Potato Research 33 (1990) 125-130

Loss of vitamin C (L-ascorbic acid) storage of Dutch table potatoes

SHORT COMMUNICATION

during long-term cold

M. J. H. KEIJBETS* and G. EBBENHORST-SELLER

Institute for Storage and Processing of Agricultural Produce (IBVL), P.O. Box 18, 6700 AA Wageningen, the Netherlands

Accepted for publication: 23 May 1989

Additional key words." dehydroascorbic acid, H PLC, Dutch Food Composition Table, Solarium tuberosum L.

S u m m a r y

Loss of vitamin C (L-ascorbic acid) from Dutch table potatoes during storage at 5 - 6 ~ over 8 months from November to July, was studied in two seasons. L-Ascorbic and dehydroascorbic acid were analysed by HPLC. The amount of dehydroascorbic acid was negligible. Total loss of L-ascorbic acid varied between 21 and 60 ~70.

Some potato lots lost L-ascorbic acid rapidly in the first four months, others more gradually over the whole storage period. The L-ascorbic acid levels detected were 75-150 ~ higher in the period March-June, but 35 ~ lower in the period December-February than those indicated by the step-wise decreases in the Dutch Food Composition Table.

Introduct ion

Tubers of potato (Solanum tuberosum L.) can be a major and cheap source of vitamin C in the human diet but its levels decrease during storage as do those of other nutrients (Woolfe, 1987). The most rapid losses occur during the first months of storage (Au- gustin et al., 1978; Finglas & Faulks, 1984; Mareschi et al., 1983) and losses may range from 40 to 60 % (Augustin et al., 1978; Faulks et al. 1982; Mareschi et al., 1983). The high initial rates of loss decrease to become small by the end of storage. Temperature as well as time may affect losses and below 10 ~ storage losses are higher than between 10 ~ and 20 ~ indeed ascorbic acid content was found even to increase in tubers stored between 16 and 28 ~ for 12 weeks (Linneman et al., 1985).

The data on loss of vitamin C in table potatoes in long-term cold storage in the Netherlands is too limited to use for reliably estimating dietary intake of this important nutrient. Modern analytical techniques enable vitamin C to be determined precisely. Separation and determination of (dehydro)ascorbic acid by high performance liquid chromatography (HPLC) gives more precise data than older colorimetric methods. This study presents such data on vitamin C loss during modern long-term cold storage of Dutch table (ware) potato lots of different cultivars and from different sources and compares them with those in the Dutch Food Composi t ion Table (Nederlandse Voedingsmiddelentabel, 1987).

* Present address: AVIKO BV, P.O. Box 8, 7220 AA Steenderen, the Netherlands.

Potato Research 33 (1990) 125

M. J. H. KEIJBETS AND G. EBBENHORST-SELLER

Materials and methods

Potatoes. Potatoes of cvs Bintje, D6sir6e, Eba, Eigenheimer, Her tha and Irene were grown on clay soil on the experimental farm De Eest, Nagele in the Netherlands in 1982 and 1983. Tubers of cv. Bintje were also collected from four other sites. Samples of 20 kg (size 3 5 - 50 mm) were cured for two weeks and then stored from November to July at 5 - 6 ~ and 95 - 98 ~ r.h. with C(IPC) powder as sprout inhibitor, and once a month 2 kg samples (about 20 tubers) were analysed.

Determination o f L-ascorbic acid and dehydroascorbic acid. Tubers were hand-peeled, divided in quarters, and one quarter of each tuber cut rapidly in cubes. A 50 g sub- sample of cubes was homogenized immediately in a mixture of 50 ml 9.5 ~ oxalic acid and 50 ml methanol (Ultraturrax). The resultant slurry was diluted to 500 ml with water and filtered through fluted paper (Schleicher & Schull 595 �89 Ten ml of the fil- trate was diluted with water to 25 ml and then partially purified by passing it through a SEP-PAK Florisil column (Millipore). Ten/~1 of this filtrate was then injected into a Waters HPLC-system using a Model U6K injector and a Model 2000 pump. The ascorbic acid was analysed according to Rtickemann (1980), but on a radially packed #Bondapak C18 column (5/zm) (Waters). Column effluents were monitored at 251 nm with a Pye Unicam LC UV-vis variable wavelength detector and peaks integrated and calculated with a Hewlett Packard H P 3390 integrator.

