Purple-fleshed Sweet Potato Cultivar Research Articles

Multi-trait selection for mean performance and stability in purple-fleshed sweet potato

Few purple-fleshed sweet potato (PFSP) cultivars are available for Brazilian growers, urging for the development of new and adapted cultivars. PFSP breeding programs should include multiple traits during the selection process to increase the chances of developing an adequate genotype, specially yield-related and quality-related traits. The objective was to select promising PFSP genotypes based on yield and tuberous-roots-related traits exploring genotype x environment interaction (GEI). Four experiments were carried out, in which 23 pre-selected PFSP genotypes were evaluated based on yield and quality traits, after screening among 2500 experimental genotypes. The first experiment adopted an augmented block design, with ‘Luiza’ interspersed as a control. From this first experiment, the 19 experimental genotypes with the best performance were selected for the following three experiments, which were conducted in a randomized block experimental design, with three replications each, including ‘Luiza’ as control. The best genotypes were selected in the first experiment using the multi-trait genotype-ideotype distance index (MGIDI). For the following experiments, the performance of the genotypes was assessed using deviance analysis, genotypic stability through weighted average of absolute scores (WAASB) index, and the multi-trait stability index (MTSI). In the first experiment, three factors were retained, being associated to commercial production of tuberous roots (‘K-104′, ‘K-25′ and ‘U1–29′), total production of tuberous roots (‘K-110′, ‘C-42′, ‘F-16′, and ‘U1–29′), and quality of tuberous roots (‘F-22′), respectively. Desired gains were observed for all traits. For the experiments II, III, and IV five factors were retained, being four related to quality of tuberous roots and one to yield components. The GEI was significant for yield-related traits and desired gains were observed for most traits. Due to high commercial tuberous root yield and low WAASB values, the genotypes ‘U1–29′, ‘K-98′, ‘F-22′, ‘K-57′, ‘C-36′, ‘U1–15′, ‘K-25′, and ‘U2–12′ were highly productive and stable. The genotypes selected by the MTSI index were ‘U1–15′, ‘U2–10′, ‘U1–29′, ‘K-98′, and ‘K-78′. The multi-trait selection enabled the identification of promising genotypes highlighting their strengths and weaknesses.

IbMYC2 Contributes to Salt and Drought Stress Tolerance via Modulating Anthocyanin Accumulation and ROS-Scavenging System in Sweet Potato.

Basic helix-loop-helix (bHLH) transcription factors extensively affect various physiological processes in plant metabolism, growth, and abiotic stress. However, the regulation mechanism of bHLH transcription factors in balancing anthocyanin biosynthesis and abiotic stress in sweet potato (Ipomoea batata (L.) Lam.) remains unclear. Previously, transcriptome analysis revealed the genes that were differentially expressed among the purple-fleshed sweet potato cultivar 'Jingshu 6' and its anthocyanin-rich mutant 'JS6-5'. Here, we selected one of these potential genes, IbMYC2, which belongs to the bHLH transcription factor family, for subsequent analyses. The expression of IbMYC2 in the JS6-5 storage roots is almost four-fold higher than Jingshu 6 and significantly induced by hydrogen peroxide (H2O2), methyl jasmonate (MeJA), NaCl, and polyethylene glycol (PEG)6000. Overexpression of IbMYC2 significantly enhances anthocyanin production and exhibits a certain antioxidant capacity, thereby improving salt and drought tolerance. In contrast, reducing IbMYC2 expression increases its susceptibility. Our data showed that IbMYC2 could elevate the expression of anthocyanin synthesis pathway genes by binding to IbCHI and IbDFR promoters. Additionally, overexpressing IbMYC2 activates genes encoding reactive oxygen species (ROS)-scavenging and proline synthesis enzymes under salt and drought conditions. Taken together, these results demonstrate that the IbMYC2 gene exercises a significant impact on crop quality and stress resistance.

Effect of Growth Stages on Anthocyanins and Polyphenols in the Root System of Sweet Potato.

