Protein-enriched soups as a practical strategy to meet protein needs in older adults

Soups are routinely included in home-delivery meals for the elderly, making them an effective vehicle for increasing protein intake in this population at risk of malnutrition. Adequate protein and essential amino acids, particularly branched-chain amino acids (BCAAs), are critical for preserving muscle mass in this group, prompting this study to examine whether enriching vegetable-based soups could improve their nutritional quality. Five soups (pumpkin, lentil, chickpea, mushroom, and split pea) were enriched with animal-derived ingredients, including ham, La Vache qui rit® processed cheeses, and egg yolk, or with spirulina as an alternative protein source. Protein content, free iron, and phytic acid were quantified, and a static in-vitro digestion model adapted to older adult gastrointestinal conditions was applied under fixed-volume conditions to assess apparent protein hydrolysis through peptide and free amino acid release, as well as iron bioaccessibility. Protein content increased in all soups after enrichment, although the magnitude of improvement depended strongly on the soup base. After in-vitro digestion, enriched soups generally showed higher soluble protein-derived fractions and higher concentrations of free essential amino acids, including BCAAs. Egg yolk and spirulina produced the greatest increases in bioaccessible BCAAs, while spirulina-enriched soups showed the highest levels of bioaccessible free iron. In contrast, lentil soup, characterized by high phytic acid content, exhibited lower iron bioaccessibility, suggesting that inhibitory matrix components may limit the effectiveness of enrichment. Overall, these findings show that both the enrichment ingredient and the food matrix modulate nutrient release during digestion, and that selected animal-derived ingredients and spirulina can improve the nutritional potential of vegetable-based soups intended for older adults