Effects of Dwarfing Treatments on the Appearance and Storage Quality of Banana Fruit
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摘要: 目的:探讨矮化处理对香蕉果实的外观和后熟品质的影响。方法:以‘桂蕉9号’为实验材料,将矮化剂(主要成份为烯效唑和磷酸二氢钾)溶于水后灌根,香蕉苗长至第18片叶时使用矮化剂第一次矮化,长至第23片叶时进行第二次矮化,果实达到商品饱满度时采收。以果实外观(果柄长度、蕉指周长)和后熟品质,包括果皮颜色(L*值、a*值、b*值、C*值、h*值)、果实硬度、呼吸速率、乙烯释放量、果肉可溶性糖(果糖、蔗糖、葡萄糖)含量和有机酸(草酸、奎宁酸、苹果酸、琥珀酸、VC、柠檬酸、延胡索酸)含量作为参考指标,研究矮化处理对香蕉果实贮藏品质的影响。结果:矮化组和对照组的果柄长度和蕉指周长分别有极显著差异(P<0.01)和显著差异(P<0.05);在22 ℃贮藏条件下,矮化组和对照组果皮色差和硬度的变化总体上无显著差异;进入跃变期后,矮化组果实的CO2释放量和乙烯释放量均高于对照组,但未达到显著水平。矮化组果实的苹果酸含量在整个后熟期间均低于对照组,并在成熟度3级时达到显著水平(P<0.05);成熟度至4级和5级时,矮化组的琥珀酸含量显著低于对照组(P<0.05),且分别达到极显著差异水平(P<0.01)和显著差异水平(P<0.05);奎宁酸含量在果实成熟度5级时,矮化组低于对照组,并达到显著差异水平(P<0.05)。两组果实果糖、蔗糖、葡萄糖的含量和变化趋势无显著差异;在成熟度达到7级时,矮化组和对照组的糖酸比无显著差异。结论:矮化处理缩小了‘桂蕉9号’的蕉柄长度和蕉指周长,改变了部分有机酸的代谢,但没有显著改变贮藏寿命和食用品质。Abstract: Objective: This study investigates the effects of dwarfing treatment on the appearance and postharvest quality of banana fruits. Methods: The experimental material used in this study was 'Guijiao No.9'. A dwarfing agent, primarily composed of uniconazole and potassium dihydrogen phosphate, was dissolved in water and applied to the roots. The banana seedlings undergo their first treatment with the dwarfing agent when they reach the 18th leaf, followed by a second treatment when they reach the 23rd leaf. The fruits were harvested once they reach the desired level of commercial maturity. Fruit appearance (peduncle length, fruit finger circumference) and postharvest quality, including peel color (value L*, a*, b*, C*, h*), fruit hardness, respiration rate, ethylene release, soluble sugar content (fructose, sucrose, glucose), and organic acid content (oxalic acid, quinine acid, malic acid, succinic acid, VC, citric acid, fumaric acid) in the flesh were taken as reference indicators to study the effects of dwarfing treatment on the storage quality of banana fruits. Results: The peduncle length and finger circumference between the dwarfed group and the control group showed extremely significant differences (P<0.01) and significant differences (P<0.05), respectively. Under the storage condition of 22 ℃, there was no significant difference in peel color chromatism and firmness change between the dwarfed group and the control group. After the climacteric stage, the CO2 and ethylene production of the dwarfed group were higher than those of the control group, but with no significant difference. The malic acid content in the fruits of the dwarfed group was lower than that of the control group during the entire ripening period and reached a significant level at maturity stage 3 (P<0.05). At maturity stages 4 and 5, the succinic acid content in the dwarfed group was significantly lower than that of the control group, with extremely significant differences (P<0.01) and significant differences (P<0.05) were observed, respectively. The quinine acid content in the dwarfed group was significantly (P<0.05) lower than that of the control group at maturity stage 5. There was no significant difference in the content and trend of glucose, fructose, and sucrose between the two groups. Finally, at maturity stage 7, there was also no significant difference in the sugar-acid ratio between the two groups. Conclusion: The dwarfing treatment reduced the peduncle length and fruit finger circumference of Banana 'Guijiao No.9' and altered the metabolism of some organic acids, but did not significantly change the storage life and eating quality.
