Preparation and characterization of a protein extract from date palm fruit (Phoenix dactylifera L.) : investigation of nutritional and functional properties
Abstract
The world’s population will reach 9 billion by 2050, increasing the pressure to find
alternative protein sources to animal protein. The high global demand for soy protein
ingredients has resulted in tropical deforestation which is associated with adverse
health impact, agronomic, environmental and climate damage and there is a need to
find alternative plant protein sources to soy protein. The Kingdom of Saudi Arabia
(KSA) is considered as the second largest producer of date palm fruit among the
current date-producing countries, resulting also in significant quantities of dates going
to waste. The aims of this study were to develop a process for extraction of protein
from date fruit suitable to be implemented in the food industry, to characterise the
protein’s electrophoretic profile by sodium dodecyl sulphate-polyacrylamide gel
electrophoresis (SDS-PAGE), to identify the proteins by Liquid-Chromatography
Coupled Tandem Mass Spectrometry (LC-MS/MS), to study the physicochemical and
functional properties of date fruit protein extract (DFPE) and the effect of thermal
treatment, to determine the chemical composition, nutritional value, anti-nutritional
factors and anti-oxidant properties and to develop an infant cereal with reduced
allergenicity.
Proximate and mineral analysis, anti-oxidant, amino acid composition and digestibility
analysis of DFPE, reported in Chapter 2 showed that the protein extract contains all
essential amino acids, is a high source of iron and has excellent anti-oxidant properties
matching that of ascorbic acid. The extract had a lower protein digestibility-corrected
amino acid score (PDCAAS) value than soy protein isolate (SPI) and contained anti nutritional factors e.g. oxalate, tannin and phytate, yet at low quantities that is assumed
not to be of anti-nutritional concern. Physicochemical and functional properties of the extract and the respective effect of
thermal treatment are reported in Chapter 3. The concentration of free and total
sulphydryl groups (FSH and TSH) were significantly less that for SPI, confirming the
results of low cysteine in the amino acid analysis of DFPE. The effect of thermal
treatment on the profile of sulphydryl (SH) groups indicates that DFPE is less
thermally stable than SPI, whilst considering the fact that DFPE had been subjected to
heat treatment during the extraction process. This physicochemical profile was
mirrored by the corresponding decrease in functionality including decreases after
longer heating times in solubility, foam capacity emulsion stability index and increased
water separation in emulsions.
Chapter 4 describes the development of a protein extract containing 25.8% protein
per dry weight using a new extraction process, which is a 13-fold enrichment compared
to the 2.8% in the initial sample. The extraction process resulted in 4.2% DFPE, 57.2%
date syrup and 38.6% waste. DFPE contains 50% protein whereas the remainder was
in the date syrup (26.7%) and in the waste (24.3%) which could also be lost due to
protease activity. The electrophoretic profile was established. LC-MS/MS results
indicated the two most abundant proteins to be sorbitol dehydrogenase-like with MW
(kDa) 39, an energy-related protein and catalase isozyme 2 with MW (kDa) 57, a
disease/defense-related protein.
Chapter 5 describes the development of an infant cereal based on date fruit protein as
a potential competitor to a commercial infant cereal (CERELAC) sold in the KSA. The
date cereal product lacked certain amino acids and calcium and contained low levels
of oxalate, phytate and tannin. A date-cereal porridge prepared with camel milk had a
proximate and mineral composition matching that of a porridge made with CERELAC
prepared with cow’s milk apart from lacking fat, calcium and selenium, resulting in a
product with reduced allergenicity to gluten and cow’s milk. DFPE could add to the rising need to find replacement for soy protein because the expansion of soy bean
production and consumption is associated with environmental threats, such as
deforestation.