Potato glycoalkaloids and metabolites: roles in the plant and in the diet

Potatoes, members of the Solanaceae plant family, serve as major, inexpensive low-fat food sources providing energy (starch), high-quality protein, fiber, and vitamins. Potatoes also produce biologically active secondary metabolites, which may have both adverse and beneficial effects in the diet. These include glycoalkaloids, calystegine alkaloids, protease inhibitors, lectins, phenolic compounds, and chlorophyll. Because glycoalkaloids are reported to be involved in host-plant resistance and to have a variety of adverse as well as beneficial effects in cells, animals, and humans, a need exists to develop a clearer understanding of their roles both in the plant and in the diet. To contribute to this effort, this integrated review presents data on the (a) history of glycoalkaloids; (b) glycoalkaloid content in different parts of the potato plant, in processed potato products, and in wild, transgenic, and organic potatoes; (c) biosynthesis, inheritance, plant molecular biology, and glycoalkaloid-plant phytopathogen relationships; (d) dietary significance with special focus on the chemistry, analysis, and nutritional quality of low-glycoalkaloid potato protein; (e) pharmacology and toxicology of the potato glycoalkaloids comprising alpha-chaconine and alpha-solanine and their hydrolysis products (metabolites); (f) anticarcinogenic and other beneficial effects; and (g) possible dietary consequences of concurrent consumption of glycoalkaloids and other biologically active compounds present in fresh and processed potatoes. An enhanced understanding of the multiple and overlapping aspects of glycoalkaloids in the plant and in the diet will benefit producers and consumers of potatoes.     

High-performance liquid chromatographic determination of the glycoalkaloids alpha-solanine and alpha-chaconine in 12 commercial varieties of Mexican potato

The glycoalkaloid content in 12 commercial varieties of Mexican potatoes was measured by HPLC in both the peel and the flesh of the potato. The principal glycoalkaloids alpha-solanine and alpha-chaconine were present in higher concentration in the peel than in the flesh of all varieties. The main alkaloid in the peel of the potatoes was alpha-chaconine and comprised about 65-71% of the total glycoalkaloids. The high concentration of alpha-chaconine in peel, which is more toxic than alpha-solanine, gives more protection to the tuber against predators. The total alkaloids in the peel of Alpha, Juanita, Michoacan, Norte?a, Rosita, and Tollocan varieties were higher than the limit recommended for food safety. However, the peel represents less than 10% of the total tuber in most of the varieties. The total alkaloids contained in the peel of Atzimba, Lopez, Marciana, Montsama, Murca, and Puebla was lower than the limits recommended for food safety. The glycoalkaloid content in the boiled peeled potatoes was less than 9 mg/100 g but in Alpha, Montsama, and Puebla varieties, both glycoalkaloids were absent. According to the results, the consumption of the 12 commercial varieties of Mexican potatoes does not represent any danger to human health.     

Inheritance of morphological characters and glycoalkaloids in potatoes of somatic hybrids between dihaploid Solanum acauleand tetraploid Solanum tuberosum.

Steroidal glycoalkaloids occur in potatoes and are reported to impart resistance to phytopathogens including bacteria, fungi, and insects. Because glycoalkaloids can be passed to progenies during breeding programs designed to develop improved potatoes, it is of importance to determine the quality of desired characteristics and the composition of glycoalkaloids of new somatic hybrids. The objective of this study was to determine the appearance, size, and shape (morphological characters) as well as the glycoalkaloid content of potato tubers of somatic hybrids between tetraploid Solanum tuberosum cv. Dejima (2n = 4x = 48 chromosomes) and the dihaploid clone ATDH-1 (2n = 2x = 24 chromosomes) induced by anther culture from Solanum acuale-T (acl-T, 2n = 4x = 48 chromosomes). Tuber size and shape in somatic hybrids were in accord with those of cv. Dejima, whereas the tuber skin color resembled that of ATDH-1. Thin-layer chromatography, high-performance liquid chromatography, and gas-liquid chromatography/mass spectrometry studies showed that the two steroidal glycoalkaloids (alpha-chaconine and alpha-solanine) were present in the tubers of S. tuberosum, whereas acl-T and ATDH-1 tubers were found to contain alpha-tomatine and demissine. The concentrations of total glycoalkaloids in both acl-T and ATDH-1 was >100 mg/100 g of fresh weight tuber cortex, much higher than in S. tuberosum. All somatic hybrids, except one clone, contained four glycoalkaloids (alpha-chaconine, alpha-solanine, alpha-tomatine, and demissine) derived from the fusion parents. The lack of alpha-tomatine in the remaining clone may be due to somaclonal variation. The results show that character expression is influenced by ploidy level and that total glycoalkaloid levels in most somatic hybrids were intermediate between those of the fusion parents. The possible significance of these findings for plant breeding and food safety is discussed.     