The storage roots of purple-fleshed sweet potato contain a variety of anthocyanins and polyphenols. Little is known about changes in the total content and composition of anthocyanins and polyphenols in the early growth stages of the root system. In this study, we investigated the changes in anthocyanins and polyphenols in the root system of purple-fleshed sweet potato cultivars at 15, 30, 45, and 60 days after transplant (DAT). Unexpectedly, the highest percentage of acylated anthocyanins in three purple-fleshed cultivars among all growth stages was at 15 DAT. On the other hand, the total polyphenol content in the early growth stages of the root system increased rapidly toward 45 DAT, just before the beginning of storage root enlargement, and then decreased rapidly as the storage roots began to enlarge. These data indicate that the early growth stage of the root system is a critical time. This timing may present a strategy to maximize the accumulation of polyphenols with high antioxidant activity, as well as acylated anthocyanins, to protect against abiotic and biotic stresses.

Effect of Fertilization Level on the Yield, Carotenoids, and Phenolic Content of Orange- and Purple-Fleshed Sweet Potato

Maintaining a diverse diet is essential for the preservation of one’s health and may contribute to the fight against significant civilization diseases such as obesity or diabetes. Sweet potato can be fitted into a diverse diet and serve as a functional food with its antioxidant content. Therefore, it is important to know how the production technology alters the content and composition of these antioxidant compounds. The objective of this study was to collect information on how the increased potassium dominant fertilizer levels and also the additional high-dose fertigation can affect the phytonutrient contents and yields in an orange- and a purple-fleshed sweet potato cultivar. Field experiments were conducted in the Hungarian county of Heves in two consecutive growing seasons in 2021–2022. Different doses of potassium-predominant fertilizer were applied to an orange flesh (Beauregard) and a purple flesh (Stokes Purple) varieties of sweet potatoes. Different application techniques were used in the form of base and top dressing at different rates. The effect on yield and polyphenol content of the different fertilizer rates was investigated. Analytical studies were carried out by high-performance liquid chromatography (HPLC). In the case of the Beauregard variety, in addition to identifying the carotenoids, we also performed their quantitative determination. We found that 87% of the carotenoid content was ß-carotene. The total anthocyanin content was investigated for the purple variety—Stokes Purple, for which a new extraction method was developed. In our study, the split dosages, when the pre-planting fertilizer was supplemented with additional liquid fertilization, resulted in 36 and 30.5% higher yields in the Beauregard in Experiment I and Experiment II, respectively, compared to the untreated control plots over the two years. The additional liquid fertilizer increased the yield to a lesser extent when compared to treatments received only pre-planting fertilizer. As for Experiment III, the split dosages resulted in 34.4% higher yields in the Stokes Purple compared to the control plots. However, the additional liquid fertilizer was not effective at all when the plants received a double dose of pre-planting fertilizer in the case of Stokes Purple. Total carotenoid (Experiment I–II) was higher and anthocyanin yield per plant (Experiment III) was significantly higher in the split-dosage treatment than in the untreated control plots.

Comparative transcriptome analysis of purple-fleshed sweet potato and its yellow-fleshed mutant provides insight into the transcription factors involved in anthocyanin biosynthesis in tuberous root.

