Written by: Marina Wang | Issue # 104 | 2021
- Although the chemical composition of human milk is well studied, sensory perceptions such as smell, taste, and mouthfeel have been seldom identified in academic literature.
- Breastfeeding mothers that tasted their own milk described the taste as sweet and bitter, the smell as neutral, creamy, and sweet, and the mouthfeel as thin, watery, smooth, and fatty.
- A correlation was found between the bitterness of the mother’s diet and the bitterness of her fore milk but not hind milk.
- Bitterness in human milk may acquaint infants with bitter foods and accept more vegetables in their diet when they grow older.
As the popular adage goes, you are what you eat, and a new study published in the Journal of Dairy Science (in a loose sense) seems to support that. A research team from the Netherlands has characterized the tastes and smells of human milk and discovered a correlation between the mother’s diet and the taste of her milk. In particular, the scientists were interested in teasing apart the sensory differences in fore and hind milk and focused on whether bitter tastes would show up through the mother’s milk [1].
“There’s an important element of breastfeeding that comes with the smell and taste of human milk,” explains Bernd Stahl, the Director of Human Milk Research & Analytical Science at Danone Nutricia Research Utrecht and Associate Professor at Utrecht University, Netherlands. “It’s a biologically important interaction between a mom and her baby.”
Different flavors from the mother’s milk could be an opportunity for the infant to get acquainted with different tastes, which can later influence their food preferences growing up [2,3]. That’s why it’s valuable for the breastfeeding mother to eat a [4–6] variety of foods so that their child can develop a taste for those foods as they grow.
Previous analytical studies looking at the chemical composition of human milk have shown that flavors from the mother’s diet, such as vanilla, carrot, and garlic, are showing up in breast milk [7–9], but very few studies have examined the sensory perception of human milk. This new study takes this more holistic approach in getting the mothers to characterize the smells and tastes of their own milk.
The aims of the study were multi-fold. For one, the research team wanted to characterize the tastes and smells of both the fore milk and the hind milk [1]. “The fore milk is the first sip of milk and the hind milk is the last sip of milk in one given breastfeeding session,” explains Stahl. “The first sip is really rich in carbohydrates and proteins but very limited in fats, but the last sip is very rich in fat.” Second, the researchers wanted to see if components of milk such as fats or sugars could be discerned in the tastes and smell of milk, and thirdly, they wanted to know if the mother’s diet could influence the taste of their milk, with a focus on bitterness [1].
To do this, the research team worked with a group of 22 lactating mothers. At the start of the trial, the mothers underwent taste training to standardize how the mother’s ranked tastes. They then tasted their own fore milk and hind milk and recorded taste, smell, and mouthfeel attributes such as sweet, creamy, or watery. Then, the volunteers kept a food diary for a day to record their diets, and the next day, repeated the tasting [1].
Overall, the research team found that human milk was most often described as having a neutral, creamy, and sweet odor, mostly sweet and some bitter tastes, and a thin, watery, smooth, and fatty mouthfeel. The hind milk was reported to have a more intense vanilla flavor and creamy odor compared with the fore milk, and the mouthfeel was described to be more creamy, fatty, less watery, and less thin [1]. This finding corroborates past research that has found that hind milk is richer in fats [10], which would account for the creamier mouthfeel.
Interestingly, on the second day, the investigators reported that the mothers who ate more bitter foods scored their fore milk but not their hind milk as more bitter, showing that tastes from their foods were transferred to their milk. Reasons for the fore milk having bitter tastes rather than the hind milk are unclear, but researchers speculate that it could be because the fore milk is more watery, how the milk is formed during lactation in the mammary gland, or the bitter tastes being masked by the high fat content in the hind milk.
The correlation between the mother’s diet and the taste of her milk supports the recommendation for lactating mothers to consume a variety of foods. According to Stahl, when the infant is consuming milk, “there’s stable intake of proteins, carbohydrates, and fats, but then it’s decorated with those flavors and smells. I think that makes it more exciting.” Stahl speculates that giving the nursing baby different flavors will be a more interesting and varied taste experience, and this may help breast-fed infants develop healthier food preferences in later life.
Stahl also emphasized that mothers shouldn’t be worried about restricting their diet because of the finding that bitterness is appearing in milk. “I think it’s our obligation to do whatever we can to support breastfeeding,” he says.
Stahl said that one limitation of the study would be an innate sensory bias when the mothers were tasting their own milk. For example, if a mother consumed a lot of garlic, her system might be so flooded with the scent that she might not be able to detect it in her own milk. But in spite of that, the researchers still found that the mothers were able to detect more bitter tastes [1].
For future studies, Stahl thinks it would be ideal to use the sensory approach taken with this study and combine it with the analytical methods used in other studies. Corroborating the two approaches would give a more robust and in-depth understanding of how diet can affect the smells and taste of milk.
References
1. Mastorakou, D., H. Weenen, B. Stahl, and M. Stieger, 2019. Sensory characteristics of human milk: Association between mothers’ diet and milk for bitter taste. J. Dairy Sci. 102:1116–1130.
2. Cooke, L., and A. Fildes. 2011. The impact of flavour exposure in utero and during milk feeding on food acceptance at weaning and beyond. Appetite 57:808–811.
3. Nehring, I., T. Kostka, R. von Kries, and E. A. Rehfuess. 2015. Impacts of in utero and early infant taste experiences on later taste acceptance: A systematic review. J. Nutr. 145:1271–1279.
4. Sullivan, S. A., and L. L. Birch. 1994. Infant dietary experience and acceptance of solid foods. Pediatrics 93:271–277.
5. Mennella, J. A. 1995. Mother’s milk: A medium for early flavor experiences. J. Hum. Lact. 11:39–45.
6. Mennella, J. A., and G. K. Beauchamp. 1991. Maternal diet alters the sensory qualities of human milk and the nursling’s behavior. Pediatrics 88:737–744.
7. Mennella, J. A., and G. K. Beauchamp. 1996. The human infants’ response to vanilla flavors in mother’s milk and formula. Infant Behav. Dev. 19:13–19.
8. Mennella, J. A., and G. K. Beauchamp. 1999. Experience with a flavor in mother’s milk modifies the infant’s acceptance of flavored cereal. Dev. Psychobiol. 35:197–203.
9. Mennella, J. A., L. M. Daniels, and A. R. Reiter. 2017. Learning to like vegetables during breastfeeding: A randomized clinical trial of lactating mothers and infants. Am. J. Clin. Nutr. 106:67–76.
10. McDaniel, M. R., E. Barker, and C. Lederer. 1989. Sensory characterization of human milk. J. Dairy Sci. 72:1149–1158.