Glycoalkaloid content and chemical composition of potatoes improved with nonconventional breeding approaches

This paper reports the results of chemical analyses performed on two distinct groups of new potato genotypes. The first group contained five clones transformed with the gene ech42 encoding for an endochitinase. The second included 21 interspecific hybrids between the cultivated potato Solanum tuberosum and the wild species S. commersonii, obtained either by somatic fusion or by sexual hybridization. Tubers from transgenic plants were analyzed for several morphological and biochemical parameters to ascertain the substantial equivalence between the transgenic genotypes and the original cultivar Désirée. The interspecific hybrids were analyzed for the same parameters in order to identify genotypes with novel improved chemical characteristics and with low levels of glycoalkaloids deriving from the wild species and potentially hazardous to human health. For transgenic tubers, the results provided evidence that indicates the substantial equivalence between the transgenic genotypes and the cultivated control for the considered traits. The results suggest that chitinase gene insertion did not alter other metabolic pathways of potato tubers and did not cause unintentional pleiotropic effects. As far as interspecific hybrids are concerned, wide variability for all of the parameters analyzed was found. For some useful traits (e.g., soluble solids and proteins, dry matter content) the interspecific hybrids performed better than both the cultivated control and the wild species. In a number of genotypes, glycoalkaloid levels were close to or lower than those of the control varieties, suggesting that selection for low glycoalkaloid content is possible. The results also indicated that glycoalkaloids from S. commersonii may be lost rapidly. Indeed, some hybrids were found to have the same glycoalkaloid profile as S. tuberosum. Finally, the results showed that among the parameters considered, glycoalkaloid content is the most sensitive to variation. Therefore, glycoalkaloid determination should be used for routine control of genotypes produced by interspecific hybridization.     

Toxic secondary metabolite production in genetically modified potatoes in response to stress

Potatoes produce a number of toxic secondary metabolites, which are divided into two groups: the sesquiterpenes and the glycoalkaloids (PGAs): whereas PGAs are largely preformed and present in toxic quantities in both the foliage and "green" potatoes, it is well documented that the levels of PGAs and sesquiterpenes are effected by many biotic an abiotic stresses. The development of genetically modified potato varieties has made it prudent to ascertain whether there may be changes in the amounts or types of these secondary metabolites either as a direct effect of the transgene or due to its interactions with environmental variables. Transgenic potato lines were exposed, along with nontransgenic lines, to a range of biotic and abiotic stresses and a range of environmental conditions in the field and store. Following stressing, a comparison was made of levels of potato glycoalkaloid and sesquiterpene levels between the two groups. Significant differences were observed in the levels of both glycoalkaloid and sesquiterpene levels between transgenic and control material and between infected and noninfected material.     

Glycoalkaloids and metabolites inhibit the growth of human colon (HT29) and liver (HepG2) cancer cells

