Development of biscuits enriched with phytosterols and fortified with iron and calcium using casein hydrolysates as carriers

Abstract

Iron and calcium deficiencies are a health problem affecting great part of the world’s population. Considering that casein phosphopeptides (CPP) have the ability to complex cations and enhance their solubility in intestinal conditions, and taking into account that biscuits are a widely consumed food product more attractive than pharmaceutical supplements, the main objective of the present thesis was to develop biscuits fortified with iron and calcium vehiculated with casein hydrolysates containing CPP, in order to increase iron and calcium availability. Additionally, phytosterols were also included due to their hypocholesterolemic effect. For this purpose short dough biscuit formulations were prepared with the following ingredient combinations: casein hydrolysates with phytosterols, casein hydrolysates with ferrous bisglycinate, and casein hydrolysates with calcium lactate, and different issues were addressed. On one way, the fortified biscuits were studied from a practical point of view assessing the effect of the new ingredients on the sensory and technological properties of the biscuit, the ratio between the casein hydrolysate and iron or calcium that provides high solubility, the scale-up of the production, and the self-life of the final product. Furthermore, the bioaccessibility of iron and calcium from the fortified biscuits was evaluated after in vitro digestion, as well as more basic aspects related with the rheological changes caused by the casein hydrolysates on biscuit dough, and the chemical characterisation of the complex formed between calcium and the peptides from the casein hydrolysates. The results showed the feasibility of producing short dough biscuits fortified with esterified phytosterols as recognised cholesterol lowering ingredients, and casein hydrolysates as carriers for iron or calcium keeping acceptable levels of the sensory quality properties. The incorporation of casein hydrolysates provided a better oxidative stability than the biscuits without them and no prooxidant effect of iron was observed, but the characteristic sensory properties given by the iron and calcium ingredients, specifically, metallic and spicy flavours respectively, were intensified during storage. The in vitro digestion experiments performed with biscuits formulated with the best ratio of casein hydrolysate and iron selected showed that the use of casein hydrolysates with an iron source of high availability such as ferrous bysglicinate did not increase iron solubility in the intestinal tract, but it was significantly increased when an inorganic form of low available iron such as ferrous sulfate was used. In the case of the biscuits formulated with the casein hydrolysates or the whole casein and calcium lactate, the in vitro digestion experiment showed similar calcium solubility than the biscuits without hydrolysates or casein, but a higher fraction of chelated calcium was obtained. The rheological study of the effects of the casein hydrolysates on biscuit dough reflected that the gluten network developed in bread dough is not completely formed in the case of biscuit short dough, and allowed to propose reasons for the overspreading of dough pieces occurred during baking in the presence of high content of casein hydrolysates, which were related to the role of some peptides as surfactants weakening the structure, presenting thus lower resistance to flow by heating, and the delay of the heat-induced protein aggregation responsible for the stopping the dough spreading. Finally, the chemical study of the complex formed between calcium and the casein hydrolysate considered as a whole, confirmed the role of phosphate on calcium binding and, consequently, the importance of casein phosphopeptides in calcium complexation, but also showed the participation of the carboxylate group in calcium binding, what suggests the contribution to calcium solubilisation of those peptides containing glutamate and aspartate residues. The calcium binding constant calculated for the casein hydrolysate was found to be dependent on the ratio between calcium and casein hydrolysate, suggesting a change in the conformation of the peptides involved in complexation after calcium addition that leads to a higher affinity in the secondary calcium binding sites of CPP. Additionally, chloride anion was found to promote the calcium binding ability of casein hydrolysates which might be related to the interaction with different peptides by hydrogen bonds.