Tempeh fermentation

Tempeh can be successfully fermented with common beans and bean/corn mixtures. However, the protein digestibility or nutritional quality of beans is not improved substantially by tempeh fermentation. 

Stillings and Hackler (54) studied the effects of the tempeh fermentation, the action of Rhizopus oligosporus on dehulled, soaked, and sterilized soybeans. The PER of tempeh reached its peak after 24 hours fermentation and then dropped. They ascribed the changes to an increase and then a decrease in tryptophan chemically present. The PER decrease after 24 hours was also attributed to an increased quantity of mold protein, which is lower in sulfur amino acid concentration than the original soy protein. Free amino acids increased markedly, presumably due to the action of the mold proteolytic enzymes. Free methionine was present in the largest amount, and as such was highly available, thus partially accounting for the initial increase in PER. 

Removal of the hulls is important to reduce oxalic acid content, increase protein content (72) and increase digestibility (74). Sesame proteinTas low solubility, and one method of increasing solubility is with partial enzymatic hydrolysis (75,). Hydrolysis with fungal enzymes increased the soluble protein content of sesame meal from 7.21 to 64.14%, values considered comparable to those in soy due to the tempeh fermentation. Increased lysine in the hydrolysis extract was accompanied by decreased methionine. 

Keuth S, Bisping B. (1994). Vitamin Bjj production by Citrobacter freundii or Klebsiella pneumoniae during tempeh fermentation and proof of enterotoxin absence by PCR. Appl Environ Microbiol, 60(5), 1495-1499. 

Tempeh. DehuUed cooked soybeans are inoculated with the mold, Thi pus oligosporus packed in perforated plastic bags, and allowed to ferment for 18 h. The mold mycelium overgrows the soybean cotyledons and forms a compact cake. When sHced and deep-fried in oil, a crisp and golden brown product is obtained. Although native to Indonesia, tempeh has become popular with vegetarians in the United States and other Western countries (93). 

It is a highly hydrated gelatinous product with a bland taste. The texture characteristics of the curds vary from soft to firm, depending on the processing conditions. Thus, tofu can be easily incorporated with other foodstuffs and used in nearly every culinary context from salad to dessert and from breakfast foods to dinner entrees. Tempeh is made by fermenting cooked soybeans with a mold, Rhizopus oligosporus. 

Preparation. Traditionally, soaked, hand-dehulled and briefly boiled soybeans are inoculated with small pieces of tempeh from a previous fermentation, wrapped in banana leaves which also serve as a source of inoculum, then left at room temperature for 1-2 days. 

Niacin, riboflavin, pantothenic acid and vitamin B6 contents are greatly increased in tempeh during fermentation, whereas thiamin exhibits no significant change. H. oligosporus appears to have a great synthetic capacity for niacin, riboflavin, pantothenic acid, and vitamin B, but not for thiamin. 

Before 1990 the composition of isoflavones in soy foods was thought to be largely determined by whether the food had been fermented. Fermented foods (e.g., miso and tempeh) contain the unconjugated isoflavones agycones, while non-fermented food (e.g., tofu, soy flower, and soy milk) contain the conjugated glucoside. Subsequent experiments have demonstrated that fermentation of soy decreased the isoflavone content of the food product, but increased the urinary isoflavonoid recovery, suggesting that fermentation increases availability of isoflavones in soy (Slavin et al., 1998). 

In 1964, Gyorgy and coworkers isolated daidzein and genistein along with 6,7,4 -trihydroxyisoflavone from tempeh and found that they possessed antioxidant activities. The activity of 6,7,4 -trihydroxyisoflavone was particularly effective. An extract of the soybean without fermentation had very little activity. However, acid hydrolysis with HC1 increased the soybean extract to that of tempeh. They assumed that... 

Gyorgy, P., Murata, K., and Ikehata, H. 1964. Antioxidants isolated from fermented soybeans (tempeh). Nature. 203 870-871. 

Murakami, H., Asakawa, T., Tero, J., and Matsushita, S. 1984. Antioxidant stability of tempeh and liberation of isoflavones by fermentation. Agric. Biol. Chem. 48 2971-2975. 

Fermented soy such as tempeh, miso, and tamari are healthy sources of both genistein and daidzein. Soy also contains two other antitumor compounds beta-sitosterol and Bowman-Birk inhibitor. 

Such traditional soybean foods as tofu (soybean curd) and tempeh have little flatus activity (42). In the case of tofu, oligosaccharides are presumably eliminated during the course of its preparation, and, in the case of tempeh, enzymes produced by the mold (Rhizopus) during fermentation probably hydrolyze the oligosaccharides. As might be expected because of their low carbohydrate content (< 1%), soy protein isolates are devoid of flatus activity (43). It follows that textured meat analogs made from isolated soy protein are most likely free of flatus activity. 

Most non-fermented soyfoods are consumed mainly for nourishment. In contrast, many fermented soyfoods are generally used as seasonings or condiments in cooking or making soups. They contribute more flavor than nutrition. The two exceptions for fermented products are tempeh and natto, which are consumed as a part of the main meal and contribute nutrients to the diet in addition to their characteristic flavor. 

The major use of okara is livestock feed, however, there are various ways of using okara as food. For examples, in some parts of China, okara is salted and spiced and served as a pickle, or simply made into a dish with meat or vegetable. In other parts of China, okara is pressed into cakes and allowed to ferment for 10-15 days until covered with the white mycelium of Rhizopm mold. The cakes are dried in the sun and then deep-fried or cooked with vegetables. A similar product, known as tempeh gembus, is also popular in Indonesia. Sometimes, okara may be mixed with soybeans before fermentation. 

Tempeh, or tempe in some literature, is made by fermenting dehulled and cooked soybeans with mold, Rhizopus sp. Freshly prepared tempeh is a cake-like product, covered and penetrated completely with white mycelium, and has a clean, yeasty odor. When sliced and deep-fat fried, it has a nutty flavor, pleasant aroma, and crunchy texture, serving as a main dish or meat substitute. In recent years, tempeh has been found to provide some health benefits, including antimicrobial and antioxidant effects and protection against diarrhea (Hachmeister Fung, 1993 Nout Kiers, 2005). 

Tempeh is widely believed to have originated in Indonesia many centuries ago. Although relatively unknown in the surrounding countries, such as Thailand, China, and Japan, where soybeans form an important part of the diet, tempeh continues to be one of the most popular fermented foods in Indonesia. Because of its meat-like texture and mushroom flavor, tempeh is well suited to Western tastes. It is becoming a popular food for a number of vegetarians in the United States and other parts of the world (Nout Kiers, 2005). 

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