ALKALINE-FERMENTED FOODS - A REVIEW WITH EMPHASIS ON PIDAN FERMENTATION

Alkaline-fermented foods constitute a group of less-known food product s that are widely consumed in Southeast Asia and African countries. Th ey can be made from different raw ingredients. For instance, Japanese natto, Thai thua-nao, and kinema are made from cooked soybeans, dawada wa from African locust beans, ogiri from melon seeds, ugba from Africa n oil beans, kawal from fresh legale leaves, owoh from cotton seeds, a nd pidan from fresh poultry eggs. In alkaline-fermented foods, the pro tein of the raw materials is broken down into amino acids and peptides ; ammonia is released during the fermentation, raising the pH of the f inal products and giving the food a strong ammoniacal smell. Most alka line fermentations are achieved spontaneously by mixed bacteria cultur es, principally dominated by Bacillus subtilis. In other cases, pure c ultures can be used. For example, Japanese natto is inoculated with a pure culture of B. subtilis var natto. Pidan is a special example of a lkaline fermentation. Instead of using microorganisms, pidan is made u sing an alkali-treated fermentation. Sodium hydroxide (NaOH) is produc ed from the reaction of sodium carbonate (Na2CO3), water (H2O), and ca lcium oxide (CaO) of pickle or coating mud. NaOH penetrates into the e ggs, causing the physicochemical changes, color changes, and gelation. The appearance of pidan differs from fresh eggs in that the white bec omes a semitransparent tea-brown color, and the yolk is solid or semis olid with a dark-green color. The nutritional value of pidan is slight ly decreased compared with fresh eggs, but pidan has an extremely long shelf life and a pleasant, fragrant taste that is preferred by most p eople in Southeast Asian countries. In a small-scale laboratory study conducted by the authors, B. subtilis was not found in pidan. Four Sta phylococcus spp. (S. cohnii, S. epidermidis, S. haemolyticus, and S. w arneri) and two strains of Bacillus spp. (B. cereus and B. macerans) w ere isolated from pidan. Staphylococcus spp, did not contribute to the fermentation and were considered contaminants.