In synthetic biology conferences, engineering improvements of food is listed in the top three applications of the new technology. As an example, George Church’s lab developed a genetic engineering technology specifically aimed at evolving super-tomatoes containing high amounts of the anti-oxident lycopene, as proof-of-concept. Frequent brainstorming “what could syn bio do?” sessions include ideas of growing thick beef steaks without the cow: in essence, this is presumed to be an improvement on quality, cleanliness, nutrition, and animal rights, than today’s factory-farming method of bringing steak to the table.
What if there is already a better “steak”? Let’s call it Meat 2.0. How about modifying Rhizopus oligosporus, the fungus used in making tempeh, to create new tastes or additional vitamins? Note that the below article states, “cost of preparing 1.5 kg of tempeh was less than US$1.”
Nutritional and sensory evaluation of tempeh products made with soybean, ground-nut, and sunflower-seed combinations
M. P. Vaidehi, M. L. Annapurna, and N. R. Vishwanath
Department of Rural Home Science and Department of Agricultural Microbiology, University of Agricultural Sciences, Bangalore, India
Tempeh products made from soybeans and from combinations of soybeans with ground-nuts and sunflower seed at ratios of 52:48 and 46:54 respectively were tested for their appearance, texture, aroma, flavour, and over-all acceptability. In addition, tempeh was prepared with and without the addition of bakla (Vicia faba) to soybeans in various ratios to obtain a tempeh of acceptable quality and nutritional value (1). Bakla tempeh at a 1:1 ratio was found to be crisper and more palatable than plain soybean tempeh, but at 3:1 the tempeh had a mushroom odour.
Tempeh culture (Rhizopus oligosporus) was obtained from the New Age Food Study Center, Lafayette, California, USA. It was grown on a rice medium and inoculated while different blended tempehs were prepared. A 2.5 9 packet of culture was used for 250 9 of substrate on a dry weight basis.
Soybeans (Hardee), ground-nuts (TMV-30), and sunflower seed (Mordon) were obtained from the University of Agricultural Sciences, Bangalore. Three varieties of tempeh -100 per cent soy, soy-ground-nut (52:48), and soy” sunflower seed (46:54)-were prepared under identical conditions.
Preparation of Tempeh and Products
Two-hundred fifty grams of soybeans, soaked for 12 hours and combined with other unsoaked seeds, were cooked for 10 minutes at 15 pounds pressure in 750 ml of water.
After drainage of excess water, the beans were transferred to 20 x 15 x 5 cm sterilized aluminium trays. Then 5 ml of vinegar and 2.5 9 of tempeh starter culture were added, using a glass rod to facilitate mixing and spreading. Perforated, new polyethylene sheeting was used to cover the trays, which were maintained at 25 to 30 C for 20 hours. At the end of this period, a white, compact, cake-like loaf of tempeh was ready to cut into cubes or slices for the preparation of tempeh curry and fried chips. These were prepared by the method described by Vaidehi and Vijayakumari (2) with fresh tempeh cubes, and the dishes were subjected to organoleptic evaluation.
A semi-trained panel of nine judges tested the curry and chips prepared from the three types of tempeh. The score sheets consisted of a hedonic scale of five points (3). The samples were served coded and at random selection in triplicate each day between 10 and 11 a.m. and 2 and 2.30 p.m., three samples per session. The data obtained were analysed statistically to determine the highest and lowest scored samples for each quality characteristic-namely appearance, texture, aroma, flavour, and over-all acceptability (4).
Nutritive Value of Tempehs
The proximate nutrient composition-i.e., protein, ether extract, ash, fibre, and carbohydrate (by difference)-was analysed by the AOAC method (5). The fatty-acid profile of 100 per cent soy tempeh prepared with two types of culture was analysed by courtesy of chemists at the Government Soap Factory.
The cost of preparing soy tempeh was calculated by considering the essential expenditure for the method applied here and the equipment requirements for small-scale production of tempeh in rural areas.
