Light‐induced glycoalkaloid accumulation of potato tubers (Solanum tuberosum L)

The total glycoalkaloid concentration of non‐sprouted potato tubers, cvs Marfona, Fianna, Maris Piper, Kestrel and Golden Wonder, was measured following 15 days of continuous illumination (250 µmol m⁻² s⁻¹ photosynthetically active radiation) using high‐performance liquid chromatography. Comparisons were made of the influence of four sources of illumination: fluorescent tube‐type warm white, high‐pressure sodium, high‐pressure mercury types MB/U and MBFR/U. Irrespective of cultivar, glycoalkaloid concentrations of tubers placed in the dark remained relatively constant from day 0 to day 15 and did not exceed food safety values of 200 mg kg⁻¹ FW. A highly significant cultivar, light and cultivar × light (P < 0.01) interaction was recorded. Cultivar Kestrel was shown to be light‐sensitive with high rates of glycoalkaloid accumulation irrespective of light source, and cv Maris Piper was demonstrated to be light‐insensitive. In the majority of cultivars tested, maximal rates of glycoalkaloid accumulation were recorded following exposure of tubers to sodium or fluorescent light, and minimal rates of accumulation were recorded following exposure of tubers to mercury (MB/U and MBFR/U) illumination. In virtually all cases glycoalkaloid concentrations steadily increased with time during light exposure with no indication of cessation. In some instances the α‐chaconine/α‐solanine ratio decreased over 15 days of illumination (P < 0.05), indicating enhanced α‐solanine synthesis over that of α‐chaconine. The implications of these results in terms of consumer safety are discussed. © 1999 Society of Chemical Industry     

Variation in glycoalkaloid concentration of potato tubers harvested from mature plants

Individual tubers from mature plants of cultivars Pentland Dell and Estima were harvested from experimental plots in two successive years and analysed for α‐solanine, α‐chaconine and total glycoalkaloid concentration (α‐solanine and α‐chaconine combined) using high‐performance liquid chromatography. Mean tuber glycoalkaloid concentration per plant was strongly affected by genotype and was much higher in plants of Pentland Dell (10.0 and 16.3 mg per 100 g fresh weight in 1994 and 1995, respectively) than Estima (4.0 and 4.3 mg per 100 g fresh weight in 1994 and 1995, respectively). The variation between plants in mean tuber glycoalkaloid concentration, expressed as coefficient of variation, was similar for the two cultivars in both years. Variation within plants was higher for cultivar Pentland Dell than Estima for both years but it was statistically significant only in 1995. Tuber position within a plant had no effect on glycoalkaloid concentrations in tubers of similar size. An inverse relationship between total glycoalkaloid concentration and tuber fresh weight of individual tubers was found for both cultivars and small tubers of Pentland Dell (20–40 g fresh weight) exceeded the safety limit of 20 mg per 100 g fresh weight. The pattern of glycoalkaloid accumulation differed between genotypes and appeared related to tuber growth. The implications of these results in terms of food safety are discussed. © 1999 Society of Chemical Industry     

High levels of glycoalkaloids in the established swedish potato variety magnum bonum

In 1986, potentially toxic levels of the glycoalkaloids α-solanine and α-chaconine were unexpectedly found in tubers of the established Swedish consumer potato variety Magnum Bonum, leading to the imposition of a conditional sales ban on such potatoes. The combined amounts of α-solanine and α-chaconine in more than 300 commercial lots of Magnum Bonum potatoes analysed as a consequence of the ban ranged from 61 to 665 mg kg^?1 fresh weight with an average of 254 mg kg^?1. Sixty-six percent of the samples exceeded a temporary maximum residue limit of 200 mg kg^?1, 8% were above 400 mg kg^?1. Peeling did not significantly remove the glycoalkaloids in tubers with a high content. The occasional glycoalkaloid elevation was initially attributed to the unusually cold and rainy conditions during the late part of the season in 1986, but subsequent investigations have failed to confirm this hypothesis. Varietal characteristics are likely to have been involved since most other common Swedish varieties seemed to have had normal glycoalkaloid levels in 1986. There were no indications of serious or widespread adverse health effects in consumers due to the high glycoalkaloid levels, although there was circumstantial evidence that a few cases of temporary gastrointestinal disturbances were caused by consumption of Magnum Bonum potatoes with glycoalkaloid concentrations in the range 310–1000 mg kg^?1.     

