Effect Of Afalfa Saponins On The Meat Color And Its Mechanism Of Sheep

Lamb meat color is one of the most important trait to estimate meat quality.A bright and stable red meat color always indicates the reduction of met-myoglobin for meat,which will appeal consumers’decision.Fifty Hu male lambs were chosen to study the effect of alfalfa saponins(AS)supplementation in diet on growth performance and meat color,which were assigned to five groups with 10 lambs in each group in a completely randomized design.Different diets were offered at a 50:50 forage to concentrate ratio in which different amounts of AS were provided(0,500,1000,2000,or 4000 mg/kg of dry matter intake),which marked as CON,ASI,ASII,ASIII,and ASIV groups,respectively.Diets were offered for a period of 90 days(three months).After 90 days,all lambs were slaughtered.Relent samples including rumen fluid,Longissimus thoracis muscle and liver were acquired from lamb.Part One Effect of dietary AS supplementation for growth performances,carcass traits and color in muscle of lambs.Exp.1.Effect of AS supplemented in diet on growth performance of lambs.The results showed that,final body weight differed among all groups during the initial and final months(P<0.05)respectively.However,no detectable effects of AS treatment on average daily gain or feed conversion ratio(P<0.05)were found.Nutrient digestibility increased with AS dose,especially the digestibility of dry matter,crude protein,and acid detergent fiber(P<0.05).No significant differences were found among treatments for all body measurement indexes and serum hormones.Serum glucose and alanine transaminase(ALT)levels decreased with increasing AS dose(P<0.05).These results indicated that AS plays an important role for increasing nutrient digestibility.Exp.2.Effect of AS on carcass traits and meat quality.Net meat weight,carcass weight were significantly increased by AS treatment in the aspect of carcass traits(P<0.05).For the meat quality traits,the AS supplementation significantly lowed the content of intramuscular fat in muscle(P<0.05).The concentrations of n-3 PUFAs and EPA were increased significantly(P<0.05).AS supplementation decreased the level of drip loss(P<0.05).In a conclusion,AS could be treated as an additive for sheep to improve the meat quality,modifying the fatty acids profiles.Exp.3.Effect of AS on meat color and myoglobins percentages in Longissimus dorsi muscle,AS dosage increased,the lightness(L*)and redness(a*)were linearly increased coupled with decreased MetMb%and greater OxyMb%(P<0.05).After 7 day storage in 4℃,redness(a*)and chrome(C*)were quadratic increased coupled with reduced MetMb%(P<0.05).The total color difference(Δ E)between the interval was decreased as AS improved,which suggested a stabilized meat color during storage.Redness had a linear and negative correlation with MetMb%,(P<0.05,R2>0.9).Since that,dietary AS supplementation made lamb meat a more saturated red for consumers.The meat color improvement contributed to the reduced MetMb%.Part Two The mechanism of meat color improvement by AS dietary supplementationExp.4.Effect of AS on rumen fermatentation and microflora.The results showed that rumen pH,content of acetic acid was impacted(P<0.05).Based the high-thoughtout sequcing for rumen microflora(bacteria),the proportion of the Bacteroidetes was increased by AS supplementation.More functional genes related with energy metabolism,cell mobility and membrane transport were found attributed AS supplementation for rumen bacteria.Then we could explore the mechanism which may related to meat color in the next Experiments..Exp.5.Effect of AS on lipid metabolism and anti-oxidation traits in plasma,muscle and liver.The AS supplementation significantly improved anti-oxidiation levels including CAT,T-AOC and SOD in muscle.It was up-regulated SOD2 gene in muscle.In addition,the AS supplementation significantly reduced the content of TG and LDL-c in liver and plasma.The up-regulated LDLR and PPARR genes in liver suggested AS played a key role in lipid metabolism.Therefore,the elevated anti-oxdiated enzymes in muscle may have great corrections with meat color.Exp.6.Effect of AS on mitochondria metabolism in muscle.We found the improved Met-Mb reducing activity and up-regulated NADHB5R gene in muscle,which explained reducation of myoglobin directly by NADH-Ctb5 system.Meanwhile,the significant elevated enzymes including SDH,LDH,and COX and up-regulated COX2 gene suggested AS acted as accelerator in energy metabolism(P<0.05).The evidence of increased ATPase(Na+ K+ ATPase,Mg2+ ATPase,P<0.05)accelerated an energy metabolism.Based on the results,AS has great function for reduction in myoglobin.In summary,AS supplementation in diet had no effects on growth traits of lambs.However,the meat quality,especially the meat color,was improved by AS.AS supplementation provided a more saturated red for consumers,which attributed to reduced MetMb(dark-brown color)percentage.The possible reason of meat quality improvement may be as following:Alfalfa saponins wound up-regulate the genes related with energy metabolism,cell mobility,and membrane transport,which indicated that AS have a function of anti-oxdiation and energy metabolism trait for lamb meat color.It is proved that AS supplementation improved the activities of anti-oxidation and mitochondria enzymes in muscle,protecting mitochondria function,accelerating the rate of energy metabolism,prompting the MRA in electron transfer chain,converting the dark-brown MetMb to cherry-red OxyMb,improving meat color.We suggested 1000 to 2000 mg/kg DMI of AS supplementation as an optimum dosage.