Carbohydrate components in sweetpotato storage roots: their diversities and genetic improvement

Sweet potato yield and quality characteristics affected by different late-season irrigation levels

BACKGROUND

Seasonal late-season water deficits negatively affect the yield and quality of sweet potatoes in northern China. However, the amount of late-season irrigation to achieve high yield and consistent quality storage root remains undetermined. We assessed the yield and some qualitative traits of sweet potatoes such as size, shape, skin/flesh colour and nutritional content, as influenced by five irrigation levels (T0: unirrigated control; T1: 33% ETc; T2: 75% ETc; T3: 100% ETc; and T4: 125% ETc).

RESULTS

Late-season irrigation significantly increased yield and marketable yield. Yields for T2 and T3 were significantly higher than other treatments, whereas T2 had the highest Grade A rating in a 2-year test. The vertical length of storage roots gradually increased with an increase in irrigation level, whereas the maximum width remained unchanged. The proportion of long elliptic and elliptic storage roots also increased, whereas the proportion of ovate, obovate and round storage roots gradually decreased. The skin and flesh colours became more vivid as the level of irrigation increased, with the skin colour becoming redder and the flesh colour becoming more orange-yellow. The levels of carotenoids, vitamin C and soluble sugar were significantly higher in irrigated crops, with the highest vitamin C and soluble sugar levels in T2 and the highest carotenoid levels in T3 treatment.

CONCLUSION

Taken together, these results demonstrate the potential of moderate irrigation in the late-season to improve both yield production and quality potential. The results are of great importance for improving the market value of sweet potatoes and increasing grower profits. © 2024 Society of Chemical Industry.

A Small Auxin-Up RNA Gene, IbSAUR36, Regulates Adventitious Root Development in Transgenic Sweet Potato

Small auxin-upregulated RNAs (SAURs), as the largest family of early auxin-responsive genes, play important roles in plant growth and development processes, such as auxin signaling and transport, hypocotyl development, and tolerance to environmental stresses. However, the functions of few SAUR genes are known in the root development of sweet potatoes. In this study, an IbSAUR36 gene was cloned and functionally analyzed. The IbSAUR36 protein was localized to the nucleus and plasma membrane. The transcriptional level of this gene was significantly higher in the pencil root and leaf.This gene was strongly induced by indole-3-acetic acid (IAA), but it was downregulated under methyl-jasmonate(MeJA) treatment. The promoter of IbSAUR36 contained the core cis-elements for phytohormone responsiveness. Promoter β-glucuronidase (GUS) analysis in Arabidopsis showed that IbSAUR36 is highly expressed in the young tissues of plants, such as young leaves, roots, and buds. IbSAUR36-overexpressing sweet potato roots were obtained by an efficient Agrobacterium rhizogenes-mediated root transgenic system. We demonstrated that overexpression of IbSAUR36 promoted the accumulation of IAA, upregulated the genes encoding IAA synthesis and its signaling pathways, and downregulated the genes encoding lignin synthesis and JA signaling pathways. Taken together, these results show that IbSAUR36 plays an important role in adventitious root (AR) development by regulating IAA signaling, lignin synthesis, and JA signaling pathways in transgenic sweet potatoes.

Development of NIRS calibration curves for sugars in baked sweetpotato

BACKGROUND

Variability in sugar content between raw and cooked sweetpotato storage roots impact nutritional and dietary importance with implications for consumer preference. High-throughput phenotyping is required to breed varieties that satisfy consumer preferences.