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Keywords:
- ‘Guijiao No.9’ /
- dwarfing treatment /
- appearance traits /
- ripe characteristics /
- storage quality
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香蕉(Musa acuminate AAA group,Cavendish cultivar)是广西重点发展的两大优势水果产业之一,香蕉产业已成为广西农村经济繁荣和农民脱贫致富的重要支柱产业之一。目前广西香蕉种植面积和鲜果产量均位居全国第二位[1]。‘桂蕉9号’是由巴西蕉芽变株系选育而来,具有中抗枯萎病的特性,是广西目前主载的抗枯萎病的香牙蕉品种。但香蕉属大型草本果树,植株假茎高大,生长周期长,叶片、果穗管护难度大,台风等自然灾害风险高,田间管理周期长,生产成本投入多。降低香蕉植株假茎高度,对降低生产成本,减轻种植风险,提高种植效益均具有重要意义[2]。与乔化果树相比,矮化果树用于建造营养器官的光合产物比较少,而用于果实生长的光合产物比较多,从而在同样投入和生物产量近似的情况下,其经济产量高于乔化果树。主要表现在开花结果早、单位面积产量高、果实品质好、易成花、管理方便等[3−4]。此外,矮化处理后的香蕉植株具有抗倒伏、果形整齐等特点,便于疏果、去蕾、套袋等田间管理,有利于节省生产成本,深受果农欢迎。矮化处理技术对香蕉产业的未来而言具有极大潜力[5]。
矮化剂是植物生长调节剂的一种,常用的矮化剂有矮壮素、多效唑、烯效唑和比久等一种或多种的组合,它们的共同效应是缩短节间距、增粗茎秆、加深叶色、加厚叶片、促进根系生长、增强抗逆性等[6]。矮化剂不仅矮化植株,同时能够影响作物果实的其他方面,如多效唑处理会减少向日葵瘦果的产量和重量[7],加速番茄果实的成熟和产量[8],延长大豆正常代谢活动周期[9],显著提高草莓的蛋白质含量[10],减轻葡萄果实掉粒程度[11]等。不同的矮化剂对植物的影响也不相同,刘明等[12]使用不同浓度的矮壮素和多效唑试剂处理向日葵植株,结果表明300 mg/L多效唑的矮化效果更佳;多效唑处理不仅抑制木棉苗生长高度还抑制了基径增粗,而矮壮素处理则起到促进基径生长的效果[13]。关于香蕉成熟过程中的生理和分子生物学机制,国内外已广泛开展了研究,随着成熟进度的推进,香牙蕉的有机酸、可溶性糖含量等会逐步升高[14];果皮颜色褪绿转黄,果实硬度下降[15]。在不同贮藏条件对香蕉后熟品质或进程影响方面,高浓度的乙烯利及较高的贮藏温度可以加快‘南天黄’香蕉果实的后熟进程[15];蓝、紫光可延缓后熟,红、橙光促进后熟,黄、绿光扰乱后熟[16];高浓度CO2可抑制叶绿素a的降解[17]。分子生物学方面,香蕉成熟过程中相关基因的表达[18],乙烯信号转导的关键通路[19],细胞壁中果胶的降解[20],初级和次级代谢物的合成和降解反应以及它们之间的相关性[21],淀粉和糖代谢[22],香气的合成[23],香蕉果皮中叶绿素的降解[24]等机制均得到了一定程度的阐释。
目前矮化处理对香蕉果实贮藏品质的影响研究目前尚不多见,本实验采用自研发的矮化剂,开展矮化处理对香蕉果实外观以及后熟品质影响的研究,研究结果对于矮化技术在香蕉产业的推广应用具有重要意义。
1. 材料和方法
1.1 材料与仪器
香蕉果实 采自广西隆安县叮当镇基地,品种‘桂蕉9号’,香蕉苗于2020年10月定植,实验面积120亩,矮化组60亩,对照组60亩;矮化剂 购于广西丰浩农业科技有限公司,编号为0802,主要成分为烯效唑和磷酸二氢钾;果糖、蔗糖、葡萄糖、草酸、奎宁酸、苹果酸、琥珀酸、VC、柠檬酸、延胡索酸标准品 购于上海源叶科技有限公司;其他试剂 购于天津科密欧化学试剂有限公司。
