摘要
为提升烟叶的晾制品质,以云雪2号作为试验材料,探究在环境温度为28 ℃,环境湿度分别为90%(高湿)、80%(中湿)、70%(低湿)的条件下雪茄烟叶晾制变黄期烟叶内在化学成分的变化。结果显示:(1)不同晾制湿度下,烟叶晾制期间质体色素、淀粉含量整体呈下降趋势,葡萄糖、果糖、蔗糖整体呈上升趋势。(2)高湿处理(变黄湿度为90%)烟叶叶绿素含量降解速率缓慢,但降解周期长,而低湿与中湿处理在变黄96 h之后含量便趋于较低水平,变化不明显。(3)低湿(变黄湿度为70%)处理葡萄糖与果糖含量在变黄前期积累量明显增加,在变黄144 h之后增量较小,而中湿与高湿含量变化趋势与低湿相反,在变黄前期增量不明显,而在变黄144 h之后显著增加;不同处理下淀粉与蔗糖含量变化趋势几近相同。(4)相关性分析结果显示,晾制过程中质体色素含量与非结构性糖类含量变化均达到了显著或极显著水平。综上,低湿(变黄湿度为70%)烟叶变黄速率较快,非结构性糖类转化迅速,烟叶提前结束变黄;高湿(变黄湿度为90%)烟叶在变黄前期各项指标变化较小,144 h之后非结构性糖类转化速率较快,一定程度上延长了变黄期时长。中湿(变黄湿度为80%)烟叶的质体色素与非结构性糖类的降解转化程度处于低湿与高湿之间。以上结果表明,高湿晾制为烟叶变黄提供了较为合适的环境、时间条件,促进了烟叶内含物质的转化,因此在实际生产中,在晾制变黄期为烟叶提供高湿的晾制环境更有利于高品质烟叶的形成。
近年来,随着我国雪茄烟生产规模的扩大,烟叶质量提升显得愈发重要,而目前雪茄烟叶含青(青斑、青筋和浮青)是影响品质的主要问题,其主要原因是烟叶晾制过程中环境温湿度调控不当引起的。雪茄烟的调制是烟叶的理化性状固定、质量风格呈现的动态调控过程。晾制温度决定了烟叶晾制速度,合适的温度有利于促进烟叶碳水化合物及质体色素类物质的降
试验于2022年在湖南省张家界市永定区教字垭镇进行(29°28′86″N,110°33′30″E),试验田土壤质地类型为黏土,试验地前茬作物为水稻,土壤pH为5.96,有机质含量40.1 g/kg、全氮2.24 g/kg,全磷1.01 g/kg,全钾32.13 g/kg,有效磷28.4 mg/kg,速效钾353.2 mg/kg、碱解氮163 mg/kg,供试品种为当地主栽茄衣品种之一—云雪2
选取云雪2号种子进行漂浮育苗,移栽前整地并开沟条施基肥,所用肥料为烟草专用复合肥(N-P2O5-K2O=8-14-8)、钙镁磷肥(P2O5-CaO-MgO=14-45-12)、提苗肥(N-P2O5=20-9)、腐熟菜籽饼肥(N-P2O5-K2O=27-6-11)、硝酸钾、硫酸钾。保证N-P2O5-K2O=1-1.5-2,基肥、追肥比例为6∶4,全部有机肥、钙镁磷肥和60%的氮肥及钾肥于整地时开沟条施,40%的氮肥和钾肥作为追肥,分2次施入,追肥时间为移栽后10 d和30 d。移栽期为2022年4月24日,单垄单行种植,按照行距120 cm,株距40 cm,20 835株/h
1)质体色素含量的测定。采用分光光度
2)非结构性糖类含量的测定。烟叶淀粉、葡萄糖、果糖、蔗糖等非结构性糖类含量的测定参照苏州科铭生物技术有限公司提供的试剂盒(型号分别为:DF-1-Y、PT-1-Y、GT-1-Y、ZHT-1-Y)说明书。
3)相关酶活性的测定。烟叶蔗糖酶、中性转化酶、淀粉酶的活性检测,参照苏州科铭生物技术有限公司提供的酶试剂盒(型号分别为:ZTM-1-Y、NI-1-Y、DFMA-1-Y)说明书。
4)数据的处理与分析。采用Microsoft Excel 2019进行数据整理、Origin2021进行相关性分析及图表的绘制。
变黄期是烟叶颜色由绿变黄的重要时期。

