Abstract
Hemicellulose, a structural polysaccharide and often underutilized co-product stream of biorefineries, could be used to produce prebiotic ingredients with novel functionalities. Since hot water pre-extraction is a cost-effective strategy for integrated biorefineries to partially fractionate hemicellulose and improve feedstock quality and performance for downstream operations, the approach was applied to process switchgrass (SG), hybrid poplar (HP), and southern pine (SP) biomass at 160°C for 60 min. As a result, different hemicellulose-rich fractions were generated and the chemical characterization studies showed that they were composed of 76–91% of glucan, xylan, galactan, arabinan, and mannan oligosaccharides. The hot water extracts also contained minor concentrations of monomeric sugars (≤18%), phenolic components (≤1%), and other degradation products (≤3%), but were tested for probiotic activity without any purification. When subjected to batch fermentations by individual cultures of Lactobacillus casei, Bifidobacterium bifidum, and Bacteroides fragilis, the hemicellulosic hydrolysates elicited varied responses. SG hydrolysates induced the highest cell count in L. casei at 8.6 log10 cells/ml, whereas the highest cell counts for B. fragilis and B. bifidum were obtained with southern pine (5.8 log10 cells/ml) and HP hydrolysates (6.4 log10 cells/ml), respectively. The observed differences were attributed to the preferential consumption of mannooligosaccharides in SP hydrolysates by B. fragilis. Lactobacillus casei preferentially consumed xylooligosaccharides in the switchgrass and southern pine hydrolysates, whereas B. bifidum consumed galactose in the hybrid poplar hydrolysates. Thus, this study (1) reveals the potential to produce prebiotic ingredients from biorefinery-relevant lignocellulosic biomass, and (2) demonstrates how the chemical composition of hemicellulose-derived sources could regulate the viability and selective proliferation of probiotic microorganisms.
Highlights
Hemicellulose, a structural polysaccharide constituting 9–34% of lignocellulosic biomass (Yadav et al, 2018), is often an undervalued and underutilized stream of biorefinery processes with untapped potential in platform chemicals, and food and cosmetic industries (Takkellapati et al, 2018; Lolou and Panayiotidis, 2019)
Our previous work has shown that hot water extraction (HWE) procedure at 160°C for 60 min could be utilized to pretreat lignocellulosic biomass, namely hybrid poplar, switchgrass, and pine bark (Wang et al, 2017; Liu et al, 2018), to decrease inorganic impurities and reduce recalcitrance such that the overall biomass quality was enhanced for subsequent thermo- and biochemical conversion processes
We can conclude that, hemicellulosic hydrolysates isolated using industrially relevant hot water extraction process from dedicated bioenergy crops such as switchgrass, and hybrid poplar and from southern pine could serve as prebiotic substrates
Summary
Hemicellulose, a structural polysaccharide constituting 9–34% of lignocellulosic biomass (Yadav et al, 2018), is often an undervalued and underutilized stream of biorefinery processes with untapped potential in platform chemicals, and food and cosmetic industries (Takkellapati et al, 2018; Lolou and Panayiotidis, 2019). The native structure of hemicellulose varies depending on the plant species, with the predominant forms in herbaceous, hardwood, and softwood biomass being arabinomethylglucuronoxylan, methylglucuronoxylan, and galactoglucomannan, respectively (Spiridon and Popa, 2008) Their unique structure and chemical composition create new opportunities for diversification and high-value nutraceutical applications such as prebiotics. In vitro and in vivo studies have shown that supplementation with xylooligosaccharides could provide additional benefits, including reduction of inflammatory cell signaling pathways (Hansen et al, 2013) and improvement in gut barrier functions (Thiennimitr et al, 2018) Together, these physiological changes have been reported to mitigate obesity (Thiennimitr et al, 2018), colon cancer (Hsu et al, 2004), type-2 diabetes (Yang et al, 2015) and improve the overall immune response (Pham et al, 2018). The demand for prebiotic ingredients is expected to reach 1.35 million tons by 2024 (Ahuja and Deb, 2017), complementing food sources with lignocellulosic feedstocks would make the prebiotic ingredient industry more sustainable
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