RESULTS

Near-infrared reflectance spectroscopy (NIRS) calibration curves were developed for analysing sugars in baked storage roots using 147 genotypes from a population segregating for sugar content and other traits. The NIRS prediction curves had high coefficients of determination in calibration (R2 c) of 0.96 (glucose), 0.93 (fructose), 0.96 (sucrose), and 0.96 (maltose). The corresponding coefficients of determination for cross-validation (R2 cv) were 0.92 (glucose), 0.89 (fructose), 0.96 (sucrose) and 0.93 (maltose) and were similar to the R2 c for all sugars measured. The ratios of the standard deviation of the reference set to the standard error of cross-validation were greater than three for all sugars. These results confirm the applicability of the NIRS curves in efficiently determining sugar content in baked sweetpotato storage roots. External validation was performed on an additional 70 genotypes. Coefficients of determination (r2) were 0.88 (glucose), 0.88 (fructose), 0.86 (sucrose) and 0.49 (maltose). The results were comparable to those found for the calibration and cross-validation in fructose, glucose, and sucrose, but were moderate for maltose due to the low variability of maltose content in the population.

CONCLUSIONS

NIRS can be used for screening sugar content in baked sweetpotato storage roots in breeding programs and can be used to assist with the development of improved sweetpotato varieties that better meet consumer preferences. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Baked sweetpotato textures and sweetness: An investigation into relationships between physicochemical and cooked attributes

Sweetpotato varieties vary greatly in perceived textures and sweetness. This study identified physicochemical factors that influence these attributes in cooked sweetpotatoes. Fifteen genotypes grown on three plots were baked and evaluated by a trained descriptive sensory analysis panel for sweetness and 13 texture attributes. Mechanical parameters were measured by texture profile analysis (TPA); and composition (starch, cell wall material, sugar contents), starch properties (thermal, granule type ratios, granule sizes), and amylase activities were characterized. TPA predicted fracturability and firmness well, whereas starch and sugar contents, B-type starch granule ratio, and amylase activities influenced prediction of mouthfeel textures. Sweetness perception was influenced by perceived particle size and sugar contents; and maltose generation during baking was highly correlated with raw sweetpotato starch content. These relationships between physicochemical sweetpotato properties and baked textures and sweetness could benefit breeders and processors in selecting biochemical traits that result in consumer preferred products.

Cyclic variable temperature conditioning induces the rapid sweetening of sweet potato tuberous roots by regulating the sucrose metabolism

This study aimed to investigate the influence of cyclic variable temperature conditioning (CVTC) on the rapid sweetening of sweet potato tuberous roots, as assessed through the analysis of sugar metabolism-related compounds and enzyme activities of tubers during storage. The results showed that CVTC effectively preserved the quality of sweet potato tuberous roots, leading to a significant elevation in soluble solids and soluble sugars. The CVTC group displayed sucrose and fructose levels that were 1.72 and 1.46 times higher, respectively, compared to the control group at the 8 d. Additionally, after storage, the activities of β-amylase, sucrose phosphate synthase (SPS), and sucrose synthase (SS) in the CVTC group were increased by 19.85 %, 60.74 %, and 82.48 %, respectively. Conversely, acid convertase (AI) activity showed inhibition of 64.72 %. In conclusion, implementing CVTC enhanced enzymatic activity in β-amylase, SPS, and SS, facilitating starch degradation and sucrose synthesis, which contributed to the overall improvement in the sweetness of sweet potato tubers.

Comparative Analysis of Saccharification Characteristics of Different Type Sweetpotato Cultivars

As an important characteristic crop in China, sweetpotato plays an important role in the intake and supplement of nutrients. The saccharification characteristics of sweetpotato determine the edible quality and processing type. Exploring the saccharification characteristics of sweetpotato is of great significance to the selection of processing materials and the formation mechanism of service quality, but there are few relevant studies. A comparison study of two high saccharification varieties (Y25 and Z13) and one low saccharification variety (X27) was conducted to analyze their storage roots physical and chemical properties. The results show that the dry matter content, starch, and amylose content of Y25 and Z13 were significantly different from those of X27. Furthermore, the total amylase activity was significantly higher than that of X27. On the other hand, the starch gelatinization temperature was significantly lower than that of X27. The starch reduction in Y25 and Z13 is four times more than that in X27, and the maltose content of Y25 and Z13 is more than two times that of X27. Finally, the scores of sensory evaluation and physiological sweetness were significantly higher than those of X27. The results provide a theoretical basis for understanding the saccharification characteristics of sweetpotato varieties and are of guiding significance for the selection of sweetpotato parents.

