A model gel of whey protein isolate (WPI) was prepared by cold gelation with calcium. This system was modified by the addition of free cysteine residues (Cys) at different steps of the process. The WPI cold-set gels obtained were then subjected to heat treatment at 90°C. First, the effect of Cys addition on the heat-induced aggregation of WPI was studied through Atomic Force Microscopy (AFM) and infrared spectroscopy (ATR-FTIR), while Cys' effect on cold gelation was observed by AFM, Confocal Laser Scanning Microscopy (CLSM) and oscillatory rheology (amplitude sweeps). The impact of heating on the microstructure and the viscoelastic properties of the WPI cold-set gels were finally investigated through several techniques, including DSC, ATR-FTIR, CLSM, cryo-SEM, and rheological measurements (temperature sweeps). When added during the first step of cold gelation, Cys modified heat-induced aggregation of WPI, resulting in the formation of a denser gel network with a fractal dimension (Df) of 2.8. However, the addition of Cys during the second step of cold gelation led to the formation of highly branched clusters of WPI and a looser gel network was observed (Df = 2.4). In this regard, the use and limitations of oscillatory rheology and the “Kraus model” to determine the Df of WPI cold-set gels was discussed. The viscoelastic properties and the microstructure of the WPI cold-set gels were irreversibly modified by heating. Gels were stiffer, more brittle, and coarser after heat treatment. New disulfide bonds and calcium bridges formed, as well as H-bonded β-sheets, all contributing to the formation of the final gel network structure.

The new static in vitro digestion model for older adults (>65 y.) proposed by the INFOGEST international consortium was implemented for the 1^st time to investigate the digestion of 2 high-protein dairy products and compared with the standard protocol.

The demographic shift towards an aged population calls for targeted nutrition strategies to support healthy aging and bridge the gap between life expectancy and a healthy life span. Older adults face various nutritional deficiencies, particularly in protein, vitamins (B12, D), minerals (calcium, iron), and dietary fiber. This work delves into the EAT4AGE project efforts that strategically aimed to develop age-oriented food products (European Joint Programming Initiative “A Healthy Diet for a Healthy Life” JPI HDHL). Currently, manufacturing of age-tailored food products presents significant complexities, from challenges of commercialization to the generation of acceptable and palatable food choices. As a first step, a literature-based comprehensive checklist has been developed to facilitate product development. This tool provides an integrated approach, ensuring that all critical aspects of product development are addressed systematically. Secondly, we describe the application of the tool in the development of a series of products, such as plant-based protein-rich cereals, reformulated dairy products, processed meat, and enriched spreads; all combining high nutritional values with adaptations to the physiological and sensory needs of seniors. Overall, this work offers insight into the current needs of seniors and a tool for product development that can be utilized for prospective product development, such as the ones detailed herein. Thus, the EAT4AGE hopes to set an example that will stimulate the fabrication of effective, well-received nutritional solutions, ultimately improving health outcomes for older adults.