 The Development of Taste During Infancy . . . page 1 Linda Clark Lowry MS PHEc It has been six years since In - Touch has examined the development of taste during infancy and during that time, research has identified new information to help care givers understand why some foods are accepted and some are not.(1) This will also support the practice of offering at a later date, foods that were rejected originally. Flavour is a combination of factors, including taste, mouth feel, aroma and aftertastes. Chemical receptors stimulate the taste receptors on the tongue to register a reaction. With smell, the chemicals stimulate the receptors on tissues in the nasal cavity. Mouthfeel sensations are perceived by nerves in the mouth (cool, metallic, hot, cold, astringent, etc.) While all these factors influence flavour, little experimental work has been done with infants beyond the influence of taste. Tastes include sweet, sour, bitter, salty and perhaps a fifth which is the taste of umami or monosodium glutamate. The most sensitive part of the tongue is the edge and not in the middle.(2) Sweet is detected on the tip of the tongue, bitter at the back, salty on the side of the tongue near the front and sour is detected on the side of the tongue near the back. Tastes develop in infants over time. The ability to detect sweet tastes occurs before birth. Pre term infants exhibited more nonnutritive sucking when offered a glucose solution compared to plain water.(2) Within days of birth, infants can detect dilute sweet solutions and differentiate different sugars. They prefer very sweet sugars such as sucrose and fructose to mildly sweet tastes such as glucose and lactose. However, there is no scientific evidence in humans that the preference for sweet-tasting foods can be altered permanently by variations in early exposure to sweets.(3) Sour is recognized at birth and can be demonstrated by lip pursing and facial grimaces.(4)There are only a few studies on sour tastes so it is not known whether sensitivity or preferences change developmentally. The ability to detect salt develops postnatally. There is no facial response to a salty taste until approximately four months of age.(5) Experience with salty tastes does not appear to be a factor in acceptance of salt at this later age, nor does it appear to be a learned response. No studies suggest that newborns prefer the taste of salt. When moderate concentrations of urea we re offered to newborns to test for a bitter taste, these hours-old infants did not reject the taste. However, when the concentration was increased, grimaces followed exposure to quinine and urea.(6) Older infants, (14 to 180 days of age) however, rejected even low concentrations of urea. This may explain why older infants reject bitter-tasting foods like some green vegetables. These foods would need to be introduced again and again so that eventually they may be tolerated and even enjoyed. Neonates responded positively to umami when given soup made with monosodium glutamate (MSG) as compare d to soup made without MSG.(1) By term, the fetus is swallowing amniotic fluid and has been exposed to glucose, amino acids, lactic acids and salts. The fact that amniotic fluid can acquire the odour of a spicy meal the mother ingested prior to giving birth suggests that odourous compounds can be passed through the amniotic fluid and give the fetus experience with those sensations.(7) Infants seem to detect and retain information about the chemical characteristics of their environment. Day old infants will spend more time orienting near a breast pad worn by their mother compared to one worn by an unfamiliar lactating woman.(8) When older, infants are able to respond differently to scented and unscented objects, dependent upon the amount of experience with that odour. Human milk is rich in flavours dependent upon the foods and spices eaten by the mother. Breastfed infants can learn about the flavour of the food of their culture long before solids are introduced . Infants feed longer and more ove rall when milk is flavoured with either garlic or vanilla . Fo rmula fed infants also responded by increasing their intake when vanilla was added to the formula. However, the response diminished after repeated exposures. Perhaps the flavour became less arousing after exposure to it. Historically, nursing mothers have long been encouraged to consume a small amount of alcohol to improve their nursing experience by relaxing the mother, improving the let-down reflex and increasing milk production. However, current research has shown that alcohol actually decreases the amount of milk consumed during the three to four hours after mothers drink an alcoholic beverage.(9) This occurred even though the infants sucked more during the initial minutes of the feeds. The transfer of ethanol to the milk also transferred a flavour change in the milk, relative to the concentration of ethanol present. Researchers do not suggest that this flavour change is the reason for the decline in milk intake. Infants are not passive receptacles for flavoured foods. They cannot be expected to develop a sweet tooth or a preference for salty foods through manipulation of their diets. They will avidly accept some flavours and reject others. Pa rents who offer a variety of foods provide the opportunity for their infants to develop their ow n personal preferences while receiving a nutritious, balanced diet. References Cited
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