In various plant species, many transcription factors (TFs), such as MYB, bHLH, and WD40, have been identified as regulators of anthocyanin biosynthesis in underground organs. However, the regulatory elements of anthocyanin biosynthesis in the tuberous roots of sweet potato have not been elucidated yet. Here, we selected the purple-fleshed sweet potato cultivar “Zhezi1” (ZZP) and its spontaneous yellow-fleshed mutant “Xinli” (XLY) to investigate the regulatory mechanism of the anthocyanin biosynthesis in the tuberous roots of sweet potato. By analyzing the IbMYB1 genotype in ZZP and XLY, we found that the IbMYB1-2, a MYB TF involved in anthocyanin biosynthesis, was missing in the XLY genome, which might lead to an extreme decrease in anthocyanins in XLY. A comparative transcriptome analysis of ZZP and XLY was conducted to find the TFs involved in anthocyanin biosynthesis in ZZP and XLY. The anthocyanin structural genes were significantly enriched among the differentially expressed genes. Moreover, one MYB activator (IbMYB1), one bHLH (IbbHLH2), three WRKY activator candidates (IbWRKY21, IbWRKY24, and IbWRKY44), and two MYB repressors (IbMYB27 and IbMYBx-ZZ) were highly expressed in ZZP accompanied with anthocyanin structural genes. We also tested the expression of these TFs in six purple- and two orange-fleshed sweet potato cultivars. Interestingly, most of these TFs were significantly positively correlated with anthocyanin contents in these cultivars. The function of the anthocyanin biosynthesis repression of IbMYB27 and IbMYBx-ZZ was verified through transient co-transformation with IbMYB1 into tobacco leaves. Further functional verification of the above TFs was conducted by Y2H, BiFC, and dual-luciferase assays. These tests showed that the MYB-bHLH-WD40/MYB-bHLH-WD40-WRKY complex activated the promoter of anthocyanin structural gene IbDFR and promoters for IbWRKY44, IbMYB27, and IbMYBx-ZZ, indicating reinforcement and feedback regulation to maintain the level of anthocyanin accumulation in the tuberous roots of purple-fleshed sweet potato. These results may provide new insights into the regulatory mechanism of anthocyanin biosynthesis and accumulation in underground organs of sweet potatoes.

Comparative Chromosomal Localization of 45S and 5S rDNA Sites in 76 Purple-Fleshed Sweet Potato Cultivars

In recent years, the purple-fleshed sweet potato has attracted more attention because of its high nutritional value. The cytogenetics of this crop is relatively unexplored, limiting our knowledge on its genetic diversity. Therefore, we conducted cytogenetic analysis of 76 purple-fleshed sweet potato cultivars to analyze the chromosome structure and distribution of 45S and 5S rDNA. We noted that only 62 cultivars had 90 chromosomes, and the others were aneuploid with 88, 89, 91, or 92 chromosomes. The number of 45S rDNA in the 76 cultivars varied from 16 to 21; these sites showed different signal sizes and intensities and were localized at the chromosomal termini or satellite. The number of 5S rDNA was relatively stable; 74 cultivars showed six sites located at the chromosomal sub-terminal or near the centromere. Only the ‘Quanzishu 96’ and ‘Yuzixiang 10’ showed seven and five 5S rDNA sites, respectively. Additionally, both parent cultivars of ‘Quanzishu 96’ showed 18 45S and six 5S rDNA sites. Overall, our results indicate a moderate diversity in the distribution pattern of rDNAs. Our findings provide comprehensive cytogenetic information for the identification of sweet potato chromosomes, which can be useful for developing a high-quality germplasm resource.

Identification and Quantitation of Anthocyanins in Purple-Fleshed Sweet Potatoes Cultivated in China by UPLC-PDA and UPLC-QTOF-MS/MS.

The identification and quantitation of the anthocyanins in 12 purple-fleshed sweet potato (PFSP) cultivars ('Jihei 1', 'Xuzi 3', 'Xuzi 6', 'Zhezi 4', 'Ningzi 1', 'Ningzi 2', 'Ningzi 3', 'Ning 2-2', 'Ning 6-8', 'Guangzi 1', 'Ziluolan', and 'Qinzi 1') in China were carried out using a combination of ultraperformance liquid chromatography-photodiode array (UPLC-PDA), quadrupole-time-of-flight mass spectrometry (QTOF-MS), and tandem mass spectrometry (MS/MS) analyses. Thirteen acylated anthocyanins were tentatively characterized, including two new PFSP anthocyanins, cyanidin 3-caffeoyl-vanilloyl sophoroside-5-glucoside and peonidin 3-caffeoyl-vanilloyl sophoroside-5-glucoside. The quantitative analyses of these anthocyanins were conducted using cyanidin 3-O-glucoside as a standard. The total anthocyanin content of the PFSPs depended on the cultivar. The five PFSP cultivars with the highest content of anthocyanins were 'Jihei 1', 'Xuzi 3', 'Zhezi 4', 'Ziluolan', and 'Qinzi 1'. This is the first report of the 'Ningzi 2', 'Ningzi 3', and 'Ning 2-2' PFSP cultivars containing only diacylated anthocyanins and of the 'Xuzi 6' cultivar containing single anthocyanidin-based anthocyanins.

