable limits after death 24 h. The p H value changed in volatility, compared with crab meat, the p H of crab roe almost no change. The change of p H value crab paste was not obviously compared with crab roe. This may be because of the more oil in crab roe, which prevent bacteria from entering the interior.The TVBN value was declined when 10 h after death and increased 15 h after death for female and male crab. The value were 31.39 mg N / 100 g(crab meat) and 28.85 mg N / 100 g(crab roe) for female crab and 18.95 mg N / 100 g(crab meat) and 29.87 mg N / 100 g(crab paste) for male crab. For all of this showed that TVBN was not a sensitive indicator in determining the extent of corruption in crustaceans. Biogenic amines were detected 5 h after dead for female crab and 10 h for male crab but the content of biogenic amines were low enough that cannot cause poisoning after dead 24 h.The high nutrients and loose connection between collagen fibers provide a rich environment for microbial growth, which lead the crab had very high background content, the initial TVC of 5.33 Log CFU/g for female crab and 6.06 Log CFU/g for male crab. The TVC increased faster from death 0 h, reached about 9 Log CFU/g at 10 h after death and about 10 Log CFU/g at 24 h after death.Sixteen amino acid were identified in crab meat, seventeen in crab roe and crab paste. The content of amino acid changed in volatility. The amino acid that umami and sweet were decreased(0-10 h after death) and then increased(10-24 h after death), however, the amino acid that bitter was increased(0-5 h after death) and then decreased(10-24 h after death).The content of hydrocarbons and aldehydes more than 93% of the overall odor of volatile compounds, dodecane, 2,6,10,14-tetramethyl-pentadecane, Tridecane were the mainly compounds of hydrocarbons and Nonanal, Hexadecanal were the mainly compound of aldehydes. With the increase of death time, the content of hydrocarbons were decreased, the aldehydes changed in volatility. Low content of ketone and alcohol were identified. The content of TMA was sharply increased as the increase of death time, which leaded to sensory odor value declined rapidly. The content of TMA crab meat increased faster than crab roe and crab paste with the increasing of death time. The TMA was 8.33 μg/g(female) and 6.94 μg/g(male) for crab meat, 2.24 μg/g(crab roe) and 6.94 μg/g(crab paste) at 24 h after death. S-containing compounds of irritating odor were identified at 5 h after death, agreed with smell reported in sensory evaluation.The above results demonstrated indicate that the crab of 10 h after death entered putrefaction stage thus not suitable for consumption. |
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