Structural Characterization of Micronized Lignocellulose Date Pits as Affected by Water Sonication Followed by Alcoholic Fractionations

Abstract

Date pits are considered waste, and micronized date pit powder could be developed for use in foods and bio-products. In this study, micronized date pit powders were extracted by alcoholic sedimentation after ultrasound treatment. The control was considered untreated, i.e., without sonication. Six micronized fractions (i.e., three from control and three from treated) were prepared by three stages of alcoholic sedimentation. In the case of untreated date pit powder, the average particle size of the fractionated date pit powder (i.e., residue) from three stages of alcoholic sedimentation varied from 89 to 164 µm, while ultrasonic treatment showed variation from 39 to 65 µm. The average particle size of the supernatant fractions of untreated date pit powder varied from 22 to 63 µm, while ultrasonic treatment showed variation from 18 to 44 µm. Ultrasound treatment produced smaller particles. In all cases, Scanning Electron Microscopy (SEM) showed that supernatant fractions contained lumped particles compared to the residue fractions. Transmission Electron Microscopy (TEM) showed the presence of nanoparticles in all extracted fractions. Two glass transitions were observed in all fractions except for the residue from the first sedimentation stage. In addition, higher levels of degradation in the fractionated date pits could be achieved by ultrasonic treatment, as is evident from the Fourier Transform Infrared (FTIR) analysis.

Keywords: SEM; TEM; alcoholic fractionation; amorphous; crystal; date pits; glass transition; nanoparticles; particle size; sonicated.

Figure 1

Scanning Electron Micrograph (SEM) of water-soaked (OWD) date pits without ultrasonic treatment. (A) (OR₁): first residue, (B) (OR₂): second residue, (C) (OR₃): third residue, (D) (OS₁): first supernatant, (E) (OS₂): second supernatant, (F) (OS₃): third supernatant.

Figure 2

Scanning Electron Micrograph (SEM) of ultrasonic-water-treated (TWD). (A) (TR₁): first residue, (B) (TR₂): second residue, (C) (TR₃): third residue, (D) (TS₁): first supernatant, (E) (TS₂): second supernatant, (F) (TS₃): third supernatant.

Figure 3

Transmission Electron Microscopy (TEM) of water-soaked (OWD) date pits without ultrasonic treatment. (A) (OR₁): first residue, (B) (OR₂): second residue, (C) (OR₃): third residue, (D) (OS₁): first supernatant, (E) (OS₂): second supernatant, (F) (OS₃): third supernatant.

Figure 4

Transmission Electron Microscopy (TEM) of ultrasonic-water treatment (TWD). (A) (TR₁): first residue, (B) (TR₂): second residue, (C) (TR₃): third residue, (D) (TS₁): first supernatant, (E) (TS₂): second supernatant, (F) (TS₃): third supernatant.

Figure 5

A typical heat DSC flow curve of extracted date pits with ultrasonic-water treatment (i.e., TS₁). (A): Complete thermogram, (B): rescaled to clearly visualize first and second glass transitions, (C): rescaled to show solids melting.

Figure 6

FTIR spectra of selected date pit fractions with water soaking without ultrasonic treatment followed by alcoholic sedimentation of date pits (OWD). (A): Residue with 2000 to 200 cm⁻¹, (B): residue within 4000 to 2000 cm⁻¹, (C): supernatant with 2000 to 400 cm⁻¹, (D): supernatant with 4000 to 2000 cm⁻¹ (1: O-H stretching, 2: C-H stretching, 3: H-C-H stretching, 4: C=O-OH or C=O, 5 and 6: C=C, 7, 8 and 9: C-H bending, 10, 11 and 12: C-O-C vibration, 13 and 14: C-H bending, 15: C-OH and C-C stretching).

Figure 7

FTIR spectra of selected date pit fractions with ultrasonic-water treatment followed by alcoholic sedimentation of date pits (TWD). (A): Residue with 2000 to 200 cm⁻¹, (B): residue within 4000 to 2000 cm⁻¹, (C): supernatant with 2000 to 400 cm⁻¹, (D): supernatant with 4000 to 2000 cm⁻¹ (1: O-H stretching, 2: C-H stretching, 3: H-C-H stretching, 4: C=O-OH or C=O, 5 and 6: C=C, 7 and 8: C-H bending, 10, 11 and 12: C-O-C vibration, 13 and 14: C-H bending, 15: C-OH and C-C stretching).

Figure 8

Flow diagram of the water-soaked or ultrasonic-water-treated whole date pit powder followed by alcoholic sedimentation: water-soaked (OWD), OR₁: first residue, OR₂: second residue, OR₃: third residue, OS₁: first supernatant, OS₂: second supernatant, OS₃: third supernatant. Ultrasonic-water-treated whole date pit powder followed by alcoholic sedimentation (TWD). TR₁: first residue, TR₂: second residue, TR₃: third residue, TS₁: first supernatant, TS₂: second supernatant, TS₃: third supernatant (photos included for treated date pits).