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香椿(Toona sinensis (A. Juss.) Roem)是楝科(Meliaceae)香椿属(Toona)多年生落叶乔木,广泛分布于黄河至长江流域,在我国已有2 000多年的栽培历史,种植面积已超6万hm2。目前,香椿的开发利用及相关研究多集中在其嫩芽的营养、保健功能测评、加工工艺开发以及逆境生理等方面[1-2],而大量的成熟复叶仍处于浪费状态,鲜有研究。本团队前期研究表明,香椿的成熟复叶年产量可达66~104 t·hm-2,其粗蛋白含量均值约17%,富含氨基酸、矿物质等营养成分,且羊喜食,饲用效果良好,属高蛋白型木本饲料原料,具有较高的饲用开发价值[2]。同时,香椿成熟复叶富含类黄酮,在常见56种果蔬中抗氧化活性最高,并具有突出的抑菌、消炎、抗癌等活性功效[3-6]。可见,香椿成熟复叶的饲用开发除避免资源浪费外,还有助于减少养殖环节的抗生素用量。
研究表明不同采收期获得的香椿复叶,其营养品质差异极大,如粗蛋白、可溶性糖、维生素C等,都呈现出生长初期较低,随复叶成熟度增加而不断增加,到衰老期前后开始下降的趋势[7]。同时,不同采收期香椿类黄酮等次生代谢物的积累量也差异显著(P < 0.01),其11月的积累量是5月的7.25倍[8]。此外,杨玉珍等[9]研究发现,香椿可大量富集硝酸盐,采收期跨度仅4月1日到13日间,其硝酸盐积累量即可从438.58 μg·g-1增加至2 950.93 μg·g-1,入列蔬菜卫生标准中硝酸盐严重污染范畴[10]。通常,硝酸盐本身不具毒性,少量摄入有利于NO信号转导,有益心血管健康[11];但由于其可在体内代谢过程中形成有毒的亚硝酸盐和致癌物质亚硝胺等,大量摄入则会严重威胁人畜健康。综上,本研究拟比较不同采收时期的香椿复叶中粗蛋白、总黄酮、硝酸盐含量及其抗氧化活性的差异,并综合考虑其生物量,筛选饲用香椿的最佳采收期,为其产业化开发提供依据。
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由图 1可知,不同采收期的香椿复叶粗蛋白含量约13.17%~22.65%,各采收期间差异显著(P < 0.05),且随复叶成熟度增加而呈下降趋势。其中,5月15日采收的复叶粗蛋白含量最高,为22.65%;11月1日所得样品中含量最低,为13.17%。不同采收期的香椿复叶中粗蛋白含量均值为17.30%±0.94%,除10月后的样品外,其余采收期香椿复叶的粗蛋白含量均大于15%,远高于饲料数据库中的粮食饲料,如玉米(9.4%)、高粱(8.7%)、小麦(13.4%),与优质牧草苜蓿(17.2%)的粗蛋白含量相近[13]。可见,除处于衰老期(10月15日及之后采收)的香椿复叶外,其余采收期获得的香椿叶片均具有高蛋白的饲用优势。
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不同采收期的香椿复叶类黄酮含量差异极显著(P < 0.01),且随其不断发育成熟而持续积累,至落叶期稍有下降(图 2)。香椿复叶类黄酮积累量在其发育前期(5—7月)增长缓慢,在生长旺盛期(7月后)积累量显著增加(P < 0.05),并于10月达到最高,为27.02 mg·g-1,此后在落叶期(11月)开始下降,降至22.93 mg·g-1。
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由图 3可知,ORAC、DPPH、FRAP法测定结果一致,5月15日样品抗氧化活性最低,为205.46 μmol·L-1·g-1(ORAC)、2.35 mg·g-1(DPPH)和1.79 mg·g-1(FRAP),此后其抗氧化活性随复叶不断成熟而持续增加。其中,ORAC和FRAP法测定显示9、10月较其它采收期(5—8月)样品差异显著(P < 0.05),而DPPH法测定7—11月样品抗氧化活性无显著差异。
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由表 1可知,香椿复叶抗氧化活性与其类黄酮含量呈极显著(P < 0.01)正相关,ORAC、DPPH及FRAP与类黄酮含量的相关系数分别为0.894、0.891和0.979。可见,类黄酮是香椿抗氧化活性的重要贡献因子,对其保健活性强弱有重要影响。
表 1 香椿类黄酮含量与抗氧化活性的相关性分析
Table 1. Correlation coefficients of total flavonoid content and each antioxidant activity assay of Toona sinensis
项目Items ORAC DPPH FRAP 类黄酮Flavonoids 0.894** 0.891** 0.979** P值P value 0.007 0.007 0.000 **在0.01水平上显著相关。** Correlation is significant at the 0.01 level. -
从图 4可知,香椿大量富集硝酸盐,且随复叶不断成熟呈“V”形积累,7、8月样品硝酸盐积累处于峰谷,含量明显低于其它阶段。其中,7月15日采收的复叶中硝酸盐积累量最少,为2 306.39 mg·kg-1,8月中旬后硝酸盐积累量迅速增加,并于10月15日达最大值,为7 346.80 mg·kg-1。
不同采收时期对香椿饲用品质的影响
Effect of Harvest Time on Forage Quality of Toona sinensis
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摘要:
目的 对不同采收时期所得香椿复叶的粗蛋白、类黄酮、总硝酸盐含量及其抗氧化活性进行分析比较,确定饲用香椿复叶的最佳采收时期。 方法 以5月15日至11月1日逐月采收的香椿复叶为材料,测定其粗蛋白、类黄酮及总硝酸盐含量,并利用ORAC、DPPH、FRAP法测定其抗氧化活性,综合营养及保健活性分析,筛选最适饲用采收时期。 结果 不同采收期,香椿复叶粗蛋白、类黄酮、硝酸盐含量及抗氧化活性差异显著(P < 0.05)。其中,复叶粗蛋白含量(全采收期13.17%~22.65%)随其成熟度增加而呈下降趋势,除10月中旬后的样品外,其余采收期复叶粗蛋白含量均大于15%,远高于常规粮食饲料,具有高蛋白的饲用优势;类黄酮含量突出(全采收期均值15.87 mg·g-1),远高于蓝莓等常见果蔬,且随复叶成熟而持续积累,并于10月达到最高27.02 mg·g-1;ORAC、DPPH、FRAP法测定结果均表明香椿复叶具有突出的抗氧化活性,且随复叶成熟而持续增加,并与其类黄酮含量呈极显著正相关(P < 0.01);香椿复叶大量富集硝酸盐(全采收期2 306.39~7 346.80 mg·kg-1),且随其叶片成熟呈"V"形积累,7—8月中旬采收的香椿复叶硝酸盐含量处峰谷阶段,此间均值为2 603.78 mg·kg-1,相对适于进行饲用采收。 