Abstract During commercial sterilization, mild to severebreakage of individual potatoes sometimes occurs and the outer layers of potatoes disintegrate into a floury tex-ture referred to as sloughing. Four cultivars of potatoesnamely Kufri Badshah, Kufri Bahar, Kufri Chandramukhiand HPS-1/13 were either treated with CaCl2 or dehy-drated before canning to reduce the sloughing. The extentof sloughing in terms of breakage observed visually de-pended on the cultivar of potatoes. Although CaCl2 treat-ment reduces sloughing, it causes turbidity of the brine.Partial dehydration of potatoes before canning was help-ful in reducing sloughing and it allowed a higher fillingof potato solids in the can thereby increasing drainedweight. HPS-1/13 cultivar was found most suitable fordehydrocanning.

Keywords Canning · Dehydration · Dehydrocanning ·Potato

Introduction

Potatoes on canning should retain their mild flavour,firm texture and should easily break to a dry crumblymass of creamy colour. However, potatoes of many vari-eties crack and their outer layers disintegrate into afloury texture referred to as sloughing. The extent ofsloughing depends on processing conditions, geneticcharacteristics and cultural practices followed during potato cultivation [1]. No significant relationship be-tween raw potato properties and incidence of breakage

was observed However, major diameter, peak viscosityand peak viscosity temperature of sterilized potatoeswere linearly related to breakage [2]. Sloughing resultsfrom excessive hydration of the cell wall material, whichcauses intercellular separation and cell disruption [3] andis affected by specific gravity [4]. During sterilization,major changes occur in starch properties. As the heatingstarts, starch granules absorb water. Amylose leaches outof the granules and a tightly packed, swollen matrix isformed at the gelatinisation temperature [5]. Structuraland physical changes in starch due to gelatinisation andheat treatment have been found to affect functional prop-erties. Dry matter content and density, which dependmainly on starch content, have been shown to influencecooking texture [6].

Sandhu and Bawa [7] suggested partial drying of potatoes of low specific gravity to improve their chip-making quality. Treatment with calcium chloride canalso improve the texture of canned potato [8]. Dehydra-tion of fruits and vegetables prior to canning has been reported to retain firmer texture and give a greater pack-ing density [9, 10]. Therefore in this study we aimed toinvestigate the effect of partial dehydration before can-ning on the quality of four cultivars of potatoes.

Materials and methods

Mature and medium sized potatoes of four cultivars (Kufri Badshah,Kufri Bahar, Kufri Chandramukhi and HPS-1/13) were harvested atthe Horticultural Research Centre and stored under ambient condi-tions in thin layers in a well-ventilated room until canned. Thecanned product was stored for one month under ambient conditions(33±5 °C, 35–80% RH) before analysis.

To determine the size, major and minor diameters of the pota-toes were measured using vernier callipers of least count 0.01 cmand their geometric average was taken. Shape was expressed onthe basis of shape-classification [11]. The average weight was cal-culated from the weight of ten potatoes. The colour of the skin andflesh was observed visually. The number of eyes in each tuberwere counted and their depth was measured using a scale [12]. Forspecific gravity calculation, 10–12 potatoes were weighed andtheir volume was obtained by collecting the water displaced bythem [13]. Sloughing was determined visually by observing the

P.S. Negi (✉ ) · N. NathDepartment of Food Science and Technology, G. B. Pant University of Agriculture and Technology, Pantanagar, U. S. Nagar – 263 145, Indiae-mail: psnegi@yahoo.comTel.: +91-0821-514310, Fax: +91-0821-517233

Present address:P.S. Negi, Department of Human Resource Development, Central Food Technological Research Institute, Mysore, 570 013, India

Eur Food Res Technol (2002) 215:231–234DOI 10.1007/s00217-002-0540-z

O R I G I N A L PA P E R

Pradeep Singh Negi · Nirankar Nath

Effect of partial dehydration on quality of canned potatoes

Received: 12 October 2001 / Revised: 19 March 2002 / Published online: 9 May 2002© Springer-Verlag 2002

extent of cracks on the surface of potatoes after canning. Duringsensory evaluation (texture scoring), panellist determined slough-ing by gently squeezing the potato between two fingers and notingthe tissue susceptibility – either cracking in half easily or not.

Moisture content was determined by drying thin slices ofpeeled potatoes in an oven at 135 °C for 3 h. Protein, fat, ash andcarbohydrates were determined by the methods described byRanganna [14]. For protein estimation a conversion factor of 6.25was used [12]. Reducing and total sugars were estimated by theShaffer-Somogyi method and starch content by the direct hydroly-sis method [14]. Calcium was estimated by the titrimetric method,and phosphorus and iron were analysed by calorimetric methods[14]. All chemicals used were AR grade.

