Kyriacou Marios C, Antoniou Chrystalla, Rouphael Youssef, Graziani Giulia, Kyratzis Angelos
Department of Vegetable Crops, Agricultural Research Institute, 1516 Nicosia, Cyprus.
Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy.
Antioxidants (Basel). 2021 Jan 5;10(1):57. doi: 10.3390/antiox10010057.
Six critical stages corresponding to major morphophysiological events in carob fruit ripening were defined, and changes in the primary and secondary metabolome and in vitro antioxidant capacity were examined in two genotypes collected at low (15 m) and high (510 m) altitudes from genetically identified and georeferenced trees. Soluble carbohydrates were analyzed by HPLC-RI, macro-minerals by ion chromatography coupled to conductivity detection and polyphenols by UHPLC-Q-Orbitrap-HRMS. spectroscopy facilitated assays for condensed tannins and in vitro free-radical scavenging capacity of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric-reducing antioxidant power (FRAP). The fruit respiration rate and moisture content declined sharply during the transition from the breaker to green pedicel stage. Sugar accumulation spiked at the onset of fruit coloration and culminated at 498.7 ± 8.4 mg g dry weight (dw) in the late ripe stage, while the ratio of reducing sugars to sucrose decreased from 3.45 ± 0.32 to 0.41 ± 0.02. The total phenolic compounds and condensed tannins declined with ripening, particularly during the transition from the breaker to green pedicel stage. Eighteen polyphenols were identified and quantitated, with catechins and hydrolyzable tannins being dominant until the onset of fruit coloration. The transition to the green pedicel stage signaled a precipitous decline (90.9%) in catechins, hydrolyzable tannins (60.2%) and flavonol glycosides (52.1%) concomitant to the rise in gallic acid, which was putatively fueled by the enzymatic hydrolysis of gallotannins in immature fruit. Catechins, hydrolyzable tannins and flavone glycosides were more abundant at higher altitudes and gallic acid at lower altitudes. An antioxidant capacity was also favored by higher elevations and declined with ripening, particularly after the breaker stage. Correlations with FRAP and DPPH assays were significant for the total phenolic content, condensed tannins, catechins and hydrolyzable tannins. The highest correlation factors were obtained for epigallocatechin-gallate (r = 0.920 and r = 0.900; < 0.01). Although the sharp drop in hydrolyzable and nonhydrolyzable tannins and catechins compromised the in vitro antioxidant capacity at physiological maturity, it also reduced the astringency and configured a palatable organoleptic fruit profile. These changes unraveled significant episodes in the ripening-related secondary metabolism of the carob fruit. They further highlighted the value of immature carob as a potent source of gallotannins, with putative in vivo anti-inflammatory action, and of catechins beneficial in preventing and protecting against diseases caused by oxidative stress.
确定了与角豆果实成熟过程中主要形态生理事件相对应的六个关键阶段，并对从基因鉴定和地理定位的树木上在低海拔（15米）和高海拔（510米）采集的两个基因型的果实进行了初级和次级代谢组以及体外抗氧化能力的变化研究。通过高效液相色谱-示差折光检测法分析可溶性碳水化合物，通过离子色谱-电导检测法分析常量矿物质，通过超高效液相色谱-四极杆-轨道阱-高分辨质谱法分析多酚。采用光谱法测定缩合单宁以及1,1-二苯基-2-苦基肼（DPPH）的体外自由基清除能力和铁还原抗氧化能力（FRAP）。从破色期到绿梗期过渡期间，果实呼吸速率和水分含量急剧下降。果实着色开始时糖分积累达到峰值，在晚熟期达到498.7±8.4毫克/克干重，而还原糖与蔗糖的比例从3.45±0.32降至0.41±0.02。总酚类化合物和缩合单宁随着成熟而下降，尤其是在从破色期到绿梗期的过渡阶段。鉴定并定量了18种多酚，在果实着色开始前，儿茶素和可水解单宁占主导地位。向绿梗期的过渡标志着儿茶素、可水解单宁（60.2%）和黄酮醇苷（52.1%）急剧下降（90.9%），同时没食子酸增加，推测这是由于未成熟果实中五倍子单宁的酶促水解所致。儿茶素、可水解单宁和黄酮苷在较高海拔处含量更高，没食子酸在较低海拔处含量更高。较高海拔也有利于抗氧化能力，且抗氧化能力随着成熟而下降，尤其是在破色期之后。总酚含量、缩合单宁、儿茶素和可水解单宁与FRAP和DPPH测定的相关性显著。表没食子儿茶素没食子酸酯的相关系数最高（r = 0.920和r = 0.900；P < 0.01）。尽管可水解和不可水解单宁以及儿茶素的急剧下降在生理成熟时损害了体外抗氧化能力，但它也降低了涩味并形成了可口的感官果实特征。这些变化揭示了角豆果实成熟相关次级代谢中的重要事件。它们进一步凸显了未成熟角豆作为五倍子单宁的有力来源的价值，五倍子单宁具有推测的体内抗炎作用，以及儿茶素在预防和抵御氧化应激引起的疾病方面的益处。
