Plant protein-based fibrous structures have recently attracted attention because of their potential as meat replacer formulations. It is, however, unclear how the process conditions and fortification with micronutrients may affect the chemical stability of such products. Therefore, we aimed to investigate the effects of process conditions and the incorporation of iron (free and encapsulated) on protein oxidation in a soy protein-based fibrous product. First, the physicochemical stability of iron-loaded pea protein particles, used as encapsulation systems, was investigated when exposed to 100 or 140 °C. Second, protein oxidation was measured in the iron-fortified soy protein-based fibrous structures made at 100 or 140 °C. Exposure to high temperatures increased the carbonyl content in pea protein particles. The incorporation of iron (free or encapsulated) did not affect carbonyl content in the fibrous product, but the process conditions for making such products induced the formation of carbonyls to a fairly high extent.

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Process conditions that are applied to make structured soy-protein-based food commonly include high temperatures. Those conditions can induce protein oxidation, leading to a decrease in their susceptibility to proteolysis by digestive enzymes. We aimed to investigate the effects of thermomechanical processing on oxidation and in vitro gastric digestion of commercial soy protein ingredients. Samples were sheared at 100 to 140 °C and characterized for acid uptake, carbonyl content, electrophoresis, and surface hydrophobicity. The enzymatic hydrolysis was determined in simulated gastric conditions. Protein ingredients were already oxidized and showed higher surface hydrophobicity and hydrolysis rate compared with those of the processed matrices. However, no clear correlation between the level of carbonyls and the hydrolysis rate was found. Therefore, we conclude that gastric digestion is mostly driven by the matrix structure and composition and the available contact area between the substrate and proteolytic enzymes.

BACKGROUND Worldwide iron deficiency in diets has led to a growing interest in the development of food‐compatible encapsulation systems for soluble iron, which are able to prevent iron's undesirable off‐taste and pro‐oxidant activity. Here, we explore the use of double emulsions for this purpose, and in particular, how the lipophilic emulsifier (polyglycerol polyricinoleate, PGPR) concentration influences the physicochemical stability of water‐in‐oil‐in‐water (W 1 /O/W 2 ) double emulsions containing ferrous sulphate in the inner water droplets. Double emulsions were prepared with sunflower oil containing 10 to 70 g kg −1 PGPR in the oil phase, and were monitored for droplet size distribution, morphology, encapsulation efficiency (EE) and oxidative stability over time. RESULTS Fresh double emulsions showed an initial EE higher than 88%, but EE decreased upon storage, which occurred particularly fast and to a high extent in the emulsions prepared with low PGPR concentrations. All double emulsions underwent lipid oxidation, in particular those with the highest PGPR concentration, which could be due to the small inner droplet size and thus promoted contact between oil and the internal water phase. CONCLUSION These results show that a too high PGPR concentration is not needed, and sometimes even adverse, when developing double emulsions as iron encapsulation systems. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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