Experimental design and statistical analysis

For canning experiments, potatoes were washed in tapwater, peeled in an abrasive peeler (M/S B. Sen Barry &Co., Mumbai, India) and blanched in hot water (70 °C)for 5 min. Blanched potatoes were divided into three lots– one was dried partially in a cabinet drier (Killburn,Mumbai, India) at 65±2 °C for 3 h (tray load15–20 kg/m2; air velocity 2.42 m/s) and the other twolots were used without partial drying. Whole potatoes,with or without dehydration, were filled into A 2 1/2cans, covered with hot (75–80 °C) sodium chloride brine(15 g/l in water), exhausted for 7 min in an exhaust boxto a can-centre temperature of 70–75 °C and sealed usinga double seamer. To the brine of one lot of potatoes with-out dehydration, calcium chloride (2 g/l in water) wasadded. Canned potatoes were processed quickly aftersealing for 25 min in a still vertical retort under a steampressure of 15 psig. Come-up time of the retort wasabout 4 min. Processed cans were cooled to about 38 °Cquickly in running tap water. The canned potatoes werestored under ambient conditions for one month. Brinestrength was selected on the basis of preliminary canningtrials using NaCl (15 g/l in water), NaCl (15 g/l in water)plus CaCl2 (2 g/l in water) and NaCl (20 g/l in water),and subjecting canned potatoes to sensory evaluationemploying the triangle test [14]. For all cultivars, threetreatments were used and in each treatment three canswere randomly selected for cut-out examination and in-cubation test [14].

The sensory analysis of canned potatoes was done bya composite scoring test [14]. Ten panellists consistingof students and faculty members evaluated the samplesfor texture, colour, flavour and absence of defects foreach treatment. The scorecard was based on BIS [15]and USDA [16] with slight modification and the maxi-mum scores assigned to the above attributes were 40, 25,25 and 10, respectively. The overall acceptability wasobtained by the weighed sum of individual scores.

The effect of partial dehydration and CaCl2 treatmenton the overall acceptability of canned potatoes was as-sessed using ANOVA. The critical difference (CD) wasused to compare the effect of different treatment. Differ-ence between two means within or between the treat-ments exceeding CD value at p≤0.05 [CD (p≤0.05)=tvalue (p≤0.05) × sed] was considered significant [17].

Results and discussion

The potatoes of the four cultivars differed in their appearances and physico-chemical characteristics (Table 1). Potatoes of the Kufri Badshah cultivars werecylindrical in shape, Kufri Bahar was oval and the othertwo cultivars were oval-round. The colour of the peel surfaces was brown to yellowish brown. CultivarHPS-1/13 potatoes had a minimum number of eyes andthey were of the superficial type. The specific gravity ofpotatoes varied from 1.054–1.074. The physico-chemicalproperties of potatoes are known to vary depending oncultivar and agro-climatic conditions [11]. Talburt andSmith [4] indicated that when density exceeds1.100 g/cm2 excessive sloughing can be seen, but no sig-nificant relationship between density and breakage wasalso reported [2]. In the present study, cultivar HPS-1/13was best for dehydrocanning and its specific gravity wasin the medium range of all the cultivars used.

The moisture content of potatoes was found to be81.2–85.2% (Table 1), which is higher than the valuesreported by others [18, 19]. These variations may be ascribed to the variations in the agro-climatic conditionsof the regions of cultivation [12]. Their protein (1.96–2.36%), fat (0.13–0.16%), starch (9.1–12.8%), minerals(0.59–0.73%), Ca (8.7–10.7 mg%), P (33.1–60.7 mg%)and Fe (2.95–3.78 mg%) were within or close to the reported values [18, 20, 21].

Drying for 3 h at 65±2 °C reduced the moisture con-tent of potatoes by 9.2, 15.0, 11.7 and 11.0% (freshweight basis) for Kufri Badshah, Kufri Bahar, KufriChandramukhi and HPS-1/13, respectively. Canning ofthese partially dried and fresh potatoes in brine with orwithout CaCl2 in A 2 1/2 cans rendered them safe andthey remained normal with no external signs of bulgingduring one month of storage under ambient conditions.They gave a negative incubation test. The net weights offreshly canned (without dehydration) and dehydrocannedpotatoes were 798–814 g and 810–830 g, respectively;drained weights were 60.1–64.7% and 70.6–73.3%, re-spectively (Table 2). The weight of potato solids per canin the case of dehydrocanned samples was 35.5–71.8%higher than freshly canned potatoes. This shows that par-tial drying before filling enabled a greater fill of potatosolids in cans. Brines from cans were clear having apleasant aroma, except for those containing CaCl2,which were turbid and chalky in appearance. Fresh pota-toes canned in brine exhibited cracks on their surfacesindicating sloughing, but potatoes with added CaCl2 orpartial dehydration retained their texture well during pro-cessing and subsequent storage. Use of calcium ions tomaintain texture in canned products [22] and partial osmotic dehydration of plums before canning to improvetexture and allow more fill in the cans has been reported[23].