Comprehensive Evaluation of Raw Eating Quality in 81 Sweet Potato (Ipomoea batatas (L.) Lam) Varieties

The raw eating quality of sweet potato is complex. As consumers start paying more attention to the raw eating quality of tuberous roots in sweet potato, the evaluation of the raw eating quality of sweet potato is becoming an important issue. Therefore, we measured 16 quality indicators in 81 varieties of sweet potato. It was found that these 16 quality traits had different coefficients of variation (C.V.). Among them, the C.V. of fructose, glucose, and adhesiveness were the largest: 87.95%, 87.43% and 55.09%, respectively. The cluster analysis method was used to define six categories of the different tuberous roots of sweet potato. Group I, III, and IV had a stronger hardness and higher starch and cellulose content. Groups II, V, and VI were softer, with a high moisture and soluble sugar content. The principal component analysis method was used to comprehensively evaluate 16 quality indicators of 81 sweet potato varieties. It was found that Futian1, Taishu14, and Nanshu022 are good varieties in terms of raw eating quality. These varieties have low hardness, high adhesiveness in texture, high soluble sugar content, and low starch and cellulose. Future research should focus on improving the raw eating quality of sweet potato by reducing hardness, starch, and cellulose, while increasing adhesiveness, soluble sugar, and moisture content.

The clonal growth in Aconitum carmichaelii Debx

Aconitum carmichaelii Debx. is used as traditional herbal medicine in China, Japan, and other Asian countries. A. carmichaelii has two modes for reproduction: sexual reproduction with seed and vegetative reproduction with vegetative propagules. The vegetative propagules are belowground and invisible. To date, only a handful of studies for the clonal growth are available. In this study, we investigated the clonal growth by anatomical and morphological changes. Results revealed that the axillary bud appeared on the rhizome. Furthermore, the axillary meristem in the axillary bud differentiated a bud upwards and an adventitious root (AR) downwards. The AR expanded to a tuberous root in order to provide the bud nutrients for the new plant. The AR branched LRs. In addition, some lateral roots (LRs) on the AR also swelled. Both the AR and LR were found to follow a similar pattern of development. However, high lignification in the stele region of LRs inhibited further expansion. AR development was attributed to activities of the cambium and meristem cell, starch accumulation, stele lignification, and a polyarch stele. Our study not only provides a better understanding of clonal growth but also provides clues to explore the regulatory mechanisms underlying AR development in A. carmichaelii.

Exploring and exploiting genetics and genomics for sweetpotato improvement: Status and perspectives

Sweetpotato (Ipomoea batatas (L.) Lam.) is one of the most important root crops cultivated worldwide. Because of its adaptability, high yield potential, and nutritional value, sweetpotato has become an important food crop, particularly in developing countries. To ensure adequate crop yields to meet increasing demand, it is essential to enhance the tolerance of sweetpotato to environmental stresses and other yield-limiting factors. The highly heterozygous hexaploid genome of I. batatas complicates genetic studies and limits improvement of sweetpotato through traditional breeding. However, application of next-generation sequencing and high-throughput genotyping and phenotyping technologies to sweetpotato genetics and genomics research has provided new tools and resources for crop improvement. In this review, we discuss the genomics resources that are available for sweetpotato, including the current reference genome, databases, and available bioinformatics tools. We systematically review the current state of knowledge on the polyploid genetics of sweetpotato, including studies of its origin and germplasm diversity and the associated mapping of important agricultural traits. We then outline the conventional and molecular breeding approaches that have been applied to sweetpotato. Finally, we discuss future goals for genetic studies of sweetpotato and crop improvement via breeding in combination with state-of-the-art multi-omics approaches such as genomic selection and gene editing. These approaches will advance and accelerate genetic improvement of this important root crop and facilitate its sustainable global production.

