Abstract
Background: Extruded cereal products are promising matrices for developing functional foods; however, incorporating plant-derived functional ingredients before extrusion exposes heat-sensitive constituents to severe thermomechanical conditions. Post-extrusion enrichment provides an alternative strategy for incorporating plant-derived components while avoiding their direct exposure to the high-temperature extrusion stage. Sea buckthorn (Hippophae rhamnoides L.) and hawthorn (Crataegus L.) are particularly attractive ingredients because of their naturally occurring phenolic compounds, carotenoids, organic acids, vitamins, and other bioactive constituents. Objective: This study aimed to evaluate the effects of post-extrusion application of sea buckthorn and hawthorn syrups on the physicochemical, moisture-related, microstructural, colorimetric, microbiological, and sensory properties of extruded cereal slices (ESC). Methods: Concentrates of wild sea buckthorn and hawthorn were obtained by ultrasound-assisted extraction and incorporated into syrups, which were subsequently applied to extruded cereal slices. Twelve samples comprising six untreated controls and six matched post-extrusion-treated samples based on rice, buckwheat, corn, wheat, and their combinations were investigated. Moisture content, water activity (a_w), ash content, rehydration ratio, water-holding capacity (WHC), oil-holding capacity (OHC), color characteristics, microstructure, microbiological quality, and sensory properties were determined. Data were evaluated using analysis of variance (ANOVA), principal component analysis (PCA), hierarchical cluster analysis (HCA), linear discriminant analysis (LDA), and Pearson correlation analysis. Results: Post-extrusion syrup application significantly modified the physicochemical and structural characteristics of ESC. Treated samples generally showed increased moisture content and a_w, decreased lightness (L*), and increased browning index (BI) and color intensity compared with untreated controls. Nevertheless, a_w remained below 0.60 in all samples, and the investigated microbiological indicators were below the method detection limit. Syrup-treated samples exhibited lower rehydration ratios, indicating reduced water penetration into the matrix, while scanning electron microscopy (SEM) revealed a denser microstructure with partial filling of surface pores and interconnected voids. PCA showed that the first two principal components (PC1 and PC2) explained 70.6% of the total variance (47.8% and 22.8%, respectively), while discriminant analysis clearly differentiated untreated and post-extrusion-treated samples. Overall sensory acceptability remained high (4.19–4.56 on a 5-point scale), with several syrup-treated formulations receiving the highest scores. Conclusion: Post-extrusion application of sea buckthorn and hawthorn syrups significantly modified the physicochemical, colorimetric, hydration, and structural properties of extruded cereal slices while maintaining a_w below 0.60 and high sensory acceptability under the conditions studied. These findings support post-extrusion syrup application as a technological strategy for producing plant-enriched cereal foods. The present study does not establish biological efficacy or health benefits; further research is required to determine bioactive retention and bioaccessibility, storage stability, consumer acceptance, and potential health-related effects. Novelty of the Study: This study systematically evaluates sea buckthorn- and hawthorn-based syrups as a post-extrusion modification step applied after formation of the porous cereal matrix. In contrast to conventional pre-extrusion fortification, this approach separates matrix formation from plant-ingredient application. The integration of SEM, physicochemical and color measurements, sensory analysis, and multivariate statistical methods provides a mechanistic link between syrup deposition, partial pore filling, altered water accessibility, and matrix-dependent changes in product properties. Keywords: functional foods; extruded cereal slices; sea buckthorn; hawthorn; post-extrusion enrichment; plant-based syrups; water activity; microstructure; physicochemical properties