In recent years, heightened consumer awareness regarding healthy nutrition an‎d its role in disease prevention has led to substantial growth in the market for functional food products. Among these, protein bars have garnered significant attention in sports regimens, dietary plans, an‎d healthy lifestyles due to their high nutrient density, portability, an‎d convenience of consumption. However, maintaining the physicochemical quality an‎d sensory acceptability of these products during storage remains a major challenge in the food industry. In response to this need, the incorporation of natural compounds rich in bioactive an‎d antioxidant constituents represents an effective strategy for enhancing product stability an‎d nutritional value. This study investigated the effects of combining two valuable natural sources—elderberry extract (Sambucus nigra) an‎d wild persimmon sap (Diospyros lotus)—in protein bar formulations. These compounds, indigenous to various regions of Iran, exhibit high potential for developing functional foods owing to their elevated levels of anthocyanins, polyphenols, natural sugars, an‎d antioxidant components. Twenty-seven treatments containing varying concentrations of these ingredients (1–2% elderberry extract an‎d 10–20% Diospyros lotus) were prepared, an‎d their physicochemical properties (moisture, ash, energy, carbohydrates, an‎d water activity), antioxidant capacity (free radical scavenging activity), structural characteristics (FTIR analysis of protein secondary structures), an‎d sensory attributes were eva‎luated. The results indicated that the addition of these compounds increased moisture content while reducing water activity, thereby contributing to improved shelf life. Furthermore, polyphenols interacted with protein chains, inducing rearrangements in secondary structures: alpha-helix content decreased, whereas beta-turn an‎d intra-molecular beta-sheet contents increased, accompanied by a reduction in inter-molecular beta-sheets. These structural modifications were associated with enhanced texture softness an‎d decreased hardness in the samples. The natural sugars in Diospyros lotus also contributed to mild sweetness an‎d cohesive texture, thereby improving sensory properties. Panelists rated samples containing these compounds as more desirable due to balanced flavor, appealing color, an‎d superior texture. The optimal formulation was determined using response surface methodology based on multiple quality criteria, comprising 0.98% elderberry extract an‎d 19.1% Diospyros lotus concentrate. Subsequently, the stability of this optimized formulation was compared to a control sample over 28 days of ambient storage, with eva‎luations at seven-day intervals. For this purpose, indices such as moisture, texture hardness, peroxide value, browning index, free radical scavenging capacity, an‎d changes in protein secondary structures were subjected to kinetic modeling. Fitting results with various models revealed that the Rational model best described changes in peroxide value an‎d beta-turns, the Gompertz model for moisture, hardness, an‎d free radical scavenging capacity, an‎d the Fourier model for alpha-helices. Overall, the findings of this research demonstrate that the combination of elderberry extract an‎d wild persimmon sap not only enhances the nutritional, physicochemical, an‎d sensory properties of protein bars but also increases their textural stability over time. These compounds, with their multifaceted functions (antioxidant, humectant, structural modifier, an‎d flavor/texture enhancer), can serve as effective agents in developing a new generation of healthy food products, providing a natural an‎d efficacious approach to improving the quality an‎d shelf life of protein bars. These results may open new horizons in functional food formulation an‎d offer significant industrial applications

اميرحسين گلي , امير پورفرزاد

مهدي كديور , مهرنوش جعفري