| Soy isoflavones have high nutritional value,and are widely used in livestock and poultry feed and food industries,but the isoflavone glycosides contained in them are difficult to be digested and absorbed by animal body.This study started with the bioconversion of soybean isoflavone glycosides by β-glucosidase,and we used high performance liquid chromatography,liquid culture and other methods to explore the optimization of fermentation conditions for β-glucosidase produced by Aspergillus niger ACCC 32589,and the hydrolysis of soybean isoflavone in soybean meal by β-glucosidase.The optimal parameters of flavonoids were applied in the breeding of local chickens to define the effect of adding β-glucosidase in the diet on the quality of local chickens,from growth performance,slaughter performance,internal organs,meat quality and antioxidant properties,etc.The effect and mechanism of β-glucosidase were discussed.The result is as follows:1.Optimization of fermentation conditions for the production of β-glucosidase:Using A.niger ACCC 32589 as the starting strain,the liquid fermentation conditions for the production of β-glucosidase were optimized.Single factor experiments such as carbon source type and content,nitrogen source type and content,temperature,p H,shaker rotation speed,inoculum amount,and liquid filling amount were carried out respectively.The Plackett-Burman experimental design was used to screen out the four factors that had the greatest impact on the results of enzyme production.Then,through the optimization method of Box-Behnken test design,the β-glucosidase activity produced was used as the response value to establish a mathematical model.The optimal fermentation conditions were obtained: the temperature was 30 ℃,the carbon source concentration was 3.5%,the inoculum amount was 6%,and the p H was5.After optimization,the resulting enzyme activity was 41.57 U/m L.2.Optimization of the hydrolysis conditions of soybean isoflavones in soybean meal by β-glucosidase: β-glucosidase produced by A.niger ACCC 32589 was added to the soybean meal of commercial local chickens diet,and the influence of temperature,enzyme addition,p H,enzymatic hydrolysis time on enzymatic hydrolysis was judged by the glycoside conversion rate.The single-factor experiments of temperature,enzyme addition,p H,and enzymatic hydrolysis time were carried out respectively,and then the Box-Behnken experiment was used to design the optimization scheme.The mathematical model was established,and the optimal hydrolysis conditions were obtained: the temperature was 50 ℃,the p H was5,the enzyme concentration was 1 U/m L,and the time was 3.5 h,the conversion rate was 94.82% after optimization.3.The effect of β-glucosidase on the quality of local chickens: 160 21-day-old local chickens with the same body weight were selected and divided into 4 groups with 40 birds in each group,CK,T1,T2,T3,and CK were fed with ordinary diets,and the soybean meal in the three experimental treatment groups was 1/3,2/3,and 3/3of the enzyme-added soybean meal(Soybean meal that has been hydrolyzed by β-glucosidase)was replaced.The effect of the enzyme on the growth of Wunong local chickens was studied and its mechanism was discussed.The results showed that: 1)During the feeding process of adding β-glucosidase to the diet,the Wunong local chickens in each group grew well,no individual died,the mental state was good,and the feathers were shiny.Compared with CK,the body weight of each experimental group was increased,and the daily weight gain of T2 increased by 11.15%(P<0.05),while that of T1 and T3 showed an increasing trend(P>0.05).There was no significant difference in the daily feed intake among all treatment groups,but the feed-to-weight ratio changed significantly.The above results indicated that the addition of β-glucosidase to the diet could improve the growth performance of Wunong local chickens,and the best effect was to replace ordinary soybean meal with 2/3 enzyme-added soybean meal.2)In the slaughter rate,shin length and other slaughter indicators,there is no significant difference in the data among CK,T1,T2,T3,indicating that the addition of β-glucosidase in the diet had no obvious effect on the body composition and skeletal development of Wunong local chickens.There was no significant difference in heart weight and heart index of Wunong local chickens under different treatments.Compared with CK,liver weight and liver index of T1,T2,and T3 decreased(P>0.05).The addition of β-glucosidase in the diet can significantly shorten the cecum length of Wunong chickens,and the shortening range is T3>T2>T1.3)The breast muscles and leg muscles of Wunong local chickens showed similar trends in various meat quality indicators.In the three indicators of yellowness,p H value and moisture content,there was no significant difference among the experimental group and the control group,and the rest of the indicators were significantly different,among which the change range of T2 was the most obvious.Compared with CK,the brightness of chest and leg muscles in each experimental group decreased,the redness increased,and the shear force decreased,indicating that β-glucosidase significantly improved the meat color and tenderness of chicken muscles.Compared with CK,the drip loss rate of the experimental group decreased,indicating that the improvement of soybean isoflavone absorption rate can slow down muscle water loss.In addition,each experimental group also showed an increase in crude protein content,indicating that the muscle nutritional content had been improved.4)Among the four serum antioxidant indexes,there were significant differences among the treatment groups.β-glucosidase had a significant effect on improving the superoxide dismutase,glutathione peroxidase and total antioxidant capacity in the serum of Wunong local chickens.Besides,the MDA content was significantly decreased.It can be inferred that the improvement of soybean isoflavone absorption rate has a significant effect on improving the antioxidant capacity of Wunong local chickens.To sum up,this study confirmed that the addition of β-glucosidase in the diet can have a positive effect on Wunong local chickens,and replacing ordinary soybean meal with 2/3 enzyme-added soybean meal had the most significant effect,which can effectively better the growth performance of Wunong local chickens,improve the feed utilization rate of them,and significantly promote the improvement of their quality and nutrients.It can also significantly enhance the antioxidant capacity of chickens. |
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