TABLE 1. Tempeh Products Ranked for Sensory Characteristics by the Panel of Judges
Appearrance Texture Aroma Flavour Over-all Acceptability Tempeh curry soy + sunflower 1 1 1 1 1 soy 2 2 3 2 3 soy +ground-nut 3 2 2 3 2 Tempeh fried chips soy + sunflower 1 1 1 1 1 soy 3 3 2 3 3 soy + ground-nut 2 2 1 2 2
TABLE 2. Proximate Nutrient Composition per 100 9 of Soy Tempeh with Other Oilseeds (Air-Dried)
Tempeh Variety Moisture Protein Fat Mineral Fibre Carbohydrate (by Difference) Calories % g g g g g Soybeans 6.60 42.50 20.00 5.20 - 25.70 453 Soy tempeh 8.00 48.60 21.60 3.90 - 18.00 461 Soy + ground-nut 6.00 36.20 35.80 3.00 - 19.00 542 Soy + sunflower 5.20 31.00 43.00 3.60 - 17.20 580
RESULTS AND DISCUSSION
Sensory evaluation of the tempeh curry and fried chips showed the sunflower-soybean combination in both dishes to be highly acceptable in all sensory characteristics, i.e., appearance, aroma, texture, and flavour (table 1). This was followed by ground-nut-soybean combination tempeh products. It appears that 100 per cent soybean tempeh was not favoured by the taste panel, not only in our studies but also in other studies reported in the literature. Soybean with bakla was more acceptable at the 1:1 ratio; an increase in soybean ratio lowered the acceptability of the tempeh, as shown by David and Verma (1). Incorporation of 5 to 6 per cent tempeh in pre-gelatinized potato or cereal starch made ground and fried tempeh products more acceptable according to Youch et al. (6).
Hesseltine (7) described tempeh fried in vegetable oil as “delicious to eat” when hot. Wang and Hesseltine (8) prepared a tempeh-like product with higher levels of B12, niacin, and riboflavin. Djion and Hesseltine (9) support the use of tempeh because growth, sporulation, and aflatoxin production from Aspergillus flavus and A. parasiticus are considerably suppressed by R. oligosporus Similarly, Wang et al. (10, 11) showed that there is an active principle against Gram-positive bacteria, including Clostridium botulinum, Bacillus subtilis, and Staphylococcus aureus.
Nutritional Value of Tempeh
The nutritional quality of soy tempeh in combination with other oilseeds (air-dried) tested here is reported in table 2. The table shows that the protein content of a tempeh-sunflower combination decreased, but the fat content increased. Ash content was highest in ground-nut-soy tempeh. Bhavani Shankar et al. showed that combination with ground-nuts improved the quality of protein in soy tempeh by increasing lysine content (12).
The free fatty acid analysis of soy tempeh is shown in table 3. There is very little difference in fatty acid content in tempeh prepared with two different cultures. Tempeh is rich in oleic and linoleic acids, as raw soybean itself is one of the richest sources of these two fatty acids.
Sundaramadiji and Markakis showed that, organoleptically, tempeh scored best at the end of the first phase (30 hours at 32°C) and retained its good quality during phase two la further 24 hours at 32 C), but deteriorated rapidly during phase three, with loss of pleasant taste (13). Furthermore, they showed that in the third phase of tempeh there was an increase in free fatty acid and bacterial growth, an ammonia odour, and collapse of texture.
TABLE 3. Fatty Acid (Percentage of Fat) Profile of Tempeh Prepared with Two Sources of Culture
CFTRI ( India) New Age Center (USA) Fat % 30.220 28.020 Caproic 6:0 0.022 0.015 Caprylic 8:0 0.033 0.021 Capric 10:0 0.031 0.018 Lauric 12:0 0.087 0.062 Myristic 14:0 0.015 0.042 Palmitic 16:0 16.309 16.345 Palmitoleic 16:1 - - Stearic 18:0 0.830 1.112 Oleic acid 18:1 20.956 22.706 Linoleic 18:2 57.763 55.980 Linolenic 18:3 3.496 3.131 Arachidic 20:0 Behenic 22:0 - 0.552 Lignoceric 24:0 0.437 0.016
TABLE 4. Approximate Costs for the Manufacture of Tempeh on a Small-Scale Industrial Basis
Quantity Cost (Rupees)
Physical plant requirements
BOD (biological-oxygen-demand) incubators 1 15,000 Aluminium trays, 20 x 15 x 5 cm 12 500 Steel ladies and utensils etc.- sizes and quantities as desired - 500 Gas stove and cylinder - 1,500 Steel strainers - 150 Steel mixing bowls 4 200 Total establishment 17,850
Tempeh preparation (for 1.5 kg fresh tempeh)
Soybeans 1 kg 5.00 Vinegar 20 ml 0.06 Fuel - 1.00 Starter culture 1 pkt 0.50 Water 20 litres 1.00 Total 7.56
10.54 rupees = US$1 (31 December 1983).
Table 4 shows the approximate costs computed for the manufacture of tempeh on a small scale for an industrial set-up.
Amino Acid Pattern in Comparison with FAO Pattern
Table 5 shows the amino acid pattern of tempeh prepared with soy and oilseed combinations. The oilseed combination rendered the lysine content of tempeh very much nearer to the FAO recommended pattern (14). Similarly, the tryptophan pattern was more favourable in both blends, but only sunflower seed combinations had better values of sulphur-containing amino acids.