As part of an effort to improve plant-derived foods such as potatoes, eggplants, and tomatoes, the antiproliferative activities against human colon (HT29) and liver (HepG2) cancer cells of a series of structurally related individual compounds were examined using a microculture tetrazolium (MTT) assay. The objective was to assess the roles of the carbohydrate side chain and aglycon part of Solanum glycosides in influencing inhibitory activities of these compounds. Evaluations were carried out with four concentrations each (0.1, 1, 10, and 100 microg/mL) of the the potato trisaccharide glycoalkaloids alpha-chaconine and alpha-solanine; the disaccharides beta(1)-chaconine, beta(2)-chaconine, and beta(2)-solanine; the monosaccharide gamma-chaconine and their common aglycon solanidine; the tetrasaccharide potato glycoalkaloid dehydrocommersonine; the potato aglycon demissidine; the tetrasaccharide tomato glycoalkaloid alpha-tomatine, the trisaccharide beta(1)-tomatine, the disaccharide gamma-tomatine, the monosaccharide delta-tomatine, and their common aglycon tomatidine; the eggplant glycoalkaloids solamargine and solasonine and their common aglycon solasodine; and the nonsteroidal alkaloid jervine. All compounds were active in the assay, with the glycoalkaloids being the most active and the hydrolysis products less so. The effectiveness against the liver cells was greater than against the colon cells. Potencies of alpha-tomatine and alpha-chaconine at a concentration of 1 microg/mL against the liver carcinoma cells were higher than those observed with the anticancer drugs doxorubicin and camptothecin. Because alpha-chaconine, alpha-solanine, and alpha-tomatine also inhibited normal human liver HeLa (Chang) cells, safety considerations should guide the use of these compounds as preventative or therapeutic treatments against carcinomas.     

A capillary electrophoresis laser-induced fluorescence method for analysis of potato glycoalkaloids based on a solution-phase immunoassay. 2. Performance evaluation

Glycoalkaloids (GAs) occur naturally in potatoes and are toxic to humans and animals. The objective of the present study was to evaluate the performance of a solution-phase immunoassay coupled to capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection for the determination of total glycoalkaloids in potatoes. The immunoassay was based on a competition between potato glycoalkaloids and fluorescently labeled solanidine. Reaction products were separated in the capillary zone electrophoresis mode. A calibration curve of signal vs log[GA] was linear from 50 to 400 nM. The CV for duplicate and day-to-day analyses averaged 5.7% and 12%, respectively. Spike recoveries ranged from 85 to 97% for spike levels ranging from 43 to 170 microg/g fresh potato. Potato samples with GA concentrations ranging from <40 to >200 microg/g were successfully analyzed, indicating that immuno-CE-LIF is a rapid alternative to traditional ELISA and HPLC methods.     

Determination of potato glycoalkaloids using a liposome immunomigration, liquid-phase competition immunoassay

Polyclonal anti-solanine antibodies were raised and used in the assembly of a liposome immunomigration, liquid-phase competition strip immunoassay. In this format, a similar cross-reactivity was observed between the glycoalkaloids alpha-solanine and alpha-chaconine. The strip assay was implemented to quantitate total glycoalkaloids (TGA) from potatoes. Recoveries in spiked potato samples using the strip assay and water:acetic acid:sodium bisulfite extracting solvent were in the range of 84-111%. The values of the TGA quantitations by the strip assay as compared with those obtained by HPLC, in nonspiked tubers coming from cloned potato samples donated by potato breeders, were equivalent and highly correlated (r(2) = 0.91). The strip assay proved advantageous over HPLC for extra-laboratory measurements such as the rapid identification of samples that should be rejected due to an elevated TGA content.     

Coloured potatoes (Solanum Tuberosum L.) – Anthocyanin Content and Tuber Quality

Anthocyanins gain more and more importance as natural colourants. Besides many other plant species, coloured potatoes could serve as a potential source. Therefore, 27 potato cultivars and four breeding clones of different origin were analysed for their anthocyanin contents in fresh weight (fw). On average the highest amounts of anthocyanins were found in the skin (0.65 g kg⁻¹ fw) of potatoes. The corresponding values of samples taken from whole tubers (0.31 kg⁻¹ fw) and flesh (0.22 kg⁻¹ fw) were significantly lower (p<0.03). The analysis revealed considerable differences in the amounts of anthocyanins between the 31 cultivars/breeding clones. Among them ȁ8Peru Purpleȁ9 revealed the highest anthocyanin content in the skin with 2.96 g kg⁻¹ fw. A similar high value was reached by ȁ8Violettfleischigeȁ9 and clone 1.81.202–92 N. Also for the other two types of samples, flesh and whole tubers, these three genotypes exhibited the highest level of anthocyanins. Interestingly, different rates of nitrogen fertilization at 100 and 200 kg ha⁻¹ had no significant effect on the pigment content of potatoes. The same was observed with respect to the year or the location of plant growth. There were also no significant changes in the anthocyanin contents of tubers during storage for 135 days. In dry matter, starch and protein contents the coloured potato cultivars/breeding clones were comparable with traditional cultivars. Further tests have shown that the glycoalkaloids were mainly localized in the skin of coloured potatoes.     

