Effects of Time, Temperature, and Solvent Ratio on the Extraction of Non-Extractable Polyphenols with Anticancer Activity of Barhi Date Palm Kernels Extracts Using Response Surface Methodology

Abstract

Dietary polyphenols exist in two forms; extractable polyphenols (EPP) or compounds solubilised by aqueous/organic solvents, and non-extractable polyphenols (NEPP) or compounds remain in the corresponding residues after the extraction. At present, most researchers focus on EEP fractions, while NEPP is neglected. Thus, this study aimed to release NEPP from the remaining powder residue of Barhi date palm kernels (BDPK) with acid hydrolysis. The related extraction conditions were determined and optimised using response surface methodology (RSM) for maximisation of NEPP with highest cytotoxic and antioxidant activities. The face-centred central composite design (FCCCD) was used to establish treatments based on three independent variables, namely; extraction temperature, time, and solvent/sample ratio. Under the optimal conditions, the experimental values for DPPH radical-scavenging capacity of NEPP (IC50=57.52µg/mL), and cytotoxicity of NEPP against A549 and HT29 cells were IC50=17.4 µg/mL and 31.4µg/mL, respectively. The experimental values were in agreement with those predicted by RSM models, confirming the suitability of the model employed and the success of RSM for optimisation of the extraction conditions for NEPP from BDPK. These results indicate that NEPP from industrial date fruit waste could be a promising candidate as natural antioxidants with significant antiproliferation effect against A549 and HT29 cancer cells in-vitro.

Non-Extractable Polyphenols from Food By-Products: Current Knowledge on Recovery, Characterisation, and Potential Applications

“…Briefly, the residues after EPPs extraction were hydrolysed with methanol/H 2 SO 4 (90:10 v/v) at 85 • C for 20 h. Then, the content of hydrolysable tannins was determined by analysing the supernatants combined with two times residues washing with distilled water. This method has been extensively used in recent years to determine the NEPs content from fruit peels or pulps [3,55,72,73], rice bran [61], palm kernels [74], and olive pomace [59]. To maximise the efficiency of acid hydrolysis, in 2014, Cheng et al optimised the treatment condition based on a response surface methodology.…”

“…The analysis of the NEPs content was based on the supernatants collected and the washing butanol [72,75]. This method was also extensively applied to extract NEPs from several by-products, including fruit peel and pomace [3,72], black rice bran [61], fruit kernels and seeds [73,74], and olive pomace [20]. In 2019, Mahmud et al carried out one-factor-at-a-time study to maximise the extraction yield based on butanol/HCl hydrolysis on date palm kernels.…”

“…Three factors were considered, namely extraction temperature (70, 85, 100 • C), time (1, 2, 3, 4, and 5 h), and the solid/solvent ratio (5:1, 10:1, 15:1, 20:1, and 25:1). The maximum recovery of total phenol compounds (TPC) (10.83 mg GAE/g) was achieved with a sample/solvent ratio equal to 1:20 under 85 • C for three hours [74].…”

“…The results published by Speroni et al in 2019 also showed that the two acid hydrolysis methods can provide significantly different results on NEPs yield from olive pomace (6.4 g and 3.2 g GAE per 100 g DW, respectively) [20]. However, in most of the published studies, experiments were performed applying just one of the two hydrolysis methods to determine the content of the NEPs [46,72,74]. Besides choosing the suitable hydrolysis method, attention also needs to be paid to the analytical techniques used for NEPs quantification.…”

“…The occurrence of the reaction produces a coloured compound, which can be further detected and quantified at 500 nm by spectrophotometry. The epicatechin standard is used for equivalency [54,74]. However, the acid condition and substrate concentration may influence the accuracy of the results [7].…”