Artificial neuronal networks (ANN) to model the hydrolysis of goat milk protein by subtilisin and trypsin.

The enzymatic hydrolysis of milk proteins yield final products with improved properties and reduced allergenicity. The degree of hydrolysis (DH) influences both technological (e.g., solubility, water binding capacity) and biological (e.g., angiotensin-converting enzyme (ACE) inhibition, antioxidation) properties of the resulting hydrolysate. Phenomenological models are unable to reproduce the complexity of enzymatic reactions in dairy systems. However, empirical approaches offer high predictability and can be easily transposed to different substrates and enzymes. In this work, the DH of goat milk protein by subtilisin and trypsin was modelled by feedforward artificial neural networks (ANN). To this end, we produced a set of protein hydrolysates, employing various reaction temperatures and enzyme/substrate ratios, based on an experimental design. The time evolution of the DH was monitored and processed to generate the ANN models. Extensive hydrolysis is desirable because a high DH enhances some bioactivities in the final hydrolysate, such as antioxidant or antihypertensive. The optimization of both ANN models led to a maximal DH of 23·47% at 56·4 °C and enzyme-substrate ratio of 5% for subtilisin, while hydrolysis with trypsin reached a maximum of 21·3% at 35 °C and an enzyme-substrate ratio of 4%.

Production of goat milk protein hydrolysate enriched in ACE-inhibitory peptides by ultrafiltration.

A global process for the production of goat milk hydrolysates enriched in angiotensin converting enzyme (ACE) inhibitory peptides was proposed. Firstly, the protein fractions (caseins and whey proteins) were separated by ultrafiltration through a 0·14 µm ceramic membrane. The casein fraction obtained in the retentate stream of the above filtration step was subsequently hydrolysed with a combination of subtilisin and trypsin. After 3 h of reaction, the hydrolysate produced presented an IC50 of 218·50 µg/ml, which represent a relatively high ACE inhibitory activity. Finally, this hydrolysate was filtered through a 50 kDa ceramic membrane until reaching a volume reduction factor of 3. The permeate produced presented an improvement of more than 30% in the ACE inhibitory activity. In contrast, the retentate was concentrated in larger and inactive peptides which led to a decrease of more than 80% in its inhibitory activity. The process suggested in this work was suitable to obtain a potent ACE inhibitory activity product able to be incorporated into food formulas intended to control or lower blood pressure. Moreover, the liquid product could be easily stabilised by spray dried if it would be necessary.

Optimisation of the hydrolysis of goat milk protein for the production of ACE-inhibitory peptides.

Goat milk protein was hydrolysed with subtilisin and trypsin. As input variables, temperature was assayed in the interval 45-70 °C for subtilisin and 30-55 °C for trypsin, while the enzyme-substrate ratio varied from 1 to 5%. The effect of the input variables on the degree of hydrolysis and ACE-inhibitory activity (output variables) was modelled by second order polynomials, which were able to fit the experimental data with deviations below 10%. The individual maximum values of the degree of hydrolysis and the ACE-inhibitory activity were found at conflicting conditions of temperature and enzyme-substrate ratio. Since such maximum values could not be reached simultaneously, a bi-objective optimisation procedure was undertaken, producing a set of non-inferior solutions that weighted both objectives.