| The contents of active ingredients and hazardous substances in the residues of Cordyceps militaris culture medium ( hereafter be shorted as residual culture medium) were determined in the research, and the safety and feasibility of incorporating residual culture medium into feed as additive for the Chinese mitten crab (Eriocheir sinensis) were assessed. The effects of residual culture mediuem on growth performance, non-specific immunity, conventional body composition, the amino acid compositions of muscle and serum, and the fatty acid of hepatopancreas were elucidated. Based on this, the optimal supplementation levels of residual culure medium in basal diet of the Chinese mitten crab were identified.As a reference to Cordyceps militaris, the content of ingredients and amino acids of residual culture media from different dry methods were compared, and the safety of residual culture medium was analysed. The results were shown as follows: 1) Uniform particles, less than 100μm in diameter, formed from residual culture medium after processed with freezing and desiccation technology, and crushed in high-speed airflow ultra-mizer; 2) The percentage content of cordycepin, cordycepic acid, adenosine and crude polysaccharide, the SOD activity and organic calcium in residual culture medium micro-powder were 0.07%, 13.1%, 0.01%, 29.6%, 290 IU/g, 170.8 mg/kg, respectively, that were 33.3%, 89.7%, 12.5%, 400.0%, 39.0% and 50.8% in fruting bodies of Cordyceps militaris, respectively. The content of essential amino acids of the residual culture media was 3.77g/100g, contributed to 43.84% of the total amino acids, which was higher than that in fruiting bodies; 3) The content of heavy metals, residue pesticides and aflatoxin B1(AFB-1) in the residual culture medium were couformed to the national standard of threshold limit values for safe pollution-free food free-pollution food, fishery formula feed (NY 5072-2002). Eight sets of feed were designed by incorporating residual culture medium into basal diet at 0.25%, 0.5%, 1.0%, 2.0%, 4.0%, 8.0% and 16.0%, respectively, to feed Chinese mitten crab (Eriocheir sinensis) with 4.0±1.0 g in weight for 75 d, and to determine the growth performance and non-specific immunity, and thereafter to identify the optimal supplementation levels of residual culture medium in basal diet of Chinese mitten crab. Overall, by comparison with that of diet-fed group, the results were shown as follows: 1) Significant increases (P<0.05) in weight gain ratio (WGR), condition factor (CF) and survival ratio (SR), and significant decreases (P<0.05) in feed coefficient (FC) occurred when residual culture medium was added at 0.5% or 1.0%, while supplementations at 4.0%, 8.0% and 16.0% caused poor growth performance except that condition factor (CF) slightly increased; 2) Lower supplementation levels were found to modify the activities of superoxide dismutase (SOD), lysozyme (LSZ), acid phosphatase (ACP), alkaline phosphatase (ALP) in Chinese mitten crab serum and hepatopancreas, and significant activity enhancement of all these enzymes were obtained by addition at 0.5% or 1.0% (P<0.05), while addition dosage higher than 2.0% lead to worse non-specific immunity; 3) The bacterial challenge test by injection with Aeromonas hydrophila AHJ-1 confirmed that the immune protection rates of treatment groups increased significantly, and the highest rate at 100% occurred when residual culture medium was supplemented at 0.5%.The conventional body components, the contents of amino acids in muscle and/or serum, and the contents of fatty acids in hepatopancreas were determined. By comparison with that of diet-fed group, the results were shown as follows: 1) There was no obvious effect on moisture and crude protein of Chinese mitten crab, but lipid content of body, muscle and hepatopancreas increased, and significant increases occurred when residual culture medium was added at 0.5% or 1.0%(P<0.05); 2) Significant content enhancement of amino acids and flavor amino acids in serum were obtained by addition at 1.0% or 16.0%(P<0.05), but no significant effect was found in muscle; 3) Significant increases in the content of unsaturated and essential fatty acids of hepatopancreas occurred when residual culture medium was added at 1.0%(P<0.05), other groups increased accordingly. The result indicated that the addition of residual culture medium to basal diet could increase the essential amino acids level in serum, unsaturated and essential fatty acids in hepatopancreas, and improve the quality of Chinese mitten crab. Results from above culturing experimentation proved that the optimal supplementation levels of residual culture medium for feeding Chinese mitten crab ranged from 0.5% to 1.0%.Result from pond culture experiment showed that supplementing residual culture medium into basal diet at 0.3% and 0.5%, respectively, caused individual weight gain by 4~5 g, improved survival ratio by 14.7% (from 50.2% to 57.6%), increased yield by 18.6% (from 86 kg/667m2 to 102 kg/667m2).In conclusion, the residual culture medium contained a higher level of active ingredients, and promoted the growth performance of Chinese mitten crab. It is concluded that the residual culture medium could be safely and reliably employed as feed additive for Chinese mitten crab. |
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