Comparison of Nutrients and Antioxidant Activities in Sweet Potatoes

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Introduction
Sweet potato (Ipomoea batatas (L.) Lam), known as groundnut and white potato, belongs to the Convolvulaceae or morning glory family.Sweet potato has been a staple food source in Central and South America for centuries.In Asia, sweet potato also provides an important source of starch in China, Korea, and Vietnam [1][2][3].
As a commercial crop, sweet potato is cultivated worldwide because it is barren tolerant, high yielding, and widely adaptable to diferent climates and farming systems [4].It contains abundant nutrients, including protein, carbohydrates, minerals, vitamins, carotenoids, dietary fber, and polyphenols.Previous studies have reported that sweet potato has many benefcial efects such as antioxidation [5][6][7], anticancer [8,9], anti-infammatory [10], liver protection [11], and prevention of cardiovascular disease [12].Owing to its nutritional components and agronomic advantages, sweet potato could help prevent and reduce mal-or overnutrition in developing and developed countries.In Japan and the United States, it is valued as "longevity food" [13].Te National Aeronautics and Space Administration has selected sweet potato as a candidate food for astronauts on space missions.Besides direct consumption, sweet potato has been processed into value-added products including starch, four, noodles, sugar bread, dessert, jams, tapioca, and natural food colorants [14].
However, global sweet potato demand is decreasing in recent years, and it might be associated with paucity of knowledge about its nutrition and bioactivity.On the other hand, new varieties of sweet potato are appearing constantly.Te nutrients of sweet potato vary greatly among diferent varieties.Finding the characteristics of diferent varieties would conduce to target consumer group with the "best ft" sweet potato varieties.To this end, the main purpose of this study was to characterize the chemical compositional profle and evaluate antioxidative activity and sensory taste of fortyeight sweet potato varieties.

Sweet Potatoes and Biological Trait
Measurement.Te germplasm resource information of 48 sweet potatoes is shown in Table 1.All of them were cultivated in Guizhou province, China, and were harvested between July and September 2020.Biological traits were determined according to the methods outlined in the "Sweet Potato Germplasm Resources Description Specifcation" (https://www.gb-gbt.cn/PDF/English.aspx/NYT2939-2016)[15].Te characteristics of the sweet potatoes are described in Table 2.

Raw Sample Preparation.
All the sweet potatoes were fresh with no germination, disease, or rot and stored away from sunlight.Fresh sweet potatoes were cleaned with tap water, and surface water was removed with tissue paper.Te sweet potatoes were then cut into slices of 1-2 mm thickness and dried at 60 °C.After being weighed, the samples were ground into a fne powder and passed through a 100 mesh sieve.Te sample powder was stored at −80 °C.All analyses were performed in triplicate.

Determination of Proximate Composition.
Te moisture, total starch, crude protein, ash, dietary fber, and vitamin C content were estimated following the AOAC method [16].

Carotenoids Extraction and Analysis.
Te method of extraction was based on the method of Kammona et al. [17] with slight modifcations.In brief, sweet potato powder (1.0 g) was accurately weighed and mixed with an equal weight of CaCO 3 .Te mixture was dissolved in 3 ml of distilled water and added with 25 ml of acetone-methanol (7 : 3) and shaken well.Te resulting mixture was left undisturbed overnight and centrifuged at 3500 rpm for 5 min.Tis step was repeated 3 times.Te supernatants were collected and placed in a partition funnel with equal volumes distill water and hexane.Te hexane layer obtained from the partition funnel was dried under nitrogen.Te dry residue was dissolved in 300 µl ethyl acetate.50 µl of the ethyl acetate extraction solution was added to 950 µl of chloroform.Te absorbance was measured at 480 nm, 648 nm, and 666 nm, respectively, by an Agilent UV-visible spectrophotometer (Cary 60, Angilent Technologies Inc., Palo Alto, USA).Te calculation was based on the Wellburn equation.Te analysis was repeated in triplicate.

