Abstract
Plum skin, a by-product of industrial plum juice production, is rich in phenolic bioactives, functional compounds, and dietary fibers. These compounds support health, while the fibers may also act as structuring agents in food processing. This study investigated the structuring properties of lyophilized plum skin (LPS) in functional plum spreads produced in laboratory (F-LS) and semi-industrial (F-IS) environments, compared to a control spread (CS). Textural and rheological properties were analyzed through penetration, spreadability, flow, and dynamic oscillatory tests. Total, soluble, and insoluble dietary fibers (TDF, SDF, and IDF) in LPS and plum purée (PP) were measured using the enzymatic gravimetric method, and pectic substances contents were quantified using the colorimetric carbazole method. Fourier transform infrared spectroscopy confirmed the presence of polysaccharides and pectins in LPS. LPS had higher TDF, SDF, and IDF compared to PP, with TDF in LPS at 38.98 ± 0.52 g/100 g d.m. and IDF as the predominant fraction. The pectin content in LPS was 0.73 ± 0.03 g/100 g d.m., and water retention capacity ranged from 3.63 to 3.86 g/g depending on temperature (room, 50, and 82 °C). Incorporating LPS into the F-IS spread significantly increased all textural and rheological parameters, with TDF three times higher (6.69 g/100 g) compared to CS. All samples exhibited viscoelastic gel-like behavior, and LPS was a statistically significant structuring agent in both functional spreads compared to CS.