*2.3. Sugar Content, Sweetness Index, and Taste Evaluation*

The sugar content was evaluated as described by Li et al. [9] with some modifications. Briefly, 2.0 g of sample was ground in 15 mL of 40% acetonitrile in a mortar on ice. The homogenate was then transferred to a centrifuge tube and sonicated for 20 min before centrifuging at 12,000× *g* for 15 min. The precipitate was reextracted twice with 2 × 15 mL extracting solvent. All supernatants were then collected to a final 50 mL volume, after which the sample was filtered through a 0.45 μm membrane filter prior to assessment.

Next, 10 μL of the filtrate was injected into a high-performance liquid chromatography (HPLC) system (Agilent 1200, Agilent Technologies, Palo Alto, CA, USA) fitted with a refractive index detector (RID-1260, Agilent) and an Agilent ZORBAX Carbohydrate Analysis Column (4.6 mm × 250 mm, Agilent). Soluble sugars were separated in 75% (*v*/*v*) acetonitrile at a 1 mL min−<sup>1</sup> flow rate at room temperature. Target peaks were identified by comparing the retention times of the compounds in the sample solutions to those of a standard mixture, and compound concentrations were determined via the area percentage method. All results were expressed as mg kg−<sup>1</sup> on a dry mass basis.

The sweetness index, an estimate of total sweetness perception, is calculated based on the amount and sweetness properties of individual carbohydrates in fruits and vegetables [13]. The sweetness contribution of each carbohydrate was calculated based on the fact that fructose and sucrose are 2.30 and 1.35 times sweeter than glucose, respectively [14]. The sweetness index was calculated using the following Equation (3):

$$\text{Sweetness index} = 1.00 \times \text{glucose} + 2.30 \times \text{fructose} + 1.35 \times \text{sucrose} \tag{3}$$

The sensory quality of sweet potato tuberous roots was evaluated by measuring the sensory quality index. Evenly sized tuberous roots were selected, cleaned, weighed, and boiled for 40 min under atmospheric pressure. After cooking, the tuberous roots were allowed to cool for 30 min prior to sensory evaluation. A group of 10 people of different ages, sex, and education levels participated in the assessment. A five-point hedonic scale: 2 = "extremely dislike"; 4 = "dislike"; 6 = "neither like nor dislike"; 8 = "like"; and 10 = "extremely like" was used to assess the sensory qualities of the boiled tuberous roots. The sensory attributes evaluated were general appearance, smell, sweetness, and overall acceptability.
