*3.3. Changes in Total Phenolics, Free Phenolic Acid Content, and Antioxidant Capacity*

The total phenol contents in tuberous roots of both groups increased after 21 d of storage (Figure 3A). Further, the total phenol content in tuberous roots of the CS group was significantly higher than that in the control group (*p* < 0.05) after 14 d of storage. Chlorogenic acid is the main phenolic compound in sweet potatoes and thus might have contributed to the increase in total phenolic. The chlorogenic acid content in CS tuberous roots was significantly higher (*p* < 0.05) than that in the control group after 14 d (Figure 3B).

**Figure 3.** (**A**) Total phenol and (**B**) chlorogenic acid contents, (**C**) 2,2-Diphenyl-1-Picrylhydrazyl (DPPH) radical-scavenging activity, and (**D**) ferric reducing antioxidant power (FRAP) of sweet potato tuberous roots during 21 d storage control and CS groups. Data are the mean ± standard error of three replicates. Data with different characters indicate significant differences between treatments at the *p* < 0.05 level.

Moreover, the DPPH scavenging activity in tuberous roots of the CS group was significantly (*p* < 0.05) higher than that in the control group after 7 d of storage (Figure 3C). As shown in Figure 3D, the FRAP in the CS group also showed a significant upward trend during storage, with CS tuberous roots showing significantly higher FRAP levels than the control group (*p* < 0.05).

#### *3.4. Changes in Free Amino Acid Content in Sweet Potato Tuberous Roots during Storage*

The free amino acids analyzed herein were glycine, phenylalanine, tyrosine, and propanine. The initial phenylalanine content was approximately 90 mg kg−<sup>1</sup> FW, followed by alanine and tyrosine. The glycine content was the lowest among the four amino acids tested. Almost all of these free amino acids tended to increase continuously between two and six times during storage at temperatures (Figure 4A–D).

**Figure 4.** Contents of (**A**) glycine, (**B**) alanine, (**C**) tyrosine, and (**D**) phenylalanine of sweet potato tuberous roots of control and CS group during 21 d storage. Results are expressed as the mean ± standard error of three replicates. Different characters indicate significant differences between means of treatments at the *p* < 0.05 level.
