| The quality attributes of fresh meat include meat colour,tenderness,water-holding capacity,flavor,juicy,etc,among which meat colour is a very important attribute of them.The good meat colour can attract the attention of consumers and promote sales.The spoilage of meat colour leads to product rejection and causes economic losses to meat industry.More than one billion dollars in revenue loss was caused by deterioration of the meat colour in meat industry every year.Therefore performing the research of this aspect has very important theoretical and practical meaning.The basic reason for the deterioration of meat colour is the accumulation of metmyoglobin,therefore the reduction of metmyoglobin is one of the most important factors affecting the stability of meat colour after slaughter.NADH is the ultimate source of reducing equivalents in the reduction of metmyoglobin,and previous studies showed that lactate dehydrogenase-B(LDH-B)can play an important role in maintaining the stabilization of meat colour during the postmortem,which is mainly through promoting the regeneration of NADH in meat to enhance colour stability.The formation of NADH was originally catalyzed by glycerol-aldehyde-3-phosphate dehydrogenase(GAPDH)in glycolysis.However,the activity of GAPDH how to affect the postmortem meat colour stability is unknown,and this study takes GAPDH as the main research object,to explore the effect of the dehydrogenase in glycolysis on the meat colour stability after slaughter,and four parts of the test were carried out in the study.Firstly,the relationship between the colour stability of muscles from different sources and the activity of dehydrogenase enzymes in glycolysis was analyzed.Longissimus dorsi(LD),semimembranosus(SM),and psoas major(PM)muscles were collected from ten Bayan Nur mutton sheep with similar weight in the first experiment and stored at 4?.The colour,p H value,NADH content,activity of GAPDH and LDHB and other biochemistry parameters were determined.Secondly,the aim of this part was to explore the activity of dehydrogenase enzymes in glycolysis of the muscle from same source with different colour stability.Sixty Bayan Nur mutton sheep which were raised in the same environment were used in this experiment.From 60 sheep,15 LDs muscles were selected on the basis of colour stability(R630/580 and a* value)during the storage and classified into three groups(5 for one group)as high colour stability(HCS),intermediate colour stability(ICS)and low colour stability(LCS).The activity of GAPDH and LDH-B,NADH and lactate content,and other biochemistry parameters were determined.Thirdly,the aim of this part was to explore the effect of inhibition of GAPDH activity on the colour stability of mutton.10 LDs of Bayan Nur mutton sheep were collected,and each LD was divided into 3 same weight parts for the experiment.In this study,ground fresh lamb was added with or without GAPDH or sodium iodoaceate(a GAPDH inhibitor),distilled water as control.And they were named as the GAPDH inhibited group(GIG),GAPDH added group(GAG)and control group(CON).The samples were stored at 4 ? for 9 days,and the meat colour(CIE L*,a*,and b*),GAPDH,NADH,and other biochemical attributes in meat were measured during storage.Fourthly,the orthotropic and in vitro model were used to verify the regulation effect of GAPDH activity on meat colour stability.In the orthotropic model,the substrate of GAPDH(GAP)was added to the minced mutton,and the sample colour value was determined;in vitro model,the myocardial mitochondria which was extracted from sheep heart,were incubated with GAPDH,GAP and Metmyoglobin,the proportion of metmyoglobin in the incubation system and oxygen consumption rate were determined.The main results were as follows:(1)The a* value of LD was higher than 11 and the R630/580 value was higher than 2.3,the a* and R630/580 values of LD were higher than that of PM during the storage from day 3 to 7;the colour stability of LD was higher than PM during storage,and the content of NADH in LD was more than 80 ug/g,and it was significantly higher than that of the PM(P < 0.05),and the activity of GAPDH and LDH-B in glycolysis was different in muscles from different source,and the activity of GAPDH in LD and SM was more than 7 U/g,and it was higher than that of the PM.Yet,the LDH-B activity of PM was more 3 mu mol/min/g,and it was higher than LD and SM.(2)The a* value of sample in HCS group was higher than 12,and the R630/580 value was higher than 2.5,and they were all higher than the other two groups during the storage from day 2 to 8.The GAPDH activity of the sample in HCS group was above 7 U/g,which was higher than the sample from ICS and LCS group,and the LDHB activity was also higher than that of the LCS group at most of the storage.The NADH content in the samples of HCS and ICS was above 30 nmol/g,which was higher than that of the LCS group.(3)The activity of GAPDH in the sample from HIG group was below 4 U/g,and it was significantly lower than the other two groups(P < 0.05).However,the R630/580,a*,pyruvate content and p H value of the sample in HIG group were significantly higher than that of the other two groups,and the content of NADH and lactate was significantly lower than that of the other two groups.The results showed that the colour stability of sample in GIG group was significantly higher than the samples in the other two groups.(4)The results of in situ model showed that the colour stability of mutton samples was significantly increased by adding GAP,and the a* value of sample in 0.05%GAP addition group was above 10.90,and the content of NADH was above 70 ug/g GAP.The results of in vitro model showed that the incubation of mitochondria with GAPDH,GAP and metmyoglobin reduced the proportion of metmyoglobin in the incubation system significantly,and increased the oxygen consumption rate of the reaction system.Based on the above research results,the following conclusions can be drawn.Both GAPDH and LDH-B can influence the colour stability of fresh meat.First of all,the GAPDH activity and NADH content of LD and SM in the muscles of different parts were higher than those in the PM,while the activity of LDH-B was lower than that of PM.Secondly,muscle with different colour stability from the same source has different activity of dehydrogenase enzymes in glycolysis.The sample in the HCS group possessed higher activity of GAPDH and LDH-B than the sample from the LCS group.Thirdly,the inhibition of GAPDH activity significantly increased the a* value of the sample,which was mainly due to inhibition of GAPDH activity significantly improved the p H value of the sample,and the higher p H value prevented the myoglobin from oxidation.Finally,the orthotropic model and in vitro model,we confirmed that the NADH produced by the GAPDH activity can be directly applied to the reduction of metmyoglobin. |
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