Physicochemical, structural, and digestive properties of pea starch obtained via ultrasonic-assisted alkali extraction

As a new and clean extraction technology, ultrasonic extraction has been demonstrated with great potential in the preparation of modified starch. In order to increase its added value, it is necessary to modify pea starch to enlarge its application. In this study, the efficiency of combining ultrasonic with alkali in the extraction of pea starch was evaluated and compared to conventional alkali extraction. Ultrasonic-assisted alkali extraction conditions were optimized using single-factor experiments and response surface methodology. The results revealed that maximum yield of pea starch (54.43 %) was achieved using ultrasound-assisted alkali extraction under the following conditions: sodium hydroxide solution with a concentration of 0.33 %, solid/alkali solution ratio of 1:6 (w/v), ultrasonic power of 240 W, temperature of 42 °C, and extraction time of 22 min. The ultrasound-assisted alkali extraction yielded 13.72 % greater pea starch than conventional alkali extraction. On the other hand, morphological, structural, and physicochemical properties of the obtained starch isolates were evaluated. The ultrasound-assisted alkali extraction resulted in pea starch with greater amylose content, water-solubility, swelling power, and viscosity compared with conventional alkali extraction. Furthermore, ultrasonication influenced the morphological properties of pea starch granules, while the molecular structure and crystal type were not affected. Moreover, the ultrasonic-assisted extraction produced starch with a slightly greater resistant starch content. Therefore, ultrasonic-assisted extraction can be suggested as a potential method for extracting pea starch with improved functional properties.

Mulching Effect on Quantitative and Qualitative Characteristics of Yield in Sweet Potatoes

Sweet potatoes have multiple uses as food, feed, and in industrial production. They are characterized by their need for high temperatures for optimal development. This study aimed to analyze the quantitative and qualitative aspects of growing sweet potato cultivars in southwest Romania using mulching and non-mulching systems. The effects of mulching on the production of tuberous roots and the contents of total soluble substance, vitamin C, starch, total polyphenols, and antioxidant activity (DPPH) were evaluated in three cultivars with white pulp (the ‘Pumpkin’ and ‘Chestnut’ cultivars) and with orange pulp (the ‘Italian’ cultivar). It was found that mulching with polyethylene film improved the production of sweet potatoes, amounting to 41.42 t/ha in the case of the ‘Italian’ cultivar. Moreover, the effect of mulch induced increases in total soluble substance (16.40%) and starch (16.01%) in the ‘Chestnut’ cultivar, in vitamin C (9.23 mg/100 g d.w.) in the ‘Pumpkin’ cultivar, and in antioxidant activity in the ‘Pumpkin’ (2716.55 µmol AsA/g d.w.) and ‘Chestnut’ cultivars (1131.31 µmol AsA/g d.w.), while the polyphenols in the ‘Italian’ cultivar decreased.

Engineering Properties of Sweet Potato Starch for Industrial Applications by Biotechnological Techniques including Genome Editing

Sweet potato (Ipomoea batatas) is one of the largest food crops in the world. Due to its abundance of starch, sweet potato is a valuable ingredient in food derivatives, dietary supplements, and industrial raw materials. In addition, due to its ability to adapt to a wide range of harsh climate and soil conditions, sweet potato is a crop that copes well with the environmental stresses caused by climate change. However, due to the complexity of the sweet potato genome and the long breeding cycle, our ability to modify sweet potato starch is limited. In this review, we cover the recent development in sweet potato breeding, understanding of starch properties, and the progress in sweet potato genomics. We describe the applicational values of sweet potato starch in food, industrial products, and biofuel, in addition to the effects of starch properties in different industrial applications. We also explore the possibility of manipulating starch properties through biotechnological means, such as the CRISPR/Cas-based genome editing. The ability to target the genome with precision provides new opportunities for reducing breeding time, increasing yield, and optimizing the starch properties of sweet potatoes.