Anticarcinogenic effects of glycoalkaloids from potatoes against human cervical, liver, lymphoma, and stomach cancer cells

Methods were devised for the isolation of large amounts of pure alpha-chaconine and alpha-solanine from Dejima potatoes and for the extraction and analysis of total glycoalkaloids from five fresh potato varieties (Dejima, Jowon, Sumi, Toya, and Vora Valley). These compounds were then evaluated in experiments using a tetrazolium microculture (MTT) assay to assess the anticarcinogenic effects of (a) the isolated pure glycoalkaloids separately, (b) artificial mixtures of the two glycoalkaloids, and (c) the total glycoalkaloids isolated from each of the five potato varieties. All samples tested reduced the numbers of the following human cell lines: cervical (HeLa), liver (HepG2), lymphoma (U937), stomach (AGS and KATO III) cancer cells and normal liver (Chang) cells. The results show that (a) the effects of the glycoalkaloids were concentration dependent in the range of 0.1-10 mug/mL (0.117-11.7 nmol/mL); (b) alpha-chaconine was more active than was alpha-solanine; (c) some mixtures exhibited synergistic effects, whereas other produced additive ones; (d) the different cancer cells varied in their susceptibilities to destruction; and (e) the destruction of normal liver cells was generally lower than that of cancer liver cells. The decreases in cell populations were also observed visually by reversed-phase microscopy. The results complement related observations on the anticarcinogenic potential of food ingredients.     

Tracer studies on the incorporation of [2-14C]-DL-mevalonate into chlorophylls a and b, alpha-chaconine, and alpha-solanine of potato sprouts

Chlorophyll and glycoalkaloids are synthesized in different parts of the potato plant including leaves, tubers, and sprouts. Although light stimulates the biosynthesis of both constituents, the question of whether the two biosynthetic pathways are under the same genetic control has not been resolved. This study investigated the dynamics of incorporation of labeled [2-(14)C]-DL-mavalonate into chlorophyll a, chlorophyll b, and the glycoalkaloids alpha-chaconine and alpha-solanine in potato sprouts after 7 and 14 days of storage in the light and in the dark. No chlorophyll synthesis occurred in the dark. Fractionation of the "glycoalkaloid" extract followed by high-performance liquid chromatography produced four peaks. The fractions were collected and analyzed for radioactivity. About 80% of the radioactivity resided in fraction 1, the composition of which is unknown. Two of the fractions, with 1-14% of the original label, were alpha-chaconine and alpha-solanine. The radioactivity derived from mevalonate largely resides in unidentified compound(s) eluting as a single peak on the HPLC column before the peaks associated with the glycoalkaloids. The specific radioactivity of alpha-chaconine and alpha-solanine increased approximately 2-fold in going from 7 to 14 days of exposure in the light and in the dark. These and additional observations point to the near identity of the dynamics of biosynthesis of the two glycoalkaloids. These data also implicate a non-mevalonate pathway for the synthesis of both chlorophylls and the glycoalkaloids and are consistent with independent genetic control of the concurrent formation of the two classes of compounds during greening of potatoes.     

不同马铃薯品种对Cd、Pb吸收累积的差异

采用田间试验法,以中南地区主要种植的11个马铃薯品种为研究对象,测定马铃薯植株各部位重金属Cd、Pb含量,探讨不同品种的马铃薯对Cd、Pb的吸收累积差异,为马铃薯的安全种植提供实践参考。结果表明:Cd—Pb复合污染下,马铃薯块茎鲜重、茎叶鲜重以及根、茎叶、块茎中Cd、Pb含量在品种间均表现出显著差异。11个马铃薯品种块茎Cd含量范围为0.39～0.67 mg/kg,超标率100%,块茎Pb含量为0.16～0.43 mg/kg,超标率81.8%。马铃薯各部位Cd、Pb含量均呈现根茎叶块茎的分布特点;马铃薯对Cd的富集系数为2.35～5.56,对Pb富集系数为0.11～0.22,马铃薯富集转运Cd的能力大于Pb。尽管复合重金属靶标危险系数(TTHQ)法评价显示,金湘等5种马铃薯的TTHQ值1,对人体健康风险较小,但结合块茎Cd、Pb含量,建议污染区种植的马铃薯作为工业原料使用更安全。     