Glycoalkaloid content of early potato varieties

Samples of Swedish domestic early potatoes were collected from wholesalers and analysed for their content of glycoalkaloids (GA), α-solanine and α- chaconine, using a modified HPLC procedure. The varieties included were, in order of increasing GA content; Maris Bard, Ukama, Pro vita, Evergood Eldorado, Maria, Early Puritan, Silla and Ulster Chieftain. The average total GA content (α-solanine and α-chaconine combined) for the different varieties ranged from 51 to 221 mg kg^?1 fresh weight. α-Solanine constituted on average between 35 and 41% of the GA detected. The GA concentrations in individual samples were in the range 31-344 mg kg^?1. The variety Ulster Chieftain accounted for 88% of the samples above 200 mg kg ^?1. The results obtained with tubers grown experimentally in field trials in two different years were consistent with the findings for commercially grown potatoes in terms of GA content rank among varieties.     

Glycoalkaloid Concentrations in Aerial Tubers of Potato ( Solanum tuberosumL)

The total glycoalkaloid concentrations in aerial and subterranean tubers of 14 potato genotypes were measured using high-performance liquid chromatography immediately after harvest. Post-harvest, aerial tubers from all genotypes were exposed to 144 h continuous fluorescent light; additionally three genotypes (cvs Home Guard, Kerrs Pink and Desiree) were subjected to mechanical wounding prior to glycoalkaloid analysis. Variations in glycoalkaloid concentrations between aerial tubers taken from a single genotype (cv Kerrs Pink) were determined by analysis of eight aerial tubers formed in the second leaf axil, selected from separate individual plants. Irrespective of genotype, total and individual glycoalkaloid concentrations were higher in aerial than in subterranean tubers. The highest glycoalkaloid concentrations were found in aerial tubers of cv Kerrs Pink (1343·0 mg kg⁻¹ FW) and lowest in cv Lindsey (301·0 mg kg⁻¹ FW). Ratios of α-chaconine: α-solanine in aerial tubers differed significantly ( P< 0·05) from those in subterranean tubers of cv Cara, Golden Wonder, Home Guard, Lindsey, Maris Piper, Record and 8859 indicating that exposure to light during aerial tuber growth enhanced the synthesis of one glycoalkaloid to a greater degree than the other. In all cultivars except cv Maris Piper, exposure of aerial tubers to 144 h continuous fluorescent light post-harvest increased total and individual glycoalkaloids compared with dark-treated controls. However, the ratios of α-chaconine: α-solanine in all genotypes except cv Golden Wonder (decreased α-chaconine: α-solanine, P< 0·05) were not significantly altered in comparison with dark controls, indicating that light exposure of aerial tubers post-harvest fails to enhance selectively synthesis of individual glycoalkaloids in the majority of cultivars. Regardless of cultivar, total glycoalkaloid, α-solanine and α-chaconine concentrations were higher in wounded than unwounded aerial tubers. Wounding stimulated synthesis of α-solanine more than α-chaconine ( P< 0·05) in cv Home Guard and Desiree. Glycoalkaloid concentrations in aerial tubers varied widely from a minimum of 1010 mg kg⁻¹ to a maximum of 2520 mg kg⁻¹ FW when harvested from individual plants of cv Kerrs Pink but selected from equivalent positions on the plant. Throughout the experiments large, non-significant increases in total and individual glycoalkaloid concentrations were recorded following light and wounding treatments. The scientific implications of aerial tuber formation are discussed.     

A simplified procedure for quantification of potato glycoalkaloids in tuber extracts by H.p.l.c.; comparison with ELISA and a colorimetric method

An improved high-performance liquid chromatography (h.p.l.c.) procedure for determination of glycoalkaloid levels in potato tubers has been developed in which Sep-Pak cartridges replace the commonly used alkaline precipitation for clean-up of tuber extracts. Glycoalkaloids are extracted from fresh tuber tissue into an aqueous medium, the extract is submitted to clean-up and α-solanine and α-chaconine are quantitatively separated on a reversed phase column with ethanolamine modifier added to the mobile phase. Potato tubers were comparatively analysed for their glycoalkaloid content by this and two other methods: a recently developed immunoassay (ELISA) and a colorimetric procedure representing the traditional chemical approach. Agreement between the h.p.l.c. and the other methods was good.     