Integrating consumer perception in the selection of purple-skin sweet potato cultivars

BACKGROUND

Sweet-potato breeding programs need to integrate sensory characterization and hedonic perception to provide global markets with widely accepted products. The present work aimed to characterize a series of purple-skin sweet potatoes differing in flesh coloration (from pale yellow to slight orange) from a sensory and physicochemical perspective. Uruguayan consumers' perceptions of the genotypes were also explored. Special focus was placed on the influence of flesh color on consumers' expectations and hedonic perception of purple-skin sweet potatoes.

RESULTS

Sensory characterization based on projective mapping showed that the evaluated genotypes largely differed in their sensory characteristics in terms of flavor, texture, and color. Soluble solids and the concentration of individual sugars were not good predictors of sensory quality. In the appearance evaluation, consumers associated orange flesh with positive expected sensory characteristics and stronger liking. Flavor (sweetness and typical flavor) and texture (creaminess) were identified as key characteristics influencing consumers' liking and description of sweet-potato samples. Among purple-skin ('criollo or boniato' type) genotypes, INIA Cambará was identified as the closest to the ideal sweet potato and was described with the terms sweet, tasty, creamy, and characteristic flavor.

CONCLUSION

Flesh color was identified as a key driver of consumers' sensory and hedonic expectations. Results showed that Uruguayan consumers positively value traditional purple-skin sweet potatoes with orange flesh, as it drives positive sensory expectations. However, after tasting, flesh color does not seem to have a relevant influence on consumer liking.

Transcriptomic and Metabolic Profiling of High-Temperature Treated Storage Roots Reveals the Mechanism of Saccharification in Sweetpotato (Ipomoea batatas (L.) Lam.)

The saccharification of sweetpotato storage roots is a common phenomenon in the cooking process, which determines the edible quality of table use sweetpotato. In the present study, two high saccharified sweetpotato cultivars (Y25, Z13) and one low saccharified cultivar (X27) in two growth periods (S1, S2) were selected as materials to reveal the molecular mechanism of sweetpotato saccharification treated at high temperature by transcriptome sequencing and non-targeted metabolome determination. The results showed that the comprehensive taste score, sweetness, maltose content and starch change of X27 after steaming were significantly lower than those of Y25 and Z13. Through transcriptome sequencing analysis, 1918 and 1520 differentially expressed genes were obtained in the two periods of S1 and S2, respectively. Some saccharification-related transcription factors including MYB families, WRKY families, bHLH families and inhibitors were screened. Metabolic analysis showed that 162 differentially abundant metabolites related to carbohydrate metabolism were significantly enriched in starch and sucrose capitalization pathways. The correlation analysis between transcriptome and metabolome confirmed that the starch and sucrose metabolic pathways were significantly co-annotated, indicating that it is a vitally important metabolic pathway in the process of sweetpotato saccharification. The data obtained in this study can provide valuable resources for follow-up research on sweetpotato saccharification and will provide new insights and theoretical basis for table use sweetpotato breeding in the future.

Analysis of β-amylase gene (Amyβ) variation reveals allele association with low enzyme activity and increased firmness in cooked sweetpotato (Ipomoea batatas) from East Africa

β-amylase is a thermostable enzyme that hydrolyses starch during cooking of sweetpotato (Ipomoea batatas) storage roots, thereby influencing eating quality. Its activity is known to vary amongst genotypes but the genetic diversity of the beta-amylase gene (Amyβ) is not well studied. Amyβ has a highly conserved region between exon V and VI, forming part of the enzyme's active site. To determine the gene diversity, a 2.3 kb fragment, including the conserved region of the Amyβ gene was sequenced from 25 sweetpotato genotypes. The effect of sequence variation on gene expression, enzyme activity, and firmness in cooked roots was determined. Six genotypes carrying several SNPs within exon V, linked with an AT or ATGATA insertion in intron V were unique and clustered together. The genotypes also shared an A336E substitution in the amino acid sequence, eight residues upstream of a substrate-binding Thr344. The genotypes carrying this allele exhibited low gene expression and low enzyme activity. Enzyme activity was negatively correlated with firmness (R = -0.42) in cooked roots. This is the first report of such an allele, associated with low enzyme activity. These results suggest that genetic variation within the AmyB locus can be utilized to develop markers for firmness in sweetpotato breeding.