HP-200精密色差仪 广东三恩时智能科技有限公司;CT3质构仪 美国博勒飞公司;Check point 3顶空气体分析仪 丹麦膜康公司;Agilent 6890N气相色谱仪 美国安捷伦科技有限公司;LC-20A高效液相色谱仪、ELSD-LT-Ⅱ蒸发光检测器、SPD-M20A二级管阵列检测器 日本岛津公司;氨基色谱柱 大连依利特分析仪器有限公司; Ultimate AQ-C18色谱柱 月旭科技(上海)股份有限公司。
1.2 实验方法
1.2.1 香蕉矮化处理及贮藏条件
将矮化剂溶于2 L水后灌根,对照施用等量清水。香蕉苗长至第18片叶时使用矮化剂第一次矮化,长至第23片叶时第二次矮化,用量均为0.25 g/株,矮化组最终平均高度为2.65 m,对照组最终平均高度为3.10 m。2021年7月13日现蕾,2021年10月12日采收。分别从生长发育基本一致的矮化处理和对照果树中随机选择三株饱满度在7~8成的果实,采收后装筐,避免曝晒并立即运送至实验室。落梳清洗后,去除畸形、特大或特小的果实,选取无病虫害、无机械损伤的蕉指,在22 ℃,RH 90%~95% 的环境下贮藏,矮化组和对照组各重复3次。矮化组标记为T,对照组标记为CK。
1.2.2 成熟等级区分
参照Stover等[25]的方法,按香蕉果皮从绿-黄的颜色分为1~7共7个成熟等级。成熟等级对应天数如下表1:
表 1 ‘桂蕉9号’果实成熟等级对应天数Table 1. Days corresponding to fruit ripening class of'Guijiao No.9'组别 1级 2级 3级 4级 5级 6级 7级 CKA 1 d 6 d 24 d 29 d 30 d 31 d 32 d CKB 1 d 6 d 24 d 29 d 30 d 31 d 32 d CKC 1 d 6 d 19 d 24 d 29 d 31 d 32 d TA 1 d 6 d 24 d 29 d 30 d 31 d 32 d TB 1 d 6 d 24 d 29 d 30 d 31 d 32 d TC 1 d 6 d 19 d 24 d 29 d 31 d 32 d 1.2.3 果柄长度测定
由于香蕉果穗由上往下发育,因此由下往上蕉指体型逐步变大,通过测量比较处理间最小或最大的蕉指果柄长度,可得知矮化处理对果柄的影响。使用游标卡尺测量果柄的长度,测量对象为香蕉果穗从下往上数的第一把蕉指(矮化组T1、对照组CK1)和第八把蕉指(矮化组T8、对照组CK8),每处理3个重复,第一把每重复测量10根,第八把每重复测量14根。
1.2.4 蕉指周长测定
通过测量比较对照和处理间最小一把蕉指的周长,可得知整体的蕉果相对大小情况。使用皮尺测量蕉指的周长,测量对象为香蕉果穗从下往上数的第一把蕉指,测量香蕉果实中部最粗处,每处理3个重复,每重复测6个蕉指。
1.2.5 果皮颜色测定
由于整串香蕉中部的蕉指体型适中,发育时间接近,大小均一,因此贮藏实验的蕉指选择为香蕉果穗从下往上数的第四、第五把蕉指,使用该部分蕉指完成色差、硬度、呼吸、乙烯和糖酸指标的取样测量。色差测量每处理3个重复,每重复测3个蕉指。参照Pelayo等[26]的方法,测试样品L*值、a*值、b*值、C*值、h*值。L*值代表的是果皮颜色的明暗度,L*值越大说明颜色越亮,越小说明颜色越暗;a*值代表红色或绿色物质的浓度,a*值正数说明颜色偏红,负数说明颜色偏绿;b*值代表黄色或蓝色物质的浓度,b*值正数说明颜色偏黄,负数说明颜色偏蓝;C*代表色饱和度,饱和度越高色彩越鲜艳,饱和度越低,色彩越暗淡;h*值代表色调角,越接近180,颜色越绿[27−28]。
