Three mathematical models, two logistic models (previously published in previous works) and one mechanistic, developed in this work and based on Michaelis-Menten kinetics, were compared to select the most adequate model in describing the angiotensin-converting enzyme (ACE)-inhibitory activity of bioactive peptide mixtures obtained from cheese whey protein. The significance of both the model and its parameters as well as the value of the regression coefficient was used as criteria to select the most adequate model for obtaining the IC(50) values corresponding to each bioactive peptides mixture. The best results were obtained with the Michaelis-Menten-based model because it provided the best fits and in addition the values for its parameters were always significant. As parameters of this model have a physical meaning, it could be used for inhibition-testing experiments in the development of novel bioactive peptides. The results obtained indicated that the peptide mixture derived from the neutrase hydrolysis exhibited strong ACE inhibition activity. The main active peptides were short, with molecular masses below 1 kDa (IC(50) = 40.37 ± 2.66 μg/mL) and represent 38% of the initial protein content in the hydrolysate.

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A one-step anion-exchange chromatography method (NaCl gradient elution on a DEAE Sepharose™ Fast Flow gel column) was developed to purify α-lactalbumin (α-LA) from whey protein isolate. α-LA nearly 100% pure (based on the total protein content) was obtained with a yield of about 39%. Besides pure α-LA, which was the main objective of this work, highly pure β-lactoglobulin was also obtained with a yield of about 59%. The high purity of the obtained α-LA samples allowed its use to synthesise protein nanotubes with excellent gelation properties for their use as food thickeners and bioactive carriers. The samples' purity degree obtained (based on the total protein content) was critical in the formation of proper nanotubes instead of random aggregates, which produced opaque and weak gels, less useful for food applications.

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