Healthy Aspects of Potatoes as Part of the Human

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Healthy Aspects of Potatoes as Part of the

Human Diet

N. U. Haase

Received: 16 July 2008 /Accepted: 19 August 2008 /

Published online: 4 November 2008

# EAPR 2008

Abstract Potatoes are constituents of many diets. Nutritionalists identify several

positive aspects but also discuss some adverse reactions. Therefore, healthiness of potato

food has to be established taking into account new knowledge about natural constituents

and food-borne substances. This paper presents data of three main areas: carbohydrates,

toxins and antioxidants. The glycaemic behaviour of prepared potatoes has discredited

the general understanding of potatoes as a healthy foodstuff. Boiled or steamed potatoes

contain a large amount of rapidly available starch, but alongside genotype driven

variability some preparation steps may also have an influence. The glycaemic load as the

most relevant criterion for healthy subjects is relatively low. Potatoes may contain

toxins, either natural (e.g. glycoalkaloids) or food-borne toxins (e.g. acrylamide).

Minimization strategies have been developed for several potato dishes to reduce the

intake substantially. Consumer handling particularly determines the specific level with

those toxins. Antioxidants are a potent source of health promoting reactions in humans.

They are present in potatoes, but specific concentrations are related to several aspects,

e.g. plant growth, time interval after lifting, genotype, and kind of preparation. Again,

the way in which consumers handle the potatoes is relevant. In summary, potatoes are

very well suited for our modern diet, but consumers need advice to ensure that they arestored and prepared in the most appropriate way.

Keywords Acrylamide . Antioxidants . Glycaemic index . Glycoalkaloids . Potato .

Vitamin C

Introduction

The human diet has reached the focus of popular debate. Malnutrition exists in manyregions of the world but, particularly in developed countries, we observe an

Potato Research (2008) 51:239 – 258

DOI 10.1007/s11540-008-9111-4

N. U. Haase (*)

Max Rubner-Institute, Schuetzenberg 12, 32756 Detmold, Germany

e-mail: [email protected]


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increasing rate of super nutrition, so that more and more people are suffering from

obesity. As a result, several food categories have come under discussion, even though

a food itself cannot be healthy or unhealthy. In many cases our eating behaviour is not

rational and officially available guidelines are not followed. Potatoes are also included

in this behaviour. Therefore, a comparison of healthy and unhealthy aspects in this paper will provide arguments to avoid any misinterpretation.

Potatoes are available all around the world, however, specific acceptance is

different between countries and population subgroups (e.g. social classes and age

groups). Next to freshly boiled or steamed potatoes, consumers request increasing

amounts of potato products.

Updated evaluations of the different food categories by nutritionists have resulted

in a downgrading of potatoes and potato products (Willett 2001). Nevertheless,

potatoes have a nutritionally favourable composition with respect to several

nutrients.An analysis of the composition clearly identifies that boiled potatoes are a good

source of protein and carbohydrates, but because of the high water content, the

nutrient density is low. Minerals and vitamins are valuable constituents. For instance

a typical meal with 200 g of boiled potatoes (at least three medium sized tubers) will

contribute to our daily diet

& 6% of energy (Guideline Daily Amount (GDA): 9,629 kJ),

& 0.3% of fat (GDA: 70 g),

& 11% of carbohydrates (GDA: 270 g),

& 9% of protein (GDA: 50 g),& 11% of dietary fibres (GDA: 25 g),

& 28% of potassium (GDA: 3 g),

& 47% of vitamin C (Recommended Dietary Allowance (RDA): 60 mg),

& 8% of vitamin B2 (RDA: 1.2 mg).

Furthermore, several other constituents, e.g. secondary plant metabolites, are

relevant.

Processed potato foods like French fries are also accepted worldwide, but

composition tends to be less healthy, as for several snacks such as potato crisps. This

snack food offers a lifestyle feeling, especially by its special taste, but of course it is

not a basic food.

Recently, the newly obtained knowledge of food-borne toxicants and food

contaminants has extended the discussion about healthy nutrition. Last but not least,

rational aspects are always accompanied by social and mental aspects, which make it

more complicated to arrive at the right choice of a so called ‘healthy diet ’. The

consumers will even enjoy their food!

Raw potatoes contain protease inhibitors, which are active against trypsin. These

inhibitors interfere with the digestion of proteins. Using raw potatoes or a potato

protein concentrate as food or feed will lead to a decreased protein efficiency.

Trypsin inhibitor (TI) concentration can be up to 174 g TI kg−1 protein (Baker et al.

1982), but heating destroys the TI. Therefore, this topic will not be discussed here.