Dehydroascorbic acid was calculated from total ascorbic and L-ascorbic acid values. For total ascorbic acid determination, dehydroascorbic acid in the potato extract was reduced to ascorbic acid with homocysteine by the procedure of Dennison et al. (1981), modified by adjusting the pH of I0 ml filtrate to 7.0 with 2 M KOH (pH 5.0) followed by 0.05 M Tris buffer (pH 7.0); the volume of this filtrate was made up to 25 ml of which 1 ml was treated in the dark for 15 rain with 1 ml 8 ~ DL-homocysteine solu- tion. After ultrafiltration (Millex 0.45 /zm filter, Millipore), 10 IA was injected into the HPLC-system and analysed as described for I~ascorbic acid.

Extraction and determination of L-ascorbic acid were done in duplicate and the results are presented as mean values. The standard deviation of L-ascorbic acid analysis was 0.44 mg/100 g (4 ~ at an average value of 11.3 mg/100 g fresh weight (f.w.) (n=8).

Results

Only L-ascorbic acid values are presented because total ascorbic acid contents were only slightly higher (0 -10 ~ than those of L-ascorbic acid; typically, 4 ~ early in the storage season and 7 ~ later. The levels in the lots o f six cultivars and in the four lots of cv. Bintje in the two seasons are shown in Fig. 1A/B and 2 A / B respectively. During 8 months at 5 - 6 ~ levels decreased steadily in all lots, but the initial level and the loss patterns differed between lots and seasons. The differences were larger between lots of the six cultivars (Fig. 1A/B) and smaller between the lots of cv. Bintje potatoes from different locations (Fig. 2A/B). Towards the end of the storage period, the L-ascorbic acid level had increased in most lots and, most notably, as storage con- tinued until the end of July 1984 by which time several tubers had small, thick sprouts.

126 Potato Research 33 (1990)

LOSS OF VITAMIN C DURING COLD STORAGE

L-ASCO~IC ACID Img,!OOg !.w.] 2~ . . . . . . . . . . .

A

: >x

\

5 ~-~ ~ _ ~ ~ ~ L MAYtt J... _ L ~ NOV. 9 DEC. ~ JAN. 20 FEB. ',5 MA~. 15 APR. !3 0 JUN. 7 JUL. 5

STOFIAGE SEASON :~182-B3

B

20-

5 L - - l I I _ ! t I 1 [ t l

NOV.22 ;D;.20 JAN.16 FEBA4 MAR.13 APR.II BY 8 JUN.5 JUL.3 JUL.3I S!I]P~A~iE SEA~,UN !983-84

Fig. 1. Levels o f L -ascorb ic ac id ( m g / 1 0 0 g f.w.) in lots o f six p o t a t o cu l t i va rs s tored at 5 - 6 ~ fo r 8 m o n t h s . A = 1 9 8 2 - 1 9 8 3 season; B = 1 9 8 3 - 1 9 8 4 season. ( � 9 B in t j e ; +D~s i r~e ; *Eba ; u E i g e n h e i m e r ; x H e r t h a ; <> I rene).

Potato Research 33 (1990) 127

M. J. H. KEIJBETS AND G. EBBENHORST-SELLER

L-ASC0~IC AC[O [mgi'lOOg f.w.)

25 . . . . . . . A

!5

NOV.9

/

i i i

i I

! "/:zY"" !

�9 _ _ L _ _ �9 L 1 . J - - J - . . . . L _ _

~C.7 JAN.20 FEBA5 MAR.15 APR.t3 MAY IO JUN.7 ,ItlL.5 STORAGE SEASON 1982-83

L-ASCO~IC ACI~ {~,'100g f.w.)