1.2.6 果实硬度测定
每处理3个重复,每重复测3个值。将样品侧面正中间的果皮剔除,把样品固定在底座上测试模式选择单次压缩模式,探头采用TA41圆柱形探头来测试果实硬度。测前速率为2 mm/s,测试速率设为2 mm/s,测后速率与测试速率一致;测试深度为1 cm,停留间隔为5 s;数据采集速率为10 pps;触发值为5 g。取测试过程中获得的最大值作为果肉硬度,单位为g。
1.2.7 果实呼吸速率测定
呼吸速率采用封罐法。每处理3个重复,每重复测3个值。选取3个蕉指,25 ℃下置于2.5 L密封罐中,测定起始时二氧化碳的体积分数,1 h后,测定终止时二氧化碳的体积分数。
呼吸速率按照如下公式计算:
RCO2=([CO2]tf−[CO2]ti)×V100M×(tf−ti) (1) 其中,RCO2代表二氧化碳生成的速率,mL/(kg·h);[CO2]ti和[CO2]tf分别代表测量的起始和终止时二氧化碳的体积分数,%;ti和tf分别代表测量的起始和终止时间,h;V是密封盒的自由体积,mL;M是样品的质量,kg。
1.2.8 果实乙烯释放量测定
乙烯释放量的测定采用封罐法。每处理3个重复,每重复测3个值。选取3个蕉指,25 ℃下置于2.5 L密封罐中1 h后测定。色谱条件:色谱柱为活性氧化铝毛细管柱(30 m×0.53 mm×0.25 μm),柱温为80 ℃,载气为氦气(He),火焰离子检测器(FID);温度180 ℃,进样口温度150 ℃,载气流速为30 mL/min。进样体积0.5 mL。
乙烯释放量按照如下公式计算:
乙烯释放量(µL⋅kg−1⋅h−1)=N×VW×H (2) 其中,N代表每毫升气样的乙烯浓度,µL/L;H代表密封时间,h;V代表密封罐的空间除去果实体积后剩余的气体体积,L。
1.2.9 果实可溶性糖含量测定
可溶性糖含量测定方法参照国标GB 5009.8-2016《食品安全国家标准 食品中果糖、葡萄糖、蔗糖、麦芽糖、乳糖的测定》-高效液相色谱法[29]进行。每个处理3个重复,每个重复测3个值。高效液相色谱条件,柱温40 ℃,流动相为乙腈:水=70:30,流速为1.0 mL/min,进样量20 μL,漂移管温度80~90 ℃,设定时间30 min。
测得‘桂蕉9号’果肉试样中可溶性糖的峰面积,并参照国标GB 5009.8-2016《食品安全国家标准 食品中果糖、葡萄糖、蔗糖、麦芽糖、乳糖的测定》[29]中的标准曲线法计算出每100 g果肉中可溶性糖的含量。
1.2.10 果实有机酸含量测定
有机酸含量测定方法参照国标GB 5009.157-2016《食品安全国家标准 食品中有机酸的测定》-高效液相色谱法[30]进行。测量对象为香蕉果穗的第四、第五把蕉指,每处理3个重复,每重复测3个值。高效液相色谱条件,柱温 40 ℃,流动相为 0.1%磷酸:甲醇=97.5:2.5,流速为 0.8 mL/min,进样量20 μL,紫外检测器波长为210 nm。
通过液相仪色谱仪测得‘桂蕉9号’果肉试样中有机酸的峰面积,并参照国标GB 5009.157-2016《食品安全国家标准 食品中有机酸的测定》[30]中的标准曲线法计算出每1 kg果肉中有机酸的含量。
1.3 数据处理
通过Excel 2013进行数据的整理,通过Graphad 9.4.0进行数据的柱形图、折线图绘制和对测定结果进行差异显著性分析。采用t检验方法,P<0.05表示差异显著,P<0.01表示差异极显著。
2. 结果与分析
2.1 矮化处理对‘桂蕉9号’外观性状的影响
2.1.1 矮化处理对香蕉果柄长度的影响
