The choice of the substitute formula for an individual child with cow’s milk allergy should be based on patients characteristics (age and symptoms), and formula’s properties, firstly documented hypoallergenicity and nutritional adequacy [25,26].
However, it is important to also consider formulas acceptance that interfere with compliance in clinical practice.
In this regard, palatability of hydrolysed formulas has been poorly investigated. This study focused primarily on the flavor and the relative palatability of hydrolysed formula and aminoacid based formulas. Moreover, it aimed also to investigate the correlation between hydrolysed formulas constituents, other than peptides, and palatability.
Our results showed significant differences of flavor of the different extensively hydrolysed formulas, with casein or whey as a nitrogen source and between eHF and amino acid based formulas. Overall, whey eHFs were judged of better palatability than casein eHF and the AAFs (p < 0.05).
It is noteworthy that whey eHF have been judged different among them for sensory attributes and overall palatability judgement. The sensory attributes that most influenced the overall judgement of palatability were taste and aftertaste, respectively.
The results also suggest that palatability improved with the increasing levels of lactose and alfa linolenic content. Concerning lactose, from a nutritional standpoint, it has several beneficial effects. Metabolic studies employing isotopic techniques in humans showed that the presence of lactose enhances the absorption and the retention of the calcium [27] and other minerals, such as magnesium and zinc [28].
Lactose naturally influences the intestinal microflora as it selectively promotes the development of putative beneficial bacteria population in the lower part of the gut [29]. In spite of the above mentioned several and well-known lactose beneficial effects, lactose continues to be excluded from the majority of the cow’s milk based-hydrolysed formulas.
Adverse reactions to lactose in cow’s milk allergy are not supported in the literature, and complete avoidance of lactose in CMA is no longer warranted. EhF containing purified lactose are now available and have been found safe and effective in the treatment of CMA [30,31].
With regard to the linolenic acid, our results agree with data on animals models that demonstrated that linoleic solutions are preferred over oleic acid and linolenic acid is preferred over linoleic acid [32].
The physiological and nutritional implications of fat sensing include gastric lipase secretion, modulated the gastro-intestinal transit, pancreatic exocrine secretions, gut hormone release, mobilization of stored lipid from enterocytes, pancreatic endocrine secretion and altered lipoprotein lipase activity [33]. Through the above activities, oral fat exposure may influence appetitive responses, food intake, nutritional status and disease risk.
Therefore, fatty acids content in special formulas needs further investigation for the all the above mentioned aspects.
The novelty of our study was to investigate the correlation between hydrolysed formulas constituents, other than peptides, and palatability.
The strenght of this study is the large number of panelists (>50) to get statistically valid data [34].
The main limitation of this study is that it was performed in young adults.
Although there are differences in taste preference between infants and adults [35], a number of studies have reported that human infants are able to discriminate different taste qualities from birth and they respond to the stimuli, especially sweet and bitter with a pattern of responses similar to those seen in adults [36].
The preference of infants and young children for sweet and aversion for bitter and sour is similar to that of most occidental adults [37].
The main differences between adults and infants are the higher preference for sweet-tasting ( meaning that infants generally prefer higher concentrations of sweet solutions than adults) and greater aversion for bitter [38,39], partly due to genetic variations and cultural differences [40].
However, it is important to point out that as preferences for taste stimuli is generally more influenced by innate factors, preferences for flavor compounds recognized by the sense of smell is more highly influenced by learning, especially early in life [41].
Experimental studies by Mennella [42] demonstrated that infants exposed before 4 month of age to hydrolysed formulas, characterized by a bitter tastes and unpleasant odor volatiles , were more wiling to accept them than older infants and the acceptance pattern that infants develop is specific to the flavor profile experienced in the first months of age [43].
However, considering that feeding with hydrolysed formulas start not infrequently after four months of age, it is as much as real that the poor palatability of hydrolysed formulas continues to be a cause of poor compliance in clinical practice [18].
Another limitation was that the ingredients of the formulas have not been independently manipulated.
Within these limitations, this study highlights that a broad range of flavor exists among the hydrolysed formulas, which seems to depend no only on the peptides content and molecular weight but also on other constituents, e.g. lipids and lactose content.