Enhanced accumulation of carotenoids in sweetpotato plants overexpressing IbOr-Ins gene in purple-fleshed sweetpotato cultivar

Sweetpotato [Ipomoea batatas (L.) Lam] is an important root crop that produces low molecular weight antioxidants such as carotenoids and anthocyanin. The sweetpotato orange (IbOr) protein is involved in the accumulation of carotenoids. To increase the levels of carotenoids in the storage roots of sweetpotato, we generated transgenic sweetpotato plants overexpressing IbOr-Ins under the control of the cauliflower mosaic virus (CaMV) 35S promoter in an anthocyanin-rich purple-fleshed cultivar (referred to as IbOr plants). IbOr plants exhibited increased carotenoid levels (up to 7-fold) in their storage roots compared to wild type (WT) plants, as revealed by HPLC analysis. The carotenoid contents of IbOr plants were positively correlated with IbOr transcript levels. The levels of zeaxanthin were ∼12 times elevated in IbOr plants, whereas β-carotene increased ∼1.75 times higher than those of WT. Quantitative RT-PCR analysis revealed that most carotenoid biosynthetic pathway genes were up-regulated in the IbOr plants, including PDS, ZDS, LCY-β, CHY-β, ZEP and Pftf, whereas LCY-ɛ was down-regulated. Interestingly, CCD1, CCD4 and NCED, which are related to the degradation of carotenoids, were also up-regulated in the IbOr plants. Anthocyanin contents and transcription levels of associated biosynthetic genes seemed to be altered in the IbOr plants. The yields of storage roots and aerial parts of IbOr plants and WT plants were not significantly different under field cultivation. Taken together, these results indicate that overexpression of IbOr-Ins can increase the carotenoid contents of sweetpotato storage roots.

Identification and thermal stability of purple-fleshed sweet potato anthocyanins in aqueous solutions with various pH values and fruit juices

Thirteen anthocyanins were identified in the purple-fleshed sweet potato cultivar Jihei No. 1. The main anthocyanins were 3-sophoroside-5-glucoside derivatives from cyanidin and peonidin, acylated with p-hydroxybenzoic acid, ferulic acid, or caffeic acid. A unique anthocyanin, delphinidin-3,5-diglucoside was also found. The thermal stability of purple-fleshed sweet potato anthocyanins (PSPAs) followed a first-order kinetics model. Aqueous solutions with various pH (2, 3, 4, 5, and 6) and fruit juices (apple, pear, grapefruit, orange, tangerine, kiwifruit, and lemon) were coloured with PSPAs. The enrichment and degradation kinetics of anthocyanins in these matrices were investigated at 80, 90, and 100°C. A higher stability of anthocyanins was obtained in aqueous solutions with pH 3 and 4 and in apple and pear juices. Moreover, the activation energies for PSPA degradation in aqueous solutions with various pH and fruit juices ranged from 66.56kJ/mol to 111.57kJ/mol and 46.76kJ/mol to 75.68kJ/mol, respectively.

Comparative proteomic study between tuberous roots of light orange- and purple-fleshed sweetpotato cultivars

This study compares the differences in proteomes expressed in tuberous roots of a light orange-fleshed sweetpotato (Ipomoea batatas (L.) Lam. cultivar Yulmi) and a purple-fleshed sweetpotato cultivar (Shinjami). More than 370 protein spots were reproducibly detected by two-dimensional gel electrophoresis, in which 35 spots were up-regulated (Yulmi vs. Shinjami) or uniquely expressed (only Yulmi or Shinjami) in either of the two cultivars. Of these 35 protein spots, 23 were expressed in Yulmi and 12 were expressed in Shinjami. These protein spots were analyzed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and electrospray ionization tandem mass spectrometry. Fifteen proteins in Yulmi and eight proteins in Shinjami were identified from the up-regulated (Yulmi vs. Shinjami) or uniquely expressed (only Yulmi or Shinjami) proteins, respectively. In Yulmi, α-amylase and isomerase precursor–like protein were uniquely expressed or up-regulated and activities of α-amylase, monodehydroascorbate reductase, and dehydroascorbate reductase were higher than in Shinjami. In Shinjami, peroxidase precursor and aldo–keto reductase were uniquely expressed or up-regulated and peroxidase and aldo–keto reductase activities were higher than in Yulmi. PSG-RGH7 uniquely expressed only in Shinjami and the cultivar was evaluated more resistant than Yulmi against the root-knot nematode, Meloidogyne incognita (Kofold and White, 1919) Chitwood 1949 on the basis of shoot and root growth. Egg mass formation was 14.9-fold less in Shinjami than in Yulmi. These results provide important clues that can provide a foundation for sweetpotato proteomics and lead to the characterization of the physiological function of differentially expressed proteins.