Determination of Total Polyphenol Content (TPC).
TPC was determined using the Folin-Ciocalteu method [18][19][20].In short, 1.0 g of sweet potato sample was weighed into 20 ml centrifuge tubes.10 ml methanol was added and the mixture was sonicated at 40 kHz for 30 min.Te supernatant was diluted 100 times with methanol and measured spectrophotometrically at 760 nm.Results were expressed as milligrams of chlorogenic acid equivalents.Te linear range was between 0 and 60 μg•ml −1 .
0.1 g sweet potato powder was weighed and placed in a 15 ml test tube with a stopper.10 ml of 70% methanolic water (containing 2 mg•ml −1 sodium hydrogen sulfte) was added, and the mixture was sonicated for 30 min at 60 °C.Te extraction was cooled to ambient temperature and centrifuged at 4000 rpm for 10 min.Te supernatant was transferred into a 15 ml brown volumetric fask and diluted with 70% methanolic water to volume.Te solution was fltered with a 0.45 μm PTFE syringe flter before high performance liquid chromatography (HPLC) analysis.

Evaluation of Antioxidant
Te method of ABTS + assay was the procedure described by Re et al. [22].Te ABTS + solution (8 mM) and potassium persulfate (3 mM) were mixed in equal quantities and reacted for 12 h at room temperature in the dark for preparation of the working solution.20 μl of the sample was mixed with 180 μl of the working solution.Te mixture was allowed to react at room temperature in the dark for 2 h.A Multiskan Spectrum plate reader (MK3, Termo Fisher Scientifc, Helsinki, Finland) was used to read the absorbance at 734 nm.Te scavenging rates of DPPH and ABTS relative to the control were calculated using the following equation: where A 0 indicates the absorbance value of the blank control (20 μl ethanol) and A 1 indicates the absorbance of the sample.Ascorbic acid (50 mg•ml −1 ) served as a standard antioxidant compound.

Sensory Analysis.
A semitrained panel comprising workers, students, and teachers was organized to conduct the assessment of sensory traits, using an evaluation group consisting of 30 people and a 1 : 1 male to female ratio for evaluation.Samples of the 48 cultivars of sweet potatoes were placed in labeled dishes and steamed for 30 min.Te cooked samples were served to panelists randomly and evaluated for taste, texture, sweetness, bitterness, fragrance, and smoothness on a hedonic scale.Te scoring criteria are listed in Table 3.  2), we encoded the data to refect these morphological characteristics.Tese encoded data were then analyzed using EXCEL, and a dendrogram was constructed with SPSS 25 to perform hierarchical cluster analysis on 48 sweet potato varieties.Tis analysis facilitated the classifcation of these varieties into distinct clusters, enabling us to measure the distance or dissimilarity between them.Te cluster analysis results provide insights into the genetic diversity and potential functional properties of these sweet potato varieties.

Statistical Analysis.
All data were shown as the means ± SD.P values were determined by one-way ANOVA.P < 0.05 was considered to be statistically signifcant.Data were analyzed by SPSS 25 software (IBM SPSS Statistics 25.0, Armonk, NY, USA).Statistical signifcance was considered at p < 0.05.

Proximate Compositions.
Proximate compositions of sweet potato samples are presented in Table 2.For the convenience of statistics, we classify the color of sweet potato fesh as purple, deep purple, and white purple as purple; orange, orange yellow, and light orange as orange; and yellow and light yellow as yellow in Figure 1.All 48 species of sweet potatoes showed a high moisture content and met the consumption and processing requirement as shown in Table 4.However, the water content showed noticeable variations in diferent color tuber fesh cultivars.Purple tuber fesh species had lower average water content than others.Taishu-14 exhibited the highest water content of 80.26%, followed by Zhanjiangcaitaishu-71 (79.39%) and Ecaishu-1 (79.04%).Te lowest water content was noticed in Jiheishu-1 and Anna, with a value around 61.00%.Starch is the main carbohydrate of sweet potato root and accounts for approximately 80% of the sweet potato dry matter.Sweet potato starch can be processed into diverse products such as glucose syrup, processed foods, and food additives in diferent industries, which generates more income [23].Terefore, the starch content is a crucial standard to measure the quality of sweet potatoes.Pale yellow fesh cultivar Nanshu-99, yellow fesh cultivar Qianshu-14, and purple-fesh cultivar Jiheishu-1, which had the greatest dry matter, also had the highest starch content of 28.08%, 26.37%, and 26.30%, respectively.Cultivar Ziyunhongxinshu which had the lowest dry matter also had the least starch content (13.48%).Te average starch content of purple-fesh varieties was over 22.89%, obviously higher than other color fesh cultivars.Dark orange fesh genotypes had less starch than others, with an average of 15.21%.Te starch content in yellow fesh cultivars (20.21%) was slightly higher than in pale yellow (19.22%), yellow orange (18.91%), and white (18.66%) fesh cultivars.
Te ash content of these test-varieties ranged from 1.69% to 4.02%.Te lowest ash content was recorded in Qianshu-11, while the highest was in Qianshu-5.
Te range of the dietary fber content was from 0.54% in Qianshu-2 to 3.52% in Guangcaishu-3.Te highest value was found in Guangcaishu-3.Te fber content of most cultivated varieties was approximately 2%.Te high fber content could afect the texture of sweet potato.On the other hand, dietary fber is benefcial for constipation by promoting the growth of probiotics [24].

