1688 Research Article Received: 5 February 2013 Revised: 4 September 2013 Accepted article published: 14 November 2013 Published online in Wiley Online Library: 12 December 2013 (wileyonlinelibrary.com) DOI 10.1002/jsfa.6480 Night milking adds value to cow’s milk Maria P Milagres, a* Valeria P R Minim, b Luis A Minim, b Andrea A Simiqueli, b Liliane E S Moraes b and H ´ ercia S D Martino c Abstract BACKGROUND: Melatonin is synthesized in greater concentration at night, and it plays an important role in sleep regulation. This study aimed to evaluate the melatonin concentration in milk collected by milking during the night and evaluates its effect, with or without tryptophan supplementation, in the sleep quality of adult Wistar rats. RESULTS: A difference (P < 0.05) was observed between the milking times, where the milk obtained at 02:00 presented a higher melatonin concentration (39.43 pg mL -1 ) than that acquired at 15:00 (4.03 pg mL -1 ). A biological assay was also performed on 32 male adult Wistar rats distributed among four groups (n = 8): those receiving an AIN-93M diet (control group) and three test groups [diets containing milk from milking at 02:00 (M 2h ), milking at 15:00 (M 15h ), and milking at 02:00 plus tryptophan supplementation (M 2h T)] for 28 days. It was observed that the control group did not differ (P > 0.05) from the M 15h group in terms of the levels of blood melatonin and urinary sulfatoxymelatonin, but differed from groups M 2h and M 2h T, whereas group M 2h T presented higher blood melatonin and urinary sulfatoxymelatonin concentrations. CONCLUSION: Combining the techniques of night milking with tryptophan supplementation resulted in production of milk that improves sleep quality in rats. c  2013 Society of Chemical Industry Keywords: melatonin; sleep; milk; tryptophan INTRODUCTION Melatonin is responsible for circadian regulation and the control of sleep, encountered in the organism at highest concentrations during the night. 1 With aging, there is a substantial reduction in melatonin production, which may impair sleep quality among the elderly. 2 Melatonin is naturally present in many foods including cherry, banana, peppermint, red wine, and milk. 3 It is not considered as a food additive by the Harmonized General List of Food Additives and their Functional Classes of the Mercosur, 4 thus not permitting it to be included as food. Cow’s milk contains roughly 5 pg mL −1 of melatonin, and studies have focused on naturally increasing the melatonin concentration by using different milking techniques. Valtonen et al. 5 showed that it is possible to increase the concentration of melatonin up to 56.4 pg mL −1 with changes in the photoperiod of cows; that is, by increasing the period in which the animals remain in the dark for 17 h. Haigh 6 increased the concentration of melatonin in milk to 35 pg mL −1 by night milking, with maximum illumination of 50 lux; Gnann 7 developed a method for naturally increasing melatonin in milk by night milking animals exposed to light at different wavelengths during the day and at night. Tryptophan is an essential amino acid, a precursor of melatonin synthesis by the pineal gland, and acts to improve sleep and reduce stress and antioxidant effects. Tormo et al. 8 and Sanchez et al. 9 demonstrated that it is possible to increase the concentration of plasma melatonin by tryptophan administration. However, no studies in the literature have described an increase in plasma melatonin concentration because of the addition of tryptophan to milk. Also, no studies have been reported on the concentration of melatonin in the milk of cows in Brazil. However, it is known that melatonin concentration in milk varies with the breed, nutrition, stress level of the animals, and ambient temperature. 10 This work aimed to evaluate the melatonin concentration in milk collected by night milking and to evaluate its effect, with our without tryptophan supplementation, in the sleep quality of adult Wistar rats MATERIAL AND METHODS Milking of the animals For milking, 10 Holstein cows (age range, 3–7 years; average weight, 580 kg; average milk production, 25 L day −1 ; and lactation period, 100 – 150 days after calving), located at the dairy house of the Federal University of Vic ¸osa, Brazil, were randomly selected for the study. The experiment was conducted in randomized blocks, with each cow representing one block. ∗ Correspondence to: Maria P Milagres, Department of Chemistry, State University of Southwest Bahia, Jequiezinho, Jequi´ e - BA, 45206-190, Brazil. E-mail: patricia@uesb.edu.br a Department of Chemistry, State University of Southwest Bahia, Brazil b Department of Food Technology, Federal University of Vic ¸osa, Av. P. H. Rolfs, Vic ¸osa, Minas Gerais, Brazil c Department of Nutrition and Health, Federal University of Vic ¸osa, Vic ¸osa, Minas Gerais, Brazil J Sci Food Agric 2014; 94: 1688–1692 www.soci.org c  2013 Society of Chemical Industry