Physical, structural and technological properties of ball-milled starches and their application to obtain innovative gels

Starch is an abundant natural biopolymer derived from cereals, tubers, and other plant sources. Despite its availability, the direct utilization of native starch in food systems is constrained by its limited cold‑water solubility, slow hydration and swelling kinetics, poor thermal stability, and pronounced retrogradation during storage. To address these intrinsic limitations, a range of chemical, enzymatic, and physical modification strategies have been developed to enhance its techno‑functional properties and broaden its applicability in food formulations. Such modifications typically enhance solubility, swelling capacity, thermal tolerance, and water‑ and oil‑binding properties, while concurrently reducing granule crystallinity. Among these approaches, physical modification techniques have gained significant attention due to their environmental sustainability, operational simplicity, and cost‑effectiveness. Ball milling (BM), commonly used in both food and non‑food sectors for particle‑size reduction, has recently emerged as an environmentally friendly technology for the structural modification of biopolymers. The mechanical forces generated during milling such as shear, impact, and friction disrupt molecular organization without the use of chemical reagents, making BM (in particular dry milling) a sustainable and efficient method for tailoring biopolymer functionality. The PhD thesis investigate the effect of ball milling (BM) on the physical, structural and technological properties of starches of different origins and their application to obtain innovative structures. The starches studied were corn, high amylose corn, potato, tapioca and wheat starch. This PhD project comprised two main phases. The first phase aimed to systematically investigate the role of the origin (corn, potato, tapioca and wheat) and of the process conditions (BM time (T), rotation speed (S), ball-starch- weight ratio (BSW)) on the morphological, microstructural (using the SEM), physical and techno-functional (e.g., water holding capacity (WHC), oil holding capacity (OHC), cold water solubility (CWS) and swelling power (SP)) properties of native starch. The second phase focused on the application of the BM modified starches (corn, high amylose corn, potato and wheat) in the development of porous structures. Results of the first part showed that generally, techno‑functional properties such as WHC, OHC, CWS, and SP increased markedly with more intensive BM conditions, particularly longer milling times. However, excessive milling significantly reduced starch functionality ascribable to extensive damages upon granule structure. Starches from different botanical origins responded differently to ball‑milling parameters (T, S, BSW), reflecting their inherent structural differences. Among the processing variables evaluated, rotation speed exerted the strongest influence on both corn and potato starch properties, while BSW and T had comparatively minor effects. Potato starch exhibited greater susceptibility to BM treatment, showing more pronounced changes than corn starch due to the different granule size and morphology. BM starches showed lower gelatinization enthalpy and onset temperature which led to the formation of weaker gel (lower G′) compared to their native counterparts. Prolonged milling also altered granular morphology, promoting aggregate formation. The second phase focused on the application of the BM modified starches (corn, high amylose corn, potato and wheat) in the development of porous structures. To this aim native and BM starch were used to obtain thermoset hydrogels, cryogels (by freeze-drying) and aerogels (by supercritical CO2). In the case of aerogels and cryogels, physicochemical properties of (e.g., volumetric shrinkage, densities (bulk and skeletal), porosity, water absorption capacity, surface area and pore diameter) were determined. Aerogels resulted being mesoporous (>20 nm), while cryogels exhibited microporosity (< 250 µm). BM aerogels showed higher surface area which correlated with higher porosity and reduced bulk density.