Tempeh starter diversity

According to a recent study of the Universitas Indonesia only one Rhizopus species, R. microsporus, can be found in tempeh produced in Java, Indonesia [1]. Traditionally tempeh starter is produced by a spontaneous fermentation of cooked soybeans wrapped in Hibiscus leaves. This method resulted in a very high diversity of Rhizopus species, such as Rhizopus arrhizus, Rhizopus delemar (synonym of Rhizopus oryzae) and Rhizopus microsporus (mainly Rhizopus oligosporus), that could be isolated from the final fresh tempeh. This loss of diversity is cause by the widespread use of commercial tempeh starter in Indonesia since the 2000s. This study also found that morphological changes occurred in Rhizopus species that were isolated from tempeh due to centuries of domestication.

In 1966 Wang and Hesseltine found that the best strain for producing tempeh from wheat and soybeans was R. oligosporus NRRL 2710. Since then many Indonesian microbiologists used R. oligosporus for their studies on tempeh. Industrial tempeh production started 1980s using a commercial tempeh starter containing R. arrhizus and R. oligosporus. But since 2001 the Indonesian commercial tempeh starter contained only R. oligosporus.

Not all original Rhizopus strains are lost. The Universitas Indonesia Culture Collection (UICC) still holds a collection of 127 Rhizopus strains isolated from tempeh between the 1960s and 2000s.

This study confirmed the loss of Rhizopus diversity in tempeh currently produced in Indonesia and that R. delemar and R. arrhizus have been lost from tempeh in Java, where tempeh originated. The researchers emphasized the importance of conserving the

traditional Rhizopus strains in order to preserve and restore the precious genetic resources.

[1] The effect of the use of commercial tempeh starter on the diversity of Rhizopus tempeh in Indonesia. W. Sjamsuridzal etal. Sci Rep. 2021 Dec 14;11(1):23932.