The Effects of Milking Time and Dairy Processes on Melatonin Contents in Milk

착유 시간 및 유처리 공정이 우유 내 멜라토닌 함량에 미치는 영향

Melatonin is one of the functional hormones in the milk and found in all mammalian species. The primary motivation for the use of melatonin as a supplement is as a natural aid to better sleep. Melatonin contents in milk vary according to the naturally occurring factors such as seasons and milking times. As a number of studies indicate melatonin supplementation helps to reduce the age-related decline in hormone production and overall enhancement of health, the more detailed studies are required to know the nature of milk derived hormones and to clarify them as a functional value adaptation. The objectives of this study were to examine the change of melatonin content in bovine milk during different milking times at the two dairy farms and during dairy process including homogenization and pasteurization. Commercial dairy products including night time milking products(night milk) marketed in Japan were also investigated. Melatonin content was determined by radioimmunoassay using 125I. Individual milk was collected from lactating Holstein cows at Kyong-Ki province in Korea. At farm A, the melatonin contents milking at 4 a.m. was higher than those of 7 p.m. and 12 p.m.($6.90{\pm}3.55,\;2.01{\pm}1.47$ and $0.16{\pm}0.04pg/mL$, respectively). At farm B, the mean melatonin contents milked from 24:00 AM to 05:00 AM have shown the highest contents ($4.65{\pm}$0.72pg/mL), and milking samples of the rest time had very little or non-detection of melatonin contents. Melatonin contents of commercial night milk samples were about 5 times higher than those of other common milk products. These results suggested that melatonin might be heat-resistant and commercial dairy process might not affect its contents in the final products.

본 연구는 숙면 유도 호르몬으로 알려진 멜라토닌의 원유 및 유제품 내 함량을 방사면역측정법으로 분석하였으며, 그 결과는 다음과 같다. 1. 착유 시간에 따른 멜라토닌 함량은 새벽 4시에 착유한 원유 샘플의 멜라토닌 함량이 평균 $6.90{\pm}3.55pg/mL$로 나타났으며, 저녁 7시 및 낮 12시 착유 원유 샘플은 각각 $2.01{\pm}1.47pg/mL$와 $0.16{\pm}0.04pg/mL$로 나타나 새벽 착유 원유 내 멜라토닌 함량이 유의적으로 높은 결과를 나타내었으며, 이는 로봇 착유기를 사용하는 농가에서도 심야 및 새벽 착유 원유에서 멜라토닌 함량이 가장 높게 나타나 2개 목장 모두 비슷한 결과를 나타내었다. 2. 일반 우유 제품과 나이트 밀크 제품 간 멜라토닌 함량비교 시, 나이트 밀크의 멜라토닌 함량이 약 5배 정도 높은 결과를 보였다. 3. 일반 우유를 대상으로 원유, 균질 및 살균 등의 공정이 멜라토닌 함량에 영향을 미치지 않는 것으로 나타났으나, 그 수준은 매우 낮은 농도로 존재하였다.