Natural food and beverage flavour enhancers - Natural Food Additives, Ingredients and Flavourings - page 86

reduced use of HVP in process fl avouring. However, the conditions for the
formation of 3MCPD were established and HVP manufacturers are now able to
effectively remove 3MCPD from their products. In 2008 the Codex Committee on
Contaminants in Food set an upper maximum of 3MCPD in acid-HVP and soy
sauces manufactured using acid-HVP of 0.01 mg/kg in fi nal product at 30-50%
dry matter (Codex 2008). HVP can also be produced by an enzyme hydrolysis
method (E-HVP), which does not lead to 3MCPD formation. The hydrolysis is
carried out at 50-55°C and pH 5-7, followed by enzyme deactivation at 85°C for
fi ve minutes (Pommer 1995).
The two types of HVP have different properties. The acidic-HVP tends to have
a darker colour and stronger fl avour, whereas the E-HVP tends to be a lighter
colour with a less meaty fl avour (Weir 1992). Due to the issues of 3MCPD
formation from the original acid hydrolysis method, use of HVP in the UK has
been largely superseded by utilisation of yeast extracts. However, the use of HVPs
remains widespread across mainland Europe, Asia and the Americas.

4.2.2 Umami ribonucleotides
The 5′-ribonucleotides that impart umami taste vary in their relative umami
concentration (RUC). 5′-Inosine monophosphate (IMP) has an RUC value of 1,
5′-guanosine monophosphate (GMP) a value of 2.3, 5′-xanthosine monophosphate
(XMP) a value of 0.61 and 5′-adenosine monophosphate (AMP) a value of 0.18
(Yamaguchi et al. 1971). The ribonucleotides act synergistically with the umami
amino acids to increase the overall umami taste impact. At threshold levels,
addition of 5mM IMP reduces the detection threshold of MSG by a factor of over
60 from 0.012% to 0.00019% (Yamaguchi and Kimizuka 1979). This synergy was
fi rst modelled by Yamaguchi et al. (1971) in determining the equivalent umami
concentration (EUC), a measure used to determine the umami intensity of a taste
mixture relative to pure MSG. EUC is calculated from the levels of umami amino
acids (aspartate and glutamate) plus the 5′-nucleotides as follows:

Y = Σ a i b i + 1218 (Σ a i b i )(Σ a j b j ) [4.1]

￿ ￿ ￿ ￿ ￿

where Y = equivalent umami concentration (EUC) of the mixture (g MSG per
100g), a i = concentration of each umami amino acid (Asp and Glu) in g/100 g,
a j = concentration of each umami 5′-nucleotides (IMP, GMP, XMP and AMP) in
g/100 g, b i is the RUC for each umami amino acid to glutamate, b j is the RUC for
each umami 5′-nucleotide to IMP, and 1218 is a synergistic constant based on the
concentration (g/100 g) used.
The most commonly quantifi ed 5′-nucleotides in foods are IMP, GMP and
AMP; literature data for these are summarised in Table 4.1. IMP is typically found
at high levels in meat and tuna, particularly in dried fermented bonito fl akes
( Katsuobushi ). The formation of IMP occurs post mortem, as ATP breaks down
into AMP and subsequently IMP (Aliana et al. 2010). Alternatively, the
5′-nucleotides are formed through phosphorylation of the purines (adenosine,
guanosine, inosine). The IMP in meat and fi sh not only acts as a tastant and fl avour