IMPACT OF MILK PROCESSING ON MINERAL BIOACCESSIBILITY UNDER SIMULATED ELDERLY DIGESTIVE CONDITIONS

Aging is associated with progressive physiological changes in the human body, with osteoporosis being the most prevalent bone disorder, characterized by low bone mass and reduced skeletal strength, leading to increased bone fragility. Within this context, milk is a major source of calcium (Ca) and magnesium (Mg). However, processing steps such as heat treatment and homogenization may alter the physicochemical properties and interactions of milk components, potentially affecting their digestion, which is already altered by aging, implicating their bioaccessibility. Hence, this study evaluated the effect of thermal processing and homogenization on Ca and Mg bioaccessibility under simulated elderly digestive conditions. Raw milk was subjected to combinations of homogenization (two-stage, 25 MPa), pasteurization (75°C/15s), and UHT treatment (140°C/3s), generating six experimental groups: raw milk, homogenized raw milk, pasteurized milk, homogenized pasteurized milk, UHT milk, and homogenized UHT milk. Samples were digested using the INFOGEST protocol adapted for the elderly, and total and soluble Ca and Mg concentrations were determined by flame atomic absorption spectrometry (FAAS). Data were analyzed by factorial ANOVA. Heat treatment affected total Ca content, with UHT milks presenting the lowest total Ca (85.55mg/100g), followed by pasteurized (92.65mg/100g) and raw milks (91.97mg/100g), with no significant differences between the latter two. A similar pattern was observed for total Mg, with UHT milks (7.49mg/100g) displaying lower total Mg than raw milks (7.95mg/100g), while pasteurized milk (7.94 mg/100 g) did not differ from the other two. This finding may be attributed to milk fouling during more intense thermal processing, a phenomenon linked to the thermal stability of mineral salts. Regarding Ca bioaccessibility, homogenized milks exhibited higher values (24–28%) than non-homogenized milks (7–8%), given that homogenization directly affected Ca release from the milk matrix (p<0,0001). These results relate to changes induced by homogenization in the structure and composition of the fat globule membrane, altering interactions among lipids, proteins, and digestive enzymes. During intestinal digestion, released long-chain fatty acids (LCFAs) accumulate at the interface, limiting lipase access. Under near-neutral pH conditions, Ca salts may interact with LCFAs to form insoluble Ca soaps, impairing Ca bioaccessibility. Interfacial modifications resulting from homogenization explain the differences observed in Ca bioaccessibility. Regarding Mg bioaccessibility, thermal processing directly affected Mg release from the milk matrix (p<0,0001). Regardless of homogenization, raw and UHT milks exhibited bioaccessible Mg percentages (20%-41%), whereas pasteurized milks presented significantly higher proportions (44–63%). These results relate to changes induced by heat treatments in protein structure and the equilibrium between serum and colloidal phases, which favor Mg release during gastrointestinal digestion. Overall, homogenization enhanced Ca bioaccessibility, whereas thermal processing dictated Mg release under simulated elderly digestion. Thus, the results indicate that tailoring dairy processing conditions can optimize mineral nutritional efficiency for aging population.