Optimization Of Solid-state Fermentation Of Rhodotorula Mucilaginosa And Its Effects On Eggs Quality And Immune Function Of Laying Hens

This study aimed to determine the optimal fermentation substrates and conditions to enhance the efficiency of carotenoid production in Rhodotorula mucilaginosa TZR2014.The study also examined the effects of R.mucilaginosa fermentation products(RMFP)on the production performance,egg quality,intestinal digestive enzymes,gut microflora,and plasma and liver biochemical indices of laying hens.Optimization of fermentation process.First,the Design-Expert software was used to optimize the design of the fermentation substrates.Then the optimal substrate ratio was determined using carotenoids yield,based on which an orthogonal design was used to optimize the design of the inoculum dose,water content,fermentation temperature,pH,and fermentation time.Thereafter,the optimal fermentation conditions for carotenoid production by R.mucilaginosa were determined based on the experimental results.The optimal ratio of solid fermentation substrates for R.mucilaginosa was 52.5% wheat bran,20.0% soybean meal,3.0% corn flour,14.0% rice bran,10.0% corn syrup,0.4% ammonium sulfate,0.05% monopotassium phosphate,and 0.04% magnesium sulfate.The optimal fermentation conditions were as follows: an inoculum dose of 5.0%,fermentation time of 72.0 h,fermentation temperature of 28.0°C,pH 6.0,and water content of 60.0%.After optimization of the fermentation process,carotenoids yield increased to 4535 ?g/kg and crude protein after fermentation increased by 9.7%.Animal experiments.Two hundred and sixteen 40-week-old roman laying hens with normal physical condition and similar weight were selected and randomly separated into four treatment groups.Each group had 3 replicates of 18 hens.Four groups were fed with a diet of 87.5% basal diet + 12.5% fermentation substrates(CON),87.5% basal diet + 12.0% fermentation substrates + 0.5% RMFP(0.5% RMFP),87.5% basal diet + 10.0% fermentation substrates + 2.5% RMFP(2.5% RMFP),87.5% basal diet + 12.5% RMFP(12.5% RMFP),respectively.The experimental period was 31 d with a pre-test period of 3 d.The results showed that adding RMFP to the basal diet significantly improved the feed intake and egg weight of laying hens(P<0.05),and increased the carotenoid content in the egg yolk(P<0.05).Adding RMFP into the basal diet also significantly improved the levels of immunoglobulin A(IgA),immunoglobulin G(IgG),and globulin in chicken plasma(P<0.05).This nutritional regulation significantly reduced malondialdehyde(MDA)levels in chicken plasma,and significantly improved the total antioxidant capacity(T-AOC)and catalase(CAT)activity in the plasma and liver(P<0.05).RMFP significantly increased chymotrypsin activity in the duodenal and jejunal chymes(P<0.05).Adding RMFP also significantly increased the amount of beneficial gut microflora(e.g.,Methanocorpusculum,Clostridium,and Ruminococcus)and reduced the amount of harmful gut microflora(e.g.,Lachnospira and Helicobacter).In summary,optimization of the fermentation process significantly increased carotenoid yield in R.mucilaginosa.Adding RMFP of 12.5% to the basal diet significantly enhanced the performance of laying hens,and improved the egg quality to a certain extent.RMFP also had a positive regulatory effect on the T-AOC,immunity,and gut microflora of laying hens.