Potatoes also contain multiple heat-labile proteins which can induce immediate

hypersensitivity reactions (Jeannet-Peter et al. 1999). Peeling of raw potatoes may

cause allergic symptoms in adults, such as contact dermatitis, sneezing and

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wheezing. For children, potatoes as food may cause various allergic reactions.

Patatin, the main storage protein in potatoes with a high nutritional value, induces

such a reaction in sensitive children (Seppälä et al. 1999), but further studies are

needed to confirm the clinical importance of patatin as a food allergen.

Material and Methods

General

Dry matter (DM) content of boiled and lyophilised samples and of potato products

was determined by water loss in an oven at 105 °C until constant weight (American

Association of Cereal Chemists (AACC) 1993a). Dry matter content of raw potatoes

was determined by drying on quartz sand (American Association of Cereal Chemists(AACC) 1993b).

The Glycaemic Approach

Potato samples of the 2005 harvest with a cooking behaviour ranking from firm and

fairly firm to floury (German classification system) were either bought from a local

retailer (Cilena, Ditta, Princess) or collected from a field trial for cultivar testing

(Agria, Albatros, Bintje, Carmona, Saturna).

Unpeeled or peeled samples of five to six tubers each were boiled in a typicalcooking pot with sufficient water. Some samples were chilled overnight in a

refrigerator at +4 °C to enhance starch retrogradation. Microwave heating of

unpeeled tubers from the same samples was carried out in a domestic microwave

oven (Miele, Gütersloh, Germany).

Potato products were processed on semi-technical processing lines with suitable

cultivars (three cultivars each) toward dehydrated potatoes, potato crisps and par-

fried French fries, which had to be finished before analysis.

Rapidly and slowly available glucose (RAG and SAG, respectively), free glucose

and sucrose released glucose of the prepared samples were analysed in triplicate

according to Englyst et al. (2000) with minor modifications.

Glucose concentration in all samples was determined enzymatically with a

glucose-oxidase-peroxidase-reagent according to Karkalas (1985) (incubation for

75 min at room temperature in the dark, and measuring at 510 nm in a

spectrophotometer (Specord 200, Analytik Jena, Germany). Calibration with pure

glucose was in the range between 3 and 30 mg kg−1.

Total glucose content was determined separately. Polysaccharides were split to

glucose by heat, lye, and enzymatic degradation.

Resistant starch (RS) content was calculated according to Englyst et al. (2000)

(RS=0.9(TG−

(RAG+SAG)) and is defined as non-digested starch in the human

small intestine.

Glycaemic index (GI) was calculated according to a statistical regression formula

created from data of Englyst et al. (1996a). Glycaemic load (GL) was calculated for

a serving size of 150 g potatoes or potato products (French fries, rehydrated

potatoes). The crisps serving size was 50 g.

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Toxins

Glycoalkaloids were analyzed by an HPLC procedure. Lyophilized and ground

samples were homogenized with a mixture of water/acetic acid/sodium bisulphite,

95:5:0.5 (v / v / w) (Hellenäs et al. 1995b). Extraction was with SPE cartridges (SepPak C18 (Waters Associates, Milford, MA, USA)) after conditioning with acetonitrile.

Glycoalkaloids were eluted with the HPLC mobile phase (acetonitrile/0.022 mol m−3

potassium phosphate buffer (pH=7.6), 55:45 v / v ). The HPLC separation was carried

out by a ODS Hypersil 5 μ m phase (C18) in a 250×4.6 mm column. Signals were

detected at 202 nm (Kontron Instruments, UV VIS) by a flow rate of 25×10−9 m3 s−1

(Kontron Instruments, HPLC pump model 420).

Acrylamide concentration of potato crisps was determined by a GC – MS

method in the EI mode. To extract acrylamide from the food material, 50×

10−6

m3

of distilled water were added to 4.00 g of ground sample by ultrasonic at 60 °C. After centrifugation (44,145 m s−1, 600 s) the supernatant solution was

defatted by petroleum ether and clarified by 5×10−6 m3 Carrez I and II solution,

each. Acrylamide was salted out with sodium chloride and extracted from the

aqueous phase by threefold extraction with 30×10−6 m3 ethyl acetate, each. These

organic phases were filtrated by water-repellent filters (MN 616 WA 1/4

(Macherey-Nagel, Germany)) to separate water and then evaporated to about

0.5×10−6 m3 before using for GC – MS. GC – MS analysis was carried out using the

electron ionization mode (EI, 70 eV) on a Hewlett Packard Instrument Model 5890

Series II/5989 A. For the determination of acrylamide and D3-acrylamide the SIM-technique (selected ion monitoring) was used and the identification was achieved

by the ions with masses (m/ z ) 74, 71, 58 and 55. The quantification was carried out

by ions with masses 74 and 71. The separation was achieved with a DB-23

capillary column (J&W Scientific Products, Germany) (30× 0.25 × 10−3 m i.d.,

0.25×10−6 m film thickness). The carrier gas was helium at a flow rate of 16.7×

10−9 m3 s−1.