Air-dried tempeh stored for future use remained without spoilage for six months in polyethylene bags with no change in flavour.
In a study conducted by Steinkraus et al. (15) tempeh yield on a dry weight basis was 725 9. In our study the yield was 750 9 of tempeh on a wet weight basis for 250 9 of raw soybeans.
In conclusion, it is significant that the soybean-sunflower seed tempeh excelled in acceptability and also in protein and calorie values among the three types of tempeh studied. Ground-nut tempeh was second in popularity. Although all combinations were high in calories, the protein content of soy tempeh was greater than that of the others. We plan to test the ratios of the various combinations in order to reach the FAO reference pattern for lysine and thus improve protein quality. The fatty acid profile in soy tempeh was 57.8 per cent linoleic and 21 per cent oleic acid of the fat content.
If these tempeh products were consumed directly or added to various high-protein-energy mixtures, even in small quantities, the nutritional value might be greatly extended. The cost of preparing 1.5 kg of tempeh was less than US$1. It is rarely this economical to produce any other popular plant food with such high energy and protein content. Therefore it would be desirable to popularize tempeh products and manufacture on a small-scale industrial level in rural and urban centres. Furthermore, this would create employment and improve the nutritional status of the people consuming these products.
TABLE 5. Amino Acid Pattern of the Ingredients for Tempeh Compared to the FAO Pattern (mg/g of N)
Amino Acids FAO* Soy Groundnut Sunflower Seed Soy-Sunflower Soy-Groundnut Methionine + cysteine 220 180 140 210 191 166 Lysine 340 400 230 230 341 341 Leucine 440 480 400 400 452 452 Isoleucine 250 320 240 270 303 292 Phenylalanine + tyrosine 380 510 550 400 472 528 Threonine 250 240 170 230 237 216 Tryptophan 60 60 60 90 84 73 Valine 310 320 280 320 320 306
* Source: Reference 14, calculated values.
1. I.M. David and J. Verma, “Modification of Tempeh with the Addition of Bakla,” J. food Technol., 16 (1): 39 (1981).
2. M.P. Vaidehi and J. Vijayakumari, “Soya Delights,” (University of Agricultural Sciences, Bangalore, India, 1981).
3. A.M. Amerine, R.N. Pengborn, and E.B. Roessler, Principles of Sensory Evaluation of Food (Academic Press, New York, 1 965), PP. 350-354.
4. R.G.D. Steel and J.H. Torrie, Principles and Procedures of Statistics (McGraw-Hill, New York, 1960).
5. Association of Official Agricultural Chemistry, Official Methods of Analysis, 12th ed. (AOAC, Washington, D.C., 1 975), p. 222.
6. M.H. Youch, G.V. Darvingas, F.J. Rigethor, and H.W. Muller, “Process for Producing a Snack Food Containing Tempeh,” United States Patent, 4: 152 (1979).
7. C.W. Hesseltine, “A Millennium of Fungi Food and Fermentation,” Mycologia, 57: 149 (1965)
8. H.L. Wang and C.W. Hesseltine, “Wheat Tempeh,” Cereal Chem., 43: 563 (1966).
9. K.S. Djion and C.W. Hesseltine, “Use of Microbial Cultivar; Legume and Cereal Products,” Economic Microbiol., 4: 115 (19791.
10. H.L. Wang and C.W. Hesseltine, “Use of Microbial Cultures: Legume and Cereal Products,” Food Technol., 35 (1): 79 (1981).
11. H.L. Wang, D.I. Ruttle, and C.W. Hesseltine, “Antibacterial Compound from a Soybean Product Fermented by Rhizopus oligosporus,” Soc. Exp. Biol. Med., 131: 57911969).
12. T.N. Bhavani Shankar, N.V Shantha, T. Rajashekaran, V.P Shreedharan, and V. Shreenivas Murthy, “Studies on Tempeh made from Groundnut and Soybean Mixture,” in Proceedings of the 1st Indian Convention of Food Scientists and Technologists, 92: 95 ( 1979).
13. S. Sundaramadiji and P. Markakis, “Lipid and Other Changes during Fermentation and Frying of Tempeh,” Food Chem., 3 (3): 165 (1978).
14. Energy and Protein Requirements, report of a Joint FAO/WHO Ad Hoc Expert Committee, World Health Organization Technical Report Series, No. 522 ( WHO. Geneva, 1973).
15. K.N. Steinkraus, Y. Bwee Hwa, J.P. Van Buren, M.l. Providenti, and D.B. Hand, “Studies on Tempeh: An Indonesian Fermented Soybean Food,” Food Res., 25: 777 (1960).