The overall acceptability score for dehydrocannedsamples was significantly higher than others (Table 3). Acomparison of scores for different sensory attributesshowed that differences in overall acceptability scores of

232

233

Table 1 Physico chemicalcharacteristics of potato cultivars

Table 2 Cut out examinationof canned potatoes carried outone month after canninga

Cultivar and treatment Net weight Head space Drained Total potato solids (g) (cm) weight (%) content (g)

Kufri BadshahControl 810±12 0.5±0.1 60.1±3.2 75.5±5.6CaCl2 treated 814±10 0.4±0.1 60.3±2.8 80.0±5.2Dehydrocanned 830±14 0.6±0.1 70.1±3.6 101.2±8.6

Kufri BaharControl 812±10 0.9±0.2 63.5±2.6 72.1±6.8CaCl2 treated 799±14 0.8±0.1 63.6±2.9 78.7±8.2Dehydrocanned 815±12 0.5±0.1 70.1±3.2 113.9±11.2

Kufri ChandramukhiControl 801±11 0.9±0.2 64.7±3.6 80.9±6.2CaCl2 treated 798±16 0.8±0.2 64.1±3.8 87.0±7.1Dehydrocanned 810±8 0.8±0.1 70.0±4.2 114.9±12.4

HPS-1/13Control 801±12 0.7±0.2 62.8±2.1 80.1±6.1CaCl2 treated 798±13 0.6±0.2 64.4±2.5 85.3±8.6Dehydrocanned 813±10 0.6±0.1 73.3±3.6 113.6±11.6

a Mean±SD (n=3)

Table 3 Effect of dehydrocan-ning on sensory characteristicsof potatoes after one monthstoragea

Parameter Kufri Badshah Kufri Bahar Kufri HPS-1/13Chandramukhi

Shapea Cylindrical Oval Oval round Oval roundSkin colour Yellowish brown Brown Yellowish brown BrownNumber of eyes per tubere 6±1 8±2 4±1 3±1Depth of eyesb Superficial Shallow Shallow SuperficialAverage tuber weight (g)c 71.1±3.2 36.6±2.1 33.5±2.6 32.5±1.9Average tuber diameter (cm)de 5.5±1.8 5.1±1.2 4.5±0.9 4.0±0.8Specific gravitye 1.074±0.011 1.054±0.016 1.071±0.021 1.061±0.006Moisture (%)e 81.2±1.1 85.2±1.4 81.5±1.0 83.9±1.3Protein (%)e 2.13±0.20 2.01±0.11 2.36±0.09 1.96±0.08Fat (%)e 0.16±0.04 0.15±0.04 0.14±0.03 0.13±0.03Minerals (%)e 0.67±0.08 0.59±0.08 0.69±0.07 0.73±0.11Calcium (mg/100 g)e 10.7±0.2 8.7±0.2 10.0±0.3 9.3±0.2Phosphorus (mg/100 g)e 49.1±5.2 33.1±3.6 36.4±3.2 60.7±4.8Iron (mg/100 g)e 2.95±0.22 3.05±0.35 3.78±0.36 3.67±0.26Carbohydrate (%)e 15.84±1.12 12.05±1.00 15.31±1.56 13.28±1.14Total sugars (%)e 1.80±0.20 1.92±0.21 1.51±0.30 1.62±0.42Reducing sugars (%)e 0.51±0.06 0.61±0.05 0.69±0.06 0.81±0.04Starch (%)e 12.8±1.1 9.1±1.0 12.2±1.6 10.4±1.4

a As per classification of Pushkarnath (1964)b As per nomenclature by Lisinska and Leszczynski(1989)c Mean±SD of ten potatoesd Geometric average of majorand minor diameterse Mean±SD of three values

Cultivar Texture Colour Flavour Absence Overall and treatment of defects acceptability*