The column temperature was initially kept at 80 °C for 120 s and then increased

from 80 °C to 220 °C at 0.17 °C s−1. The final temperature was held for 60 s. Other

operating conditions were a split/splitless injector (splitless, temperature 240 °C), an

interface temperature of 250 °C, and an ion source temperature of 200 °C. For

quantification deuterated acrylamide was used as internal standard.

Ascorbic Acid

Ascorbic acid (L-AA and DHA) was analyzed by means of a colorimetric method

according to Roche Diagnostics, Mannheim, Germany: L-AA reduces the

tetrazolium salt MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide)

in the presence of the electron carrier PMS (5-methylphenazinium methosulfate) at

pH 3.5 to a formazan (MTT-formazan), which is determined by means of its light

absorbance at 578 nm (Specord 200, Analytik Jena, Germany). After reduction of

DHA to L-AA in the presence of dithiothreite (DTT), the difference between total-

AA and L-AA content is DHA.

Because of different dry matter concentrations of individual samples, all values

are expressed on a dry matter basis.

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Antioxidant Capacity

The antioxidant capacity was estimated with the FRAP-procedure according to

Benzie and Strain (1996). After a lengthened extraction procedure (7,200 s at 37 °C)

with respect to phenolic compounds of the potato (Pulido et al. 2000), samples werefiltered (folded paper filter), and an aliquot was stained: 90×10−9 m3 filtrate and

270×10−9 m3 aqua bidest. were combined with 2.7×10−6 m3 of the FRAP reagent

(50×10−6 m3 of 100 mol m−3 Na-acetate-buffer+5× 10−6 m3 10 mmol TPTZ (2,4,6-

tripyridyl-s-triazine)+5×10−6 m3 20 mmol FeCl3 ·6H2O) and measured at 593 nm

(Specord 200, Analytik Jena, Germany). Trolox was used for calibration.

Results and Discussion

Carbohydrates

Available potato carbohydrates are present as starch or as free sugars, whereas non-

available carbohydrates are considered as dietary fibres. Starch is the main source

with a typical concentration range between 8 and 29% in fresh weight (Lisinska and

Leszczynski 1989). Genotype and environment may have a strong influence upon

specific levels. Potatoes with a low to medium content of starch are often preferred

for fresh consumption (firm to fairly firm cooking type), whereas higher starch levels

are requested by the food industry. Raw potato starch has a high amount of non-digestible units, on the other hand gelatinized starch is easily available. Resistant

starch (RS) is not available for human digestion, but fermentation towards short

chain fatty acids (SCFA) takes place. The RS level in potato food is generally low,

but may increase throughout a longer stay after preparation or by storage of pre-

cooked potatoes (e.g., potato salad, par-fried French fries (Goni et al. 1997)). Raw

potato starch has a very high level of RS — but only few people are going to eat raw

potatoes. Some sugars in the potato may be involved in heat-induced reactions (e.g.,

Maillard reaction) resulting in adverse effects (see below). Furthermore, the debate

on ‘low-carb’ food has enveloped potatoes, too. Principally, the absolute

carbohydrate concentration in potatoes is low, but a range is still given. If consumers

want to select low-carb potatoes, they may choose firm cooking tubers.

Nutritionists have downgraded the relevance of potatoes within our diets

especially in view of the glycaemic behaviour, because all the available

carbohydrates are relatively rapidly available and can be absorbed as monosacchar-

ides and metabolized by the body (Ludwig 2000; Willett 2001). As a consequence

the postprandial blood glucose response (Englyst et al. 1996b) is elicited. The

resulting glycaemic index (GI) of boiled potatoes, calculated as the relationship

between food-borne blood sugar and reference index (glucose or white bread), ranks

between 20 and 100, indicating potatoes as a food with medium to high GI. The

overall insulin mediated glucose uptake is based upon the glucose level in

consequence of the carbohydrate concentration in a food. Therefore, the term

glycaemic load (GL) combines GI and the concentration of carbohydrates. The

glycaemic load of potatoes is low or medium. Several nutrition guidelines were

developed within the last few years reflecting the GI or GL of a single food (e.g. a

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low glycaemic index pyramid — LOGI (Ludwig 2000) and a healthy eating pyramid

(Willett 2001)). Potatoes appear near the top of those pyramids and the guidelines

suggest their limited consumption, but the reason for that positioning is based upon

U.S. preferences of convenience food consumption (esp. French fries, baked

potatoes, potato mash) (Buyken and Kroke 2006). The GI measurement itself implicates several points of criticisms (Brouns et al. 2005). For instance, the

availability of GI-data does not reflect the high variance of carbohydrates in

potatoes. GI is not a stable feature of a food, but is considerably modified by its

processing, composition, preparation, the composition of a mixed food and many

other factors which renders it difficult to precisely predict the actual blood glucose

increase in an individual situation (Hauner 2006). GI of potatoes may be changed

dramatically by parallel consumption of proteins and fats (Gulliford et al. 1989).

