Here are 2 studies on the subject.
Study # 1 :
Hydrolysis of casein accelerates gastrointestinal transit via reduction of opioid receptor agonists released from casein in rats. - PubMed - NCBI
So what we have here is that 1) hydrolysis of casein removed the latency in gastrointestinal transit by undenatured casein and 2) the same result is achieved by blocking opioid receptors with naloxone. Hence, this is proof that the only variable affecting gastrointestinal transit in casein is the presence of opioid receptor agonists.
Conclusion : Casein Hydrolysate (protein powder) has no opioid receptor agonist property.
Study # 2 :
Isotope dilution liquid chromatography-tandem mass spectrometry for simultaneous identification and quantification of beta-casomorphin 5 and beta-c... - PubMed - NCBI
Here we see that transforming milk into yoghurt immediately reduces the betacasomorphins content, and it reduces below their detection limits after 1 day of storage, and so after 7 days when it was tested again. In other words, bacterias digest it for us.
BCM7 is referred in other studies as the most inflammatory type and exclusively present in A1 milk, and it is hypothesized that it explains its more troublesome nature compared to A2 milk. A2 milk also contains various betacasomorphins.
It is interesting to note that their detection limits are quite high (0.5 and 0.25, still being an half and a quarter of the original content of BCMs in milk). This means that a physically relevant opioid effect could still be found in yoghurts.
Conclusion : Yoghurt has a lower content of opioid receptor agonists compared to milk.
Study # 1 :
Hydrolysis of casein accelerates gastrointestinal transit via reduction of opioid receptor agonists released from casein in rats. - PubMed - NCBI
BACKGROUND:
Protein hydrolysate accelerates gastrointestinal transit (GIT) and feeding advancement in preterm infants compared to native protein. In rat pups, opioid receptor agonists released from casein during digestion such as beta-casomorphins slow down GIT. We hypothesized that hydrolysis of casein reduces the opioid activity released during digestion thereby accelerating GIT compared to native casein.
OBJECTIVE:
The aim of the present study was to investigate whether casein hydrolysate accelerates GIT compared to native casein and whether pretreatment with naloxone, an opioid receptor blocker, abolishes this difference in rat pups.
RESULTS:
GIT was significantly higher with hydrolyzed casein compared to native casein formula (77.4 +/- 17 and 51.2 +/- 20%), but there was no difference after naloxone pretreatment (77.1 +/- 16 and 76.5 +/- 17%).
DISCUSSION:
The present data suggest that hydrolysis of casein accelerates GIT via reduction of opioid activity released during digestion. Further studies are required to investigate to which extent these rat pub data apply to preterm infants.
So what we have here is that 1) hydrolysis of casein removed the latency in gastrointestinal transit by undenatured casein and 2) the same result is achieved by blocking opioid receptors with naloxone. Hence, this is proof that the only variable affecting gastrointestinal transit in casein is the presence of opioid receptor agonists.
Conclusion : Casein Hydrolysate (protein powder) has no opioid receptor agonist property.
Study # 2 :
Isotope dilution liquid chromatography-tandem mass spectrometry for simultaneous identification and quantification of beta-casomorphin 5 and beta-c... - PubMed - NCBI
The method limits of detection (MLDs) in yoghurt extracts were found to be 0.5 and 0.25ng/g for BCM5 and BCM7, respectively.
The validated isotope dilution LC-MS/MS method was used to measure BCM5 and BCM7 in ten commercial and laboratory prepared samples of yoghurt and milk. Neither BCM5 nor BCM7 was detected in commercial yoghurts. However, they were observed in milk and laboratory prepared yoghurts and interestingly their levels decreased during processing.
BCM5 decreased from 1.3ng/g in milk to 1.1ng/g in yoghurt made from that milk at 0day storage and <MLQ at 1 and 7days storage. BCM7 decreased from 1.9ng/g in milk to <MLQ in yoghurts immediately after processing. These preliminary results indicate that fermentation and storage reduced BCM5 and BCM7 concentration in yoghurt.
Here we see that transforming milk into yoghurt immediately reduces the betacasomorphins content, and it reduces below their detection limits after 1 day of storage, and so after 7 days when it was tested again. In other words, bacterias digest it for us.
BCM7 is referred in other studies as the most inflammatory type and exclusively present in A1 milk, and it is hypothesized that it explains its more troublesome nature compared to A2 milk. A2 milk also contains various betacasomorphins.
It is interesting to note that their detection limits are quite high (0.5 and 0.25, still being an half and a quarter of the original content of BCMs in milk). This means that a physically relevant opioid effect could still be found in yoghurts.
Conclusion : Yoghurt has a lower content of opioid receptor agonists compared to milk.