Total Antioxidant
Capacity.Some studies seek to compare the antioxidant potentials of fesh from white and purple-skinned sweet potato.Results show that the evaluated antioxidant indices DPPH and ABTS radical-scavenging capacity against lipid oxidation were higher in peels of the studied potato compared to the fesh [28].DPPH and ABTS + free-radical scavenging capacity of all varieties are shown in Table 7. TAC (DPPH) of Mianzishu-9 was obviously higher than other cultivars, followed by Pushu-32 and Qianshu-18-5-3.Chuanshu-1386-4 had the lowest TAC (DPPH).Sweet potatoes with purple fesh had stronger DPPH free-radical scavenging activity than others.Te performance of Mianzishu-9 on ABTS + quenching capacity was far better over the rest of cultivars.Higher TAC (ABTS + ) was recorded in Chuanshu-1386-4, Qianshu-18-5-3, Qianshu-5, Jiheishu-1, and Pushu-32, similar to the rank of DPPH free-radical scavenging capacity.In contrast, TAC (ABTS + ) was the lowest in the yellow fesh type Huangyecaishu.Te TAC of sweet potato was positively related to the contents of vitamin C, TPC, phenolic acids, and carotenoids.All these compounds with reductive groups have activity scavenging free radicals.Purple fesh varieties which contained the greatest content of vitamin C, TPC, and phenolic acids exhibited potent antioxidative efects.Mianzishu-9 with the highest TPC, phenolic acids, and vitamin C performed best in TAC, followed by Jiheishu-1, both cultivars were purple feshed.Te strong TAC of the dark orange cultivar Pushu-32 was correlated to the abundance of carotenoids.As we know, excessive free radicals could damage large molecules such as proteins, DNA, and cell membrane, causing aging and disease [29].Ingestion of food with antioxidative efects is benefcial for maintaining homeostasis in the human body.Mianzishu-9, Qianshu-18-5-3, Jiheishu-1, Ganshu-3, Pushu-32, Qianshu-5, and Ecaishu-1 could be selected as antioxidant profle-enriched cultivars.

Sensory Taste Evaluation.
Tere is research for the sensory evaluation of 12 sweet potatoes with orange, purple, and yellow fesh, and it was found that consumers liked smooth texture, brown sugar and dried apricot favor, and sweet taste and disliked bitter, umami, astringent mouthfeel, vanilla aroma, and residual fbers [30].Te sensory score is listed in Table 8 and Figure 3.In all 48 cultivars, Hongxiangjiao got the highest score (82.9) for all sensory traits.Ziyunhongxinshu, Qianshu-18-5-4, and Xushu-18 also had good scores.Te purple-fesh varieties Qianshu-18-5-3, Jiheishu-1, and Mianzishu-9, which had great contents of starch, protein, and antioxidants, conducted excellent performance on TAC.However, they were less preferred, scoring around 60, owing to the mild bitterness and poor texture.Tis might be associated with the height content of antioxidants.Polyphenols give a bitter taste, and vitamin C afects the sweetness.Dry matter weight is correlated to the texture of sweet potato.Higher dry matter made the sweet potato less watery, denser, and adhesive.Te lower moisture content made the purple cultivars feel lightly dry and frm.Chuancaishu-211, Qiancaishu-2, Wancaishu-19, Huangyecaishu, and Zhanjiangxiyecaishu received low scores in all sensory characters with higher dietary fber contents.Although dietary fber has benefcial efects on relieving constipation, promoting the growth of probiotics and decreasing blood sugar levels, it makes the sweet potato taste rough [31].Tese cultivars might not be suitable for staple consumption and could be further processed into other products.Generally, the orange and yellow cultivars were favored.