Also a high intra-individual variability exists in response to a carbohydrate load

(Jenkins 2007). Finally, a relationship between GI, GL and cancer risk could not bevalidated until now (Michaud et al. 2005; WHO/FAO 2003).

Soh and Brand-Miller (1999) have described the influence of cultivar and

preparation type to the glycaemic index of potatoes (Table 1). GI in this overview

was between 65 and 101, but only the difference between lowest and highest value

reached a statistical significance. Another study by Fernandes et al. (2005) has

expanded the experiment toward the time interval between preparation and

consumption (Table 2), pointing out a GI between 56 (boiled cold potatoes) and

89 (boiled hot potatoes). This principal range of GI data from potatoes reflects a

collection of international data (Foster-Powell et al. 2002).To overcome the time and money consuming in vivo measurements of the GI, an

in vitro technique was developed. Englyst et al. (1996b) have suggested measuring

the rapidly and slowly available glucose (RAG and SAG, respectively). Brand-

Miller (2007) states, that the GI of a food cannot be guessed, it must be tested

according to the standardized in vivo method. Nevertheless, Englyst et al. (2003)

have described, that GI values of cereal products can be explained by the RAG and

SAG contents. A high SAG content identifies low-GI foods which are rich in slowly

released carbohydrates for which health benefits have been proposed.

Table 1 GI values of test foods (n=9 or 10)

Food GI±s.d.

Cultivar

Désirée, peeled and boiled 101±15

Pontiac, peeled and boiled 88±9

Sebago, peeled and boiled 87±7

Cooking method

Pontiac, peeled and boiled 88±9

Pontiac, peeled, boiled and mashed 91±9Pontiac, peeled and microwaved 79±9

Pontiac, peeled and baked 93±11

Maturity

New, unpeeled and boiled 78±12

New, canned and microwave heated 65±9

Modified from Soh and Brand-Miller (1999)

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The fate of dietary carbohydrates in eight potato cultivars was determined in vitroaccording to the protocol of Englyst et al. (2000) by its rapidly available (RAG),

slowly available (SAG), and total glucose (TG) content. Different preparation and

processing techniques were included for three cultivars each. The relationship

between RAG and TG varied within 55 and 78% irrespective of the individual

cooking behaviour. The preparation techniques indicated a cultivar-specific

behaviour. Peeling enhanced the relative RAG in two of three cultivars. Chilling

after boiling reduced the glucose release in one cultivar only. Microwave heating had

a positive effect upon SAG, but RAG was also enhanced in two of three cultivars.

Dehydrated potatoes (DP), French fries (FF), and potato crisps (PC) were processed

from three suitable cultivars each. Differences between cultivars were negligible.

RAG and SAG were related to TG for a better comparability between the products.

A concurrent comparison of boiled and processed tubers from identical cultivars of

the same lot identified specific changes during processing (Fig. 1).

Processing of dehydrated potatoes and of crisps resulted in a faster RAG-

availability compared with the alternately boiled samples. RAG of French fries was

definitely reduced, indicating a shift in physical behaviour.

Fig. 1 Rapidly available glucose ( RAG ) in boiled and processed tubers of three cultivars; relative data:

means, and standard deviation ( DP dehydrated potatoes, FF French fries, PC potato crisps, *_B boiled

samples)

Table 2 GI values for 50 g available carbohydrate portions of seven potatoes tested by a cohort of 12

subjects

Food GI±s.d.

Baked Russet potato 76.5±8.7xyz

Instant mashed potato 87.7±8.0xy

Roasted California white potato 72.3±8.2xyz

Baked Prince Edward Island white potato 72.8±4.5xyz

Boiled red potato (hot) 89.4±7.2x

Boiled red potato (cold) 56.2±5.3z

French fried potatoes 63.6±5.5yz

Modified from Fernandes et al. (2005). xyz means not sharing the same letter superscript differ

significantly ( P


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Total glucose content (TG) was positively correlated with the glycaemic index

(GI, calculated) ( R2=0.58) in processed samples. All firm and fairly firm cooking

cultivars had a high GI, whereas one of the floury cooking cultivars had the lowest

GI (Saturna) and the other one the highest GI of all cultivars (Albatros) (Table 3).

