**4. Influence of other factors on bioavailability of bioactive peptides**

they all contained the tripeptide IPP and exerted a hypertensive effect [65–67]. Another study demonstrated the effect of the time of cheese ripening on the ACE-inhibitory activity. Cheese was produced with a mixture of 12 different strains and showed an increase of the inhibitory effect during ripening as long as a certain level of proteolysis was not exceeded [68]. In 10 Swiss cheese types, the ACE-inhibiting peptides V-P-P and I-P-P were quantified. They detected contents of 19.1 mg/kg to 182.2 mg/kg depending on the cheese type that shows the huge effect of different processing ways probably via different lactic acid bacteria [69]. Also, the application of new techniques like next-generation sequencing that reveals the whole genome of bacteria strains might help to select promising strains with specific protease expressions. It was also demonstrated that fermentation reduced the allergenic potential of α-lactalbumin and β-lactoglobulin [41, 42]. The peptides that result after fermentation and enzyme hydrolysis might remain susceptible to further hydrolysis as long as the process goes on. This might lead to a decrease of bioactive function of these peptides. More important is also the stability of the generated peptides. They might be degraded by the digestive enzymes and result in zero activity in the body. The stability versus the action of gastric and pancreatic enzymes has to be tested beforehand. Another problematic point is that the microbial fermentations have to be reproducible [8]. Fermentation with known and established lactic acid bacteria cultures is a great strategy to enrich certain bioactive peptides with a special functionality. This would be a possibility to enhance a bioactive function in a natural way with a minimal processing approach that meets the interests of the consumer. The functionality and bioavailability of bioactive

The use of milk-clotting enzymes and digestive enzymes to produce bioactive peptides is another processing approach. However, most of the resulting peptides had a bitter taste [7]. Membrane-separation technique is applied to enrich peptides with a specific molecular weight [3]. It was also shown that hydrolysed infant formulas show a different peptide profile compared to the standard formulas assuming that infants fed hydrolysed formulas might obtain bioactive peptides that promote other bioactive functions than the ones provided by

Homogenization applies pressure (14–18 MPa) and shear stress that alter the protein structure and improve the digestibility [52]. Use of ultra-high pressure homogenization with pressure around 400 MPa results in more severe protein denaturation [71]. Application of high hydrostatic pressure processing increased digestibility of β-lactoglobulin with pepsin with increasing pressures (400–800 MPa) [72]. Penas et al. also combined high hydrostatic pressure processing with selected food-grade proteases and demonstrated a reduction in antigenicity of the whey protein hydrolysates that can be used as ingredients of hypoallergenic infant formulae [73]. Ultrasound treatment is a non-conventional processing technique that can denature α-lactalbumin and β-lactoglobulin. In whole milk compared to skim milk, the denaturation was stronger and heat addition even increased this effect [74]. A very soft technology is membrane filtration that enables to separate proteins in their native state. This technology only enables a fractionation of different milk components and does not alter the protein struc-

peptides generated via fermentation has to be more clarified.

118 Technological Approaches for Novel Applications in Dairy Processing

ture as such, and it only influences the milk composition.

the standard formulas [70].

**3.4. Physical treatment**

Not only processing can influence the profile of bioactive peptides. Also, other external factors can influence protein digestion and therefore the bioavailability and generation of bioactive peptides. It is important to consider the effect of the food matrix and meal composition on digestion. For example, the addition of inulin to the dairy product can influence digestion and peptide bioavailability [75]. Also, proteins can form complexes with polyphenols, etc. that could lower protein bioavailability [76]. Furthermore, internal factors can influence the peptide profile. Children and the elderly have different enzyme activities and therefore the digestion enzymes will act slightly different and change the peptide profile [77, 78]. Genetic variations in people for example enzyme deficiencies or changes in the composition of the digestion juices due to different transporter expression can have an impact. The action of digestion enzymes depends on daytime, age and on *Helicobacter pylori* infection [79]. Also for a lot of other special physiological states, certain diseases and so on, the enzyme activity is affected and might therefore result in a different bioactive peptide bioavailability. It is very important to consider all the factors that can affect peptide bioavailability in the target group of the product.
