Kokumi Substances in Thai-Fermented Freshwater Fish, “Pla-ra”

Pla-ra, a semisolid/liquid fermented fish product, has been a stable ingredient for Thai cuisine since ancient times. It is made from three main ingredients (freshwater fish, salt, and carbohydrate sources). Lately, Pla-ra’s popularity has been growing and it has become one of Thailand’s industrial products. This chapter begins with an introduction to many Thai dishes where Pla-ra plays different roles in the dishes (i.e., protein source, flavoring agent and flavor enhancer) and the Pla-ra production process where intricate interactions between the raw materials and the 2-step fermentation process happen. In the first stage that lasts from 2 weeks to several months, unwanted microorganisms are inhibited and screened; meanwhile, desired microorganisms remain and flourish. The ratio of salt to fish (w/w) used in this stage depends on the size of the fish, and it ranges from 3:1 to 5:1. In the second stage, carbon source(s) is added to promote flavor development from the surviving halophilic bacteria. Roasted rice, rice bran, flour, and/or sugar are the most common carbon sources. After the introduction to Pla-ra production, the development of umami and koku in Pla-ra is explained. Besides providing saltiness to the dish, Pla-ra contains many taste-and flavor-enhancing substances (e.g., γ-glutamyl-peptides), especially those that provide richness, continuity, and mouthfulness to the dish. This section provides evidence about the additive effect of kokumi substances that influence the mouthfulness intensity of food and the subthreshold synergistic effect of kokumi substances in Pla-ra. Lastly, the Kokumi substance formation is discussed along with the role of bacterial diversity on kokumi substance creation.