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Food science


The shelf-life of soy-sunflower tempeh and its acceptability to Indian children


M. P. Vaidehi and A. Rathnamani

Tempeh is an Indonesian food obtained by fermenting soybean dhal with Rhizopus oligosporus [1]. The fermentation totally transforms the soybeans, creating a new texture, flavour, and aroma and enhancing their nutritional value and digestibility [2]. Tempeh is rich in thiamine, riboflavi, and pyridoxine and is an especially rich vegetarian source of vitamin B12. It has great acceptability among housewives in both rural and urban areas of India in the form of chips and curry [3]. Tempeh made from a blend of soybeans and sunflower seeds is more popular than that made from soybeans alone [4; 5].

This study was conducted to help introduce nutritious fermented soy-sunflower tempeh in the rural areas and prepare products that can be used for supplementary feeding programmes if they appeal to preschool and school-age children. The results indicate an excellent possibility for the large-scale production of tempeh, based on an assessment of its shelf-life.

Materials and methods

Several test products - toffee, sweet and salted chips, and stew - were prepared from fresh blended tempeh. The sweet and salted chips and the stew were prepared as described by Vaidehi et al. [6].

The toffee was prepared using one cup of blended tempeh slices, oil, one-fourth cup of sugar, and onefourth cup of cardamom powder. The tempeh slices were shallow-fried in the oil to a golden brown. A sugar syrup of soft-ball consistency was prepared, and the cardamom powder was added to it. The fried tempeh slices were dipped gently to coat them with the sugar syrup and transferred to a greased plate. On cooling, the slices separated and resembled the traditional Indian peanut preparation called chikki.

The acceptability study

One hundred children five to seven years old from a rural school were given the tempeh products in small quantities to test their acceptability. The children were first interviewed individually and their evaluation of each product noted and then together, ranking the products in order from best liked to least liked.

The shelf-life study

Shelf-life was studied by keeping 100-gram samples of fresh and 50-gram samples of dry tempeh in polythene pouches, plastic containers, and glass bottles separately at room and refrigeration temperatures, 30 C and 7 C, respectively.

Observations were made once in two hours of the fresh samples kept at room temperature and once in twelve hours for the refrigerated samples. The dried tempeh was tested once a week for optimum shelf-life. Changes in texture to the touch and in appearance and odour were noted by the investigator and two members of the staff of the Department of Home Science. Their agreed observations were recorded.

Fresh tempeh was also stored in polythene pouches in the freezer compartment of the refrigerator and observed once a week.

Cost computation

The cost of one kilogram of soy-sunflower tempeh was calculated. A blend of 242 grams of soybean dhal with 285 grams of sunflower seed yielded one kilogram of fresh tempeh. The soybeans and sunflower seed cost Rs 6. The processing and preparation came to Re 1 and the labour to Rs 8, resulting in a cost of Rs 15 per kilogram of blended tempeh.

The costs of lamb and poultry meat based on a survey of three different markets are shown in table 1. The proximate nutritive value of the meat per kilogram was calculated from the food-composition table of Indian foods [7]. The nutrient value of the blended tempeh was analysed in the laboratory, and the values were compared with lamb and poultry.

TABLE 1. Proximate nutrient content and cost of lamb, chicken, and soy-sunflower tempeh per kilogram dry-weight basis

 

Nutrients

Cost
(Rs)
a
Protein (g) Fat (g) Energy (kcal) Thiamine (mg) Riboflavin (mg) Niacin (mg) Pyridoxine (mg)
Lamb 185 133 1,940 1.8 1.4 68 0.32 38
Chicken 259 6 1,090 1.4 0.13 23
Tempeh 289 400 6,200 0.15 3.1 61.8 9.5 115

Moisture content: lamb, 71%; chicken 73%; tempeh 56%
a. Rs 12 = US$1.

Results and discussion

Acceptability

All the blended tempeh products showed a high percentage (90%) of acceptability. The toffee scored the highest (100%). Only 6% of the children disliked the sweet chips, 4% the salted chips, and 2% the stew. Toffee was also first, followed by stew, salted chips, and sweet chips, when the children were asked to rank the products in order of preference. The similarity of the toffee to the traditional sweet chikki, which is a favourite snack among Indian children, perhaps accounts for its instantaneous acceptance.

Shelf-life

Fresh tempeh is perishable and cannot be preserved for more than 20 hours at room temperature; refrigerated, it can be preserved for three to four days. When frozen, the type of package did not influence its keeping quality.

Dried tempeh can be preserved for one and a half months at room temperature, and for six months refrigerated and packed in polythene pouches.