Relationships between isolated sweetpotato starch properties and textural attributes of sweetpotato French fries

Sweetpotato French fry (SPFF) textures have been associated with dry matter and starch contents, but these do not fully account for all textural differences. This study investigated the relationships between the physicochemical properties of sweetpotato starch and textural attributes of sweetpotato fries. Starches from 16 sweetpotato genotypes that varied in dry matter content were isolated and analyzed. The amylose content, pasting temperatures and viscosities, and textural properties of equilibrated starch gels were measured. Correlational analysis was performed with the respective SPFF mechanical and sensory texture attributes. Sweetpotato starch amylose content ranged from 17.3% to 21.1%, and the pasting and gel textural properties varied significantly between starches. Starch from orange-fleshed sweetpotatoes had lower pasting temperatures than starches from yellow/cream-fleshed genotypes, 72.2 ± 2.0 and 75.5 ± 1.1 °C, respectively. Notable inverse correlations were observed between the starch pasting temperature and perceived moistness (r = -0.63) and fibrousness (r = -0.70) of fries, whereas SPFF denseness was positively associated with starch pasting viscosity (r = 0.60) and nonstarch alcohol-insoluble solids content. Fry textures were likely affected by cooked starch properties, which should be considered when selecting varieties for sweetpotato fries. PRACTICAL APPLICATION: Without the aid of a batter, sweetpotato French fries (SPFFs) tend to be soft and limp-undesirable attributes in a fried food. The physiochemical properties of starch, the most abundant component in sweetpotato fries, were further explored in this study to better understand the properties of sweetpotato starch that influence SPFF textures. These findings can be used by sweetpotato processors and breeders for developing new sweetpotato varieties that are designed for production of fried products with desirable textures.

Fried sweetpotato user preferences identified in Nigeria and Ghana and implications for trait evaluation

Fried sweetpotato quality is important for variety adoption in West Africa. To inform breeding efforts, the study developed a product profile for sweetpotato chunk fries using mixed qualitative and quantitative methods. Root characteristics, processing attributes, in-mouth attributes and appearance of fried product were critical to final product quality. Raw roots should be hard, have smooth skin and no off-odours. Peeled roots should be hard to slice and not sticky. Stickiness and moist surface indicate high moisture content, associated with excessive oil absorption during frying. Hard to slice roots connote high dry matter. Fried product should be crisp, slightly sugary and mealy, have a uniform colour with brown tint and not be soggy. Crispness, mealiness and short frying time with limited oil absorption may be functions of starch. Understanding starch characteristics and other attributes that contribute to quality fried sweetpotato is critical for breeding sweetpotato genotypes with superior quality for frying.

Sensory characteristics and consumer segmentation of fried sweetpotato for expanded markets in Africa

Prepared foods are increasing in popularity in West Africa alongside rapid urbanisation. Growing demand for fried products calls for targeted breeding efforts to meet consumer needs, but little is known regarding consumer preferences. This research identified the sensory attributes of fried sweetpotato preferred by different consumer groups using a combination of consumer acceptance testing and descriptive sensory analysis. Market and community surveys identified three consumer segments in Ghana and Nigeria with contrasting preferences for fried sweetpotato sensory attributes. One group preferred crispy, crunchy, mealy and sweet fried sweetpotato; another preferred characteristic yam flavour and dry texture; and the third preferred uniform orange colour appearance, ripe plantain flavour and palm nutty flavour. Such consumer segmentation can help emerging West African fried sweetpotato industries identify target markets and provides valuable information to breeders, growers and retailers to prioritise attributes in their breeding, growing or product sourcing decisions.

Quantitative trait loci and differential gene expression analyses reveal the genetic basis for negatively associated β-carotene and starch content in hexaploid sweetpotato [Ipomoea batatas (L.) Lam.]

