Table 5.
Occurrence of TRP and its KP metabolites in milk and fermented products. 3HAA, AA, 3HKyn, XA, CA, PIC, and QA were not included in a target list of the analytical methods utilized for quantitative analysis.
| Product | N | Concentration Range (mg/kg) or (mg/L) | Ref. | ||
|---|---|---|---|---|---|
| TRP | KYN | KYNA | |||
| Bread | 3 | 31.70–72.50 | <LOD–0.14 | <LOD | [18] |
| – | n.a. | n.a. | 0.01 | [38] | |
| Cheese (white) | 6 | 3.80–37.60 | 0.03–0.32 | 0.03–0.08 | [18] |
| Cheese (hard) | – | n.a. | n.a. | 0.008 | [38] |
| Milk | 11 | ~0.30 | ~0.08 | n.a. | [16] |
| Milk (1.5%) | – | n.a. | n.a. | 0.02 | [38] |
| Milk (human) | – | n.a. | n.a. | 0.03 | |
| 24 | ~200.0–300.0 a | ~0.02–0.07 a | ~0.01–0.04 a | [113] | |
| – | n.a. | n.a. | 0.004–0.06 b | [13] | |
| 82-88 | 0.22–10.90 c | 0.01–0.22 c | n.a. | [93] | |
| Kefir | 3 | 2.90-5.40 | 0.37–0.76 | 0.11–0.24 | [18] |
| – | n.a. | n.a. | 0.01 | [38] | |
| Probiotic drinks | 31 | 0.22-5.16 | ~0.06 | n.a. | [16] |
| Yoghurt | 5 | 3.20-13.40 | 0.29–0.75 | 0.07–0.29 | [18] |
| 9 | ~0.70 | ~0.07 | n.a. | [16] | |
| – | n.a. | n.a. | 0.02 | [38] | |
a—samples collected on day 7 and day 14 of post-partum; b—samples collected during the first 6 months after post-partum; c—samples collected during the first 4 weeks of lactation; n.a.—data are not available, the analyte was not included in the target list of the applied analytical methods; <LOD—not detected; and N—number of analyzed samples. AA—anthranilic acid; CA—cinnabarinic acid; 3HAA—3-hydroxyanthranilic acid; 3HKyn—3-hydroxykynurenine; KYN—kynurenine; KYNA—kynurenic acid; PIC—picolinic acid; QA—quinolinic acid; TRP—tryptophan; and XA—xanthurenic acid.