Glycoalkaloid Concentration of Potato Tubers Following Exposure to Daylight

The total glycoalkaloid concentrations in white- (cv Pentland Hawk), pink- (cv Kerrs Pink) and red- (cv Desiree) skinned potato tubers were measured following 21 days exposure to daylight using high-performance liquid chromatography. Average daytime irradiance during this period was 232 μmol m⁻² s⁻¹. Regardless of cultivar, glycoalkaloid concentrations were increased after light exposure compared with initial concentrations. Glycoalkaloid concentrations fluctuated with time and continuous accumulation of glycoalkaloids with time was not demonstrated. Glycoalkaloid synthesis was maximal in the sequence cv Kerrs Pink<cv Pentland Hawk<cv Desiree. Exposure to daylight altered the ratio of α-chaconine: α-solanine in tubers of cv Desiree but not those in cv Pentland Hawk and Kerrs Pink. Glycoalkaloid concentrations in all cultivars were higher than the recommended food safety level, this was reached after 8 days in cv Kerrs Pink and Desiree and at 13 days in Pentland Hawk. The implications of these results in terms of food safety are discussed.     

Comparative composition of aerial and subterranean potato tubers (Solanum tuberosum L)

The composition of aerial and subterranean tubers of two potato genotypes cvs Desiree (red skin) and Epicure (white skin) was compared immediately after harvest using a range of analytical methods. Irrespective of genotype, aspartic acid, arginine, glycine, glutamic acid, histidine, leucine, serine, threonine and total amino acid concentrations were significantly higher (P<0·05) in aerial compared with subterranean tuber tissue. Significant increases (P<0·05) in valine in aerial tubers, but no significant differences in alanine, tyrosine and iso-leucine, when compared with subterranean tubers of cv Desiree, were found. In cv Epicure, alanine, tyrosine and iso-leucine were significantly higher in aerial tubers (P<0·05); however, no significant differences in valine were recorded. There was no significant increases in lysine and phenylalanine between tuber types. Regardless of genotype α-solanine, α-chaconine, chlorogenic acid, chlorophyll and crude protein concentrations were significantly higher in aerial tubers compared with subterranean ones (P<0·01). No significant increases in total lipids between tuber types were found. In cv Desiree, ascorbic acid content was not significantly different between aerial and subterranean tuber tissue, but in cv Epicure concentrations were significantly higher (P<0·01) in aerial tubers. Starch concentrations were significantly higher in subterranean tubers of both cultivars (P<0·05). Sugar content was significantly higher in aerial tubers of cv Epicure (P<0·01), but not significantly different between aerial and subterranean tubers of cv Desiree. Regardless of genotype, phosphorus, magnesium, potassium, zinc, manganese and sodium concentrations were significantly higher (P<0·05) in aerial tubers. Iron and copper concentrations were significantly higher in aerial tubers of cv Desiree (P<0·01), but significantly less in cv Epicure compared with subterranean tubers (P<0·01, P<0·05). Calcium concentrations were not significantly different between aerial and subterranean tubers of cv Desiree, but significantly higher in aerial tuber tissue of cv Epicure (P<0·01). Total gross energy (mJ kg⁻¹ FW) was higher in aerial tubers of cv Desiree compared with subterranean tubers (P>0·05), but not significantly different between aerial and subterranean tubers of cv Epicure. The potential applications of aerial tubers for industrial purposes are discussed. © 1997 SCI.     

Changes in anthocyanin,flavonoid and phenolic acid concentrations during development and storage of coloured potato (Solanum tuberosum L) tubers

