2.3.1. Overview of khaomak and khaomak-like products
Fermentation is a well-known method of food preservation from ancient time. In Asia-Pacific region, rice paddy is widely cultivated due to its tropical and subtropical humid climate. This climatic condition is also suitable for mold and yeast growth. Aside from soy, rice is another cereal in Asia, which is considered as the most regular substrates for plant-based fermented food (Hutkins 2006). The rice was first fermented to develop a nutty flavor and to ease hulling (Dr. Y. Lan and Mahapatra 2007). The consumption of rice as a staple food, and the high population density which limits animal husbandry practices in that region, has resulted in a typical food processing technology - cereal fermentation with molds (Norman F. Haard, S.A. Odunfa et al. 1999).
Khaomak is a fermented rice product from Thailand. It is traditionally prepared by fermenting Thai white glutinous rice with starter culture (look-pang) to create a mildly alcoholic flavor, partially juicy rice paste having a sweet and sour taste. The dessert can be found in Thai markets but it is also easy to be manually cooked at home. In Thai folklore wisdom, khaomak has been considered to boost the growth of malnutrition children and used as a dietary supplement. It also promotes the healthy bacteria gut flora by providing an increasing amount of food for these bacteria (Manosroi, Ruksiriwanich et al. 2011).
The process of khaomak is alcohol fermentation because yeasts and molds are utilized as the starter culture. In general, fermentation is defined as a metabolite process in which substrate such as carbohydrates and related compounds are oxidized with the release of energy in the absence of external electron acceptors or simply as a process in which chemical changes are brought about in an organic substrate through the action of enzymes elaborated by microorganisms. This resulted in the alteration of the chemical composition and other characteristics of the final products. Particularly, molds grow on the rice materials and produce microbial amylases during first stage of fermentation (Rhee, Lee et al. 2011). These enzymes convert the starch present in the rice into sugars. The acid-forming bacteria then use sugars to produce organic acids, reducing the pH to below 4.5, which is optimum for yeast growth at the later stage of alcohol fermentation (Mike Battcock and Azam-Ali 1998, Rhee, Lee et al. 2011).
Khaomak is a very perishable product because the fermentation continues even after the optimum stage (Merican and Quee-Lan 1989). Overfermentation results in a sour taste and strong alcohol aroma that are unaccepted by consumers. Therefore, khaomak has to be consumed immediately when it reaches the desired flavor. However, if it is chilled, the shelf-life can extend to 2 weeks.
In Asia, similar products to khaomak are found in many countries but are known under different names. Starters are used in the manufacture of these products and these starters are also known by different names although the product is basically the same (see Table 1). They may differ from appearance, texture or way of serving.