Thermo-Chemical Preservation of Date Palm (Phoenix dactylifera) Sap: Effect on Physical, Chemical, and Sensory Properties

Abstract

Date palm sap, a nutritious and popular beverage, is highly prone to spoilage due to rapid fermentation, limiting its commercial potential. In order to prolong the shelf life of date palm sap, this study investigated the effectiveness of combining heat treatment (100°C) with chemical preservatives such as potassium metabisulfite (200 ppm), potassium sorbate (0.15 g), and citric acid (0.02 g) per 100 mL of sap. Freshly harvested sap was treated and concentrated into samples with total soluble solids (TSS) concentrations of 11%, 15%, and 19%, and then stored under refrigerated conditions of 4°C to assess the impact of these treatments on the sap's stability and quality. Throughout the storage period, the samples were evaluated for changes in physicochemical properties, such as pH, acidity, total soluble solids, and sugar content, as well as microbial load and sensory attributes. The results have shown that, while chemical preservatives assisted in preventing microbial development during the first 7 days of storage, heat processing was beneficial in concentrating the sap and enhancing its stability. Although, as time progressed, the effectiveness of these preservation techniques diminished, leading to eventual spoilage. Sensory evaluations indicated that the treated sap maintained favorable qualities during the first 7-day storage period, though some degradation in taste and appearance was observed later. This research highlights the potential for preserving date palm sap through a combination of heat treatment and chemical preservatives; of these, S2 (15% TSS) proved to be the most effective in retaining overall quality throughout storage. S2 showed a balance between microbial stability and sensory attributes, making it the most favorable for short-term preservation. However, further optimization of preservation methods such as, using Pulsed Electric Field (PEF) or High Hydrostatic Pressure (HHP) along with additional chemical preservatives is necessary to ensure long-term stability and offer promising prospects for the sap's commercialization.