# Production of Sustainable Postbiotics from Sugarcane Straw for Potential Food Applications
## 3 Results and Discussion
### Impact of Postbiotics on Gut Microbiota Modulation
Regarding propionate concentrations, the most significant increase was in the presence of straw extract, increasing from 0.95 to 4.93 mM, while the FOS inoculum had a lower increase (0.95-2.37 mM). Due to its anti-lipogenic, cholesterol-lowering, anti-inflammatory, and anti-carcinogenic properties, propionate may have positive impacts on health [88]. Propionic acid content may be related to the high numbers of _Bacteroides_ present or to the presence of specific compounds in the extracts [89]. Its production was associated with side chains found in xilooligosaccharides [90]. Another reason may be the presence of oligosaccharides derived from hemicellulose, which is a rich source of xylan, which is composed by xylooligosaccharides (XOS) [91]. According to some reports, XOS promotes the growth of _Lactobacillus_ at the expense of the growth of dangerous bacteria, leading to an increase in short-chain fatty acids including butyrate, acetate, and propionate [18; 92]. Richness of postbiotic extract in lactate and acetate can positively influence downstream butyrate and propionate content at the level of the gut when converted by butyrate and propionate producers [93]. Microbes such as _Annaerobutyricum_ and _Annaerostipes_ species can convert lactate to butyrate via the CoA-transferase pathway. Moreover, there are two ways that lactate can be converted to propionate: either through the acrylate pathway, which is used by microorganisms such as _Coprococcus catus_ and _Megasphaera elsdenii_, or by the succinate pathway, which is used by microbes such as _Veillonella_ species [94; 95; 96]. Valerate did not increase in the positive control; however, straw extract induced an increase (\(p<0.05\)) from 0.4 to 6.2 mM after 48 h. In the negative control, also visible was an increase in valerate content but to a lower extent, increasing to 3.2 mM. The isovalerate only revealed differences in the negative control, which increased from 0.2 to 1.5 mM. The treatment of sugarcane straw during saccharification with cellulase can release xylooligosaccharides (XOS) but also cello-oligosaccharides (COS), which are oligomers of \(\beta\)-1,\(A\)-linked D-glucose units that have proved prebiotic effect by stimulating in vitro growth of several _Lactobacillus_ and _Bifidobacterium_ strains [97; 98]. In this work, no significant growth was observed for _Bifidobacterium_ or lactic acid bacteria (LAB), probably because the amount of oligomers released was not strong enough to stimulate bacteria growth but was enough to increment their production of SCFA. It is described in the literature that XOS or COS production from lignocellulosic material requires other enzymes such as xylanases or higher temperatures and alkaline pH to increase the material breakdown [16]. Besides the potential increase in oligomers in the extract medium that may exert prebiotic effect, the observed decrease in _Bifidobacterium_ growth after 48 h and no changes observed in the growth of LAB may be related to the presence of some polyphenols. It was reported that depending on the phenolic compounds, they may stimulate the _Bifidobacterium_ growth, as was the case with coumaric acid, caffeic acid, and vanillic acid [99], or may inhibit it, as was the case with some flavonoid aglycones [100]. Studies on both humans and animals (rats, pigs, and chickens) revealed an increase in the growth of _Lactobacillus_ and a decrease in _Entrobaructeriaceae_, _Clostridium_, and Bacteroides, after stimulus with monomeric flavan-3-ols from blackcurrant extract [101] or grape seed extract [102]. In this work, also visible was a decrease in _Entrobaructeriaceae_ group after 48 h contact with fermented straw extract, indicating that the polyphenols content was inhibiting their growth. These findings allow us to state that sugarcane straw extract fermented with _S.