Contents - Previous - Next
This is the old United Nations University website. Visit the new site at http://unu.edu
Production and use of raw potato flour in Mauritian traditional foods
Karuna D. Kulkarni, Noel Govinden, and Dilip Kulkarni
Potato flour is a highly versatile raw material that can be used in several processed food products. Two Mauritian potato cultivars were turned into flour and used to prepare mash, gulab jamuns, and paratha, three traditional Mauritian foods. The samples were compared for peeling losses, drying characteristics, chemical changes, and functional properties. The Exodus cultivar was more economical for producing potato flour due to its higher yield and lower drying ratio compared with Spunta. The chemical composition of the two cultivars did not vary, and most of the functional properties were comparable. A slight variation in water-absorption capacity was observed. Slurries of 8% potato flour were pseudoplastic. Mash prepared from Spunta flour was superior to that from Exodus, but both were comparable to the control. Experimental mash samples were superior to a commercial instant potato mash. Gulab jamuns with milk and potato flour in ratios of 3:1 and 5:1 were superior to commercial samples, and parathas made with 40% potato flour were more acceptable than those made with wheat flour alone.
Currently, a large proportion of fresh potatoes are cold stored for use in the off season. Cold-stored potatoes reportedly accumulate reducing sugars, which cause a decline in the colour quality of the processed products . Dehydrating potatoes in season is one way to overcome the problem of sugar accumulation. It also helps reduce bulk for storage and transportation, with few physiological and biochemical changes. Potato processing at the village level has considerable potential to reduce post-harvest losses and to generate income through the manufacture of value-added food products . Processed potato products, especially potato flour, are highly versatile in manufacturing convenience foods.
Because it is rich in starch, potato flour can improve the functional properties of several food products. It can be used in a great variety of foods. It has its own distinctive flavour and texture but is sufficiently bland to be incorporated easily into traditional local preparations. The nutritional advantages of potato have been demonstrated in comparison with other major staples and vegetable crops in terms of the total number of people who can be fed, and as a food for individual consumers .
Compared with products made from other starchy staple foods of tropical Africa, Latin America, and the Asian subcontinent, potato flour ranks quite high in its supply of principal nutrients. Its protein content is superior to that of cassava and yam flour, slightly inferior to that of refined maize meal and wheat flour, and similar to that of rice . Potato flour has higher levels of fibre than refined wheat flour, maize meal, and rice but lower levels of fibre than cassava and yam flour. Its carbohydrate and energy contents are comparable to those of similar foods .
Potatoes contain lower levels of phytic acid than other plant foods and reasonable amounts of all the essential amino acids except methionine and cystine. They are well balanced in terms of protein and energy.
Considerable attention has been given recently to using potato in prepared or processed foods in developing countries [3, 6]. In developed countries, potato flour is produced commercially using sophisticated methods such as drum drying and spray drying of pre-cooked mashed potatoes [7, 8]. These methods have limited applications for village-level processing in developing countries. Moreover, the ingredients of several traditional dietary products of these regions have to be raw to retain their desired properties, which are considerably modified by pre-cooking and mashing.
Raw potato flours were made from three Indian cultivars by slicing, blanching, sulphitation, and drying in a hot air dehydrator, and were compared for proximate composition and functional properties . Others have evaluated the proximate composition, mineral content, and nutritional quality of solardried potato flour . However, information on the use of raw potato flour in traditional food products is lacking. We compared two Mauritian potato varieties in terms of flour quality and their use in some traditional foods.
Materials and methods
The two types of potatoes, Spunta and Exodus, harvested at optimum maturity, were obtained from the experimental farm at the Mauritius Sugar Industry Research Institute and were used to prepare flours. Other materials required for the preparations were purchased from the local market.
The potatoes were dried using the process reported earlier . Potatoes of the two cultivars were washed thoroughly in water, hand-peeled using a stainless steel knife, and sliced with an automatic electric slicer. The slices were immersed in water to prevent enzymatic browning of the surface. The slices were sulphited to 1% sodium hydroxide by soaking them in a potassium methabisulphite solution. The blanched slices were drained and dehydrated at 60°C in a cabinet air-flow dehydrator. When the slices are placed in a single layer, it takes about three hours to reduce the moisture of the slices to below 10%. The rate of drying was measured as the amount of water removed per unit weight of the sample with time. The dehydrated slices were ground to yield a flour of 70 mesh. The flour was packed in 250-gauge polyethylene bags and stored in a refrigerator (see FIG 1. Flow sheet for potato flour production).