Kufri BadshahControl 20.1±1.1 15.7±1.1 14.2±1.6 6.4±0.6 56.4±4.4a

CaCl2 treated 29.7±1.2 18.4±1.3 14.8±1.4 7.4±0.5 70.3±3.3b

Dehydrocanned 34.5±1.6 16.7±1.3 15.5±1.2 7.7±0.2 74.0±5.0b

Kufri BaharControl 22.2±1.8 18.0±1.8 16.9±1.8 5.6±0.5 62.7±2.7a

CaCl2 treated 29.4±1.6 22.1±2.2 18.1±1.4 7.6±0.6 77.2±3.2b

Dehydrocanned 34.0±2.4 18.5±1.6 20.4±2.0 8.7±0.7 81.6±1.6c

Kufri ChandramukhiControl 26.6±1.6 17.3±1.1 16.0±1.1 7.1±0.9 67.0±2.0a

CaCl2 treated 32.0±2.4 18.5±1.3 6.5±1.0 5.6±0.6 62.6±3.3b

Dehydrocanned 34.9±2.8 22.0±2.2 20.2±1.8 5.3±0.4 82.4±2.4c

HPS-1/13Control 24.5±1.9 17.4±1.2 17.8±1.1 7.3±0.8 67.0±5.2a

CaCl2 treated 28.3±1.9 18.6±1.6 20.1±2.0 7.6±0.8 74.6±3.2b

Dehydrocanned 33.4±2.1 20.9±1.8 20.6±2.0 8.7±0.5 83.6±2.9c

a mean±SD (n=10); maximumscores for texture, colour, flavour, absence of defects andoverall acceptability were 40,25, 25,10 and 100, respectively* figures followed by same letter for each cultivar are notsignificantly different (p≤0.05)

the canned samples were mainly due to scores for tex-tures and flavour. Breakage affects the texture scores andit occurs during canning when the internal portion of thepotatoes swells sufficiently to exceed the strength of theouter layers of potatoes. Potatoes with low dry matter(<20% wet basis), small size, uniform roundness andearly maturity are good for canning [3]. Reid et al [2]also observed that the incidence of breakage increases asthe major diameter increases. Large potatoes have a highswelling potential during gelatinisation and sterilisation,and they break more. The overall score was highest fordehydrocanned HPS-1/13 potatoes that were of oval-round shape and smaller in size. Improvement of textureby partial drying before canning may be responsible forhigher texture scores [10, 23]. Although CaCl2 also helpsin firming texture [22] the turbidity caused by it proba-bly led to reduced sensory scores.

Conclusion

Potatoes are sensitive to sloughing during canning. Al-though calcium chloride is used to firm the texture, itmay impart a bitter taste to the product. This studyshowed that partial dehydration of potatoes before can-ning firmed up the texture of tubers, allowed greater fillof potato solids per can, prevented sloughing during pro-cessing and improved flavour and drained weight.Among the four cultivars tested, HPS-1/13 was found tobe the best for canning because of lower peeling losses,the lower number and the superficial nature of eyes, andthe firmer texture of the canned potatoes.

References

1. Eipson WE, Paulus K (1973) Potato Research 16:270–2842. Reid NB, Marks BP, Gonzalez AR, Siebenmorgen TJ (2000)

American J Potato Research 77:319–3243. Rose DJ, Southcombe S (1987) Technical memoranda, Camp-

den Food Preservation Research Association 467:344. Talburt WF, Smith O (1987) Potato processing. AVI, Westport5. Jing-ming L, Sen-lin Z (1990) Starch 42:96–986. Reeve RM (1977) J Textural Studies 8:1–177. Sandhu KS, Bawa AS (1993) Indian Food Industry 12:47–508. Marwaha RS (1997) J Food Sci Technol 34:457–4719. Mathur VK, Siddaiah CH, Bhatia BS, Nath H (1973) Indian

Food Packer 27:15–1710. Andreotti R, Tomasicchiom M, Macchiavelli L (1982) Indu-

stria Convserve 57:172–17511. Pushkarnath (1964) Potatoes in India. Indian Council of Agri-

cultural Research, New Delhi12. Lisinska G, Leszczynski W (1989) Potato science and technol-

ogy. Elsevier Applied Science, London13. Dean BB, Thornton RE (1992) Extension Bulletin of Wash-

ington State University Cooperative Extension Service, Pull-man, WA

14. Ranganna S (1986) Handbook of analysis and quality controlfor fruit and vegetable products. Tata-McGraw Hill, New Delhi

15. Bureau of Indian Standards (1981) Canned potatoes specifica-tions, IS:2389,New Delhi

16. United States Department of Agriculture (1977) United StatesStandards for Grades of Canned White Potatoes, Washington

17. Panse VG, Sukhatme PV (1985) Statistical methods for agri-cultural workers. Indian Council of Agricultural Research,New Delhi

18. Sandhu KS, Bawa AS, Thind SS, Senkhon KS, Mohan Singh,Randhawa KS (1987) Indian Food Packer 41:18–25

19. Marwaha RS (1999) J Food Sci Technol 36:157–15920. Burton WG (1989) The potatoes. Longman, New York21. Kulkarni SD, Joshi KC (1992) Indian Food Packer 46:36–4322. Weinert IAG, Solms J, Escher F (1990) Lebensmittel-

Wissenschaft and Technologie 23:117–12123. Sharma KD, Lal BB (1999) J Food Sci Technol 36:136–138

234