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Sufu

Figure 3. Flow sheet for preparation of sufu. Source: Ref. 18.

Coagulant

Actinomucor, Mucor or Rhizopus

Salt

Dressing mixture blocks of desired size. The firm blocks of tofu are cut into small cubes (2x4x4 cm) weighing approximately 18 g. Because adept tofu workers are becoming scarce, the automatic tofu machine was developed in recent years. This machine saves a lot of labor and unifies the quality of tofu.

Preparation of Pehtze. Pehtze is tofu overgrown with grayish hairlike mycelium of molds of the genus Actino-mucor spp., Mucor spp., or Rhizopus spp. To avoid contamination and bacterial spoilage, tofu cubes are exposed to bright sunlight for several hours before inoculation with mold. Instead of being sun dried, tofu cubes can be dried in a hot-air oven at 100°C for about 15 min (17). Before hot-air drying, tofu cubes may be immersed in an acidic saline solution (prepared by dissolving 6 g NaCl and 2.5 g citric acid in 100 mL water) (20). The hot tofu cubes are cooled to 20°C. A pure culture of molds is inoculated onto the surface of the tofu cubes. The inoculated tofu cubes are put in a tray for incubation. The room temperature is maintained at 10 to 20°C. After 3 to 7 days, white fungal mycelium can be seen on the surface of tofu cubes, and at that time they are taken out and immediately salted.

Salting. Pehtze is transferred to large earthenware jars (having a volume of 7 hL) for further curing. It is put in layers in the jars. Each layer of pehtze is sprinkled with a layer of salt and kept for 3 to 4 days. During this period, the pehtze absorbs most of the salt. The salted pehtze is removed from the jars, washed with water, and transferred to other jars for further processing.

Processing and Aging. Pehtze is processed and aged in earthenware jars containing a dressing mixture. The most commonly used dressing mixture consists of 2 kg salt, 1 kg soy sauce mash, 0.6 kg red koji, 0.6 kg jaggery, and 6 kg water. Additional essence can be added to the dressing mixture to give a special flavor. For aging, alternate layers of pehtze and dressing mixture are packed into the jar to 80% of its volume, then the jar is filled with brine containing 12 to 20% salt. The mouth of the jar is wrapped with sheath leaves of bamboo shoots and sealed with clay. The sealed jars are aged for 1 to 3 months or longer for further fermentation before packing into small containers for marketing (16,19). The salt in the dressing mixture imparts a salty taste to the sufu and retards the growth of contaminating microorganisms and mold. Shelf life is a major problem with sufu. Alcohol in the dressing mixture helps to preserve sufu; however, it gives a harsh flavor to the sufu. Therefore it is important to find a method for preservation of fermented pehtze and sufu without the use of alcohol in the dressing mixture.

Composition

The chemical composition of fresh and dried tofu., pehtze, and sufu is presented in Table 6. Enzymes such as inver-tase, emulsin, trypsin-like protease, pepsin-like protease, oxidase, and catalase are found in pehtze. These enzymes are produced by the mold during fermentation and act on their respective substrates. During the first 10 days of aging, the mold enzymes act on substrates such as proteins

Table 6. Composition of Tofu, Pehtze, and Sufu

Tofu Pehtze Sufu

Table 6. Composition of Tofu, Pehtze, and Sufu

Tofu Pehtze Sufu

Component (%)

Fresh

Dried

Fresh

Dried

Fresh

Dried

Moisture

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