图1 不同晾制湿度下雪茄烟叶叶绿素a(A)、叶绿素b(B)及总叶绿素(C)含量
Fig. 1 Chlorophyll a(A),Chlorophyll b(B) and total chlorophyll(C) content of cigar tobacco leaves under different air-curing humidity
烟叶在变黄期的类胡萝卜素含量如

图2 不同晾制湿度下雪茄烟叶类胡萝卜素含量
Fig. 2 Carotenoid content in cigar tobacco leaves under different air-curing humidity
葡萄糖、果糖属单糖类化合物,在烟叶内可直接代谢,参与糖酵解过程,为烟叶的各项生命活动提供能量。试验测定不同晾制湿度下雪茄烟叶葡萄糖、果糖含量变化的动态情况如

图3 不同晾制湿度下雪茄烟叶葡萄糖(A)与果糖(B)含量
Fig.3 The content of glucose (A) and fructose (B) in cigar tobacco leaves under different air-curing humidity
蔗糖是植物体内重要的能源和碳源物质,在烟草体内蔗糖也是糖类运输的主要形式。淀粉是由多个D-葡萄糖通过苷键结合而成的多糖,是烟叶各项生命活动的重要供能物质。

图4 不同晾制湿度下雪茄烟叶蔗糖(A)与淀粉(B)含量
Fig.4 Contents of sucrose (A) and starch (B) in cigar leaves under different air-curing humidity
脂氧合酶既是类胡萝卜素降解的关键酶,又和叶绿素降解密切相关。

图5 不同晾制湿度下雪茄烟叶变黄期脂氧合酶活性
Fig.5 Lipoxygenase activity of cigar tobacco leaves at yellowing stage under different air-curing humidity
蔗糖酶、中性转化酶和淀粉酶是植株碳代谢强度的重要指标,可将大分子碳水化合物分解为单糖等小分子化合物。不同晾制湿度下雪茄烟叶变黄期蔗糖酶、中性转化酶以及淀粉酶活性动态变化情况如

图6 不同晾制湿度下雪茄烟叶变黄期蔗糖酶(A)、中性转化酶(B)和淀粉酶(C)活性
Fig.6 Activities of sucrase (A), neutral invertase (B) and amylase (C) in cigar tobacco leaves at yellowing stage under different air-curing humidity
如

图7 不同晾制湿度下烟叶变黄期非结构性糖类、质体色素与相关酶活相关性分析
Fig.7 Correlation analysis of non-structural sugars, plastid pigments and related enzyme activities in yellowing stage of tobacco leaves with different air-curing humidity
变黄期是雪茄烟叶品质形成的重要环节,在此过程中由于烟叶内各种色素含量占比不断变化,烟叶颜色由采收时的嫩绿色逐渐转变为黄中带
碳水化合物是晾制过程中维持烟叶生命活动以及品质形成的重要物质。本研究中各处理烟叶在变黄期碳水化合物的含量、转化速率以及相关酶活性不尽相同。低湿环境下的叶片小分子糖类含量始终最高,而淀粉含量变化幅度在144 h前明显高于其他处理,而在144 h之后变化幅度又低于其他处理。一方面是由于在水分亏缺的状态下,低湿度晾制的烟叶所受的逆境胁迫更为严重,叶片与环境湿度存在较大的湿度差,叶片失水量较大,而细胞为调节内外渗透压,迫使淀粉等多糖迅速降解为小分子糖类用于维持烟叶内外渗透压的平
通过分析不同晾制湿度下雪茄烟叶质体色素降解与非结构性糖类代谢及其相关酶活性的相关性可知,不同湿度下质体色素的降解与非结构性糖类的转化关系密切,究其原因可能是因为在晾制过程中,烟叶淀粉等不溶性多糖的降解生成了大量的葡萄糖等小分子糖类,在此过程中,不仅细胞内氢离子增多,并且由于细胞的呼吸作用,葡萄糖发生的糖酵解、三羧酸循环等分解代谢,为质体色素的降解提供大量的能量,促使其分解与转化,进而影响烟叶颜色的变
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