Subcritical water extraction of tannins, phenolics and fiber from Canadian faba bean hull and green pea pod

• Author / Creator

  Boroomand, Alaleh

• Processing of pulses such as faba bean and green pea provides 15% hull and 30% pod as by-products, respectively, which are good sources of bioactives such as tannins, phenolics, and carbohydrates. In this study, subcritical water (SCW) was used as an environmentally friendly extraction technique to remove bioactives from faba bean hull and green pea pod. Extracts were obtained using a semi continuous SCW extraction system. SCW extractions of faba bean hull and green pea pod were performed at 100-200℃ and 50-100 bar for 40 min. Particle size (0.5 mm) and flow rate (5 mL/min) were maintained constant. Also, solid-liquid (S-L) extraction was performed using water, 70% acetone, and 70% ethanol with a solid to solvent ratio of 2:20, 2:30, and 2:40 w/v at 50℃ and 70℃ within 3h. For both systems, temperature was the most important process parameter. Pressure had no significant effect on the SCW extraction of bioactives. For faba bean hull, the highest removal of total tannins (~73.6 mg tannic acid/g hull), and condensed tannins (42.3 mg catechin/g hull) were obtained at 160℃ and 50/100 bar. Also, the highest total phenolics (~44.4 mg gallic acid/g hull) were removed at 120℃. Total tannin removed using SCW (~73.6 mg tannic acid/g hull) was 3.4 times more than the one obtained by water at 70℃ and atmospheric pressure (~22 mg tannic acid/g hull).
  For green pea pod, the highest removal of total tannins) ~12.9 mg tannic acid/g pea pod), and total phenolics (~56.6 mg gallic acid/g pea pod) were obtained at 180℃ and 50 bar. SCW removed more total tannins (12.96 mg tannic acid/g pea pod) than water at 70℃ and atmospheric pressure (3.6 mg tannic acid/g pea pod). Furthermore, 70% acetone was the most efficient solvent for the total tannin removal at 70℃ and atmospheric pressure using the S-L extraction.
  These two by-products have in common a major component of dietary fiber (faba bean hull: 79.29±0.04% DW, and green pea pod: 55.10±0.05 % DW). For green pea pod, SCW extraction at 200℃ and 50 bar decreased fiber values to the lowest content of 3.25±0.02% DW soluble fiber and 45.09±0.16% DW insoluble fiber. For faba bean hull, SCW at 200°C and 50 bar led to a faba bean hull solid residue containing the lowest total dietary fiber (~71.14% DW), soluble fiber (4.36% DW), and insoluble fiber (65.71% DW). However, using the S-L extraction with acetone or ethanol was obtained 5.6-5.9% DW soluble fiber and 78.29-80.77% DW insoluble fiber in the residue. The SCW extraction is an environmentally friendly method better than the S-L extraction for the removal of bioactives such as tannins, phenolics, and carbohydrates from faba bean and green pea by-products.

• Subjects / Keywords

  • Subcritical water, Faba bean hull, Green pea pod

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3CZ32M6V

• License

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