Changes in the anthocyanin concentration of coloured potato tubers have been investigated in cultivars with coloured skin and coloured or white flesh. The biosynthesis of anthocyanins coincided with tuber initiation in cultivars with intensely coloured mature tubers and, after a slight increase as the smaller tubers increased in size, anthocyanin concentrations remained relatively constant. Thus, because tubers were increasing in weight, anthocyanin was being synthesised to maintain a more or less constant concentration. In cultivars with less coloured tubers, the developing tubers remained white for a longer time, with anthocyanin concentrations increasing gradually up to a maximum at a certain tuber weight depending on the cultivar. The concentration of flavonoids was lower than that of anthocyanins but followed a similar pattern. Phenolic acid levels were about twice those of the anthocyanins and reached their maximum at a slightly lower tuber weight than anthocyanins and flavonoids. During cold storage (4°C) the anthocyanin concentration in coloured tubers increased, whereas tubers stored at higher temperatures did not show this increase. The increased colour in cold‐stored tubers is discussed in terms of its relationship to ‘cold sweetening’ and the increased concentration of sugars in cold‐stored tubers. The distribution of anthocyanins altered during tuber development and also during cold storage. In very small developing tubers the anthocyanins appeared first at the stem end of the tuber whilst the bud end remained white. As the anthocyanin concentration increased during tuber development, it increased over the whole tuber, but the concentration at the stem end was always higher than that at the bud end, until the tuber reached maturity, when the concentration became approximately equal at both ends. After cold storage, tubers had a higher concentration of anthocyanin in the bud end than the stem end; the opposite to that found in developing tubers. © 1999 Society of Chemical Industry     

Glycoalkaloid concentration of potato tubers following continuous illumination

The total glycoalkaloid concentration of dormant (non-sprouted) and sprouted potato tubers cv Pentland Hawk was measured following 13 days continuous illumination (250 μmol m^?2 s^?2 photosynthetically active radiation) using high-performance liquid chromatography. Comparisons were made of the influence of three sources of illumination: high-pressure mercury, high-pressure sodium and fluorescent tube type warm white. Glycoalkaloid concentrations in both dormant and sprouted tubers increased over 13 days illumination regardless of the form of illumination used. Glycoalkaloid concentrations accumulated with time in dormant and sprouted tubers exposed to sodium and fluorescent light but fluctuated in those exposed to mercury light. Dormant tubers were more sensitive to illumination than sprouted tubers regardless of light souce. Fluorescent light was associated with maximum glycoalkaloid synthesis in dormant tubers; while sodium light enhanced glycoalkaloid synthesis in sprouted tubers to the greatest extent. Mercury light weakly elicited glycoalkaloid synthesis in both sets of tubers. Exposure of dormant tubers to continuous light altered the ratio of α-chaconine to α-solanine irrespective of illumination source.     

Starch properties of various potato (Solanum tuberosum L) Cultivars susceptible and resistant to low-temperature sweetening

Properties of starch granules isolated from different varieties and selections of potato (which vary in their degree of chill sweetening) were examined. Differential scanning calorimetry (DSC) showed an increase in resistance to gelatinisation of isolated starch granules which correlated (r = 0.911) with higher chip scores following storage at 4°C and 12°C. Varying water level content during DSC studies resulted in significantly lower water content required to produce two endotherms for starch isolated from varieties resistant to chill sweetening. These data strongly suggest that starch granule composition might be a factor differentiating the low temperature sweetening sensitive from resistant cultivars, and may provide a screening method for predicting chip colour of potatoes out of storage.     

Effects of gibberellic acid and chlorocholine chloride on tuberisation and growth of potato (Solanum tuberosum L)

Treatment of potato plants with gibberellic acid (GA₃) enhanced both shoot and stolon growth and dry weight but delayed tuber initiation and decreased tuber yield. Conversely, treatment with chlorocholine chloride (CCC) growth retardant reduced shoot and stolon growth and dry weight but promoted tuberisation. Chlorophyll a and b contents were both increased appreciably with CCC. In the tubers, CCC increased starch content by 11% compared to untreated control, whereas GA₃ decreased starch content by about 13%. A very high reducing sugar content in the stem of GA₃-treated crop indicated active hydrolysis of sucrose coming from the leaves, leading to its reduced supply to the tubers because of further possible sucrose hydrolysis while passing through the long stolons. However, in the CCC treated crop, the higher chlorophyll content of the leaves with reduced stolon length will promote efficient sucrose supply to the tubers. © 1998 Society of Chemical Industry.     

