Casoxins and lactoferroxins are not widely known group of µ-opioid antagonistic peptides. Their functions are not fully recognized, however coexistence of both agonistic and antagonistic peptides in milk and dairy products suggests a complex mechanism of peristalsis control, by competitive interaction of those peptides with opioid receptors.

Few different variants of ELISA were developed and evaluated with the use of rabbit polyclonal antibodies against the following peptides: lactoferroxin A, lactoferroxin C and casoxin 6.

Direct ELISA was influenced by a high level of unspecific binding, and pre-coating of plates with polylysine was found to be ineffective. Sensitivity of reaction decreased by 19.1% for lactoferroxin A and was completely extinguished for casoxin 6. Blocking with 1% gelatin and use of 0.05% Tween-20 with PBS (TPBS) as a buffer for primary antibodies allowed to decrease the level of unspecific binding. All of the following experiments have been conducted under those conditions.

Sensitivity of developed ELISA assessed by reaction with synthetic peptides was found to be 0.002 mg for lactoferroxin A, 0.0007 mg for lactoferroxin C and 0.012 mg for casoxin 6.

ELISA was used for determination of lactoferroxin A, lactoferroxin C and casoxin 6 in selected dairy products. The content of lactoferroxin A, lactoferroxin C and casoxin 6 in kefirs (Fromako, Maluta, Robico) was found to be 3.0-4.2 mg per 100 mL, 2.0-4.9 mg per 100 mL and 28-39 mg per 100 mL, respectively. Values for yoghurts (Bakoma, Sokólski, Zott) were: 2.0-3.1 mg per 100 mL of lactoferroxin A, 0.5-1.3 mg per 100 mL of lactoferroxin C and 27.7-51.8 mg per 100 mL of casoxin 6. Hard (Edam, Gouda, Mozarella, Ricotta) and mold (Sekret Mnicha, Dor Blu, Brie) cheeses contained 6.2-9.2 mg per 100 g of lactoferroxin A, 1.4 mg per 100g and 5.6 mg per 100 g of lactoferroxin C (hard and mold cheeses respectively) and 24-26 mg per 100 g of casoxin 6.

It can be concluded that µ-opioid antagonistic peptides are released by proteolysis of milk protein and are common constituents of fermented dairy products, however their content is diversified and depends of the product. The content of both µ-opioid agonistic and antagonistic peptides can be a new criterion of food quality assessment.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/11150 must be provided.

1. Biologic and immunogenic properties of protein and peptide fractions isolated from soy-based infant formulas
2. Influence of glycation (non-enzymatic glycosylation) on antigenicity of soy (Glycine max) and pea (Pisum sativum) 7S globulin
3. Human β‑casomorphin transport across Caco-2 monolayer