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I am trying to understand how the authors calculated the TRP/LNAA (mol/mol) ratios in Table 1 in this paper.

For example, when I calculate the TRP/LNAA (mol/mol) ratio for HPROT, I get 0.14 instead of 1.1. What am doing wrong?

I'm using the following values for the molecular weights (g/mol):

  • Isoleucine 131.2
  • Leucine 131.2
  • Phenylalanine 165.2
  • Tyrosine 181.2
  • Valine 117.1
  • Tryptophan 204.2

And here are the tables from the paper:

Table 1: Composition of the standard protein (PLC), alpha-lactalbumin whey protein (ALAC), protein hydrolase (HPROT), pure tryptophan (TRP), and synthetic dipeptide (SYN) condition

\begin{array}{llll} \hline \text{Source} & \text{Product}~(\mathrm{g}) & \text{TRP}~(\mathrm{g}) & \text{TRP/LNAA}~(\mathrm{mol}/\mathrm{mol}) \\ \hline \text{PLC} & 20~\mathrm{g}/312~\mathrm{mL} & 0.4 & 0.04 \\ \text{ALAC} & 15~\mathrm{g}/312~\mathrm{mL} & 0.8 & 0.1 \\ \text{HPROT} & 312~\mathrm{mL} & 0.8 & 1.1 \\ \text{TRP} & 0.8~\mathrm{g}/312~\mathrm{mL} & 0.8 & \infty \\ \text{SYN} & 1.2~\mathrm{g}/312~\mathrm{mL} & 0.8 & \infty \\ \hline \end{array}

Table 2: Amino acid profile

\begin{array}{llll} \hline \text{Amino acid profile}~(\mathrm{g}) & \text{HPROT} & \text{PLC} & \text{ALAC} \\ \hline \text{Isoleucine} & 1.004 & 1.800 & 2.012 \\ \text{Leucine} & 0.745 & 2.733 & 3.306 \\ \text{Phenylalanine} & 0.480 & 1.467 & 1.309 \\ \text{Tyrosine} & 1.216 & 1.867 & 1.451 \\ \text{Valine} & 0.554 & 2.133 & 1.322 \\ \text{Tryptophan} & 0.8 & 0.4 & 0.8 \\ \hline \text{Total} & 3.999 & 10 & 9.4 \\ \hline \end{array}

Acronyms:

  • LNAA: large neutral amino acids
  • HPROT: hydrolyzed protein
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  • $\begingroup$ How did you calculate moles of LNAA since there are 6 of them? I'd also point out what I consider to be a flaw in the paper in general, and that is that serotonin synthesis is not directly dependent on TRP, but rather on 5-hydroxtryptophan since tryptophan hydroxylase is the rate limiting enzyme in 5-HT synthesis. Feeding tyrptophan to humans does little to raise brain 5-HT. Giving human 5HTP however does increase brain 5-HT. $\endgroup$ – Dr. J. Jun 20 '18 at 13:05
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    $\begingroup$ @DrJ I calculated the moles for each individual amino acid and then summed the resulting values. $\endgroup$ – Jacob Jun 20 '18 at 13:20
  • $\begingroup$ By the way, the paper does not make claims regarding serotonin synthesis. Rather, they investigate links between dietary intake of TRP/LNAA, serum levels of TRP/LNAA, and mood scores $\endgroup$ – Jacob Jun 20 '18 at 13:23
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    $\begingroup$ Yes, the calculated ratio is 0.14. Hard to imagine how it could be > 1.0 considering the combination of 6 LNAA compared to the lonely tryptophan. Unless there is something unique about the HPROT being used in this study, i.e. what is the TRP content of the hydrolysate? I didn't read the entire manuscript, so I don't know what else to suggest. $\endgroup$ – Dr. J. Jun 20 '18 at 14:27
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    $\begingroup$ @DrJ Thanks for checking the calculation, much appreciated. I think there's something funny going on in this paper but I'm not sure what yet - I'll continue thinking about it. Though at this point, I think Table 1 is just plain wrong. $\endgroup$ – Jacob Jun 20 '18 at 15:36

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