자색고구마 품종별 안토시아닌 색소의 분해에 대한 속도론적 연구

국내에서 재배되는 목포 62호, 보라미, 자미, 신자미, 아야무라사키의 자색고구마 품종에 대해 안토시아닌 함량 및 pH에 따른 적색도, pH와 가열온도에 따른 안정성을 평가하였다. 그 결과, 안토시아닌 함량은 각 3.9, 3.8, 4.7, 4.1, 4.2 mg/g dry weight로 자미가 가장 높았으며, pH에 따른 a 값은 pH 3 에서 20.2, 59.3, 41.4, 37.7, 26.9로 보라미가 가장 높았다. pH에 따른 품종별 안토시아닌 색소의 반감기는 pH 3에서 22.2, 28.3, 26.3, 23.4, 22.7일로 보라미가 가장 안정하였다. 그리고 온도에 따른 품종별 안토시아닌 색소의 반감기는 온도가 낮을수록 증가하여 안정하였으며, 특히 자미는 <TEX>$20^{\circ}C$</TEX>에서 401일로 매우 높은 안정성을 나타냈다. 또한 가열온도에 따른 활성화에너지는 54.67, 60.93, 71.73, 59.35, 62.28 kJ/mol로 자미가 가장 높았다. The effects of pH and temperature on degradation of anthocyanin in purple-fleshed sweet potato cultivars(Mokpo No.62, Borami, Jami, Sinjami and Ayamurasaki) were determined at pH ranges of 1 to 5 and temperature ranges of 20 to <TEX>$80^{\circ}C$</TEX>. The anthocyanin contents of five sweet potato varieties were 3.9, 3.8, 4.7, 4.1, 4.2 mg/g of dried sweet potato, respectively. Degradations of anthocyanins at different pHs and temperatures followed the first-order reaction. Our results clearly showed that the anthocyanin stability of purple-fleshed sweet potato was dependent on the source of the sweet potato cultivars. Anthocyanin obtained from Borami showed the highest stability. The half-life of antocyanin degradation of purple sweet potato cultivars(Mokpo No.62, Borami, Jami, Sinjami and Ayamurasaki) at pH 3 were 22.2, 28.3, 26.3, 23.4, 22.7 days at <TEX>$60^{\circ}C$</TEX>, respectively. A significant decrease in anthocyanin stability was observed at temperatures above <TEX>$40^{\circ}C$</TEX>. Activation energies of purple-fleshed sweet potato cultivars at different temperatures were 54.67, 60.93, 71.73, 59.35, 62.28 kJ/mol, respectively.

Structural and functional characterization of IbMYB1 genes in recent Japanese purple-fleshed sweetpotato cultivars

To elucidate further the genetic mechanism underlying anthocyanin accumulation in the storage roots of recent Japanese purple-fleshed sweetpotato cultivars, we compared the structure of the IbMYB1 gene in cultivar Ayamurasaki and its spontaneous mutant, AYM96, whose storage roots do not accumulate anthocyanin. Amplification of the IbMYB1 genomic fragment covering the coding sequences suggested that the genome of Ayamurasaki contained three types of IbMYB1 sequences, named IbMYB1-1, IbMYB1-2a and IbMYB1-2b, whereas AYM96 had only IbMYB1-1. Although these three IbMYB1 sequences had identical coding sequences, IbMYB1-1 had a 7-bp insertion in the first intron. IbMYB1-2a and IbMYB1-2b were characterized by a single nucleotide polymorphism in the second intron. Further cloning and sequencing of the flanking regions of these IbMYB1 sequences showed that the promoter and 3′ flanking regions of IbMYB1-2a and IbMYB1-2b were different from those of IbMYB1-1. Genetic analysis using an F1 population derived from a cross between the purple-fleshed cultivar Murasakimasari and AYM96 suggested that IbMYB1-2 sequences are responsible for anthocyanin accumulation in the storage roots. The structural features of these three IbMYB1 sequences and identification of the IbMYB1-2null sequence, which contained sequences very similar to those of the flanking regions of IbMYB1-2a and IbMYB1-2b, but which lacked the sequence around the coding region, suggested that IbMYB1 genes in recent Japanese purple-fleshed cultivars had been established through multiple gene-duplication events.