2 5 - - B

2 0 -

',5 - ~ :

~0 -

5L-L I40V.22

1 l . J I 1 J 1 1 1 , , - , ~ p ~ . DE(;.20 J,E:6 rEfl.I, MAR.13 . , M~Y B ,~N.5 JUL.3 JUL.31

STO~AGE SEASOI4 I~83-84

Fig. 2. Levels o f L-ascorbic acid (mg/100 g f.w.) in lots of cv. Bintje potatoes from four growing locations stored at 5 - 6 ~ for 8 months. A = 1 9 8 2 - 1 9 8 3 season; B=1983-1984 season ( �9 + * t2 growing locations).

128 Potato Research 33 (1990)

LOSS OF VITAMIN C DURING COLD STORAGE

Discussion

Because both L-ascorbic acid and dehydroascorbic acid have vitamin C activity both should be determined. However, we found only small amounts of dehydroascorbic acid which were rarely outside the standard deviation of the L-ascorbic acid determinations. We considered, therefore, that the L-ascorbic acid values adequately represent the levels of vitamin C activity and we have presented only those values.

In her review, Woolfe (1987) reported that dehydroascorbic acid has been detected in potatoes during storage. Using HPLC, increases ranging from 0 to 4.2 rag/100 g were found in fresh potatoes after 7 weeks storage at 20 ~ by Wills et al. (1984b) ac- companied by decreases in ascorbic acid from 13.8 to 4.7 mg/100 g. At that tempera- ture potatoes became unacceptable for consumption by the eight week of storage be- cause of the extent of sprouting. We have found negligible levels of dehydroascorbic acid after storage for 8 months at 5 - 6 ~

The total losses of ascorbic acid in our experiments ranged from 21% ('Irene', Fig. IA) to 60 % ( 'Hertha' , Fig. I B), but most were between 30 and 50 %. Similar losses during storage for 6 - 8 months at temperatures between 6 ~ and 12 ~ have been reported by Augustin et al. (1978), Blumenthal et al. (1981), Faulks et al. (1982) and Mareshi et al. (1983). The losses were most rapid during the first phase of storage in some lots and more gradual over the whole period in others. About two-thirds or more of the total loss occured during the first four months in lots of cv. Bintje, D6sir6e and Hertha (Figs. IA/B and 2A/B) and one-third to half was lost after four months in lots of cv. Eba, Eigenheimer and Irene. Again a similar pattern of rapid early loss has been reported by Augustin et al. (1978), Blumenthal et al. (1981), Finglas & Faulks (1984), Mareschi et aI. (1983), Somogyi & Schiele (1966) and Wills et aI. (1984a). After 8 months storage in both years levels in all lots were similar at about 8 - 12 mg of ascor- bic acid per 100 g fresh weight (f.w.). This disappearance of initial differences was also reported by Augustin et al. (1978), Blumenthal et al. (1981), Somogyi & Schiele (1966).

According to the Dutch Food Composition Table (Nederlandse Voedingsmiddelen- tabel, 1987) the vitamin C content of untreated raw potatoes decreases from 25 in new potatoes (mid-June to July) to 15 (August to February) and 5 (March to June) mg/100 g f.w. Our data for 10 lots of Bintje, the main table cultivar grown in the Netherlands, show that the ascorbic acid level was 75-150 % higher in the period March to June than is shown in the Dutch Food Composition Table but 35 % lower in the period November to February (Figs. 1A/B and 2A/B). These differences were also evident for lots of two other important table potatoes, cvs. Eigenheimer and Irene, which, how- ever, had levels somewhat higher than those of Bintje in the period November to Febru- ary.

When compared to our data, the low figures for vitamin C in the Dutch Food Com- position Table for main crop table potatoes in the period of March to June may reflect improvements in storage techniques over recent decades. Thus for 1950-51, levels of only 5 - 8 mg/100 g f.w. were found in potatoes of cv. Bevelander stored from Oc- tober/November to May with outside air cooling (De Jong & Hofstra, 1950; De Jong et al., 1951).

Acknowledgement

We thank G. Hulstein for supervising the supply of potatoes.