果柄长度决定了香蕉果实的整体形状和耐储运性,果柄过长,果实货架期间容易脱把。由图1a可知,T1果柄长度的中位数小于CK1果柄长度的中位数,T8果柄长度的中位数小于CK8果柄长度的中位数。CK1果柄长度在23 mm左右较为集中,T1果柄长度在19~22 mm左右较为集中,CK8果柄长度在30 mm左右较为集中,T8果柄长度在25 mm左右较为集中,从分布情况可以看出矮化组果柄长度比对照组果柄长度短。由图1b得知T1果柄长度平均值小于CK1果柄长度平均值,两者差异达到极显著水平(P<0.01);T8果柄长度平均值小于CK8果柄长度平均值,两者差异达到极显著水平(P<0.01)。根据上述分析,矮化组和对照组果柄长度有显著差异。
图 1 矮化组和对照组果柄长度分布(a)及果柄长度比较(b)注:*表示组间差异显著(P<0.05),**表示组间差异极显著(P<0.01);图2同。Figure 1. Comparison of the approximate distribution of petiole length (a) in the dwarfed group and the control group and the mean value of plantain petiole length (b)2.1.2 矮化处理对香蕉蕉指周长的影响
蕉指的周长可以反映香蕉果实的粗细程度。由图2a可知,T1蕉指周长的中位数小于CK1蕉指周长的中位数,CK1蕉指周长在11.20 cm左右较为集中,T1蕉指周长在10.70 cm 和11.20 cm 左右较为集中,从分布情况可以看出矮化植株的蕉指周长比对照植株蕉指周长小。由图2b得知CK1蕉指周长平均值大于T1蕉指周长平均值,两者差异显著(P<0.05)。根据上述分析,矮化处理会显著降低‘桂蕉9号’的蕉指周长。
2.2 矮化处理对‘桂蕉9号’后熟过程中果皮颜色变化的影响
为了方便比较矮化和对照香蕉果实在贮藏寿命与成熟进程上的差异,果皮颜色、果实硬度、呼吸速率、乙烯释放速率变化的折线图横坐标为香蕉采摘后的贮藏天数。果皮颜色是果实外观品质的重要指标之一,香蕉在成熟过程中果皮颜色变化为:绿色→黄绿色→黄色[31]。图3为矮化组和对照组香蕉果实贮藏期间外观图。由图4得知,果实随着贮藏时间的延长,L*值、a*值、b*值、C*值整体趋势增大,h*值整体趋势减小。矮化组和对照组果皮颜色变化多呈相同趋势。L*值、a*值、b*值、C*值在0~24 d期间变化较为平缓,24 d 后呈现逐渐上升趋势;h*值呈有序下降趋势。两者果皮颜色变化均无显著差异。
2.3 矮化处理对‘桂蕉9号’后熟过程中果实硬度变化的影响
硬度变化可以直观地反映香蕉果实的成熟进程,并影响果实的食用口感品质[32−33]。由图5得知,随着果实的成熟,果肉逐渐变软,果实硬度逐渐减小。矮化组和对照组果实硬度变化呈相同趋势。0~24 d期间果实的硬度浮动较小,24 d后硬度迅速下降,两者果实硬度变化进程没有显著差异。说明矮化处理对‘桂蕉9号’成熟过程中果实硬度变化进程没有显著的影响,即矮化处理不会影响香蕉的果肉软化。
2.4 矮化处理对‘桂蕉9号’后熟过程中呼吸强度和乙烯释放量的影响
呼吸和乙烯的变化可以反映果实的代谢状态,呼吸或乙烯高峰的出现是跃变型果实进入后熟的标志[34]。从图6a、图6b可知,24 d之后是‘桂蕉9号’的跃变时期。由图6a可知,贮藏0~24 d期间,果实CO2释放量上下轻微浮动,24 d后开始迅速上升。总体上看,矮化处理后的香蕉果实在进入呼吸高峰后(29 d),CO2释放量的平均值高于对照,但二者CO2释放量差异不显著。由图6b可知,在贮藏时间24 d内,矮化组和对照组乙烯释放量都极低,到24 d两者开始逐步上升,贮藏24 d后,矮化组乙烯释放量都高于对照组,但二者差异不显著。说明矮化处理对‘桂蕉9号’成熟过程中果实呼吸的强度和乙烯的释放无显著影响。