Different preparation types indicated cultivar dependent reactions. Cilena had alower GI after boiling and chilling (application C), whereas Bintje had a lower GI

after microwave heating.

Dehydration and crisping showed stable or increased GI compared with boiling

(variant A), while French fries had a lower GI.

The range of GL was absolutely between 17 and 27 with one single exception (35

for Albatros) (Table 3). GL data of the products were not comparable with the

corresponding GL of boiled samples. Both, higher and lower values were found for

French fries and potato crisps, while dehydrated potatoes showed a trend for slightly

increased values.Dehydration and crisps production resulted in an increase of RAG, whereas in

French fries a significant decrease of RAG and, simultaneously, a significant

increase of SAG were present. RS was different between cultivars, but not between

preparation and processing techniques. Calculated data of the glycaemic index and

glycaemic load reflected comparable trends shown with temporal glucose release.

The investigated set of potato cultivars clearly indicates the need of specific

considerations to prevent inaccuracies in rating of potato.

Toxins (Natural vs. Food-borne)

Glycoalkaloids

Potato tubers contain several glycoalkaloids, especially α -solanine and α -chaconine.

They belong to the class of solanidine tri-glycosides and account for more than 95%

of total glycoalkaloids (TGA) in potatoes. They are haemolitically active like

saponin and highly toxic to humans (Jadhav 1983). Symptoms involve gastrointes-

Table 3 Glycaemic index (GI) and glycaemic load (GL) of eight potato cultivars, calculated according to

Englyst et al. (2003)

Cultivar GI (preparation/processing) GL (preparation/processing)

A B C D E F G A B C D E F G

Marabel 74 86 81 76 – – – 17 20 18 18 – – –

Cilena 78 88 69 80 – – – 23 20 17 20 – – –

Ditta 77 – – – – – – 23 – – – – – –

Agria 79 – – – 87 64 89 20 – – – 27 23 22

Bintje 78 71 74 65 79 61 –

18 20 21 21 23 26 –

Carmona 70 – – – 83 – – 21 – – – 21 – –

Saturna 65 – – – – – 83 24 – – – – – 22

Albatros 84 – – – – 63 76 35 – – – – 26 21

Cells without values: no analysis. Serving size: 150 g, dehydrated potatoes after rehydration; crisps: 50 g

(applications: A boiled with skin; B boiled without skin; C boiled without skin and chilled over night at 4 °

C; D microwave heating with skin; processing E dehydration; F French fries; G potato crisps)

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tinal disturbances by membrane damages (Roddick 1987) and neurological disorders

by inhibition of the enzyme acetylcholinesterase (Bushway 1987). An oral dose of

1 – 2 mg kg−1 body weight initiates a poisoning while a dose of 3 – 6 mg kg−1 body

weight may be lethal (Morris and Lee 1984). Serious glycoalkaloid poisoning of

humans is rare, but it is suspected that mild poisoning is more prevalent thansupposed. It seems to be rarely diagnosed or treated, because the symptoms are

similar to those of other gastrointestinal disorders (Smith et al. 1996). Otherwise

anti-carcinogenic effects of glycoalkaloids against human cervical, liver, lymphoma,

and stomach cancer cells will get pharmacological interest (Friedman et al. 2005).

TGA play an important role by natural defence strategies of plants (Roddick 1988).

The level within potato plants is not equal. High levels are reported in leaves (up to

1,000 mg kg−1 Fresh Weight (FW)) and sprouts (up to 7,300 mg kg−1 FW). In whole

tubers TGA concentrations between 20 and 350 mg kg−1 FW are reported (cited by

Maga 1980). Levels above 200 mg kg−1

FW may be a potential health risk, whichwas proposed as early as 1924 (Bömer and Mattis 1924). Mechanical impacts and

weather are relevant factors for increased values (Cepl and Zrust 1996). In Sweden,

the cultivar Magnum Bonum had an extreme TGA enrichment during a cold and

rainy period before lifting (Hellenäs et al. 1995a). Maturity stage at lifting, tuber size

and storage conditions have an influence, too (Cieslik and Praznik 1998). High TGA

concentrations in the potato flesh will lead to a bitter taste, a natural barrier against

non-controllable potato consumption. With respect to the uneven distribution of

TGA even within one single tuber, the level within the peel fraction easily reaches a

toxic level, whereas the peeled tuber is still usable (Table 4).Green or partly green tubers may have increased TGA concentrations because of

a de novo synthesis of TGA, but increase may be different between cultivars (Fig. 2)

(Haase 1999).

With respect to different tuber sizes, a correction formula between size and mass

was proposed by Engel et al. (1998): ln TGA=ln a+(b×ln m).