Potato Research 33 (1990) 129

M. J. H. K E I J B E T S A N D G. E B B E N H O R S T - S E L L E R

References

Augustin, J., S. R. Johnson, C. Teitzel, R. B. Toma, R. L. Shaw, R. H. True, J. M. Hogan & R. M. Deutsch, 1978. Vitamin composition of freshly harvested and stored potatoes. Journal of Food Science 43: 1566-1570, 1574.

Blumenthal, A., P. Sheffeldt & G. Dtinnenberger, 1981. Zu den N~hrstoffgehalten tischfertiger Nahrungsmittel. 3. Mitt: Die Ver~inderungen der Vitamin-, Magnesium- und Spurenelement- gehalte roher und zubereiteter Kartoffeln der Soften Bintje, Maritta, Ostara und Urgenta in Abh~ingigkeit der Lagerdauer. Alimenta 20:115 - 119.

Dennison, D. B., T. G. Brawley & G. L. K. Hunter, 1981. Rapid high performance liquid chro- matographic determination of ascorbic acid and combined ascorbic acid-dehydroascorbic acid in beverages. Journal of Agricultural and Food Chemistry 29:927-929.

Faulks, R. M., N. M. Griffiths, M. A. White & K. I. Tomlins, 1982. Influence of site, variety and storage on nutritional composition and cooked texture of potatoes. Journal of the Science of Food and Agriculture 33: 589.

Finglas, P. M. & R. M. Faulks, 1984. Nutritional composition of UK retail potatoes, both raw and cooked. Journal of the Science of Food and Agriculture 35: 1347-1356.

Jong, W. H. de & D. Hofstra, 1950. Ervaringen met aardappelbewaring in gebouwen en kuilen in het seizoen 1949-1950. Landbouwkundig Tijdschrift 62: 680- 696.

Jong, W. H. de, D. Hofstra & B. G. Oude Ophuis, 1951. Verdere gegevens over gestorte bewaring van aardappelen met buitenluchtkoeling in gebouwen, naast opslag in kuilen. Landbouwkun- dig Tijdschrift 63: 485-508.

Linneman, A. R., A. van Es & K. J. Hartmans, 1985. Changes in the content of L-ascorbic acid, glucose, fructose, sucrose and total glycoalkaloids in potatoes (cv. Bintje) stored at 7, 16 and 28 ~ Potato Research 28: 271-278.

Mareschi, J. P., J. P. Belliot, C. Fourlon & K. E Gey, 1983. Evolution de la teneur en Vitamin C de la pomme de terre Bintje au cours du stockage et des preparations culinaires usuelles. International Journal of Vitamin and Nutrition Research 53: 402-411.

Nederlandse Voedingsmiddelentabel, 1987. 35e gewijzigde druk. Voorlichtingsbureau voor de Voeding, Den Haag.

Rfickemann, H., 1980. Methoden zur Bestimmung von L-Ascorbins~.ure mittels Hochleistungs- Fltissigchromatographie (HPLC). I. Bestimmung von L-Ascorbins~iure in Obst und Gemfise. Zeitschrift fiir Lebensmitteluntersuchung und -forschung 171: 357- 359.

Somogyi, J. C. & K. Schiele, 1966. Der Vitamin-C-Gehalt verschiedener Kartoffelsorten und seine Abnahme w~ihrend der Lagerung. International Journal of Vitamin Research 36: 337-359.

Wills, R. B. H., J. S. K. Lim & H. Greenfield, 1984a. Variation in nutrient composition of aus- tralian retail potatoes over a 12-months period. Journal of the Science of Food and Agricul- ture 35: 1012-1017.

Wills, R. B. H., P. Wimalasiri & H. Greenfield, 1984b. Dehydroascorbic acid levels in fresh fruit and vegetables in relation to total vitamin C activity. Journal of Agricultural and Food Chemistry 32: 836-838.

Woolfe, J. A., 1987. The potato in the human diet. Cambridge University Press, p. 93-96.

130 Potato Research 33 (1990)