One-step process for producing prebiotic arabino-xylooligosaccharides from brewer's spent grain employing Trichoderma species.

TLDR: One-step fermentation proved to be a promising strategy for AXOS production from BSG, presenting a performance comparable with the use of commercial enzymes, enabling further developments of low-cost bioprocesses for the production of these valuable compounds.

About: This article is published in Food Chemistry.The article was published on 2019-01-01 and is currently open access. It has received 56 citations till now. The article focuses on the topics: Trichoderma reesei & Lignocellulosic biomass.

Figures

Table 2 Monosaccharide concentration and AXOS production yield, YXeq, obtained by direct fermentation (20 g/L BSG, pH 7.0 and 30 °C) and using commercial enzyme preparation (20 g/L BSG, pH 4.5 and 40 °C).

Fig. 1. TLC of the supernatants obtained from the direct fermentation of BSG by (A) Trichoderma viride and (B) Trichoderma reesei using 100 g/L of residue. Glucose (G, 2 gL/) and a mixture containing 2 g/L of xylose (X1), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5) and xylohexaose (X6) was used as standard (S). (C) sugar production yield (YRS) obtained for Trichoderma viride and Trichoderma reesei using 10 g/L of BSG. The fermentation assays were performed at 30 °C and 180 rpm with BSG in 2% (w/v) Vogel media pH 5.0.

Fig. 2. Sugar production yield (YRS) obtained for Trichoderma reesei using: (A) different substrate concentration (5, 10, 20 and 60 g/L of BSG) at 30 °C, 180 rpm with BSG in 2% (w/v) Vogel media pH 5.0; (B) different pH (3.0, 4.0, 5.0, 6.0, 7.0, 8.0 and 9.0) at 30 °C, 180 rpm and 20 g/L BSG in 2% (w/v) Vogel media; (C) different temperatures (20, 27, 30 and 37 °C) at 180 rpm and 20 g/L BSG in 2% (w/v) Vogel media pH 7.0.

Table 1 Potential of several residues evaluated for XOS production using Trichoderma viride and Trichoderma reesei.

Fig. 3. Confocal Laser Scanning Microscopy images showing BSG (green channel) colonized by hyphae (blue channel) of Trichoderma reesei at (A) 3 days and (B) 6 days of fermentation under optimal operational conditions: 20 g/L of BSG, pH 7.0 and 30 °C. Dashed area shows the fungi adhesion to the intricate surface of BSG. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Frequently asked questions

Q1. What were used as standards for identification and quantification of sugars in the hydrolysates?

Chromatographic grade sugars glucose, xylose, arabinose were used as standards for identification and quantification of sugars in the hydrolysates. 

Q2. What have the authors contributed in "One-step process for producing prebiotic arabino-xylooligosaccharides from brewer's spent grain employing trichoderma species" ?

This study reports for the first time an optimization study of XOS production from agro-residues by direct fermentation using two Trichoderma species. This study provides new insights towards the bioprocess integration, enabling further developments of low-cost bioprocesses for the production of these valuable compounds. A total of 13 residues were evaluated as potential substrates for single-step production. One-step fermentation proved to be a promising strategy for AXOS production from BSG, presenting a performance comparable with the use of commercial enzymes. 

Q3. What was used for the detection of T. reesei?

Calcofluor was used for the detection of T. reesei (laser excitation line 405 nm and emissions filters BA 430–470) and auto-fluorescence (laser excitation line 488 nm and emissions filters BA 505–540) for BSG. 

Q4. What was the procedure used to evaluate the possible sugar extraction from BSG?

A negative control, without inoculum, was performed in parallel for the optimal conditions selected, to evaluate the possible sugar extraction from BSG during the fermentation time. 

Q5. Why is the demand for prebiotics growing?

Due to the increasing of health consciousness and consumer awareness, the demand of prebiotic products as functional food ingredients has been growing in the recent years (Antov & Đorđević, 2017). 

Q6. How many days of cultivation were needed to obtain the xylanase crude extract?

For instance, Bian et al. (2013) used crude xylanase extract to hydrolyze pretreated sugarcane bagasse during 12 h, however 7 days of cultivation were needed to obtain the xylanase crude extract. 

Q7. What was the retention factor used to compare the different components of the spotted mixtures?

The retention factor, corresponding to the ratio between the distance traveled by the sample and the distance traveled by the solvent, was used to compare the different components of the spotted mixtures. 

Q8. What is the main advantage of the direct fermentation approach?

This is one of the main advantages of the direct fermentation approach using T. reesei, i.e. allowing the simplification of the downstream process, which generally represents up to 80% of the total entire production costs (Urmann, Graalfs, Joehnck, Jacob, & Frech, 2010). 

Q9. What was the method used to quantify the total reducing sugars?

The DNS (3,5-dinitrosalicylic acid) method (Miller, 1959) was used to quantify the total reducing sugars, RS (mg), using xylose as standard for the calibration curve (Jeffries, Yang, & Davis, 1998). 

Q10. How many bands are observed for T. reesei?

3 bands can be observed for T. reesei (Fig. 1B), which possibly indicates oligosaccharides with DP from 3 up to 5, while for T. viride (Fig. 1A) only 2 clear bands are observed in the DP=4 and DP=5 region. 

Q11. How was the pH of the BSG fermented?

In order to study the effect of temperature on the YRS, 20 g/L of BSG were fermented by T. reesei at optimum pH (7.0) and using a temperature range from 20 °C up to 37 °C (Fig. 2C). 

Q12. What is the way to determine the YRS of T. reese?

It is known that different types of enzymes, including different types of xylanases, can be produced by T. reesei depending on the pH of the medium (Häkkinen et al., 2015).