Abstract
Date ( Phoenix dactylifera L.) seeds have gained interest as a valuable by-product of the date fruit industry and have been identified as a rich source of functional and bioactive ingredients. In this study, date seeds from five varieties ( Medjool, Deglet Nour, Barhee, Bou Sthammi and Dayrie ) cultivated in Australia were analysed for their total phenolic and flavonoid contents, ferric reducing antioxidant power (FRAP), Trolox equivalent antioxidant capacity (TEAC), and in-vitro inhibition against α-amylase and α-glucosidase. The date seed powders (DSP) were extracted with acetone-methanol-water (2:2:1, v:v:v) to obtain free polyphenols. The bound polyphenols were extracted from the residual solids with butanol-HCl (97.5:2.5; v/v) treatment at 100 °C. The greatest quantities of total phenols (4166±227 mg Gallic Acid Equivalents 100g -1 DSP), total flavonoids (52.1±9.6 mg Quercetin Equivalents 100g -1 DSP), FRAP (1589±47 µmol Iron[II] Equivalents g -1 DSP) and TEAC (45.2±1.4 µmol Trolox Equivalents g -1 DSP) were detected in seeds from Deglet Nour variety. Both free and bound polyphenol fractions showed significant (p<0.05) inhibition against rat intestinal α-glucosidase with little or no inhibition against pancreatic α-amylase. Bound polyphenols showed stronger α-glucosidase inhibition compared with free polyphenols. The IC 50 for α-glucosidase were reported as mg GAE mL -1 ranged from 0.39±0.02 ( Deglet Nour ) to 0.68±0.02 ( Medjool ) for bound polyphenols, and from 0.907±0.08 ( Medjool ) to 1.75±0.15 ( Barhee -khalal) for free polyphenols. Bound polyphenol fraction, with strong α-glucosidase inhibition and weak α-amylase inhibition, was suggested as a significant source of functional food ingredients with anti-hyperglycaemic properties.
Highlights
The Date crop has been identified as a suitable crop for the arid regions of Australia, with a very good marketing potential for both date fruit industry and its by-products (Reilly, Reilly, & Lewis, 2010) The total world production of date fruits was 7.5 million tons in 2012 (FAO-STAT, 2015), and date seeds are an abundant by-product from this well-established industry (Besbes et al, 2004)
PC Proanthocyanidins TEAC Trolox equivalent antioxidant capacity TFC Total flavonoid content Total polyphenol content (TPC) Total phenol content been suggested that utilizing this by-product in profitable ways will benefit the date industry (AlFarsi & Lee, 2008a)
As previously mentioned in the introduction, it is evident that analysis of antioxidant capacity and other health benefits derived from fruit polyphenolics must include both free polyphenols (FPP) and bound polyphenols (BPP)
Summary
The Date crop has been identified as a suitable crop for the arid regions of Australia, with a very good marketing potential for both date fruit industry and its by-products (Reilly, Reilly, & Lewis, 2010) The total world production of date fruits was 7.5 million tons in 2012 (FAO-STAT, 2015), and date seeds (approximately 10% of fruit weight) are an abundant by-product from this well-established industry (Besbes et al, 2004). Plant polyphenols (free and bound) is expected to delay postprandial hyperglycaemia by inhibiting intestinal α-glucosidase (Phan, Wang, Tang, Lee, & Ng, 2013), and provide additional benefits against oxidative diseases such as diabetics due to their antioxidant properties (Maritim, Sanders, & Watkins, 2003). Some of the PCs are strongly bound to cell wall components (Hamauzu & Mizuno, 2011), and Perez-Jimenez, Elena Diaz-Rubio, and Saura-Calixto (2013) indicated that BPPs contribute 60-90% to the total polyphenol content in most fruits. These studies have emphasised the importance of including the bound (non-extractable) polyphenols in plant polyphenol analysis. The aim of this study was to determine the effect of date seeds’ free and bound polyphenols
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