Table 2. Storage of fresh soy-sunflower tempeh in polythene pouches, plastic containers, and glass bottles

Storage time and method Appearance Texture Odour
0 hours Cottony white cake with no discoloration Firm cake with no surface moisture, sliminess, or loose beans Pleasant smell of fresh mushrooms

At room temperature (30 C)

4 hours Slight sporulation No change No change
8 hours Severe surface sporulation giving a black appearance Firm texture but with a slight accumulation of moisture No change; still pleasant
12 hours  
polythene No further change Slight sliminess Distinct ammonia smell
plastic Light creamish yellow patch Sliminess only at the yellow patch No change
glass No further change No further change Slight ammonia smell
20 and 24 hours No further change Highly slimy and sticky Strong, unpleasant ammonia

smell with slight sour smell

Refrigerated (7 C)

12 hours      
polythene Slight sporulation

No change

 
plastic   No change
glass Grey to black sporulatedl patches  
24 hours No further change Some accumulation of moisture No change
36 hours No further change No further change No change
48 hours      
polythene Black spots due to increased sporulation Slight softening

No change

plastic No further change No further change
glass  
60 hours      
polythene No further change Slight stickiness Slight ammonia smell
plastic Increased sporulation No further change

No change

glass Black patches and a slight greenish patch Stickiness around the patch
72 hours No further change No further change No further change
84 hours  
polythene One light yellow patch

Increased sliminess with softening

Distinct ammonia smell
plastic Discoloured patch

No further change

glass Green patch
86 hours Yellow-green patches Moist. slimy, sticky Strong, unpleasant ammonia smell

TABLE 3. Storage of dried soy-sunflower tempeh at room temperature (30 C)

Storage time Polythene pouches Plastic containers Glass bottles
1 day

Light brown with crisp texture and pleasant smell

15 and 30 days No change No change No change
45 days Slight infestation; slightly crumbly texture Moderate infestation; crumbly texture Slight infestation; no change in texture
60 days Crumbly texture, with Crumbly, porous pieces yellow powder at the bottom Porous. yellow pieces with powder at the bottom: infested smell

Cost evaluation

Soy-sunflower tempeh costs 61)% less than lamb and 35% less than chicken. Its energy content is much higher than that of either meat. It has high protein and fat content and no cholesterol. It is low in moisture and rich in essential fatty acids. It is rich in vitamin B complex. Unlike most meats, there is no wastage in tempeh in the form of bones or undesirable fat. It is versatile and can be used in any form to replace meats, as reported by others [8].

Conclusions

Tempeh in the form of toffee is highly acceptable to children. As it has good nutritional value and a long shelf life in dried form, its widespread use as a supplementary food is recommended.

Eighty grams of fresh tempeh provides 300 kcal of energy and 14.0 grams of protein, efficiently meeting one-third of the recommended daily allowance of nutrients for pre-school children. It should be made available in rural areas and to the general public as a high-nutrient food for those with poorly balanced diets.

The tempeh industry on a small scale, as in Indonesia, can improve the economic status of the rural population, while on a large scale it can cater to the needs of both rural and urban populations. Agricultural extension services should make intensified efforts to promote and make this product popular.

References

  1. Steinkraus KH, ed. Handbook of indigenous fermented foods. Basel; New York: Marcel Dekker, 1977.
  2. Steinkraus KH, Vanveen AG. Biochemical, nutritional and organoleptic changes occurring during production of traditional fermented foods. Global impacts of applied biology. IBP-Unesco Symposium on Single-Cell Protein. Bombay: University of Bombay, 1971:444-50.
  3. Wang HL, Hesseltine CW. Use of microbial cultures: legume and cereal products. Food Tech 1981;35:79-83.
  4. Vaidehi MP, Vijayalakshmi D, Annapurna ML. Consumer evaluation of tofu, tempeh, curd and meal maker in rural and urban areas. Ind J Nutr Diet 1985;22:190-93.
  5. Girija Bai R, Prabha TN, Ramachandra Rao TN, Sreedhara VP, Sreedhara N. Studies on tempeh. 1. Processing and nutritional evaluation of tempeh from a mixture of soybean and groundnut. J Food Sci Technol 1975;12(3):135-38.
  6. Vaidehi MP, Annapurna ML, Vishwanath NR Nutritional and sensory evaluation of tempeh products made with soybean, ground-nut. and sunflower-seed combinations. Food Nutr Bull 1985;7(1):54-57.
  7. Gopalan C, Ramasastry BV, Balasubramanian SC. Nutritive value of Indian foods. Hyderabad: National Institute of Nutrition, ICMR, 1982.
  8. Shurtleff W, Aoyagi A. The book of tempeh. New York: Harper and Row, 1985.

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