Second-grade dates can be valorized by its uses in the production of nutritive foods with health benefits. Date syrup (DS), date powder (DP), and their different concentrations, using D-optimal mixture design, were used for the formulation of dairy desserts: syrup dairy dessert (SDD) and mixture dairy dessert (MDD). The optimized mixture proportions of the best dairy dessert formulation, containing date syrup (14%) and powder (2%) as a sugar substitute (0%), were determined to achieve the desired sensory for the effective formulation process. Significant differences in water, protein, fat, and sugar contents were found between SDD, MDD, and commercial dairy dessert (CDD) used as standard, respectively. SDD exhibited the highest total phenolic content (0.65 ± 0.04 mg GAE/g), DPPH inhibition (4.00 ± 0.82%), and reducing power (2.75 ± 0.10%) followed by MDD and CDD. The absence of germs indicated a high microbiological quality of dairy desserts. Rheological measurements revealed that all samples exhibited a weak gel structure and shear thinning behavior. Desserts supplemented with dates led to desserts with an homogeneous structure. Practical applicationsThe evolution of technological processes, conservation techniques, and distribution has led to the development of a wide range of "milks for consumption". The success of these fresh dairy desserts is explained by their beneficial effect on health and organoleptic properties that are appreciated by the consumers. The most delicate in the production of dairy dessert is the development of a "formulation" with the choice of ingredients, and their respective proportion; the amount of sugar, aroma, taste, and color. Phoenix dactylifera L. have a vital therapeutic properties, it represents an inexhaustible source of bioactive compounds such as polyphenols. So the objective of the present study is to formulate new dairy desserts with date syrup and powder (by-products from common date fruits) as a sweetener-ingredient in order to substitute sugars. How to cite this article: Djaoud K, Boulekbache-Makhlouf L, Yahia M, et al. Dairy dessert processing: Effect of sugar substitution by date syrup and powder on its quality characteristics. J Food Process Preserv. 2020;44:e14414.

Background: In Algeria, important quantities of secondary date variety (Phoenix dactylifera L.) are generated in each campaign; their chemical composition is similar to that of commercial dates. The present work aims to valorize this common date variety (Degla-beida) which is often poorly exploited. Methods: In this context, we tried to prepare syrup from the secondary date variety and evaluate the effect of conventional extraction (CE) or water bath extraction (WBE) and alternative extraction (microwaves assisted extraction (MAE) and ultrasound-assisted extraction (UAE)) on its total sugar content (TSC), using response surface methodology (RSM). Then, the analysis of individual sugars was performed by high performance liquid chromatography (HPLC). Results: Maximum predicted TSC recoveries under the optimized conditions for MAE, UAE and CE were 233.248 ± 3.594 g/l, 202.889 ± 5.797 g/l and 233.535 ± 5.412 g/l, respectively, which were close to the experimental values: 233.796 ± 1.898 g/l; 202.037 ± 3.401 g/l and 234.380 ± 2.425 g/l. HPLC analysis revealed high similarity in the sugar composition of date juices obtained by MAE (60.11% sucrose, 16.64% glucose and 23.25% fructose) and CE (50.78% sucrose, 20.67% glucose and 28.55% fructose), although a large difference was detected for that obtained by UAE (0.00% sucrose, 46.94% glucose and 53.06% fructose). Conclusion: Microwave-assisted extraction was the best method for the preparation of date syrup with an optimal recovery of total sugar content. However, ultrasound-assisted extraction was the best one for the preparation of date syrup with high content of reducing sugars.

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Date fruits have vital therapeutic properties, in the way that they represent an inexhaustible source of bioactive compounds such as polyphenols. Therefore, the objective of this work was to evaluate the phytocomposition by High Performance Liquid Chromatography (RP-HPLC-PAD-ESI-MS/MS) of the optimized microwaveassisted extraction (MAE) phenolic extract by using the response surface methodology (RSM) compared to the ultrasound-assisted and conventional extractions (UAE and CE), and to test its antioxidant activity in vitro. The resulting regression model indicated that a quadratic polynomial model was best suited for the spectrophotometrically determined total phenolics. The maximum total phenolic content, TPC, (4.27±0.09 mg GAE/g DW) was obtained with a 50% (v/v) ethanol's concentration, a 700 W microwave power and an extraction time of 2.42 minutes. HPLC analysis revealed the presence of organic sugars and acids, nucleoside, carotenoids, proanthocyanidins, lignans, flavonols, flavones, saponin and sterol glucosides. The MAE phenolic extract showed 58.72±0.29% DPPH radical scavenging activity and a 1.88±0.09 mg AscAE/mL reducing power.

The present study aims to optimize the extraction of phenolics by microwave-assisted extraction (MAE) using the response surface methodology (RSM), from Lemon verbena leaves. The optimized extract was tested for its antioxidant activity using two methods (DPPH and reducing power) and its antibacterial efficiency by using disk diffusion assay and broth microdilution, against two Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) and two Gram-positive (Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC 6633) strains. Under the optimized conditions (40% (v/v): of ethanol concentration, 188 s of irradiation time, 600 W of microwave power and 1:40 g/mL of solid-to-liquid ratio) the total phenolic content (TPC) was 67.87±1.61 mg GAE/g DW. The IC50 of the extract was 139.65±1.44 µg/mL and 56.60±2.79 µg/mL for DPPH inhibition and reducing power, respectively. The best antibacterial activity was shown by the extract obtained by MAE with lower MBC (1.56 to 18.75 mg/mL) and MBC/MIC ratio. Lemon verbena extract can be used as an ingredient in cosmetics, food supplements and herbal medicinal products due to its interesting biological properties.