Effect of phenolic nonprotein amino acid L-dopa (L-3,4-dihydroxyphenylalanine) on growth performance, metabolic rates and feed nutrient utilization of common carp (Cyprinus carpio L.)

Two experiments (I and II) were conducted to evaluate the effect of nonprotein phenolic amino acid, L ‐dopa (L ‐3,4‐dihydroxyphenylalanine) on growth, metabolism and feed assimilation of common carp. Six isonitrogenous and isoenergetic diets (diets 1–6 containing 0, 2.5, 7.0, 14, 28 and 56 g kg^–1L ‐dopa, respectively) were prepared by replacing wheat meal in the feed with L ‐dopa. For experiment I (8‐week duration), each treatment had two replicates with five fish each per replicate (mean initial body mass of 13.4 ± 1.0 g), whereas five groups of carp, each consisting of three fish, individually kept in respiration chambers, giving three replicates per treatment with a mean body mass of 25.0 ± 1.8 g were used for experiment II (4‐week duration). Fish were fed six times their maintenance ration daily (3.2 g feed kg^–0.8 day^–1). No fish died during either experiment. In experiment I, the growth rate, feed conversion ratio (FCR), protein efficiency ratio (PER) and apparent net protein utilization (ANPU) of carp fed diets 1, 2 and 3 were similar but they were significantly (P < 0.05) higher than those in dietary groups 4, 5 and 6. However, no significant differences were observed with regard to body composition (moisture, protein, lipid, ash and energy contents) between control (1) and the diets 2, 3, 4 and 5. Fish fed diet 6 had reduced lipid and energy contents (P < 0.05) when compared with other dietary groups. In experiment II, L ‐dopa significantly increased the oxygen consumption per unit body weight gain in treatments 4, 5 and 6. The average metabolic rate also tended to be higher in these groups. The energy expenditure was similar in treatment groups, but the energy retention was significantly lower and energy dissipated significantly higher in dietary groups 4, 5 and 6. The cholesterol level in blood plasma between the control and L ‐dopa containing diets was not significantly different. It may be concluded that at higher inclusion rates (>7 g kg^–1) L ‐dopa appears to be a major antinutrient and hence the protein sources of plant origin, containing high amounts of L ‐dopa (i.e. mucuna beans) should be used with caution as fish meal substitutes in carp diets.     

对不同品种蚕豆芽苗菜生长期内产量、品质及相关性的研究

为选出品质较好,特别是左旋多巴产量较高的蚕豆以及最适的芽苗菜采收期,选择‘临蚕二号’、‘启豆一号’、‘海门大青皮’、‘北斗七星’、‘黑蚕豆’和‘红香蕉’共6个供试品种进行试验,设置4个采收期(萌发后第3、6、9和12天),分别对芽苗菜的生长指标和营养指标进行测定和分析。结果显示:随着采收期的延长,蚕豆芽苗菜苗高和可食鲜重均增加,于第12天采收时达最大值,此时左旋多巴产量也达到最高。‘黑蚕豆’在第12天采收时可食鲜重最大,可溶性蛋白、游离氨基酸和总黄酮含量均表现最佳,且左旋多巴产量最高,为1 392.48mg/10株,‘海门大青皮’和‘启豆一号’分别位居第二和第三位。综合来看,适宜左旋多巴提取的最佳蚕豆品种为‘黑蚕豆’,最适采收期为第12天。本研究为后续蚕豆芽苗菜药用成分的规模生产提供了一定的理论依据。