Optimization of plum marmalade formulation containing date syrup using constrained mixture design

Marmalade is a processed product of some plant organs such as fruit, flower, fruit peel and tuber in which the plant parts used are small and well homogenized. Sugar is used as a sweetener in the preparation of marmalade. In this study, the use of date syrup as a substitute for sucrose used in marmalade formulation was studied. The constrained mixture design was used to achieve the optimal formulation and the effect of sugar substitution with date palm syrup on properties of marmalade was studied. The ingredients used in the formulation were plum paste (35-65%), sugar syrup (0-65%) and date syrup (0-65%). Ten formulas were produced based on the constrained mixture design and their physical, chemical and sensorial properties were investigated. The results showed that plum paste had the greatest effect on increasing the viscosity and total acidity of marmalade, while total soluble solids decreased with increasing the amount of plum paste in the formulation. The L* index of the samples decreased with increasing date syrup and plum paste and the redness of marmalade increased with increasing plum paste. Sensory evaluation of the produced formulations showed that the increase in plum paste increased the consistency, spreadability, color and overall acceptance, while the sweetness and taste and flavor were more affected by the increase in date syrup. Optimal formulation was obtained in the ratios of 58% plum paste, 12% sugar syrup and 30% date syrup and in the optimal formulation the total acidity, total phenolic compounds, and viscosity of marmalade at 20 °C were equal to 2.07 g citric acid/100 g, 112.4 mg gallic acid/100 g, and 3961 cp, respectively.