Validation of a paper‐disk approach to facilitate the sensory evaluation of bitterness in dairy protein hydrolysates from a newly developed food‐grade fractionation system

Abstract

Casein-hydrolysates (NaCaH) are desirable functional ingredients, but their bitterness impedes usage in foods. This study sought to validate a paper-disk approach to help evaluate bitterness in NaCaHs and to develop a food-grade approach to separate a NaCaH into distinct fractions, which could be evaluated by a sensory panel. Membrane filtration generated <0.2-μm and <3-kDa permeates. Further fractionation of the <3-kDa permeate by flash-chromatography generated four fractions using ethanol (EtOH) concentrations of 5, 10, 30 and 50%. As some fractions were poorly soluble in water, the fractions were resolubilzed in EtOH and impregnated into paper-disks for sensory evaluation. Bitterness differences observed in the membrane fractions using this sensory evaluation approach reflected those observed for the same fractions presented as a liquid. The flash-chromatography fractions increased in bitterness with an increase in hydrophobicity, except for the 50% EtOH fraction which had little bitterness. Amino acid analysis of the fractions showed enrichment of different essential amino acids in both the bitter and less bitter fractions. Practical Applications The developed food-grade fractionation system, allowed for a simple and reasonably scaled approach to separating a NaCaH, into physicochemically different fractions that could be evaluated by a sensory panel. The method of sensory evaluation used in this study, in which NaCaH samples are impregnated into paper-disks, provided potential solutions for issues such as sample insolubility and limited quantities of sample. As the impregnated paper-disk samples were dehydrated, their long storage life could also be suitable for sensory evaluations distributed by mail for large consumer studies. The research, in this study, allowed for a greater understanding of the physicochemical basis for bitterness in this NaCaH. As some essential amino acids were enriched in the less bitter fractions, selective removal of bitter fractions could allow for the incorporation of the less bitter NaCaH fractions into food products for added nutritional value, without negatively impacting sensory properties. There is potential for this approach to be applied to other food ingredients with undesirable tastes, such as polyphenols.

Using rejection thresholds to determine acceptability of novel bioactive compounds added to milk-based beverages

“…The bitterness ratings of the hydrolysate samples in water show no significant difference in bitterness between the HMW and the LMW. This was surprising, considering that hydrolysate bitterness is associated with an increased concentration of low molecular weight peptides (Leksrisompong et al, 2010;Murray et al, 2017). However, the large standard deviations of the bitterness ratings of the hydrolysate samples in water highlighted the wide variation in how consumers perceived the bitterness of the HMW and LMW.…”

“…However, there are a number of challenges which affects the commercialisation of these NaCaHs; one of which is their taste. NaCaHs are associated with an intense bitter taste (Newman et al, 2014;Murray et al, 2017) which would negatively affect consumption in individuals who already suffer from reduced appetite.…”

Peptidomic screening of bitter and nonbitter casein hydrolysate fractions for insulinogenic peptides

“…Despite the strong scientific and commercial interest in this insulinogenic NaCaH (Brennan et al, 2015), its incorporation into foods remains a challenge due to its intense bitter taste. The bitterness of DPH is determined by several factors, including the molecular weight and hydrophobic profile of the peptides present in the DPH (Leksrisompong et al, 2010;Newman et al, 2014;Murray et al, 2017), the type of enzyme used to hydrolyze the protein (O'Sullivan et al, 2017), and the hydrolysis processing conditions (e.g., pH, temperature, degree of hydrolysis, enzyme: substrate ratio; Nongonierma and FitzGerald, 2017;O'Sullivan et al, 2017). The sequence of AA in a peptide chain can also influence peptide bitterness (Ishibashi et al, 1987a, b), but as DPH contain hundreds of peptides, the task of tasting synthesized peptides to determine the peptide(s) responsible for imparting a bitter taste is a long and difficult process.…”

“…Sensory-guided fractionation involves fractionating DPH into less-complex fractions (in terms of peptide composition) and then evaluating the fractions for bitterness. This approach was used by Murray et al (2017) to identify the fractions or physicochemical characteristics most responsible for bitterness in the NaCaH described by Brennan et al (2015).…”

“…Therefore, the objective of the present study was to elucidate the relationship between bitterness and bioactivity of the insulinogenic NaCaH described by Brennan et al (2015). To achieve this objective, we used peptidomics to establish the sequences of the many peptides present in the NaCaH and each of its subfractions, which were generated as described by Murray et al (2017). Bioinformatic analysis of the peptidomic data was then used to identify which fraction(s) contained the most bioactive peptides through sequence search-ing against databases such as BIOPEP (Minkiewicz et al, 2008) and the Milk Bioactive Peptide Database (Nielsen et al, 2017).…”