Production and faecal fermentation of pentose oligomers of hemicellulose: Study of variables influencing bioprocess efficiency

Enzymatic production of cello-oligosaccharides with potential human prebiotic activity and release of polyphenols from grape marc

Grape marc, the main winemaking byproduct, is an excellent source of bioactive polyphenols, such as anthocyanins, resveratrol and quercetin. An enzyme-catalysed treatment of marc was developed using endo-1,4-β-d-glucanase to release polyphenol O-glucosides and simultaneously generate the optimal concentration of water-soluble cello-oligosaccharides (COS), including cellopentaose, cellotriose, and cellobiose from the marc matrix. The prebiotic properties of marc hydrolysate rich in COS was assessed using human probiotic monocultures of Lactobacillus spp. and Bifidobacterium spp. strains, and invitro human faecal fermentation. The COS-rich hydrolysate showed excellent prebiotic effect in both studies, successfully supporting the growth of beneficial probiotic strains, and was highly fermentable by faecal microbiota producing gas and short chain fatty acids. Acetate and propionate production were the highest when faecal bacteria fermented COS-rich solution compared with standard substrates. For the first time, COS was shown to be fermented by faecal microbiota, demonstrating the potential benefits of valorised grape marc.

Screening dietary fibres for fermentation characteristics and metabolic profiles using a rapid in vitro approach: implications for irritable bowel syndrome

The therapeutic value of specific fibres is partly dependent on their fermentation characteristics. Some fibres are rapidly degraded with the generation of gases that induce symptoms in patients with irritable bowel syndrome (IBS), while more slowly or non-fermentable fibres may be more suitable. More work is needed to profile a comprehensive range of fibres to determine suitability for IBS. Using a rapid in vitro fermentation model, gas production and metabolite profiles of a range of established and novel fibres were compared. Fibre substrates (n 15) were added to faecal slurries from three healthy donors for 4 h with gas production measured using real-time headspace sampling. Concentrations of SCFA and ammonia were analysed using GC and enzymatic assay, respectively. Gas production followed three patterns: rapid (≥60 ml/g over 4 h) for fructans, carrot fibre and maize-derived xylo-oligosaccharide (XOS); mild (30-60 ml/g) for partially hydrolysed guar gum, almond shell-derived XOS and one type of high-amylose resistant starch 2 (RS2) and minimal (no differences with blank controls) for methylcellulose, another high-amylose RS2, acetylated or butyrylated RS2, RS4, acacia gum and sugarcane bagasse. Gas production correlated positively with total SCFA (r 0·80, P < 0·001) and negatively with ammonia concentrations (r -0·68, P < 0·001). Proportions of specific SCFA varied: fermentation of carrot fibre, XOS and acetylated RS2 favoured acetate, while fructans favoured butyrate. Gas production and metabolite profiles differed between fibre types and within fibre classes over a physiologically relevant 4-h time course. Several fibres resisted rapid fermentation and may be candidates for clinical trials in IBS patients.

Production of Oligosaccharides from Agrofood Wastes

The development of biorefinery processes to platform chemicals for most lignocellulosic substrates, results in side processes to intermediates such as oligosaccharides. Agrofood wastes are most amenable to produce such intermediates, in particular, cellooligo-saccharides (COS), pectooligosaccharides (POS), xylooligosaccharides (XOS) and other less abundant oligomers containing mannose, arabinose, galactose and several sugar acids. These compounds show a remarkable bioactivity as prebiotics, elicitors in plants, food complements, healthy coadyuvants in certain therapies and more. They are medium to high added-value compounds with an increasing impact in the pharmaceutical, nutraceutical, cosmetic and food industries. This review is focused on the main production processes: autohydrolysis, acid and basic catalysis and enzymatic saccharification. Autohydrolysis of food residues at 160–190 °C leads to oligomer yields in the 0.06–0.3 g/g dry solid range, while acid hydrolysis of pectin (80–120 °C) or cellulose (45–180 °C) yields up to 0.7 g/g dry polymer. Enzymatic hydrolysis at 40–50 °C of pure polysaccharides results in 0.06–0.35 g/g dry solid (DS), with values in the range 0.08–0.2 g/g DS for original food residues.