3.6.2. ·OH Radical Sequestration

To determine the scavenging activity of the hydroxyl radical (·OH), the method described by Li et al. [53] was applied. The antioxidant activity of AV, AV-TNDF, AP and AP-TNDF was assessed at 12.5, 6.25, 3.12, 1.56 and 0.78 mg/mL. Both 1,10-phenanthroline (0.75 mM) and FeSO4 (0.75 mM) were dissolved in phosphate buffer (pH 7.4) and mixed thoroughly. To start the reaction, H2O<sup>2</sup> (0.01%) and samples were added. The mixture was incubated at 37 ◦C for 60 min and the absorbance was measured at 536 nm. Finally, the scavenging activity of the hydroxyl radical in the kinetic fermentation

samples (AVF4, AVF8, AVF24, APF4, APF8 and APF24) was determined but only with a concentration of 12.5 mg/mL his was the concentration that gave the best result in the previous samples and was chosen for this second part of the work.

#### *3.7. Statistical Analysis*

Differences between experimental groups were analysed by one-way ANOVA and Tukey'post hoc test for repeated samples. To compare the maximum and minimum values of the total SCFA concentration, the data were analysed by a paired one-tailed Student's t-test. Data were processed using GraphPad Prism 6.0 (GraphPad Software Inc., San Diego, CA, USA). Values of *p* ≤ 0.05 were considered statistically significant.

#### **4. Conclusions**

*Aloe vera* gel (AV) and polysaccharide extract of *Aloe vera* (AP) are a matrix mainly composed of non-digestible oligosaccharides or polysaccharides of slow fermentation, since that produces a lower pH. The behavior of AV and AP during in vitro colon fermentation was similar to that of lactulose, what indicates the possibility of using *Aloe vera* and polysaccharide extracts as prebiotics. The SCFA production and their potentially delivery to the distal colon due to AV and AP digestion and fermentation process, may result in a protective effect, firstly of human large intestine, since this could be colonised by dense microbial communities that utilized both diet-derived and host-derived energy sources for growth predominantly through fermentative metabolism. In the same way, the antioxidant activity also increases significantly in both the reducing power test and the ·OH radical sequestration when going from AV and AP to its indigestible fraction AV-TNDF and AP-TNDF. Finally, we can conclude that there were no significant differences during the digestion and fermentation of *Aloe vera* and its extract despite the fact that the content of dietary fibre in AP was significantly higher than that of *Aloe vera* gel. During in vitro colon fermentation, the unfermented fibre of AV and AP had a similar response to that of lactulose, as well as the total volume of gas produced, which indicates that *Aloe vera* and polysaccharide extract can possibly be used as prebiotics.

**Author Contributions:** Conceptualization, A.T.-M., R.M.-E. and M.E.J.-F.; Methodology, A.T.-M.; P.O.-D., S.V.Á.-R.; G.M.A.-J.; Validation, A.T.-M. and R.C.-O.; Formal analysis, A.T.-M.; Investigation, A.T.-M.; Resources, R.M.-E.; writing A.T.-M., R.M.-E., Supervision, R.M.-E., M.E.J.-F. and P.O.-D.; Funding acquisition, R.M.-E. All authors accepted the final version of the manuscript.

**Funding:** This research was supported by grants from the Instituto Politécnico Nacional (SIP:20181718 project) and CONACyT (PY-SEP-CONACyT 242860, project), The work was also supported by a PhD scholarship to A.T.-M., from CONACyT.

**Conflicts of Interest:** The authors declare no conflicts of interest.

#### **References**


**Sample Availability:** Samples of the compounds are not available from the authors.

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