Abstract: Yogurt can be digested in the gastrointestinal tract of humans to produce β-casomorphin (β-CM), which is believed to be able to relieves emotional tensions. In order to explore its release in the gastrointestinal tract and biological activity, an in vitro digestion model was used to simulate the digestion of yogurt in the body. The release of β-CM-7 and β-CM-5 was monitored by high performance liquid chromatography (HPLC); the opiate activity was measured by NG108-15 neurohybridoma cell in vitro assay and mouse behavioral test. After digestion in simulated gastric and pancreatic juices, the concentrations of β-CM-7 released were 40.24 and 47.81 μg/mL, respectively; the concentrations of β-CM-5 released were 88.00 and 82.04 μg/mL, respectively. Both digests could reduce the intracellular cAMP level in NG108-15 cells, which could be reversed by naloxone, reflecting the opiate activity of β-CM. The mouse experiments showed that the strongest analgesic activity was achieved at 30 minutes after injection of the gastric digest, giving an increase in pain threshold of 59.80%. Ingestion of the high-dose purified gastric digest prolonged the average swimming time of mice by 18.94 min, indicating good anti-fatigue effect. The experimental results show that β-CM with opiate activity and analgesic and anti-fatigue effects is produced from yogurt when ingested into in the body.

Key words: yogurt, β-casomorphin-7, β-casomorphin-5, in vitro digestion model, isolation and purification, opiate activity