Dale et al. (1998) have found an increase of TGA-values between 27 and 130% in

case of blackspot bruise. Also mechanical damage and light stress increase TGA-

level (Olsson 1996).

TGA may affect the flavour of boiled potatoes at higher concentrations. Sinden et

al. (1976) have described a lower critical level of 140 mg TGA kg−1 FW following

an astringent and bitter taste.

With respect to several unsolved questions in combination with factors of TGA-

biochemistry and toxicity, it was proposed to reduce the acceptable level in fresh

tubers down toward 60 – 70 mg kg−1 FW (Parnell et al. 1984).

Table 4 Glycoalkaloid distribution within potato tubers (Haase 1999)

Tuber section α -Solanine

(mg kg−1 FW)

α -Chaconine

(mg kg−1 FW)

Total glycoalkaloids

(mg kg−1 FM)

Relationship Sol.:

Chac.

Skin 1,285 1,764 3,049 1:1.4

Peel 795 1,378 2,173 1:1.7

Kernel 15 12 27 1:0.8

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Heat Induced Toxicants

In the last few years, acrylamide formation has been intensively investigated with

regard of findings in several food categories, including fried and baked potato

products. It is mainly formed in food by the reaction of asparagine with reducingsugars as part of the Maillard reaction (Stadler et al. 2004; Mottram et al. 2002;

Weisshaar and Gutsche 2002; Becalski et al. 2003). In the early Maillard pathway, the

glycoconjugate of asparagine and sugar undergoes a Strecker-type degradation leading

to azomethine ylides, that affords acrylamide after a β -elimination reaction of the

decarboxylated Amadori compound (Yaylayan et al. 2003). Furthermore, a β-proton

in the formation of the corresponding vinylogous compounds is important (Stadler et

al. 2004). Other precursors have also been proposed, such as 3-aminopropionamide (3-

APA) (Zyzak et al. 2003). More detailed studies demonstrated that 3-APA is a key

transient intermediate, i.e. furnishes acrylamide in a thermally-driven deamination

reaction in very high yield (Granvogl and Schieberle 2007). It was also shown that 3-

APA can be generated in an enzyme-catalysed reaction directly through decarboxyl-

ation of asparagine (Granvogl et al. 2004).

Efficiency of the acrylamide reaction is low (Stadler et al. 2004) and

concentration inside a food represents a snapshot of parallel synthesis and

degradation (Biedermann et al. 2002a). Trials with different food matrices have

shown that further specific factors are involved, like recipe components, pH-value of

food, fermentation products, and pre-treatments (washing, blanching, enzymatic

degradation) (Amrein et al. 2003; Becalski et al. 2003; Biedermann et al. 2002a, b).

Acrylamide is under suspicion to be mutagenic via its metabolic glycidamid. Also

neurotoxic and reproductive genotoxic properties are under discussion (Dybing

2007). The lifetime risk of cancer based on acrylamide was estimated by animal

experiments with 1.3× 10−3 to 5.2×10−3 (average and high consumers, respectively)

(corresponds to 13 to 52 cancer diseases per 10,000 individuals) (Dybing and Sanner

2003). Furthermore, a positive association was seen between acrylamide-hemoglobin

Fig. 2 Glycoalkaloid content of potato lots from seven cultivars, separated into faultless ( f ) and green

tubers ( g )

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levels and estrogen receptor positive to breast cancer (Olesen et al. 2008), but other

studies did not show this (Mucci et al. 2003; Pelucchi et al. 2006). Acrylamide

uptake is between 0.5 and 1 μ g acrylamide kg−1 body weight and day−1 for average

consumers, but high consumers may take up till 4 – 8 μ g kg−1 body weight and day−1

(Dybing 2007). The margin of exposure (MOE) as a ratio between benchmark doselower confidence limit (BMDL) and estimated intake in humans was calculated

between 300 and 75 (average and high consumers, resp.), using a BMDL of 0.3 mg

kg−1 body weight and day−1 for induction of mammary tumours in rats (FAO/WHO

2005). The FAO/WHO committee of experts on food additives (JECFA) considered

these MOEs to be low for a compound that is genotoxic and carcinogenic and that

they may indicate a human health concern. Therefore, despite of contradictory data

from epidemiological studies (U.S. Environmental Protection Agency 1999; Bader et

al. 2005; Calleman 1996; Pelucchi et al. 2006), the ALARA principle (as low as

reasonably achievable) is worthwhile being applied.Acrylamide containing animal feeding-stuff may enhance the total exposure, but

first experiments with chicken have shown a low carry-over rate (Halle et al. 2006).

Smokers have a high acrylamide intake from tobacco, which may over-ride any

additional effects from different eating habits (Bader et al. 2005).

