Investigation of the effects of heat treatment on milk melatonin and vitamin c levels in goat milk

Aim: In this project, it was aimed to investigate the effects of pasteurization (15 seconds at 72 ºC) and boiling processes (5 minutes at 100 ºC) on goat milk melatonin, vitamin C and total protein levels. Material and Methods: The milk of 20 healthy goats (10 Aleppo, 10 Kilis goats) obtained from a private goat farm were used as materials. In April, milk was supplied from goats that returned from pasture in the morning (between 10:30 and 11:00) during routine milking. Each milk sample was divided into 3 for raw milk, for pasteurization process (15 seconds at 72 ºC) and for boiling process (5 minutes at 100 ºC). Melatonin levels in raw, pasteurized and boiled milk were determined with commercial ELISA kit, while, vitamin C and total protein levels were determined by manual spectrophotometric methods. Results: Melatonin levels in boiled milk samples (4.20 ± 0.39 pg/ml) increased (p <0.05) compared to both raw milk (3.19 ± 0.25 pg/ml) and pasteurized (3.42 ± 0.24 pg/ml) milk samples. Vitamin C levels did not differ in the pasteurization group (2.99 ± 0.16 mg/100 ml) compared to the raw milk group (3.18 ± 0.24 mg/100 ml). On the other hand, vitamin C levels obtained after boiling process (2.03 ± 0.12 mg/100 ml) were lower than that in the raw and pasteurized milk samples (p <0.001). While there was no difference between the heat treated groups in terms of total protein levels determined by Bradford method, the total protein levels determined by Lowry method decreased significantly in boiling group compared to other groups (p <0.001). Total protein levels in raw milk and pasteurized milk were found not to differ in terms of levels determined by Bradford method and Lowry method (p >0,05). On the other hand, total protein levels (2.26 ± 0.13 g/dl) determined by the Bradford method in boiled milk were determined to be higher than total protein levels (1.92 ± 0.09 g/dl) determined by Lowry method (p <0.05). Significant but weak negative correlations were determined between melatonin and vitamin C levels in milk with pasteurization (r =-0,114, p <0.05) and boiling process (r=-0,572, p <0.01). Positive correlations were determined between total protein levels determined by Bradford and Lowry methods in raw milk (r=0,723, p <0,01), pasteurized (r =0,838, p <0,01) and boiled (r=0,449, p <0,05) milk samples. Conclusion: It was determined that pasteurization process applied to goat milk did not change milk melatonin, total protein and vitamin C levels, and boiling process decreased total protein and vitamin C levels. Pasteurization was considered to be superior to the traditional boiling process in the bioavailability of goat milk. Before melatonin analysis was performed in milk by ELISA method, it was predicted that a pre-treatment of milk may be useful in order to separate melatonin from the protein it is bound to, thus may result in achieving more accurate results.