2.5 矮化处理对‘桂蕉9号’后熟过程中果肉可溶性糖含量变化的影响
香蕉果实品质差异在后熟状态一致的情况下比较才有意义,因此将可溶性糖和有机酸的含量变化折线图的横坐标展示为香蕉成熟等级。由图7可知,随着成熟级别的增加,果实果糖含量、蔗糖含量、葡萄糖含量整体呈上升趋势。矮化组和对照组的果糖含量、蔗糖含量、葡萄糖含量变化多呈相同趋势。3级之后果糖、蔗糖、葡萄糖含量上升速率明显加快。矮化组和对照组的果肉果糖含量、蔗糖含量、葡萄糖含量没有显著差异。说明矮化处理对‘桂蕉9号’成熟过程中果实可溶性糖的含量没有显著的影响。
2.6 矮化处理对‘桂蕉9号’后熟过程中果肉有机酸含量变化的影响
有机酸种类和含量影响果实的风味。由图8a可以看出,矮化组和对照组草酸含量变化总体呈下降的趋势,且2~3级下降幅度较大,3~4级下降幅度较小,4级后缓慢上升。二者草酸的最终含量没有显著差异。矮化组和对照组奎宁酸含量5级之前有序下降(图8b),到达5级时,对照组继续下降,矮化组回调上升。在5级时,对照组奎宁酸含量高于矮化组,且二者达到显著水平(P<0.05);7级时,二者奎宁酸含量没有显著差异。矮化组和对照组苹果酸含量变化规律接近(图8c),都呈先升后降的趋势。随着果实成熟,苹果酸逐渐积累,在5级达到最高点后有序下降。同时,对照组苹果酸含量始终高于矮化组,在3级时,两者差异达到显著水平(P<0.05)。由图8d可以看出,香蕉果实从2级到3级转变过程中琥珀酸含量迅速下降,之后变化趋势趋于平缓。对照组在3级到6级的转变期间琥珀酸含量整体高于矮化组,并且在4级和5级时分别达到了极显著水平(P<0.01)和显著水平(P<0.05)。果实达到6级后琥珀酸含量开始回升,7级时含量趋于一致。矮化组和对照组VC含量变化趋势基本接近(图8e),均呈现出“降-升-降”的趋势:2级~3级略微下降,3级~6级逐步上升,6级到达最高点后下降。二者VC含量没有显著差异。随着果实后熟,矮化组和对照组柠檬酸含量同时上升(图8f),且矮化组在5级前柠檬酸含量高于对照组,5级~6级时二者柠檬酸含量非常接近,6级后二者柠檬酸含量均下降。二者柠檬酸最终含量没有显著差异。在整个后熟阶段,延胡索酸含量在矮化组和对照组的果实中均呈有序下降的趋势(图8g),4级前矮化组延胡索酸含量平均值比对照组低;4级后矮化组含量比对照组高,但二者差异未达到显著水平。
总体上,矮化和对照组中的草酸、奎宁酸、富马酸、琥珀酸在后熟中逐渐下降,而苹果酸、VC、柠檬酸在后熟进程中呈现先上升,后下降的趋势。虽然在部分时间点二者的某些有机酸含量差异达到显著水平,但在最终体现果实食用品质的6~7级时间点上,矮化组和对照组的各有机酸含量均未出现显著差异,说明矮化处理不会对果实最终的有机酸含量产生显著影响。
2.7 矮化处理对‘桂蕉9号’后熟过程中糖酸比的变化的影响
将可溶性糖总量和上述7种有机酸总量的比值作为糖酸比的参考。由图9可知,矮化组和对照组糖酸比及其变化趋势相当接近,都呈现上升趋势。1~3级浮动不大,3级之后开始上升,5级之后迅速上升,7级时糖酸比达到最高。二者的糖酸比无显著差异。
3. 讨论与结论
研究表明,矮化剂通过阻碍赤霉素的生物合成,导致活性赤霉素的数量减少,从而减缓植物茎端分生组织细胞分裂、伸长和生长速度,并缩短节间距[6,35]。赤霉素参与香蕉蕉柄的伸长生长,香蕉果皮的扩张,矮化处理抑制赤霉素的合成从而抑制香蕉蕉柄伸长生长以及果皮细胞分裂[36]。本研究发现,矮化处理缩小了‘桂蕉9号’的蕉柄长度和蕉指周长,蕉柄缩短,能有效减轻香蕉货架期的掉果程度。
