# _Oncom_: A Nutritive Functional Fermented Food Made from Food Process Solid Residue
## 4 Microbiology of _Oncom_  
Moulds are the main microorganisms responsible for _oncom_ fermentation. The black _oncom_'s principal mould is _R. oligosporus_, while in _oncom_ merah (red _oncom_), it is _N. intermedia_ var. _oncomensis_. The moulds of red _oncom_ were previously identified as _N. sitophila_ and _N. crassa_, but lately, it has been suggested that the mould was _N. internedia_ var _oncomensis_[74]. The molecular method used to identify the red _oncom_ mould also revealed that the red _oncom_ mould was identified as _N. internedia_[75]. Although those two moulds are the main _oncom_, other moulds have also been reported to be part of mould fermentation in black _oncom_, such as _Mucor_, and its presence could produce high-quality _oncom_[3]. A recent study on the microbiology of _oncom_ produced by household industries in Bogor revealed that based on the morphology of the mould isolates, moulds present in black _oncom_ also include _Rhizopus_ sp., _Neurospora_ sp., _Geotrichum_ sp., and _Penicillium_ sp. In contrast, those in red _oncom_ include _Neurospora_ sp., _Mucor_ sp., _Acernonium_ sp., and _Cladosporium_ sp. [76]. Previously, [PERSON] et al. [77] found _R. arrhizus_ var. _debarar_ (_R. debarar_), _R. arrhizus_ var. _tonkinensis_ (_R. oryzae_), and _R. microsporus_ var. _chinensis_ in black _oncom_. The study by [PERSON] [76] showed that yeast, lactic acid bacteria (LAB), and Enterobacteriaceae were also present in considerable amounts (>7 log CFU/g). Meanwhile, bacterial spores were present to a lesser extent. A considerable amount of LAB and yeast (up to >7 log CFU/g) was also found in _tempeh gembus_, using tofu dreg (_okara_) as the raw material similar to red _oncom_ but fermented by _R. oligosporus_[78]. Some _Bacillus_ species, such as _B. thuringiensis_ and _B. megaterium_[79], _B. pumilus_[80], and _B. licheniformis_[81], have been isolated from red _oncom_. _B. cereus_, _B. thuringiensis_, and _B. tequilensis_ have also been isolated from _tempeh gembus_[79]. The researchers also showed that other bacteria, such as _Staphylococcus carosus_ and _S. hominis_, were present in red _oncom_. Studies on microbiology of _oncom_ were mostly based on culture-dependent, enumerating or isolating viable microorganisms in fully fermented _oncom_. A recent study deploying culture-independent methods revealed differences in microbial community composition between red _oncom_ and black _oncom_ samples from Indonesia as well as between _oncom_ producers [82]. The study revealed that _Neurospora_ was the main fungus detected in all red _oncom_ samples, while _Rhizopus_ was the main fungus in black _oncom_. The study also confirmed that _N. internedia_ is the major fungal species in red _oncom_. In contrast to the culture-dependent method, the culture-independent method did not detect _Bacillus_ in all _oncom_ samples. Although other microorganisms are present during _oncom_ fermentation, research on the characteristics of microorganisms during _oncom_ fermentation has focused on the role of the principal moulds. _R. oligosporus_ of black _oncom_ is similar to that for tempeh fermentation. This mould produces several extracellular hydrolases, such as amylase, protease, lipase, and polygalacturonase [74]. _R. oligosporus_ has the highest protease activity among _Rhizopus_ strains [20] and produced at least two proteolytic systems with pH optima of 3.0 and 5.5 [83]. The cell-wall-bound proteases were primarily responsible for proteolysis [84]. _R. oligosporus_ is also an active lipase producer, hydrolysis triglycerides to produce free fatty acids. In soy fermentation, the mould's utilization of oligosaccharides depends on the presence of enzyme \(\alpha\)-galactosidase and \(\beta\)-fructosidase [74]. [PERSON] and [PERSON] [68] showed that _N. sitophila_ had a definite \(\alpha\)-galactosidase activity with a decrease in raffinose and stachyose content of ferments, while strains _R. oligosporus_ showed varying results. A recent study conducted by [PERSON] et al.