Different tools have been identified to lower the acrylamide formation in heated

potato food, including selection of potato cultivar, potato storage regime, process

control (thermal input, pre-processing), final preparation, and colour control (Haase

et al. 2004). Most of them have been collected in a toolbox system (Confederation of

the food and drink industries of the EU (CIAA) 2006; European Commission DGHealth and Consumer Protection 2007). A strong correlation was found between

acrylamide formation and the concentration of reducing sugars in the potatoes. It

was further improved by including the concentration of asparagine (Amrein et al.

2003). In fact, asparagine concentrations in fresh potatoes are typically between

2,000 and 4,000 mg kg−1. Concentrations of reducing sugars range between 100 and

3,000 mg kg−1 after harvesting and may reach 20,000 mg kg−1 after currently used

storage at low temperature (Amrein et al. 2003; Haase et al. 2004; Haase 2006).

Traditionally, potato processors advise plant breeders to develop cultivars with low

sugar content, and they have been encouraged to check potatoes either by fry test or

sugar determination before accepting deliveries.

To minimise losses from spoilage and shrinkage, the potatoes are stored at low

temperatures. However, low temperatures tend to increase the sugar levels,

particularly when stored below 6 °C, through a process known as cold induced

sweetening (CIS) (Sowokinos and Preston 1988), resulting in dark flavoured and

bitter tasting fried products. For potatoes to be held in storage for the longest period

prior to processing, the minimum storage temperature used by producers of French

fries or potato crisps is generally 6 °C.

Storage at higher temperature may result in breaking the dormancy of the tubers.

Sprouting can be controlled through the use of suppressants, such as chloropropham

(CIPC). For organically grown potatoes, compatible growth inhibitors are used.

Reconditioning by warming the tubers to some higher temperatures (e.g. 12 °C)

for a few weeks reduces the sugar levels, but does not restore initial levels.

Slicing or cutting potatoes to a specific surface to volume ratio is particularly

important, because acrylamide formation typically occurs on the surface layer of the

Potato Research (2008) 51:239 – 258 249


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products. Coarse-cut French fries strips (14 ×14 mm) with a surface to volume ratio of

3.3 cm−1 resulted in significant lower ( P


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The acrylamide concentration in par-fried French fries and other potato products

produced for final cooking at home or in a restaurant, are typically very low, because

acrylamide is formed primarily during final frying with a non-linear rate of

formation with increased temperature (Grob et al. 2003). At lower frying temper-

atures and longer frying times, acrylamide concentrations were reduced, but there isa lower temperature limit below which quality is affected, such as by higher fat

uptake and poorer texture (Taeymans et al. 2004).

Latest data have shown that bound 3-monochloropropane-1,2-diol (3-MCPD

esters) is present in some fried potato products. The potato itself is not the problem

rather the refined frying oil. At the moment the amount of release during human

digestion is still unclear.

Acrylamide has become a signal effect, but the highly variable reaction pathways

during heating of food should be considered. Therefore, we can expect to identify a

number of other heat induced chemicals with potentially adverse health effects.

Antioxidants (Vitamin C)

Vitamins of the potato are well known to contribute substantial amounts of the

recommended daily intake. Vitamin C, which is present as L-ascorbic acid (L-AA)

and as mono-dehydro ascorbic acid (MDHA), particularly has been studied

intensively (Davey et al. 2000).

The biological function of L-AA is focused on the antioxidant properties. In humans,

both forms, L-AA as well as MDHA, are active. MDHA can be reduced to L-AA. The plasma level of L-AA in large sections of the population is sub-optimal. Therefore, the L-

AA level of plant food should be improved or losses may be minimized.

Several growing factors have an influence upon the final vitamin C level. Next to

the right choice of a cultivar, fertilization, and weather conditions have effects, too

(Kolbe 1997; Weber and Putz 1998; Rogozinska et al. 2005).

Following the post-harvest period, the sum of L-AA and MDHA declines,

because some MDHA molecules convert to dehydro ascorbic acid (DHA), which

undergoes decomposition toward 2,3-diketo gulonic acid, which is no longer active.

An experiment with three different cultivars stored at two different temperature

regimes (4 and 8 °C) confirmed the results. The first storage section especially

indicated a fast decline, whereas a more stable level was reached after three months.

Slightly warmer stored tubers (8 °C) had a slower decline of vitamin C than the 4 °C

samples (Fig. 3).

Preparation is best when boiling potatoes with skin on. However, high losses can

occur during potato preparation, because vitamin C is heat sensitive. The warm

keeping of boiled potatoes may reduce the initial level for about 40%. Leaching is

also a reason for a reduced concentration, especially in processing lines. While

potatoes for French fries production had a relatively low reduction, tubers for crisps

or flakes production had a loss of 60% (Fig. 4).

