*3.2. Changes in Soluble Sugars, Sweetness Index, and Sensory Qualities*

Soluble sugars are the main nutritional components of sweet potato tuberous roots, among which fructose, glucose, and sucrose are the main free sugars that determine their sweetness. Particularly, sucrose content was significantly higher in tuberous roots of the CS group compared with the control (*p* < 0.05) after 14 d of storage. In contrast, glucose and fructose contents did not change significantly in tuberous roots of either CS or control groups during storage (Figure 2A–C).

**Figure 2.** Contents of (**A**) glucose, (**B**) fructose, (**C**) sucrose, and (**D**) sweetness index and sensory score (**E**) 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. Data with different characters are significantly different from each other at the *p* < 0.05 level.

As shown in Figure 2D, the sweetness index in CS group tuberous roots peaked at day 14, reaching a level that was significantly higher than that of the control group. Therefore, sweet potato tuberous roots stored at 5 ◦C successfully achieved low-temperature sweetening. However, the sweetness index of sweet potato tuberous roots not further improved after 14 d of cold storage. Results from the sensory evaluation indicated that rates of consumer acceptance of tuberous roots did not change after 21 d of storage at 13 ◦C. In contrast, the sensory score of tuberous roots stored at 5 ◦C for 14 d was significantly higher than that of the control tuberous roots; however, these scores decreased in tuberous roots stored for 21 d at 5 ◦C due to flesh browning and CI-induced off-flavors after cooking (Figure 2E).