Fresh potatoes and the dehydrated potato flours were analyzed with respect to moisture, protein, fat, carbohydrates, ash, reducing sugars, and vitamin C using standard procedures . The processing characteristics of potatoes with respect to the rate of drying, drying ratio, and percentage yield of flour were estimated.
The paste viscosity of 8% slurry in distilled water was measured with a Brookfield synchroelectric viscometer, RVT model and spindle no. 2. The hot paste viscosity was determined at 90°C, and cold paste viscosity at 30°C. The effect of the rate of shear on paste viscosity was recorded.
The water-absorption capacity of the flours was evaluated by placing 5-g samples in a centrifuge tube. Distilled water, 50 ml. was added and the resultant slurry was allowed to stand for one hour before centrifugation at 1,700 x g for 20 minutes. The supernatant was decanted and the amount of water in grams gained by a 100-g sample was determined. The effect of particle size on water absorption capacity was also determined for each sample.
The bulk density of the flour was determined by placing a sample in a 10-ml graduated cylinder with gentle uniform tapping during filling. The cylinder was filled to the mark and the weight of the flour was measured. The bulk density was calculated as mass by volume in grams per millilitre (g/ml). The average values of three de terminations are reported. The effect of particle size was also observed.
The temperature at which the potato flours became gelatinized was measured by placing 2-g samples in a wide-mouthed test tube. A slurry of 10% concentration was prepared by adding distilled water and mixing thoroughly. The slurry was then heated in a boiling water bath with continuous monitoring of the rise in temperature with a thermometer. The temperature at which the slurry started to lose birefringence (i.e., appearance of transparency) was recorded. Similarly, the temperature at which the maximum transparency appeared was reported as the gelatinization temperature range.
The colour of the potato flours was measured using the Munsell colour chart. With samples in transparent, non-tinted glass tubes, the colour was matched with the charts and recorded for hue, value, and chroma.
Potato flour use
Three products were prepared with potato flours- mash, gulab jamun, and paratha. Potato mash is a common item in the Mauritian diet. Gulab jamun is a popular sweet and is sold in many shops and restaurants. Paratha is eaten like bread during meals.
Potato flour of both cultivars, particle size 0.425 mm, was used to prepare the mash. The amount of water required was determined in initial trials. The mash was cooked slowly with constant stirring. A standard sample to be used as a control was prepared with fresh potato. A commercial instant potato mash flour sample was also used for comparison.
Milk was mixed with potato powder in ratios of 1:1, 3:1, and 5:1. Another formulation contained milk powder, potato flour, and wheat flour in a 4:1:1 ratio. Gulab jamun was prepared by a conventional procedure and compared with a commercial sample as control.
Paratha is a pan-baked, unleavened bread generally made with wheat flour. Sample parathas were prepared by mixing 40% potato flour with wheat flour and processed by a conventional method, maintaining uniform thickness, diameter, baking temperature, and time. Freshly prepared sample parathas were compared with wheat flour as control.
A panel of 15 judges performed sensory evaluations of the samples. The judges were selected on the basis of their ability to detect threshold values. Those with the lowest threshold values were selected for the sensory evaluations. They evaluated the products for colour, aroma, consistency, taste, appearance, and overall acceptability using a hedonic scale with scores from 1 to 9 (1 = dislike extremely, 9 = like extremely). The values were compared statistically by analysis of variance.
Results and discussion
Several physical characteristics of raw potato can affect flour yield and quality. The potato's weight can affect the peel percentage and peeling loss during processing, with small potatoes having the greatest loss.
The average weight of the Spunta cultivar is much higher than that of the Exodus cultivar with a proportionate shape index (table 1). The specific gravity of Exodus potato tubers is higher than that of Spunta tubers, and hence Exodus tubers are better for flour production. These tubers also have fewer eye buds, which means less processing loss. Spunta tubers, being larger, have lower peel percentage and reduced peeling loss. The pulp of Exodus is off-white, and that of Spunta is slightly yellowish.
