# _Oncom_: A Nutritive Functional Fermented Food Made from Food Process Solid Residue
## 4 Microbiology of _Oncom_
using transcriptomic, metabolomic, and phylogenomic analysis showed that _N. intermedia_ of _oncom_ utilizes pectin and cellulose degradation during fermentation [82]. The enzyme activity during _oncom_ fermentation contributes to the chemical, biochemical, and sensory characteristics of _oncom_. The \(\alpha\)-galactosidase activity increased the digestibility of _oncom_ as _N. sitophila_ utilized the flatulence-causing sugars such as raffinose and stachyose during the first 21 h of fermentation [68]. When tofu dreg (_okara_) is used as a substrate for fermentation, extracellular enzymes, especially proteases and carbohydrates, might facilitate the hydrolysis of tofu dreg (_okara_) protein that yielded antioxidative amino acids and peptides, as well as the release of isoflav-derived components [85]. Their research showed that fermentation of tofu dreg (_okara_) with _R. oligosaccharides_ yield enhanced antioxidant activity 2.6-fold. Similar to _R. oligosaccharides_, _N. sitophila_ is also an active lipase producer [74]; however, the proteolytic activity was lower than that of _R. oligosaccharides_, as shown by a study applying both moulds as a starter culture for fermentation of peanut press cake, which revealed that _oncom_ produced with _R. oligosaccharides_ had higher soluble nitrogen compounds than that with _N. sitophila_[3]. As a raw material for black _oncom_, peanuts contain anti-nutritional factors such as phytic acid. _R. oligosaccharides_ and _N. sitophila_ reduced phytic acid after 72 h of fermentation, with the highest reduction by _R. oligosaccharides_ (decreased from 1.4% on a dry basis to 0.5%); meanwhile, that with _N. sitophila_ contained 0.7% [19]. _N. sitophila_ produces carotenoids in its spores. Five carotenoids have been identified, including lycopene, neuropheres, g-carotene, \(\beta\)-carotene, and phytoene [75]. The presence of carotenoids may contribute to the availability of nutrition in red _oncom_. The safety consideration of using peanuts is aflatoxin, which may be present in peanut press cake as a raw material for black _oncom_. Fermentation has been reported to reduce aflatoxin. _N. sitophila_ and _R. oligosaccharides_ could decrease the aflatoxin content of peanut press cake by 50-70% during fermentation [74]. _N. intermedia of oncom_ origin did not encode mycotoxins [82]. Moulds such as _R. oligosaccharides_, _R. oryzae_, _A. Aspergillus oryzae_, some osmophilic yeasts, and lactic acid bacteria have been reported to be capable of reducing aflatoxin [86]. Adding about 0.2% of _R. oligosaccharides_ starter to the mixture significantly decreased the aflatoxin content, such as aflatoxin B1 and total aflatoxin, compared to the peanut cake [29]. _L. plantarum_ added during soaking of peanut press cake and mould fermentation reduced aflatoxin by 87.3% [87]. The role of other microorganisms in _oncom_ fermentation has yet to be well elucidated, apart from the possibility of yeast and LAB contributing to the safety of the _oncom_, which is primarily related to the reduction in aflatoxin [86]. However, in tempeh fermentation, yeast and LAB play a role in flavour development and chemical substrate modification [88]. A similar role may also be played in _oncom_ fermentation. [PERSON] et al. [89] showed that the addition of yeast, such as _Saccharomyces cerevisiae_, _S. boulardi_, _Pichia anomala_, and _Kluyveromyces lactis_, in tempeh starter culture did not inhibit the growth of _R. oligosaccharides_ and contributed to increased ergosterol content. Co-culture of _R. oligosaccharides_ and yeast _Yarrowia lipolytica_ in tofu dreg (_okara_) fermentation enhanced the flavour, digestibility, and nutritional value, primarily related to the significant increase in antioxidant activities [90]. Similarly, the addition of LAB did not affect the growth of _R. oligosaccharides_[91]. LAB may be involved during the soaking of peanut press cake and the mould fermentation stage, which also happens for tempeh fermentation.