English abstract
Date-pits are waste from the date-fruit processing factory. The objective of this study
was to develop date-pits fibers having hygroscopic characteristics with molecular
structural damage and easy to digest. In this work, two types of date-fibers were
prepared by alkaline digestion of date-pits at 70oC for 24 h. Two fractions of date-pits
fibers were developed, one from the residue and other one from the supernatant after
digestion of date-pits. The physico-chemical and molecular characteristics, proton
mobility, and health functionality of these fiberes were measured.
Date-pits showed FTIR absorption peaks at 3422 cm-1
(O-H stretching), 2924 cm-1
(asymmetric C-H stretching), 2856 cm-1
(symmetric C-H stretching), 1744 cm-1
(C=O
vibration acetyl and ester linkages), 1656 cm-1
and 1638 cm-1
(C=C vibration aromatic
region), 1532 cm-1
and 1458 cm-1
(C=C stretching of aromatic skeletal mode). Other
peaks were at 1384 cm-1
(C-H stretching of cellulose), 1252 cm-1
(C-O-H deformation
and C-O stretching of phenolic), 1146 cm-1
(C-O-C vibration of cellulose and
hemicellulose), 1113 cm-1
, 1059 cm-1
(C-O stretching vibration of cellulose and
hemicellulose), 885 cm-1
, 814 cm-1
, 610 cm-1
, and 495 cm-1
, respectively. The alkaline
treated residue and supernatant date-pits fibers showed similar peaks. The structural
damage of the residue and supernatant fibers was evaluated from the missing and new
peaks, and increased or decreased intensity values at specific peaks. This indicates that
treated fibers could have the ability to make inter links when it is used in food products
and other applications. Therefore, residue and supernatant fibers showed higher
hygroscopicity as compared to the date-pits powder (p<0.05), while there was no
difference between them (p>0.05). Similar trends were also observed for water
absorption and solubility, and showed higher interactions of the fibers with water as
compared to the date-pits.
Proton mobility was measured by Low-Frequency Nuclear Magnetic Resonance (LFNMR) and three pools of the protons were identified: rigid protons, semi-rigid protons,
and mobile protons. At low similar moisture content (1.5 g/100 g sample), the
relaxation time of the rigid protons of residue (21.8 s) and supernatant (24.3 s) fibers
xi
was significantly higher as compared to the date-pits (11.1 s) (p<0.05). In the case of
semi-rigid protons, relaxation tioms of the residue (0.22 ms) and supernatant (0.33 ms)
fibers decreased as compared to the date-pits (1.30 ms). Similarly, relaxation times of
mobile protons decreased in the cases of residue (7.01 ms) and supernatant (9.94 ms)
fibers as compared to the date-pits (59.78 ms). It is expected that the relaxation time of
protons in the macromolecules should be increased (i.e. higher mobility) with structural
damage unless protons are interfering each other. The decrease of relaxation times in
the case of semi-rigid and mobile protons indicated that these pools of protons were
interfering each other causing a decrease instead of increase in relaxation. In the case
of same water activity (i.e. 0.90) samples, rigid proton showed similar trends as the
samples with similar moisture content. However, in the case of semi-rigid protons, both
residue and supernatant showed increased relaxation times, while in the case of mobile
protons, relaxation time decreased for residue and it increased for supernatant. The
moisture content of residue and supernatant fibers was 3.8 time higher than the datepits. Therefore, large pools of water protons were exited with the protons of the
macromolecules and interacted differently. In general, alkaline treatment damaged the
molecular structure of the fibers and affected their mobility.
The supernatant fibers were effective in reducing in-vitro aluminum toxicity as
observed by the decrease of oxidized glutathione (OG). In the case of 0.01 g/ml
supernatant fibers, OG increased with the reaction time at 37oC, while OG decreased in
the cases of 0.03 and 0.05 g/ml fibers addition. However, reduction of toxicity reached
equilibrium after 30 min and remained until 2 days as used in this study.
Overall, the improved functionality observed in the residue and supernatant fibers could
be used to determine the proper applications of these fibers in different products, such
as fiber supplements, use of fibers as ingredient in food products, and bio-composites.
In the case of bio-composites, date-pits could be used when non-hydroscopic and low
water soluble rigid particles are required as fillers. The residue and supernatant fibers
could be used in food products due to its structural damage and higher ability to interact
with the other food components; and easy digestibility.
