Variation in nutritional compositions, antioxidant activity and microstructure of Lycopus lucidus Turcz. root at different harvest times

The objective of this study was to investigate the variation in nutritional compositions, antioxidant activity and microstructure of Lycopus lucidus Turcz. root at different harvest times. L. lucidus Turcz. roots, harvested from two sites (S1 and S2) at three different times (T1: 19-11-2013, T2: 22-12-2013 and T3: 27-01-2014), were analyzed for nutritional compositions, antioxidant activity by DPPH, FRAP and TEAC assays and microstructure. The results revealed that the protein content in L. lucidus Turcz. root first decreased and then increased to a maximum at T3. The reducing sugar content had no significant differences among the three harvest dates studied. The starch content decreased drastically along with an increase of crude fat content with the harvest time delayed. The major amino acids in L. lucidus Turcz. root were aspartic acid and glutamate and the highest total amino acid content was found for the root harvested at T3. The most common element in L. lucidus Turcz. root was detected to be potassium followed by calcium, iron, magnesium, copper and manganese, and their changes were discrepant in the period of harvest. The FP and SGP possessed the highest and lowest phenolic content, respectively. The change of SEP was significantly correlated to the SGP at different harvest times. The highest TPC was found for the root harvested at T3 and the most abundant phenolic acid was chlorogenic acid. The highest and lowest DPPH radical scavenging capacity was observed for the SGP and FP, respectively. The highest and lowest FRAP and TEAC were observed for the FP and SGP, respectively. The results of correlation analysis indicated that there was significant correlation between phenolic content and FRAP and TEAC, and different antioxidant assays. The microstructure of L. lucidus Turcz. root also varied greatly with the harvest times.