Cancer Prevention of Anthocyanins in the Purple Sweetpotato bred in Kansas

Anthocyanins are versatile and plentiful flavonoid pigments that account for the purple color in may plant foods such as red grapes, berries, red cabbages, and purple sweetpotato. Although anthocyanins have been epidemiologically associated with reduced cancer risk, the anticancer ability of the purple sweetpotato has not been well investigated. Considering the high contents of anthocyanin in the purple sweetpotato, we have bred purple‐fleshed sweetpotato cultivars using seeds from controlled crosses provided by the International Potato Center in Lima, Peru. Over 2000 seedlings from four full‐sib progenies cultured at the John C. Pair Horticulture Research Center, Kansas, have been segregated by multiple traits based upon flesh pigmentation and fiber contents. We and determined the prominent anthocyanin contents by HPLC‐MS, including cyanidin 3‐sophoroside‐5‐glucoside (m/z 774), p‐hydroxybenzoylated cyanidin 3‐sophoroside‐5‐glucoside (m/z 894), caffeoylated cyanidin 3‐sophoroside‐5‐glucoside (m/z 908), and peonidin 3‐(6,6′‐caffeoyl‐p‐hydroxybenzoylsophoroside)‐5‐glucoside (m/z 1055). Furthermore, the selected purple sweetpotato extracts with high levels of anthocyanins have been assessed in the human colon cancer SW480 cells for potential anticancer mechanisms. Better understanding of the underlying mechanisms may provide scientific evidence and health benefits of purple sweetpotato grown in Kansas.

Maintaining the Anthocyanin Content and Improvement of the Aroma of an Alcoholic Fermented Beverage Produced from Raw Purple-Fleshed Sweet Potato

We have been developing and studying an alcoholic fermented beverage produced from a raw purple-fleshed sweet potato cultivar (Ipomoea babatas cv. Ayamurasaki) containing high amounts of anthocyanin. In this study, we investigated the relationship between the anthocyanin content and aroma of the beverage and its manufacturing process. When raw sweet potatoes were allowed to stand for 1h at 5°C or 30°C between grinding and the initiation of fermentation, the anthocyanin content of the resulting beverage was considerably lower than that of an otherwise identical beverage produced from sweet potatoes ground immediately before fermentation. With that in mind, we investigated the effect of pH on maintenance of the anthocyanin content of ground sweet potato and found that decreasing the pH to 3.0 with citric or lactic acid made it possible to allow the ground sweet potatoes to stand for 3h at 30°C before starting fermentation, without any loss of anthocyanin. Moreover, the addition of citric acid led to the production of large amounts of higher alcohols such as isoamyl alcohol and isobutyl alcohol. These findings suggest that citric acid has desirable effects on both the color and the aroma of the alcoholic fermented beverage produced from raw purple-fleshed sweet potato.

紫サツマイモ「アヤムラサキ」から調製したアントシアニン含有物の高血圧自然発症ラットに対する血圧降下作用

紫サツマイモ「アヤムラサキ」から調製したアントシアニン含有物の高血圧自然発症ラットに対する血圧降下作用

Characterization of Acylated Anthocyanins in Callus Induced From Storage Root of Purple-Fleshed Sweet Potato, Ipomoea batatas L.