TABLE 1. Physical and processing characteristics of potato tubers
|Average weight (g)||89.00 ± 37.00||130.00 ± 81.00|
|Shape index||1.70 ± 0.20||2.10 ± 0.50|
|No. of eyes per tuber||10.00 ± 2.00||14.00 ± 4.00|
|Blanching time (min)||3.00||3.50|
|Yield (%) (whole potato basis)||15.60||13.30|
To prevent enzymatic browning and off-flavour, slices of the two cultivars underwent a blanching adequacy test. The slices were dipped in boiling water, and the presence of polyphenol oxidase and peroxidase enzymes was tested every 30 seconds by treating the slices with 1% catechol and hydrogen peroxide solution until a negative result was observed. Exodus potato slices required 3.5 minutes. Hence a blanching time of 3.5 to 4 minutes is recommended.
Potato slices dried at 60°C for 3 hours in a single layer had drying ratios of 5.68 for Exodus and 6.74 for Spunta. The lower ratio for Exodus was expected, as the cultivar has a higher specific gravity. This quality is also responsible for the higher yield (2%-3%) of flour for Exodus. The drying rate at 60°C was similar for both varieties (see FIG. 2. Drying rate of potatoes at 60°c). Potato slices could be dried by several techniques, including solar drying at the village level and mechanically for controlled drying.
When analysed for chemical composition, fresh samples of Exodus and Spunta did not vary significantly in moisture, protein, lipids, starch, total sugars, and crude fibre. The ash content was slightly higher for Exodus, and vitamin C was higher in Spunta tubers (table 2).
Potato flours of the two cultivars did not differ significantly in chemical composition. Potato flour is an excellent source of starch, and most of its functional characteristics and applications depend on its starch content. Potato flour is also a good source of protein, comparable to wheat and slightly better than rice on a dry weight basis. Potato flour of the Exodus cultivar retained more vitamin C than flour from Spunta, in agreement with values reported by others [5, 9, 10].
Functional properties of potato flour
Functional properties are very important, as they determine the application and use of potato flour in various food products.
TABLE 2. Chemical composition of potato and potato flour (% edible portion)
(N x 6.25)
|Total lipids||Ash||Crude fibre||Starch||Total sugar||Vitamin C (mg)|
TABLE 3. Functional properties of potato flour
|Colour (Munsell notations)|
|Spunta||Coarse||0.748||357 61||69||Pale yellow
2.5 y 8/4
|Fine||0.862||405 61||69||Pale yellow
2.5 y 8/4
a Gelatinization temperature range
The bulk density is generally affected by the particle size and the true density of the matter in potato flour. It was not different in the two potato flours; however, a particle size of 425 pm had lower bulk density than flour with particle size smaller than 425 pm (sable 3). Bulk density is important for determining packaging requirements, material handling, and application in wet processing in the food industry.
The water absorption of potato flour is important in the preparation of potato mash, snack foods, extruded foods, and bakery products, with higher absorption preferred for making mash. It generally depends on starch and protein contents and particle size. Fine particle size (425 pm) was associated with higher water absorption than coarse particle size regardless of variety. Coarse-particle Spunta had lower water absorption than a similar Exodus flour. This trend was reversed for fine-particle flour. No specific reason could be given for this.
Gelatinization temperature range
A crude estimate of the gelatinization temperature range was 60° to 69°C for both cultivars.
The hot paste viscosity of 8% potato flour slurry was comparable for the samples. In both cases hot paste viscosity decreased with increases in shear rate, indicating pseudoplastic non-Newtonian characteristics (see FIG. 3. Paste viscosity of 8% potato flour slurries). The starch slurry was also thixotropic, as its viscosity increased on cooling and when it was allowed to stand. This is due to the retrogradation of starch in potato flour
The cola paste was also pseudoplastic, as its viscosity decreased with increased shear rate. Lower viscosity is desirable for preparing cola paste weaning foods.
