le très mauvais goût des hydrolysats les rendait difficilement utilisables dans les protéines en poudre.
en s'attaquant à la proline, ça devient acceptable
Bitterness in Bacillus proteinase hydrolysates of whey proteins
D. Spellman a, G. O’Cuinn b, R.J. FitzGerald a,*
a Department of Life Sciences, University of Limerick, Ireland
b Department of Life Sciences, Galway-Mayo Institute of Technology, Ireland
a r t i c l e i n f o
Article history:
Received 21 July 2008
Received in revised form 17 September
2008
Accepted 23 September 2008
Available online xxxx
Keywords:
Enzymatic hydrolysis
Whey protein
Proteinase
Glutamyl endopeptidase
Bitterness
Hydrophobicity
a b s t r a c t
Whey protein concentrate (WPC) hydrolysates were generated with three commercially available Bacillus
proteinase preparations (pH 7.0, 50 C, 20% (w/v) WPC). Alcalase 2.4L hydrolysates were more bitter than
Prolyve 1000 and Corolase 7089 hydrolysates when the proteinase activities were included at equivalent
high and low addition levels. A glutamyl endopeptidase (GE) activity present in Alcalase was not detected
in the Prolyve and Corolase preparations. Hydrolysate bitterness significantly increased when GE activity
was included during Prolyve hydrolysis of WPC, indicating that inclusion of the GE activity was linked
with the higher bitterness in Alcalase hydrolysates. A peptide present at higher levels in Prolyve
compared to Alcalase hydrolysates was identified by mass spectrometry as b-lactoglobulin f(43–57).
Hydrolysis of this peptide by GE was shown to release fragments with increased average hydrophobicity
(Q-value). This may, in part, explain the higher level of bitterness associated with Alcalase compared to
Prolyve hydrolysates of WPC.
2008 Elsevier Ltd. All rights reserved.
1. Introduction
Whey protein hydrolysates have many advantages over the intact
proteins in terms of enhanced functional and biological properties.
Enzymatic hydrolysis has been widely used to modify the
solubility, foaming, emulsification and gelation properties of whey
proteins (Foegeding, Davis, Doucet, & McGuffey, 2002 and references
therein). Enzymatic hydrolysis of food/whey proteins has
been shown to reduce antigenicity, and increase biological activity
for example by the release of immunomodulating, opioid and antihypertensive
peptides (Mine & Shahidi, 2006; Morris & FitzGerald,
2008 and references therein). Furthermore, the small peptides
present in protein hydrolysates are absorbed more rapidly from
the intestine than free amino acids or intact proteins (Webb, 1990).
However, a major disadvantage of protein hydrolysis is the release
of bitter tasting peptides. The bitter taste of protein hydrolysates
can limit their potential use, as bitter hydrolysates can only be
incorporated into foods at low concentrations without producing
an unacceptable flavour. Detailed investigations have revealed that
low molecular mass peptides containing hydrophobic amino acid
residues are responsible for hydrolysate bitterness (Kim & Li-Chan,
2006a, 2006b; Matoba & Hata, 1972; Ney, 1979). In intact globular
proteins, most hydrophobic amino acids are oriented towards the
interior of the molecule, however, during proteolysis peptides containing
hydrophobic amino acids are released and interact with
taste buds resulting in a bitter taste (Matoba & Hata, 1972). As proteolysis
continues, more hydrophobic amino acid residues become
exposed and therefore hydrolysate bitterness generally increases
with increasing hydrolysis. The ‘Q-rule’ devised by Ney (1971)
established a quantitative relationship between the amino acid
composition of a peptide and its bitterness. Using the values calculated
by Tanford (1962), the Q-rule stated that peptides with an
average hydrophobicity (Q) value greater than 1400 cal mol1 and
with molecular masses below 6000 Da elicit a bitter taste.
Bitterness may also be influenced by the position of the hydrophobic
amino acid residue in the peptide sequence. Hydrophobic
amino acids were more bitter when both the a-amino and carboxyl
groups were involved in peptide bond formation than when occurring
at the N- or C-terminus of peptides (Matoba & Hata, 1972).
Ishibashi et al. (1988a) showed that when a proline residue was located
at the N-terminus of peptides the bitter taste was weak or
absent, but that the presence of proline at the centre of a peptide
could increase bitterness by altering the conformation of the peptide
which enabled it to bind to taste receptors. Therefore, if the
position of the hydrophobic amino acid residue can influence peptide
bitterness, it follows that the bitterness of protein hydrolysates
can depend on the specificity of the proteolytic enzyme
used to generate the hydrolysate. For example, an hydrolysate generated
with a proteinase which specifically cleaves after hydrophobic
amino acid residues would be expected to be less bitter than an
hydrolysate generated with a proteinase which specifically cleaves
after charged amino acid residues, as the former would have fewer
long sequences of hydrophobic amino acids and contain more
0308-8146/$ - see front matter 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.foodchem.2008.09.067
* Corresponding author. Tel.: +353 61 202598; fax: +353 61 331490.
E-mail address: dick.fitzgerald@ul.ie (R.J. FitzGerald).
Food Chemistry xxx (2008) xxx–xxx
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Food Chemistry
journal homepage: www.elsevier.com/locate/foodchem
ARTICLE IN PRESS
Please cite this article in press as: Spellman, D., et al. Bitterness in Bacillus proteinase hydrolysates of whey proteins. Food Chemistry
(2008), doi:10.1016/j.foodchem.2008.09.067