射流式马铃薯输送泵性能试验

为了研究射流式马铃薯输送泵的性能,该文根据马铃薯输送的特点设计了一台射流式马铃薯输送泵,通过试验的方法对流量比、面积比和输送高度3个因素对输送性能的影响进行了研究,并分析了不同工况对马铃薯损伤的影响。研究结果表明:马铃薯的最高输送能力达1 667.46 kg/h;在相同的输送高度和面积比下,输送能力和泵水功率随着流量比的增加而增加;在相同的被吸流体流量和扬程下,输送能力随着面积比升高而降低;在相同的面积比和工作流体流量下,输送能力随着输送高度的升高而降低,而输送单位质量马铃薯的能耗随之升高;在大部分工况中,马铃薯在输送过程中没有损伤;但是在少数流量比较低的工况中,由于回流的作用,马铃薯可能与喷嘴或者泵内壁面碰撞而导致损伤;综合考虑输送能力和马铃薯损伤,在试验所涉及的工况中,射流式马铃薯输送泵面积比1.75,流量比0.49,输送高度1.40 m为输送马铃薯的最优工况。     

Glycoalkaloid and calystegine contents of eight potato cultivars

Diverse procedures have been reported for the separation and analysis by HPLC of the two major glycoalkaloids present in potatoes, alpha-chaconine and alpha-solanine. To further improve the usefulness of the HPLC method, studies were carried out on the influence of several salient parameters on the analysis of the two potato glycoalkaloids. Effects on retention (elution, separation) times of the (a) composition and pH of the mobile phase (acetonitrile and phosphate buffer), (b) concentration of the phosphate buffer, (c) capacity values of column packing of four commercial HPLC amino columns, (d) column temperature were studied. Except for pH, all of the variables significantly influenced the retention times. The results make it possible to select analysis conditions that produce well-separated as well as symmetrical peaks of the two glycoalkaloids. This improved HPLC method (limit of detection of approximately 150 ng) was evaluated with extracts from the cortex of one whole potato variety (May Queen) grown in Japan and the freeze-dried peel and flesh from the following eight cultivars grown in the United States: Atlantic, Dark Red Norland, Ranger Russet, Red Lasoda, Russet Burbank, Russet Norkota, Shepody, and Snowden. In addition, the same samples were analyzed by GC-MS for the presence of two water-soluble nortropane alkaloids, calystegine A(3) and calystegine B(2), reported to be potent glycosidase inhibitors. The following ranges for the eight varieties of total glycoalkaloid and calystegine levels were observed: dry flesh, 5-592 and 6-316 mg/kg; dry peel, 84-2226 and 218-2581 mg/kg; dry whole potatoes, 40-883 and 34-326 mg/kg; wet flesh, 1-148 and 1-68 mg/kg; wet peel, 12-429 and 35-467 mg/kg; wet whole potatoes, 7-187 and 5-68 mg/kg. The possible significance of the results to plant and food sciences is discussed.     

Effects of genotype,environment, and postharvest storage on the total ascorbate content of potato (Solanum tuberosum) tubers

The total ascorbate content of potato tubers from 33 Solanum tuberosum genotypes grown at three geographically diverse sites in Europe in each of two years was determined immediately postharvest and after approximately 4 months of storage at 4 degrees C. Statistically significant differences in total ascorbate concentration were observed between genotypes both at harvest and after storage. In all genotypes, the levels of ascorbate decreased during storage. These results are discussed in terms of their implications for diet and health as well as in terms of breeding for improved vitamin C content in potatoes.     