TABLE 4. Mean sensory scores for potato mash
|Type of mash||Sensory attributes|
|S1 (mashed potato from fresh Spunta variety)||6.8||7.1||6.4||6.9||6.7||6 7a|
|S2 (mashed potato from Spunta flour)||7.1||6.7||6.5||6.7||6.9||6.5a|
|E1 (mashed potato from fresh Exodus variety)||6.7||6.7||6.1||6.7||6.2||6.6a|
|E2 (mashed potato from Exodus flour)||6.9||6.2||6.6||5.9||6.6||6.2a|
|C1 Commercial instant potato mash||5.7||5.8||5.8||5.7||5.9||5.9b|
1= very poor; 9 = excellent.
a, b. Means with different superscripts are significantly different (p = .05).
TABLE 5. Mean sensory scores for gulab jamun
|Type of gulab jamun||Sensory attributes|
|A (commercial sample)||7.2||5.2||6.9||6.4||6.8||6.1a|
|B (milk: potato flour 1 :1)||6.2||7.2||6.6||6.9||6.5||6.3a|
|C (milk: potato flour 3:1)||7.1||7.1||7.2||7.5||7.0||7.2b|
|D (milk: potato flour 5 :1)||7.2||6.9||6.5||6.8||6.0||6.8b|
|E (milk: potato flour: wheat flour 4:1 :1)||6.8||7.2||6.2||7.2||6.9||6.8b|
a, b. Means with different superscripts are significantly different (p = .05).
TABLE 6. Mean sensory scores for paratha
|Wheat flour + potato flour (3:2)||7.1||7.6||7.4||6.5||7.4a|
|Wheat flour (100%)||7.3||5.3||6.4||5.9||6.3a|
a, b. Means with different superscripts are significantly different (p = .05).
The colour of the potato flours differed with respect to hue and chroma. Spunta flour was pale yellow, whereas Exodus flour was off-white with a neutral hue. Both flours had similarly good lightness or value. The effect of colour on the acceptability of potato flour-based products depends on the product itself and on consumer preference.
Use of potato flours
Potato flour can be used to prepare potato mash, snack foods, extruded foods, sweets and other bakery products, weaning foods, and baby foods.
Potato mash was prepared using flours of the two varieties and compared with controls (i.e., mash prepared from fresh potatoes of respective varieties using standard formulations and processing methods). A commercial sample of instant potato mash was also compared.
All samples of potato mash were acceptable for colour, odour, consistency, taste, appearance, and overall acceptability, as none scored below 6.2 (out of 9) for overall acceptability (table 4). This indicates that potato flour can be used to prepare potato mash. Mash made from Spunta flour scored higher for odour, taste, appearance, and overall acceptability, and was comparable for consistency to mash prepared from Exodus flour. The off-white colour of Exodus mash was preferred over the yellowish Spunta.
All the samples had good acceptability compared with the control. Thus the two cultivars are equally recommended for the preparation of potato mash. Experimental samples were significantly superior to the commercial instant potato mash.
This is a sweet preparation of Indian origin, commonly consumed in Mauritius, and commercially prepared and sold in shops and restaurants. It is generally made from coagulated milk in India, but it is made with milk powder in Mauritius. Milk powder is expensive, so wheat flour is generally added in a ratio of 3:1. However, wheat flour adds an unpleasant flavour and causes hardening of the product.
In our investigation, potato flour was mixed with milk powder in the ratios of 1:1, 3:1, 5:1, and also a formulation was prepared containing milk, potato flour, and wheat flour in a 4:1:1 ratio. The gulab jamun samples were prepared using the standard procedures and were subjected to sensory evaluation along with a commercial sample from the market. The formulation containing milk powder and potato flour in a 1:1 ratio was comparable to the commercial sample in overall acceptability (table 5). The aroma of all the experimental samples was superior to that of the commercial samples. All other samples were significantly superior to the commercial sample. Thus the addition of potato flour is recommended for making gulab jamun.
Paratha with 40% potato flour was superior to paratha made of wheat flour (table 6). Its taste, texture, and aroma scores were higher, although the appearance did not vary. It is recommended that potato flour be used to make paratha.
The investigation indicated that dehydration could be used to manufacture potato flour for making several Mauritian foods. The Spunta and Exodus varieties are similar in composition and make good flour. Potato flour can be used to prepare mash without any pre-treatment. It also can be used to make gulab jamun and paratha. The use of potato flour in place of cold-storage potato will now require further economic analysis.
Contents - Previous - Next