香蕉为呼吸跃变型果实,通常在果实田间饱满度达到约7成时采收,贮藏初期呼吸速率极低,后期呼吸速率迅速升高,出现呼吸跃变[34]。观察本实验的果皮颜色变化、果实呼吸速率以及乙烯释放量变化折线图可发现,矮化组和对照组的呼吸跃变发生在24~29 d之间,即采收贮藏的中后期,与李朋超等[34]的研究结论一致。在24~29 d开始呼吸跃变之时,果皮的颜色由绿色转变为黄绿色,果实硬度迅速下降,呼吸速率上升,乙烯释放量突升,对照组和矮化组出现跃变的时间基本一致,说明矮化处理对香蕉果实的后熟进程没有显著影响,两者的贮藏期没有显著差异。
本研究发现,贮藏29 d后,矮化组苹果酸、琥珀酸含量平均值小于对照组,且在后熟过程中矮化组的奎宁酸、琥珀酸、柠檬酸、延胡索酸含量平均值都在不同等级和阶段与对照组存在着差别,但未达到显著水平。果实呼吸作用的强度与果实生命活动的状态有关,当中涉及到呼吸代谢途径的变化[37],糖酵解-三羧酸(EMP-TCA)循环是呼吸代谢的主途径,苹果酸、琥珀酸、柠檬酸、延胡索酸都是三羧酸循环中的主要反应物[38]。结合矮化组跃变期间呼吸强度平均值大于对照组,而苹果酸、琥珀酸含量在跃变期间低于对照组以及多种参与代谢活动的有机酸含量在跃变期间的差异情况,可以推测矮化处理的果实在跃变期更多的苹果酸、琥珀酸等有机酸作为底物参与了代谢活动,但最终在适宜食用的6~7级成熟度,矮化和对照的有机酸含量没有显著区别。
成熟香蕉果实中含有蔗糖、葡萄糖和果糖,其中蔗糖含量最高[39]。本研究结果表明,矮化处理后香蕉果肉中三种主要糖类的相对比例并未改变,且在各个成熟等级中,对照和矮化处理组果实的糖含量差异均不显著,说明矮化处理对‘桂蕉9号’的糖代谢途径没有显著影响。‘桂蕉9号’由巴西蕉芽变选育而来,本研究实验中‘桂蕉9号’后熟末期与前期相比果实里的草酸、奎宁酸、琥珀酸含量减少,苹果酸、柠檬酸含量增加与孙佩光等[40]对巴西蕉的研究结果基本一致。再根据两者糖和酸的各项指标在成熟度达7级时均无显著差异,说明矮化处理不会影响其食用品质和口感。
总的来说,矮化处理缩小了‘桂蕉9号’的蕉柄长度和蕉指周长,改变了部分有机酸的代谢水平,但没有显著改变贮藏寿命和食用品质。
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图 1 矮化组和对照组果柄长度分布(a)及果柄长度比较(b)
注:*表示组间差异显著(P<0.05),**表示组间差异极显著(P<0.01);图2同。
Figure 1. Comparison of the approximate distribution of petiole length (a) in the dwarfed group and the control group and the mean value of plantain petiole length (b)
表 1 ‘桂蕉9号’果实成熟等级对应天数
Table 1 Days corresponding to fruit ripening class of'Guijiao No.9'
组别 1级 2级 3级 4级 5级 6级 7级 CKA 1 d 6 d 24 d 29 d 30 d 31 d 32 d CKB 1 d 6 d 24 d 29 d 30 d 31 d 32 d CKC 1 d 6 d 19 d 24 d 29 d 31 d 32 d TA 1 d 6 d 24 d 29 d 30 d 31 d 32 d TB 1 d 6 d 24 d 29 d 30 d 31 d 32 d TC 1 d 6 d 19 d 24 d 29 d 31 d 32 d -
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