further reduces the allergenicity of many food proteins, most likely by altering the conformation structure of heat-labile proteins and consequently destroying their allergenic epitopes [10]. Microwave treatment (at 200 W for 3 min) increases hydrolysis of β-Lg and bovine whey proteins in comparison with conventional heating and the same proteolytic treatment [11]. High pressure also induces structural changes in (whey) milk proteins, such as denaturation, and enhances accessibility of potentially immunogenic hydrophobic regions to the enzymes and formation of aggregates, which may affect and reduce the allergenic potential of CMPs [12].
Table 1. Effect of different methods hydrolysis on milk proteins
Proteolytic enzymes are even produced during fermentation by certain lactic acid bacteria that fragment epitopes and reduce allergenicity of both β-Lg and Cas [13-15].
Partially and Extensively Hydrolyzed Formulas
There is no general agreement on unique standards to specifically define partially hydrolyzed formula (pHF) and eHF, but the MW and percentage of the peptide fragments are generally used to classify the formulas into pHF or eHF. Both pHF and eHF consist of a wide range of peptide sizes. A pHF contains peptides with a MW generally <5 kDa, ranging from 3 to 10 kDa, with some commercial pHF containing 18% of peptides over 6 kDa [16]; an eHF should contain only peptides that have an MW <3 kDa [17] but usually has more than 90% of peptides <3 kDa, with 1-5% of peptides >3.5 kDa [16]. In contrast, the MW of whole CMP ranges from 14 kDa (α-Lac) to 24 kDa (Cas) and up to 67 kDa (BSA) [7]. The weight of peptides has immune and clinical relevance because the ‘bigger’ the peptides the ‘more allergenic’ they can be. Peptides >6 kDa and predominantly >10 kDa frequently act as allergens [18]. However, allergenic peptides of 3-5 kDa MW have been described more than 20 years ago [19]. For peptides <3 kDa, there is no agreement about the lowest MW cutoff for allergenicity [20]. In vitro assays showed reaction of sera of allergic patients to peptides of estimated MWs of 500-600 Da [21, 22]. Disagreement found in the literature about this issue may be due to the hydrolysis process of proteins used and the sensitivity of patients against the allergen [20].
pHFs are developed with the aim of minimizing the number of sensitizing epitopes within milk proteins, while at the same time retaining peptides with sufficient size and immunogenicity to possibly stimulate the induction of oral tolerance. Because pHF contains large CM peptides that can cause severe reactions in CMA patients, pHF is not recommended for the treatment of CMA [1-3]. eHFs are extensively hydrolyzed in order to destroy allergenic epitopes, maintaining the nitrogen in the form of free amino-acid formulas (AAFs) or very small peptides which are indicated in treatment but can as well be used in prevention. Which type induces the best oral tolerance in infants, pHF or eHF, is still debated. The MW profile of proteins only enables to differentiate protein characteristics of formulas, but does not clearly determine the allergenic properties and clinical response [18].
Because of the different responses to whey or Cas allergens, children who do not tolerate whey-based eHF (eHF-W) may be able to tolerate Cas-based eHF (eHF-C) and the other way round [23].
Commercial HFs vary in protein source (e.g. Cas, whey, soy or rice), method and percentage of hydrolysis, content of β-Lg or other proteins, content of nonprotein components (such as lactose, DHA, nucleotides or probiotics) and osmolarity implying that the immune and clinical ‘results’ of one formula cannot be transferred to another.
Prevention of Allergy
The prevention of allergic diseases is a public health priority in many developed countries due to high morbidity, impaired quality of life, and impressive social and medical costs related to allergy. Tolerance development and allergy risk are influenced by a complex array of factors, including genetics, epigenetic regulation of gene expression, birth and feeding mode, microbial environment, and exposure to environmental toxins or pollutants [24].
Allergy prevention can be directed at three potential stages: primary prevention, which inhibits immune sensitization; secondary prevention, which avoids disease expression subsequent to sensitization, and tertiary prevention, which suppresses symptoms after disease expression [25]. However, tertiary prevention can be considered as early treatment.
Prenatal prevention is complex and multifactorial, and dietetic intervention during pregnancy is not currently substantiated by scientific evidence [2]. Postnatally, dietetic prevention is based on the promotion of breastfeeding and HF with a documented preventive effect for the first months in formula-fed high-risk infants [2, 26].
For infants >4-6 months of age, there are insufficient data to support a protective effect of any dietary intervention regarding the development of atopic disease [2, 17]. A recent study showed that the early introduction of peanuts modulated immune-specific responses and significantly decreased the frequency of the development of peanut allergy among children at high risk for this allergy [4].
Target Population: Who Is the High-Risk Infant?
The risk of atopy is increased to about 1:3 if the parent or sibling is atopic, and 70% if both parents are atopic [26]. Hence, the presence of a positive family history of atopic disease represents the condition to define the newborn baby as at-risk infant. In the literature, this definition varied from infants/children having two allergic parents or relatives [25] to (a more recent one) at least one parent and/or sibling [17] with a documented (history of) allergic disease sometimes also supplemented with an increased cord blood IgE [2]. However, familiar allergy should be doctor diagnosed and not based on self-reported symptoms, as the perceived prevalence of food allergy is far greater than the real occurrence, determining