Oligosaccharides production and purification from barley bran using sequential supercritical CO2 extraction, subcritical water hydrolysis and membrane filtration

• Author / Creator

  Aghashahi, Azadeh

• Barley bran is a by-product of the food industry, and a good source of lipid, protein and fiber. In this thesis research, fractionation of barley bran was carried out to remove lipid, starch and protein to obtain a sample enriched in fiber, specially arabinoxylan. Fiber concentrate was used for further hydrolysis, targeting the production of xylooligosaccharides (XOS) with degree of polymerization 2-4. Lipid was extracted using supercritical CO2, followed by enzymatic hydrolysis to remove starch. Defatted bran with 0.3% lipid was obtained. Defatted-destarched bran had 1% starch and 26.3% db arabinoxylan. Subcritical water (SCW) was used as an environmentally friendly approach to hydrolyse defatted-destarched bran. Temperature had a significant effect on the XOS production. The highest XOS content was produced at 180℃, where 112.5 mg of total XOS was obtained within 30 min, with no significant difference after 60 min hydrolysis. Deproteinized bran with 42.2% db arabinoxylan was hydrolyzed using SCW at 180℃/50 bar/30 min. Amounts of 100.9, 120.6, 112.4 and 334 mg of xylobiose, xylotriose, xylotetraose and total XOS were obtained in the hydrolysate. Deproteinized bran was also treated using enzymatic hydrolysis with endo-xylanase. Maximum amount of total XOS was 21.11 mg obtained using 10 U of enzyme at 40℃, pH of 4.5 after 4 h incubation. The recovery of total XOS from initial xylan of deproteinized bran was 78.4 and 45.1% for SCW and enzymatic hydrolysis, respectively. Purification of deproteinized bran SCW hydrolysate was performed using ultrafiltration with 1 kDa membrane to remove compounds with high molecular weight. In total, 68% of initial total XOS was recovered after passing through 1 kDa membrane. This permeate was treated by activated carbon adsorption (10% w/w) to remove monomers (arabinose and xylose) from XOS. Activated carbon was washed with aqueous ethanol solutions (15 and 30% v/v) to liberate the adsorbed XOS. Finally, 55% of xylose and 51% of arabinose were removed and 52% of total XOS was recovered in the ethanol fraction. The results suggest that SCW hydrolysis is a promising method to produce XOS from barley bran in a short time with higher recovery than the enzymatic hydrolysis. The obtained XOS has potential use in the functional food products as prebiotics.

• Subjects / Keywords

  • Supercritical CO2
  • Nano/ultrafiltration
  • Arabinoxylan
  • Subcritical water
  • Xylooligosaccharides.
  • Barley bran

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-8fb7-2w30

• License

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