结论 不同采收期香椿复叶的饲用品质差异显著,综合考虑其营养价值及保健功效,7—8月中旬是对香椿复叶进行饲用采收的最适采收时期。 Abstract:Objective To reveal and compare the contents of crude protein, flavonoids, nitrates and their antioxidant activity of Toona sinensis harvested in different time, and to find the optimal harvest time for fodder utilize. Method The contents of crude protein, flavonoids and total nitrates of rachises of T. sinensis harvested from May to November were analyzed, and their antioxidant activity were determined by ORAC, DPPH and FRAP. Combining the nutritional and healthy analysis, the optimal harvest time was determined. Result There were significant differences in the crude protein, flavonoids, total nitrates contents and antioxidant activity of T. sinensis harvested in different time(P < 0.05). The crude protein content (varied from 13.17% to 22.65%) presented a downward trend with the maturity of T. sinensis. But except the samples harvested after mid-October, the rest samples showed protein forage advantage with the crude protein contents higher than 15%, which were far higher than the conventional grain feedstuffs. The flavonoids content of T. sinensis harvested at any time were highlighted (15.87 mg·g-1 in average), which was far higher than that of the common fruits and vegetables, such as blueberries, and was persistently accumulated with the maturity of rachises, and reached the highest in October (27.02 mg·g-1). The results of ORAC, DPPH and FRAP assay all showed outstanding antioxidant activities which increased with the maturity of rachises. Meanwhile, very significant positive correlations (P < 0.01) were detected between the flavonoids content and the antioxidant activities. A large amount of nitrates was detected in T. sinensis from different harvest time (2 306.39~7 346.80 mg·kg-1). The accumulation of nitrates in T. sinensis followed a V-shape along with its maturity. The T. sinensis harvested in the mid-July and August, with the average nitrates content of 2 603.78 mg·kg-1, contained the lowest nitrates content. Conclusion The feeding quality of T. sinensis harvested in different time is proved to be significantly different. Comprehensively considering the nutritional value and health care effect of T. sinensis, the mid-July and August are the optimum harvesting time for the forage development of T. sinensis. -
Key words:
- Toona sinensis
- / harvest time
- / crude protein
- / flavonoids
- / antioxidant activity
- / nitrate
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表 1 香椿类黄酮含量与抗氧化活性的相关性分析
Table 1. Correlation coefficients of total flavonoid content and each antioxidant activity assay of Toona sinensis
项目Items ORAC DPPH FRAP 类黄酮Flavonoids 0.894** 0.891** 0.979** P值P value 0.007 0.007 0.000 **在0.01水平上显著相关。** Correlation is significant at the 0.01 level. -
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