Antioxidant capacities and moldinhibitory effects of phenolic compounds in several Jin Cheng lines

Abstract:【Objective】The study was to determine the total phenolic contents, total flavonoid contents, thecompositions and contents of the flavonoids and phenolic acids in the peels of 5 local Citrus sinensis osbeck Jin Cheng lines and to evaluate their antioxidant capacities and mold-inhibitory effect of phenolics.【Methods】Phenolic compounds in fruit peels were extracted using methanol with ultrasonic assistance.The total phenolic and total flavonoid contents were determined using ultraviolet spectrophotometer. Phenolic composition and content were detected by high performance liquid chromatography (HPLC), andstandard chromatography maps were used for qualitative and quantitative analysis. Their antioxidant capacities were comparatively analyzed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, ferric reduc⁃ing antioxidant power (FRAP), and 2,2′-azino-bis (3-ethylbenzthiozoline-6)-sulfonic acid (ABTS) methods. The mold-inhibitory effect of phenolics in the peels of various lines was tested using myceliumgrowth rate method. The phenolic extracts were concentrated and dissolved in DMSO. To investigate theeffects of the peel extracts on the mycelium growth of Penicillium digitatum and P. italicum. under eightconcentration gradients (0.65, 1.3, 2.6, 5.2, 10.4, 20.8, 41.6 and 83.2 g·L^-1).【Results】The total flavonoidcontents were significantly higher than the total phenolic contents. The total phenolic content varied from6.52 to 7.71 mg·g^-1 (gallic acid equivalents). The line of‘Fuling’(FL) had the highest total phenolic content (7.7±0.35 mg·g^-1), followed by‘Peng an 100’(PA) (7.45±0.41 mg·g^-1). Likewise, variation in totalflavonoid content ranged from 11.75 to 15.68 mg·g^-1 (rutin equivalents) and the highest content of the total flavonoids was found in PA (15.68±0.48 mg·g^-1) followed by‘Kaixian’(KX) (12.46±0.18 mg·g^-1). Atotal of 14 phenolic compounds including 10 flavonoids and 4 phenolic acids were tested from the peels ofthe 5 local lines. The main components of phenolics in the peels of different lines were basically the same,but their contents were significantly different. Hesperidin (75.52 mg·g^-1)，naringenin (3.46 mg·g^-1)，nobiletin (3.12 mg·g^-1) and diosmetin (2.61 mg·g-1) were the main flavonoids. PA had the highest hesperidin(90.43±0.63 mg·g^-1) and naringenin (3.91±0.05 mg·g^-1) contents.‘Beibei 447’(BB) had the highest nobi⁃letin content (2.62±0.03 mg·g^-1).‘Tongshui 72-1’(TS) had the highest nobiletin content (2.89±0.05 mg·g^-1).Four phenolic acids including gallic acid, chlorogenic acid, ferulic acid and caffeic acid were detectedand gallic acid (1.12 mg·g^-1) was the prevailing phenolic acid, and FL had the highest content (1.29±0.01mg·g^-1). The antioxidant capacities of all the lines were strong. The DPPH values ranged from 12.88 to16.01 μmol·g^-1. The highest DPPH value was found in‘Beibei 447’(BB), whereas the lowest was foundin FL. The FRAP values of the 5 lines ranged from 14.64 to 17.74 μmol·g^-1. The highest FRAP value wasobtained in PA, while the lowest was from FL. The ABTS values varied from 93.31 to 108.17 μmol·g^-1.The highest ABTS value was found in FL, while the lowest was found in BB. Because the three methodsemployed to evaluate antioxidant capacity generated differential rank orders among the lines studied, anoverall antioxidant potency composite index (APC index) of these lines was calculated. The APC index ofall the lines studied showed overt variation (55.48-96.42). The line that had the strongest comprehensiveantioxidant capacity was PA, and TS had the lowest value among all the line. Therefore, the peel of PAwas a good antioxidant phytochemical material. The phenolic extracts had strong inhibitory effects onmold. However, the inhibitory effects between different lines were not significant. The inhibition rateagainst P. digitatum and P. Italicum was 100% at the concentration of 78 g·L^-1. With the decrease in concentration, the inhibition rate against the mold decreased. The MIC of P. digitatum was 2.6 g·L^-1 and waslower than that of P. Italicum(5.2 g·L^-1). Thus the sensitivity of P. digitatum to phenolic extracts was higher than that of P. Italicum.【Conclusion】The peel of PA is the richest in phenolic compounds among allthe lines, and has strong antioxidant activity and anti-fungal effect, and is an excellent source of antioxidants and antimicrobial agents.