Discussion
Sweet potato, a vital food crop, holds a place of particular importance in tropical and subtropical regions where it serves as a staple food and primary energy source.Its global recognition as one of the world's top ten foods is attributed to its diverse sizes, shapes, colors, and health benefts [33].
Te extensive cultivation of sweet potatoes worldwide is driven not only by their nutritional value but also due to their health-promoting properties [34].In this global context, China has emerged as one of the leading producers, contributing signifcantly through the development of new varieties that enhance the crop's diversity and utility [35].Due to the genetic diversity, chemical components along with the bioactive efects are variable in diferent cultivars [36].In this present work, we evaluate the sensory taste, proximate composition, phytochemicals, and antioxidant efects in forty-eight cultivars of sweet potato.Our results suggested that sweet potato had abundant nutritional elements together with phytochemicals.Among them, protein is a unique and important nutrient.Te crude protein content of sweet potato was generally around 4.00%.In this work, the protein contents of sweet potatoes from 48 varieties ranged from 2.00% to 12.16%.Cultivars containing abundant protein could serve as a complementary source of protein, especially for low-income people.Te range of starch content of the 48 genotypes was between 13.48% and 28.08%.Te cultivars combined high protein and starch, such as Jiheishu-1, Mianzishu-9, and Ganshu-3, and were ideal for staple consumption.More recently, the demand for wholesome foods has increased among consumers.Sweet potato possesses abundant functional phytochemicals including vitamin C, carotenoids, polyphenols, and dietary fber.Tese constitutions difered signifcantly in terms of genotypes.Terefore, the selection of stable and high-yielding genotypes and accordance with consumer and industry preferences is one of the focuses of sweet potato research [37].Our research indicates that the purple-feshed cultivars Mianzishu-9, Jiheishu-1, and Qianshu-18-5-3 contained remarkably high vitamin C, total polyphenols, and phenolic acids.Tese cultivars not only displayed stronger antioxidant efects than similarity, carotenoids can eliminate the symptoms of vitamin A defciency.Sweet potato, especially orange and yellow fesh varieties, is an abundant source of carotenoids [39].Te carotenoids content in sweet potato was positively related to the color of fesh.Te highest carotenoids content was recorded in dark orange fesh cultivars such as Pushu-32, Taishu-14, Sushu-14, and Qianshu-5.Te average value of dark orange fesh varieties was 183.70 µg•g −1 •DW, followed by yellow orange fesh varieties (25.07 µg•g −1 •DW).
Dark orange fesh cultivars such as Pushu-32 and Taishu-14, with its rich nutrient profle, could play a key role in reducing the hidden hunger for vitamins and antioxidants.Tis aligns with the fndings of Tang et al. [40], who systematically compared the carotenoid profles in both raw and cooked sweet potatoes across fve varieties-white, yellow, orange, light purple, and deep purple.Tang et al.'s study revealed that yellow and orange varieties of sweet potato have higher carotenoid contents, particularly noteworthy given the essential role of carotenoids in human health as antioxidants and as precursors to vitamin A. Tese  Journal of Food Biochemistry insights underscore the importance of selecting specifc sweet potato varieties, like Taishu-14, in dietary strategies aimed at combating micronutrient defciencies.
Sweet potato breeding programs must integrate sensory characterization and hedonic perception, including aspects such as taste, texture, aroma, and appearance, to deliver products that meet the diverse demands of global markets.In addition to considering proximate composition, functional phytochemicals, and bioactivity, the taste emerges as a pivotal factor for the acceptability of food products.Understanding and catering to these sensory preferences is the key to ensuring that these nutritionally rich crops are not only benefcial but also appealing to consumers worldwide.In the present study, albeit the purple-fesh varieties had abundant protein, starch, and antioxidants, they did not score high in sensory taste.Te reason might be that the large amounts of polyphenols could increase the bitter taste [31] and the low water content infuenced the texture.Te dark orange fesh cultivars received the best average score among all genotypes.Dark orange fesh cultivars Hongxiangjiao and Ziyunhongxinshu were best for all sensory traits.Both cultivars were not abounding in starch, protein, and antioxidants.Hongxiangjiao had higher contents of protein, vitamin C, carotenoids, and phenolic acids and exhibited stronger antioxidative capacity than Ziyunhongxinshu.Tese cultivars might not suitable for staple foods, but they were recommended for people who have a desire for better favor and taste.Numerous investigations have suggested a positive efect on human health from the consumption of foods rich in bioactive substances with antioxidant activity, particularly phenolic compounds [41].Tese compounds are known to reduce the risk of various diseases, including cancer, heart disease, and diabetes.Sweet potatoes, in this context, emerge as a valuable dietary choice due to their signifcant content of polyphenols.Te presence of these compounds in sweet potatoes not only contributes to their antioxidant capacity but also positions them as a functional food with potential health-promoting properties.In a study conducted by Hana et al. [42], the antioxidant activity, total polyphenol content, and selected chlorogenic acids in diferent varieties of sweet potatoes were analyzed.Te results suggested that the purple-feshed variety of sweet potatoes possesses a signifcantly higher total polyphenol content, thereby exhibiting the highest antioxidant activity among the varieties tested.Similarly, our fndings revealed that the chlorogenic acid, 3,5-dicafeoylquinic acid, 3,4-dicafeoylquinic acid, and 4, 5dicafeoylquinic acid had positive and prominent relationship among each of them and with TPC and TAC (ABTS + ).All phenolic acids mentioned above, except 3,4-dicafeoylquinic acid, were positively correlated to TAC (DPPH).It demonstrated that the increment of one phenolic acid was directly related to an increase of another phenolic acid.TAC (ABTS + ) had a signifcantly positive association with chlorogenic acid, 3,5-dicafeoylquinic acid, 3,4-dicafeoylquinic acid, 4, 5-dicafeoylquinic acid, TPC, vitamin C, and TAC (DPPH).Carotenoids had a substantial positive correlation with TAC (DPPH).Vitamin C contributed to TAC (ABTS + ), chlorogenic acid, 3,5-dicafeoylquinic acid, and 4, 5-dicafeoylquinic acid as well.Tese fndings revealed that polyphenols, carotenoids, and vitamin C were involved in the antioxidant capacity of sweet potatoes.
All these results can conform to the consequences from the total phenolic content and the total carotenoid content.

