Melatonin Content in Food Materials and Its Application to Prepare High Melatonin Pasteurized Milk

Abstract

Milk is a functional food that contains many nutrients and bioactive compounds essential to human health. Consumer demand for milk products has recently increased resulting in high competition in types and pricing. Production of functional milk adds value and increases competitive marketing. Products containing high antioxidants improve relaxation and sleep quality but have not been extensively produced. Functional milk high in melatonin has recently attracted interest. Natural milk is low in melatonin and tryptophan compared to edible plants. Mulberry leaf tea and edible grains were analyzed for melatonin and tryptophan as a precursor to produce a pasteurized milk product with high melatonin content and antioxidant activity. Edible grains studied included five rice, three corn, four legumes, and two oilseed cultivars. Highest melatonin concentrations were observed in white sesame, sunflower seed and soybean (75.24, 67.45 and 56.49 ng/g dry weight (dw), respectively). Highest free tryptophan was detected in soybean, red bean and mung bean (2.62, 1.53 and 0.85 µg/g dw, respectively). Total phenolic content was highest in sunflower and white sesame seeds (30.86 and 21.42 mg GAE/g dw). Antioxidant activity evaluated using DPPH, FRAP and ABTS assays showed sunflower seed extract as strongest followed by white sesame. Results indicated that white sesame, sunflower, and soybean were good sources of melatonin, free tryptophan and antioxidants. Soybean was selected and incorporated into pasteurized milk as it contained high concentrations of melatonin, free tryptophan and antioxidants. Soybean was also easy to incorporate in milk at a reasonable price. Mulberry leaves were dried using solar energy, a hot air oven, and freeze drying to compare melatonin content. Results indicated no significant difference in melatonin content between leaves dried by solar energy and the freeze drying technique.

To develop pasteurized milk high in melatonin content, nine treatments were developed by mixing raw milk with mulberry leaf tea and soymilk powder. Results revealed that milk quality, milk composition, bioactive components, and antioxidant activities significantly increased (p<0.05). Highest parameter values were observed in pasteurized milk added with 6% mulberry leaf tea, 6% soymilk powder, and 85.80% milk. For the shelf life study, melatonin, free tryptophan, and total phenolic content were not significantly different and slightly reduced during storage. Sensory evaluation of pasteurized milk comprising 4% mulberry leaf tea, 4% soymilk powder, and 89.80% milk yielded the highest overall liking score of 7 by consumer testing.

To obtain a higher quality pasteurized milk product in terms of milk standard, mulberry leaf tea, soymilk powder, and raw milk were optimized using mixture design. A total of eleven treatment results revealed that the optimum quality of pasteurized milk contained 3.90% soymilk powder, 4.50% mulberry leaf tea and 89.40% raw milk.

A clinical study of pasteurized milk in healthy volunteers was conducted. Urinary 6-sulfatoxymelatonin (aMT6-s) was determined as an indicator of melatonin levels in the human body after milk consumption. Urinary antioxidant was performed using ferric reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC). Results indicated that after consumption of high melatonin pasteurized milk, including pasteurized milk mulberry leaf tea (PMM) and high melatonin pasteurized milk mulberry leaf tea mixed with soybean powder (PMMS), urinary aMT6-s and urinary antioxidant of FRAP and TEAC increased compared with the baseline.

Overall results indicated that both mulberry leaves and soybean are good sources of nutrients, bioactive compounds, and antioxidants. Supplementation of both ingredients in milk improved melatonin, free tryptophan, phenolic content and antioxidant activity. Therefore, milk supplemented with mulberry leaf tea and soymilk powder is beneficial as a health-promoting functional food. This product showed potential for use in assisting relaxation and sleep quality.

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