Antioxidant Capacity

Several secondary constituents of the potato have an antioxidant activity, which

contributes to the physiological defence against oxidative and free-radical-mediated

Potato Research (2008) 51:239 – 258 251


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reactions. After vitamin C, several secondary constituents, e.g. flavonoids,

carotenoids, and other phenolic compounds, are involved in these reactions (Chu

et al. 2000; Chaillou and Nazareno 2006). Wang et al. (1996) have shown a limited

contribution (less than 15%) of vitamin C to the total antioxidant activity in several

fruits. Another study has estimated that vitamin C extracted from an unknown potatosample contributes 13% to the total antioxidant activity (Chu et al. 2002).

Nevertheless, our knowledge about potato antioxidants is still low. At least a diet

with antioxidant rich food will result in a high antioxidant level in the blood (Cao et

al. 1998; Welch et al. 2005), which will reduce the incidence of degenerative

diseases like cancer and atherosclerotic heart disease.

Fig. 3 Vitamin C levels in tubers of three cultivars over the storage period, following two strategies (+4

and +8 °C storage)

Fig. 4 Remaining vitamin C level (relative values) in a number of potato preparations ((Weber and Putz

1998), modified, and (Haase and Weber 2003)) (FF: French fries)

252 Potato Research (2008) 51:239 – 258


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Data from antioxidant potato compounds are also rare. Most of them are available

from raw materials. Flesh colour (e.g. dark yellow, blue or red) in particular has been

reported to induce different levels of antioxidants (Reyes et al. 2005; Gromes and

Herrmann 2008). Coloured cultivars contain higher amounts of anthocyanins and

flavonoids compared to white or yellow flesh tubers (Lewis et al. 1998), whereby theantioxidant level increases considerably (Lachman and Hamouz 2005). However,

white flesh cultivars may also contain several colourless compounds that are

probably either flavonoids or phenolic acids with a high antioxidant potential (Hale

2003). Phenotype of coloured cultivars does not seem to be stable all the time. Reyes

and Cisneros-Zevallos (2003) have found an influence of the growing location upon

anthocyanin concentration. These authors have also described a significant increase

in case of physiological stress during storage. The concentration of phenolic acids

accounted for relatively little of the total antioxidant activity ( R2=0.18). In a ranking

of different phenolic acids for antioxidant capacity, caffeic acid and chlorogenic acidwere the lowest (Hale 2003). Carotenoids include primarily lutein, zeaxanthin, and

violaxanthin (Lu et al. 2001; Nesterenko and Sink 2003), whereas the amounts of α -

or β-carotene are negligible (Gross 1991). Antioxidative behaviour of single

carotenoids is still a matter of research. In comparison with lycopene, both lutein

and zeaxanthin were about as half as effective (Miller et al. 1996; Böhm et al. 2002).

Generally, the preparation of potatoes will lower the antioxidants, because of heat

sensitivity of most substances involved. Long heating (e.g. boiling) reduces more

than short preparations (e.g. microwave heating, frying), but an average remaining

antioxidant capacity of 75% is reported (Blessington et al. 2005). Experiments with bread crust have shown a de novo synthesis within the Maillard reaction

(Lindenmeier and Hofmann 2004). Consequently, fried potato products may have

enhanced values in relation to boiled tubers, but valid data are still under research. In

comparison with legumes and fruits, potatoes offer a low but substantial contribution

to the daily requirement for antioxidants (Halvorsen et al. 2002). Methodical studies

Fig. 5 Antioxidant capacity in stored potato tubers from three cultivars, stored at +4 °C (left ) or +8 °C

(right )

Potato Research (2008) 51:239 – 258 253


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have shown that potato antioxidative capacity is often undervalued with respect to

the slow release of phenolic substances (Pulido et al. 2000).

In contrast to a vitamin C decline (see Fig. 3), the total antioxidant capacity

increased over the storage season, as was found in an experiment (Fig. 5). Lewis et

al. (1999) have described the same phenomenon in coloured cultivars. Theyexplained it with a de novo synthesis of anthocyanins, which happened especially in

relation to cold sweetening, because sugars are an anthocyanin precursor.

Conclusion

Potato tubers offer several nutritional benefits. Potatoes provide a substantial

contribution to the daily supply of minerals, vitamins, and secondary compounds as

well as carbohydrates and protein. Potatoes have the highest satiety index of all plant foods. Alongside these positive aspects only few adverse factors are identified,

including the existence of glycoalkaloids and acrylamide, but the right treatment can

reduce these levels substantially. Unfortunately, many consumers have a limited

knowledge about all these facts. Education campaigns could help to promote the

nutritionally positive methods of preparation and to increase the daily potato intake.

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Healthy Aspects of Potatoes as Part of the Human

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