Conclusion
Sweet potato is a widely distributed root and tuber crop with great variability and phenotypic plasticity.Besides starch, sweet potato also provides protein, vitamin C, carotenoids, dietary fber, and other natural antioxidants.Tus, sweet potato has a strong potential to prevent and improve maland undernutrition.In this study, 48 sweet potato varieties were comprehensively evaluated in terms of proximate compositions, phytochemicals, antioxidant activity, and sensory taste.It turned out that the chemical components and antioxidant activity difered markedly.Tese fndings would contribute to the variety choice of sweet potato to meet the needs of diferent consumer groups in human food systems.For example, purple fesh cultivars with high starch, protein, and bioactive phytochemicals were encouraged to plant for improving malnutrition and combating hidden hunger.Cultivars with good taste were more suitable for enriching the diversity of food.Te genotypes with high starch but low other ingredients could be used for four processing.
Capacity.A 0.15 g sweet potato sample was accurately weighed and ultrasonically extracted with 3 ml of distilled water.Te extract was 2 Journal of Food Biochemistry centrifuged at 4000 rpm for 15 min.Te supernatant was collected and stored at −4 °C for the antioxidant tests.

Table 1 :
Origin information of samples.

Table 2 :
Biological characteristics of samples.
2.9.Cluster Analysis.Based on biological characteristics identifed, such as leaf shape, leaf color, skin color, and fesh color of sweet potatoes (Table

Table 3 :
Sensory evaluation criteria for steamed sweet potato.

Table 8 :
Sensory evaluation values of 48 sweet potato cultivars.