KEY MESSAGE

β-Carotene content in sweetpotato is associated with the Orange and phytoene synthase genes; due to physical linkage of phytoene synthase with sucrose synthase, β-carotene and starch content are negatively correlated. In populations depending on sweetpotato for food security, starch is an important source of calories, while β-carotene is an important source of provitamin A. The negative association between the two traits contributes to the low nutritional quality of sweetpotato consumed, especially in sub-Saharan Africa. Using a biparental mapping population of 315 F1 progeny generated from a cross between an orange-fleshed and a non-orange-fleshed sweetpotato variety, we identified two major quantitative trait loci (QTL) on linkage group (LG) three (LG3) and twelve (LG12) affecting starch, β-carotene, and their correlated traits, dry matter and flesh color. Analysis of parental haplotypes indicated that these two regions acted pleiotropically to reduce starch content and increase β-carotene in genotypes carrying the orange-fleshed parental haplotype at the LG3 locus. Phytoene synthase and sucrose synthase, the rate-limiting and linked genes located within the QTL on LG3 involved in the carotenoid and starch biosynthesis, respectively, were differentially expressed in Beauregard versus Tanzania storage roots. The Orange gene, the molecular switch for chromoplast biogenesis, located within the QTL on LG12 while not differentially expressed was expressed in developing roots of the parental genotypes. We conclude that these two QTL regions act together in a cis and trans manner to inhibit starch biosynthesis in amyloplasts and enhance chromoplast biogenesis, carotenoid biosynthesis, and accumulation in orange-fleshed sweetpotato. Understanding the genetic basis of this negative association between starch and β-carotene will inform future sweetpotato breeding strategies targeting sweetpotato for food and nutritional security.

Textural character of sweet potato root of Korean cultivars in relation to chemical constituents and their properties

A relationship between chemical constituents and physicochemical and textural properties of different Korean sweet potato (SP) cultivars were investigated in terms of the hardness of raw and cooked root, alcohol insoluble solid (AIS), starch and amylose content, amylase activities, and pasting properties. Correlation coefficients were analyzed and principal component analysis was performed. The hardness of cooked root was found to correlate with the hardness ratio of cooked/raw SP, AIS content (0.75**), starch content (0.64**), and peak viscosity of SP powder (0.56*). It was discovered that SP cultivars could be classified into mealy (Sincheonmi, Daeyumi, Sinyulmi), intermediate (Dahomi, Sinjami, Geonhwangmi, Yeonjami, Pungwonmi), and waxy (Juhwangmi, Sinhwangmi) types depending on the first principal component (PC1, 68%). Therefore, it was found that the texture types of SP cultivars could be predicted from hardness of cooked root and are in relation to AIS and starch contents, and peak viscosity of raw powder.

Recent progress in sweetpotato breeding and cultivars for diverse applications in Japan

Sweetpotato (Ipomoea batatas (L.) Lam.) is an outcrossing hexaploid that is cultivated in the tropics and warm-temperate regions of the world. Sweetpotato has played an important role as a famine-relief crop during its long history and has recently been reevaluated as a health-promoting food. In Japan, sweetpotato is used for a wide range of applications, such as table use, processed foods, and alcohol and starch production, and two groups at National Agriculture Research Organization (NARO) undertake the breeding of cultivars for these applications. Sweetpotato breeders utilize breeding processes such as grafting for flower induction and the identification of incompatibility groups before crossing to conquer problems peculiar to sweetpotato. For table use, new cultivars with high sugar content were released recently and have become popular among Japanese consumers. New cultivars with high anthocyanin or β-carotene content were released for processed foods and use as colorants. As raw materials, new cultivars with high alcohol yield were released for the production of shochu spirits. In addition, new cultivars with high starch yield and a cultivar containing starch with excellent cold-storage ability were released for starch production. This review deals with recent progress in sweetpotato breeding and cultivars for diverse applications in Japan.