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 Bioactive and Nutritional Constituents, In Vitro Functionality, and Food and Therapeutic Potentials of a Syrup Prepared from Oil Palm (Elaeis Guineensis) Sap

Fred Omon Oboh, Chioma Ndukwe, Ozioma Ononuju
Department of Biological Sciences, Benson Idahosa University, P.M.B. 1100, Benin City
Received: 11 December 2022; Accepted: 22 December 2022; Published: 21 February 2023

Abstract: – A syrup prepared from the sap of the African oil palm (Elaeis guineensis Jacq) was evaluated in vitro, for application as a nutritional, bioactive sweetener and flavouring by determination of its carbohydrate content, sugar, organic acid, and phenolic compositions, and also, its pH, titrable acidity, vitamin C, and functional characteristics at various concentrations. The syrup exhibited high total phenolic content (TPC) (70.82-510.2 mg GAE/L) at the various concentrations studied (5-40% wt/vol). Thirty-four phenolic compounds were identified, with syringic (28.91%), vanillic (24.48%), gallic (17.93%) and ferulic (10.88%) acids as the dominant constituents; 30 others were present in minor and trace concentrations. The various concentrations of palm syrup exhibited acid pH values of 3.2-3.0, high vitamin C (7.67-61.34 mg %) and low titrable acidity (0.31-1.49%), with malic (35.76%), tartaric (21.86%), lactic (16.36%), acetic (12.71%), and oxalic (9.81%) as the major organic acids. Total carbohydrate content was 67.73±0.72%, and glucose (75.69 %) and fructose (19.31%) were the major sugars; sucrose (4.83%) was a minor constituent. The favourable organic acid, carbohydrate, and phenolic profiles, high carbohydrate, vitamin C, and total phenolic contents, high DPPH radical scavenging activity (IC50 = 2.88 g/ml), modest reducing power (IC50 = 25.3 g/ml), and high α-amylase inhibitory activity (IC50 = 0.45 mg/ml) of the palm syrup recommend it as a functional sweetener and flavouring, with possible therapeutic benefits.

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Keywords: Palm sugar, phenolic compounds, organic acids, sugars, antioxidant capacity, α-amylase inhibitory activity.

I. Introduction

Growing incidence of obesity, type 2 diabetes mellitus (T2DM), and hypertension, and the search for dietary interventions for their management have resulted in the emergence of a number of previously little-known food sweeteners, among which are palm syrup, sugar, and jaggery, prepared by the evaporation of the sweet saps collected from palms. Prominent among these are the brown products from the evaporation of saps from the coconut (Hebbar et al., 2015), Phoenix canariensis (Luis et al., 2012), Arenga pinnata, and Borassus flabellifer (Srikaeo et al., 2019) palms, which are popular in the cuisines of areas where they are produced, and also feature in international trade. Palm sugar has gained international recognition because it is considered to be natural and healthy, with a low glycaemic index (GI) (Trinidad et al., 2010), and high micronutrient content, compared with traditional natural sweeteners such as honey, table sugar (sucrose), and high fructose corn syrup (Hebbar et al., 2015).

Low GI foods play an important role in the dietary management of obesity, diabetes, weight reduction, peak sport performance, and the reduction of risks associated with heart disease and hypertension (Jenkins et al., 1981; Jenkins et al., 2002, Foster-Powell et al., 2002; Strikaeo & Tonga, 2015). Other properties are the high in vitro α-amylase, α-glucosidase and ACE (angiotensin 1-converting enzyme) inhibitory activity of brown sugar preparations (notably palm sugar), with potential for low-cost dietary management of type 2-diabetes and hypertension (Ranilla et al., 2008). These findings have resulted in growing demand for palm sugar as replacement for traditional sweeteners (especially cane sugar and brown syrups derived from it) for use in food and beverage formulations. This demand which currently outstrips supply (due largely to the fact that palm sugar is largely produced by artisanal and small-scale operators) is driven mainly by the favourable health claims, especially of lower glycaemic index, higher micronutrient content, and higher antioxidant capacity, compared with white and brown sugars based on sugar cane, and honey (Trinidad et al., 2010; Hebbar et al., 2015).