Four anthocyanins were isolated from a highly pigmented callus induced from the storage root of purple-fleshed sweet potato (Ipomoea batatas L) cultivar Ayamurasaki. The anthocyanins were respectively identified as cyanidin 3-O-(2-O-(6-O-(E)-caffeoyl-β-D-glucopyranosyl)-β-D-glucopyranoside) -5-O-β-D-glucopyranoside, cyanidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-caffeoyl-β-D-glucopyranoside)-5-O-β-D-glucopyranoside, cyanidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-p-coumaroyl-β-D-glucopyranoside)- 5-O-β-D-glucopyranoside, and peonidin 3-O-(2-O-(6-O-(E)-p -coumaroyl-β-D-glucopyranosyl)-6-O-(E)-p-coumaroyl-β-D-glucopyranoside)-5-O-β-D-glucopyranoside by chemical and spectroscopic analyses. These anthocyanins were examined with respect to the stability in neutral aqueous solution as well as the radical scavenging activity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. These acylated anthocyanins exhibited both higher stability and higher DPPH radical scavenging activity than corresponding nonacylated cyanidin and peonidin 3-O-sophoroside-5-O-glucosides.

Physiological Functionality of Purple-Fleshed Sweet Potatoes Containing Anthocyanins and Their Utilization in Foods

Studies on the physiological functionality of purple-fleshed sweet potatoes and their dominant anthocyanin pigments are described. The purple-fleshed sweet potato cultivar 'Ayamurasaki' contained anthocyanins, which consisted of mono- or di-acylated forms of cyanidin (YGM-1a, -1b, -2 and -3) and peonidin (YGM-4b, -5a, -5b and -6). It was also rich in anthocyanins with peonidin aglycon. The 'Ayamurasaki' extract and the purified YGM exhibited multiple physiological functions such as radical-scavenging, antirnutagenic, angiotensin I-converting enzyme-inhibitory, and α-glucosidase-inhibitory activities in vitro. Moreover, they also showed an ameliorative effect on carbon tetrachloride-induced liver injury and decreased postprandial blood glucose levels in rats. In addition, their role in restoring the liver function and blood pressure levels to normal in volunteers with impaired hepatic function and/or hypertension was also confirmed. The acylated anthocyanins, which were the major radical scavengers in 'Ayamurasaki', were directly absorbed into the blood stream of rats and were present as intact acylated forms in the plasma, and could also enhance the plasma antioxidative capacity. Based on these evidences, the purple-fleshed sweet potato can be recommended as a superior source for the production of foods with health benefits. Some foods and beverages in Japan that utilize these characteristics of anthocyanin pigments are also introduced in this paper.

Simple and Rapid Spectrophotometric Method for Selecting Purple-Fleshed Sweet Potato Cultivars with a High Radical-Scavenging Activity

Purple-fleshed sweet potato (Ipomoea batatas) plants containing anthocyanin pigments display a potent antioxidative activity. An 80 % ethanol extract from purple-fleshed sweet potato cultivars harvested in 2000 showed a 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity of 8.6 to 49.0 μmol expressed as Trolox equivalent/g of fresh weight. Although this DPPH radical-scavenging assay is convenient for the direct measurement of the radical-scavenging activity, a simpler and faster method should be developed for estimating the activity of a large number of breeding lines. For this purpose, the characterization of the UV-vis spectrum was performed in an 80 % ethanol extract from the purple-fleshed sweet potato. The extract exhibited absorption maxima near 325 nm and 530 nm due to the presence of cinnamic acids (or their related compounds) and anthocyanins, respectively. The absorbance at 325 nm was more highly correlated with the DPPH radical-scavenging activity than that at 530 nm and showed a correlation coefficient of 0.925. Multiple linear regression analysis using the absorbance of the extract at 325 nm and 530 nm elevated the value of the correlation coefficient to 0.979. When a prediction using this calibration curve was applied to extracts of purple-fleshed sweet potatoes harvested in 2001, a high correlation coefficient of 0.977 was obtained with lower SEP values of 1.686. Measurement of the absorbance of extracts from purple-fleshed sweet potatoes at 325 nm and 530 nm enable to obtain estimates of their DPPH radical-scavenging activity simply and rapidly. This assay could be suitable for selecting breeding lines of purple-fleshed sweet potato with a high DPPH radical-scavenging activity.