Antioxidant Capacity of Hydroponically Cultivated and Grafted Tomato Varieties

Heirloom tomato varieties are in demand by consumers due to high antioxidant levels. However, these varieties are difficult to produce and are prone to disease and low yield. To overcome these problems, heirloom tomatoes may be grafted onto disease-resistant rootstocks and cultivated in hydroponic systems. However, it is unknown if the antioxidant capacity of hydroponically grown tomatoes is affected by grafting.
Heirloom (Black Krim and Green Zebra) and standard (Big Beef) varieties were grafted onto wild type (WT) or productive rootstocks (Arnold and Supernatural). Tomatoes were harvested at maturity, freeze-dried, ground into a powder, and stored at -20ºC until further analysis. Antioxidant capacity of methanol extracts was evaluated by the 2,2’-azino-di[3-ethylbenzthiazoline sulfonsyr]sulphonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays.
For the ABTS assay, the antioxidant capacity was measured by incubating 10 uL tomato extract was with 95 uL 3.5 mM ABTS• for 30 s at room temperature, and the absorbance at 734 nm was measured spectrophotometrically (Spectra Max 250 Microplate Reader, Molecular Devices, San Jose, CA). Trolox was used as an antioxidant standard for calculations of trolox equivalents (TE; μmol/g tomato dry weight). The antioxidant capacity of Big Beef, Black Krim, and Green Zebra grafted onto WT, Arnold, and Supernatural was 12.18±0.82, 12.34±0.65, 12.26±0.79 (Big Beef), 12.35±0.83, 11.99±1.31, 11.60±1.54 (Black Krim), and 11.42±1.12, 11.76±1.93, 11.71±0.83 (Green Zebra; TE; mean±std), respectively.
For the DPPH assay, 10 μM DPPH in 90% aqueous methanol was measured spectrophotometrically at 517 nm (Spectra Max 250 Microplate Reader, Molecular Devices, San Jose, CA) to ensure that the absorbance was between 0.510-0.540. To determine the antioxidant capacity, 10 uL tomato extract was mixed with 195 uL 10 μM DPPH in 90% aqueous methanol and incubated in the dark for 15 min. The decrease in absorbance at 517 nm was then measured. Trolox was used as an antioxidant standard for calculations of TE. The antioxidant capacity of Big Beef, Black Krim, and Green Zebra grafted onto WT, Arnold, and Supernatural was 7.88±0.72, 7.62±0.87, 7.99±0.68, (Big Beef), 7.59±0.78, 8.11±0.54, 7.70±0.88 (Black Krim), and 8.00±0.53, 7.66±0.78, 8.19±0.64 (Green Zebra; TE; mean±std). The results further showed that none of the tomato varieties exhibited statistically significantly different antioxidant capacity.

古法番茄品种因其富含抗氧化物质而受到消费者青睐。然而，此类品种的种植难度较大，易受病害侵扰且产量较低。为克服这些难题，古法番茄可嫁接到抗病性强的砧木上，并在水培系统中进行栽培。然而，尚不清楚水培生长的番茄其抗氧化能力是否受嫁接影响。古法番茄品种（如黑克里姆和绿斑纹）与标准品种（如大牛肉）分别嫁接到野生型（WT）或高产品种砧木（如阿诺德和超自然）。番茄在成熟期收获后，经冷冻干燥、研磨成粉，并储存在-20℃条件下，待进一步分析。通过2,2'-联氮二（3-乙基苯并噻唑啉-6-磺酸）二磺酸盐（ABTS）和2,2-二苯基-1-苦肼基自由基（DPPH）方法评估了甲醇提取物中的抗氧化能力。在ABTS试验中，通过将10 μL番茄提取物与95 μL 3.5 mM ABTS•在室温下孵育30秒，并使用分光光度法（Spectra Max 250微量板阅读器，Molecular Devices，圣何塞，CA）测定734 nm处的吸光度来测量抗氧化能力。以Trolox作为抗氧化标准，计算Trolox当量（TE；μmol/g番茄干重）。大牛肉、黑克里姆和绿斑纹嫁接到WT、阿诺德和超自然砧木上的抗氧化能力分别为12.18±0.82、12.34±0.65、12.26±0.79（大牛肉）、12.35±0.83、11.99±1.31、11.60±1.54（黑克里姆）和11.42±1.12、11.76±1.93、11.71±0.83（绿斑纹；TE；平均值±标准差）。对于DPPH试验，通过分光光度法（Spectra Max 250微量板阅读器，Molecular Devices，圣何塞，CA）在517 nm处测量10 μM DPPH在90%水溶液甲醇中的吸光度，确保吸光度在0.510-0.540之间。为了确定抗氧化能力，将10 μL番茄提取物与195 μL 10 μM DPPH在90%水溶液甲醇中混合，并在黑暗中孵育15分钟。然后测量517 nm处吸光度的降低。以Trolox作为抗氧化标准，计算TE。大牛肉、黑克里姆和绿斑纹嫁接到WT、阿诺德和超自然砧木上的抗氧化能力分别为7.88±0.72、7.62±0.87、7.99±0.68、7.59±0.78、8.11±0.54、7.70±0.88（黑克里姆）和8.00±0.53、7.66±0.78、8.19±0.64（绿斑纹；TE；平均值±标准差）。结果进一步表明，没有任何番茄品种表现出统计学上显著的抗氧化能力差异。