Physico‐chemical characteristics of non‐irradiated and γ‐irradiated yams cultivars (Dioscorea rotundata,Dioscorea alata) and sweet potato (Ipomoea batatas (L) Lam)

Physico‐chemical (pasting) properties of non‐irradiated (fresh) and γ‐irradiated yam cultivars and sweet potato were determined using Rapid Visco Analyser (RVA). Generally, pasting characteristics of the commodities decreased significantly with increased γ‐irradiation dose. Non‐irradiated sweet potato showed significantly higher peak (45.79), trough (35.25), breakdown (10.54), final (75.21) and setback (39.96) viscosities (in RVU) than γ‐irradiated samples. Also, peak time (6.97 min) and pasting temperature (50.18 RVU) significantly reduced with increased γ‐irradiation dose of tubers. The pasting properties of non‐irradiated and γ‐irradiated sweet potato showed similar but clearer trend compared with yam flours. Also, non‐irradiated and γ‐irradiated Dioscorea rotundata and Dioscorea alata showed significantly higher values of each of the pasting characteristics than values noted in sweet potato. Aside from the TDr 03/00196, peak time did not vary significantly with γ‐irradiation dose.     

Effect of the Malting Barley Variety (Hordeum vulgare L) on Fermentability1

The influence of the malting barley genotype on the apparent attenuation limit (AAL) was investigated. The AAL level correlated closely with the maltose concentration in the wort but was not affected by other fermentable sugars or by the total carbohydrate content. The chemical composition, modification, amylolytic enzyme activities and several starch properties of selected malts were studied in detail. Variations in the maltose concentration could almost solely be traced back to genotype‐dependent disparities of β‐amylase thermostability. These differences are due to interallelic polymorphisms of the β‐amylase gene and are easily detected by PCR. Hence, PCR primers offer remarkable prospects for breeding barley on the basis of a marker‐assisted selection (MAS).     

Photo-induced changes in the total chlorogenic acid content of potato (Solanum tuberosum) Tubers

The exposure of potato tubers to light resulted in a significant cultivar-dependent increase in chlorogenic acid content. The magnitude of the observed increase resulting from 48 h light exposure was significantly correlated with the initial chlorogenic acid content of the tubers and also with the previously reported photo-induced increases in total glycoalkaloids. Time-course studies indicated that the greatest rate of increase occurred between 8 and 16 h continual exposure. Prolonged storage under light revealed that chlorogenic acid values in some cultivars reached a maximum value after 48 h, whilst in others these continued to increase almost linearly until the end of the experiment 5 days later.     

Effect of triacontanol on sprout growth in potatoes (Solanum tuberosum)

The effects of a 3-min dip in various concentrations (0–1–100 mg litre^?1) of a triacontanol emulsion on sprout growth from single-eye pieces of seed potato (Solanum tuberosum L) tubers were assessed after 10 days' growth in acid-washed sand. Treatment effects were compared with those resulting from immersion for 3 min in a mixture of gibberellic acid (6 mg litre^?1) and ethrel (4 mg litre^?1). Triacontanol dips were more effective than gibberellic acid and ethrel. Treatments increased the fresh weight of sprouts but had little effect on sprout number per tuber fragment. The optimum concentration of triacontanol was 10 mg litre^?1.     

Impact‐induced blackspots and membrane deterioration in potato (Solanum tuberosum L) tubers

Tubers of the potato cultivar Maris Piper (MP) were grown in 1996 and stored for 8 months, whereas tubers of the cultivar Colmo (CM) were grown in 1997 and harvested immature. In a timecourse study the two cultivars, which had two distinct physiological ages, were investigated for blackspot susceptibility in relation to cellular integrity. Tubers were equilibrated at 5 °C and struck by a falling bolt. The site of impact was analysed for cation efflux from tuber half‐discs and enzymatic activity of polyphenoloxidase (PPO), lipoxygenase (LOX), ascorbate peroxidase (APX) and catalase after 0, 1, 2, 4, 8, 16 and 32 h of tuber incubation. Tubers of MP were 10 times more blackspot‐susceptible than those of CM. The membranes of MP leaked more K⁺, Mg²⁺ and Ca²⁺ than those of CM. Both cultivars showed a very fast increase in K⁺ leakage immediately after impact. Thereafter, CM seemed to reconstitute the membranes, while high efflux of K⁺ from MP continued for up to 32 h of incubation. Mg²⁺ efflux from MP increased and peaked 8 h after impact, but no effect was found on CM. Ca²⁺ and Na⁺ effluxes were not influenced by the impact. More than twice the activity of LOX and more than three times the activity of PPO were found in CM compared to MP, but little effect of impact was registered. The activity of APX was higher in MP than in CM, and again little effect of impact was found. Little effect of impact on catalase activity was found and the level of catalase activity was similar in both cultivars. © 2000 Society of Chemical Industry