Dynamic Changes in Phenolics and Antioxidant Capacity during Pecan (Carya illinoinensis) Kernel Ripening and Its Phenolics Profiles

Abstract

Pecan (Carya illinoinensis) kernels have a high phenolics content and a high antioxidant capacity compared to other nuts—traits that have attracted great interest of late. Changes in the total phenolic content (TPC), condensed tannins (CT), total flavonoid content (TFC), five individual phenolics, and antioxidant capacity of five pecan cultivars were investigated during the process of kernel ripening. Ultra-performance liquid chromatography coupled with quadruple time-of-flight mass (UPLC-Q/TOF-MS) was also used to analyze the phenolics profiles in mixed pecan kernels. TPC, CT, TFC, individual phenolics, and antioxidant capacity were changed in similar patterns, with values highest at the water or milk stages, lowest at milk or dough stages, and slightly varied at kernel stages. Forty phenolics were tentatively identified in pecan kernels, of which two were first reported in the genus Carya, six were first reported in Carya illinoinensis, and one was first reported in its kernel. The findings on these new phenolic compounds provide proof of the high antioxidant capacity of pecan kernels.

Metabolic profiling revealed the organ‐specific distribution differences of tannins and flavonols in pecan

“…The TPC and antioxidant capacities of pecan shell were also relatively high, which is consistent with previous results. At present, the research on antioxidant capacities of pecan is limited to kernel and shell (Biomhoff et al, 2006;de la Rosa et al, 2011de la Rosa et al, , 2014Prado et al, 2013Prado et al, , 2014Flores-Cordova et al, 2017;Hilbig, Alves, et al, 2018;Jia et al, 2018;Robbins et al, 2015;Villarreal-Lozoya et al, 2007;Wu et al, 2004). Although there were some differences among different research results due to the differences of producing areas, varieties, and extraction methods, the antioxidant capacities of shell were higher than that of kernel in all reports, about 5-7 times of that of kernel.…”

“…The total phenolic content was measured according to the methods of our previous report (Jia et al, 2018). Briefly, methanol extract (10 μl) was mixed with 2 ml of 7.5% (w/v) sodium carbonate and 2.5 ml of 10% (v/v) Folin-Ciocalteu regent, and put in water bath at 50°C for 15 min in the dark.…”

“…The antioxidant capacities were firstly measured by the DPPH free radical scavenging assay according to the methods of previous report (Jia et al, 2018). Briefly, 4 ml of DPPH radical solution (39.43 mg DPPH in 1 L methanol) was mixed with 10 μl of methanol extract and kept in dark for 30 min.…”

“…have excellent antioxidant capacities (Biomhoff, Carlsen, Anderson, & Jacobs, 2006;de la Rosa et al, 2014;Prado et al, 2014;Flores-Cordova et al, 2017;Hilbig, Alves, et al, 2018;Jia et al, 2018;Robbins, Gong, Wells, Greenspan, & Pegg, 2015;de la Rosa, Alvarez-Parrilla, & Shahidi, 2011;Villarreal-Lozoya, Lombardini, & Cisneros-Zevallos, 2007), daily consuming of pecan nut is good to chronic diseases like inflammatory (Robbins, Greenspan, & Pegg, 2016), hyperlipoidemia (Domínguez-Avila et al, 2015), and can protect human brain, blood, and liver from the damage of oxidant (Domínguez-Avila et al, 2015;Müller et al, 2013;Reckziegel et al, 2011). Phenolic metabolites in other organs of pecan trees also play critical roles in the defense of pathogens, injuries, and environment stresses.…”

“…By far, the phenolics in pecan were mostly studied in kernels (Gong & Pegg, 2017;Jia et al, 2018;Robbins et al, 2015;Robbins, Ma, Wells, Greenspan, & Pegg, 2014;de la Rosa et al, 2011), while studies in shell (Hilbig, Alves, et al, 2018), leaf (Gad et al, 2007;Ishak, Ahmed, Abd-Alla, & Saleh, 1980;Lei et al, 2018), and bark (Abdallah et al, 2011) were much less. There is no report of the rest of the organs.…”