Rapid screening of ascorbic acid, glycoalkaloids, and phenolics in potato using high-performance liquid chromatography

Evaluation of phenolic metabolism in potato tubers (Solanum tuberosum) would be facilitated by faster analytical methods. A high-throughput HPLC method was developed for the qualitative and quantitative determination in potato of numerous phenolic compounds, the sum of the glycoalkaloids chaconine and solanine, plus ascorbic acid. Following a fast extraction, HPLC run times of 12 min were achieved with the use of a monolithic RP C18 column. UV and MS analyses were used to characterize the phenolic complement in extracts from two white-fleshed varieties. Over 30 compounds were identified, some of which are thought to possess either nutritional value or are involved in plant disease resistance. This method is expected to be useful for germplasm mining and for varietal development programs in which large numbers of lines are generated.     

Acute toxicity of high doses of the glycoalkaloids, alpha-solanine and alpha-chaconine, in the Syrian Golden hamster

Sprouted, stressed, or spoiled potato tubers have reportedly led to human acute intoxication, coma, and death when consumed in high amounts. These effects have been attributed to glycoalkaloids (GAs), primarily alpha-solanine and alpha-chaconine, naturally present in all potatoes. The level of GAs in potato tubers has previously been shown to increase substantially as a result of improper handling and postharvest storage. A short-term study was performed to investigate the dose-response profile of alpha-solanine and alpha-chaconine alone or in combination, administered daily by oral gavage to Syrian Golden hamsters. Daily doses of 100 mg of alpha-solanine [kg body weight (BW)] (-1) induced death in two of four hamsters within 4 days, when administered by gavage to female Syrian hamsters. Doses of 100 mg of alpha-chaconine alone or alpha-solanine and alpha-chaconine combined in a ratio of 1:2.5, in doses of 75 or 100 mg (kg BW) (-1), induced death in one of four hamsters within the same period. Animals dosed with alpha-solanine alone or in combination with alpha-chaconine suffered from fluid-filled and dilated small intestines. The GA administration had no effect on acetyl cholinesterase (AChE) or butyryl cholinesterase (BuChE) activity in plasma or brain. Liquid chromatography-mass spectrometry-based metabolomics showed that there was a specific accumulation of alpha-chaconine in the liver tissues. In addition, metabolomics gave direct evidence of glycolytic metabolism of the GA with the beta 1, beta 2, and gamma-GAs detected in the urine and, to a lesser extent, the feces. Doses from 75 mg (kg BW) (-1) of alpha-chaconine, alpha-solanine, or the two compounds combined were potentially lethal within 4-5 days in the Syrian Golden hamster. However, the cause of death in these studies could not be established. No synergistic effects of alpha-solanine combined with alpha-chaconine were evident.     

Method for the detection of synthetic cry3A in transgenic potatoes

All transgenic cultivars of potatoes registered in Canada and the United States have been modified to express a synthetic cry3A gene as a means of conferring resistance against the Colorado potato beetle, an important economic pest of potatoes. A PCR method was developed to amplify a 499 bp region of the synthetic cry3A gene. Using this method, synthetic cry3A could be detected in six different transgenic cultivars. Positive results could be confirmed with PvuII restriction digestion of the PCR-generated amplicon, which resulted in two fragments that were 283 and 216 bp in size. Of the 52 tuber extracts tested with this method, no false positive or false negative results were obtained, suggesting the method could be used with a high degree of accuracy. The absolute limit of detection was the number of cry3A copies present in one or perhaps two haploid copies of the potato genome. The practical limit of detection in tubers on a fresh weight basis was 0.02% for the NL 10-SUP and 0.01% for the remaining cultivars. Synthetic cry3A could also be detected in processed food products such as potato chips, shoestring potatoes, and frozen French fries. The method was suitable for screening potato tuber lots and some processed foods for the presence of synthetic cry3A.     

制取淀粉用甘薯的最佳收获期及磨浆分离机的研究

通过对河北省甘薯集中产区“一窝红”和“卢选1号”两个具有代表性的甘薯品种,在不同收获时间甘薯淀粉亩产量的试验测定,确定出该区甘薯用来制取淀粉的最佳收获时间。同时,为在甘薯最佳收获时间内制取淀粉,提高甘薯淀粉的亩产量,研究设计了适合甘薯集中产区的6SF-20型薯类磨浆分离机。该机的淀粉分离率为96.4%,淀粉提取率为92.0%,达到国际先进水平