Víctor Marín Delgado. Master´s student of Biotechnology and Bioengineering (2015-2016).
Reference: Methven L, Allen VJ, Withers CA, Gosney MA. Ageing and taste. Proceedings of the Nutrition Society 2012; 71: 556-565.
The elderly are at risk of malnutrition due to numerous factors, which can be classified into 3 categories: psychological, physiological, and socio-economical. In this context, one of the complaints of this population group is the blandness of the food. This perception is due to the sensorial changes that affect their sense of taste, and as a consequence affects their food consumption, increasing the risk for malnutrition.
The review presented here revised a total of 69 articles, selected using certain inclusion and exclusion criteria. The inclusion criteria include that the research was performed both in young adults and elderly and that both populations were healthy. The articles revised presented a large variety of populations studied, from 12 individuals to 761, the average being approximately 60. The studies focused on the minimum perception for certain tastes, which are known as taste concentration thresholds for the modalities of sweetness, salty, bitter, sour and umami (meaty taste).
There are many discrepancies in these studies, due to the variability of the number of individuals analysed (age range, variation in percentages of men and women, different inclusion and exclusion criteria, etc), as well as the methodologies used. In this manner, a large variability was observed in the method that the tastes were administered, as this will determine the sensibility of each individual for each taste. Furthermore, the techniques to measure the level of sensibility differs. For example, some studies used electrogustometry, a common technique to detect the threshold of complex flavours, although of little use to measure them individually. The studies that assessed the flavours individually have occasionally used different flavourings to measure the same category, and very little of them have assessed whole foods or beverages.
The results obtained in the different studies that analyse the flavour categories separately were:
- Salty: The studies used NaCl (sodium chloride) as flavouring, although similar results were observed with other salts. Taste threshold increased with age, although variability was observed with different salts.
- Sour: Different acids were used, such as citric acid, tartaric or acetic. In the majority of the studies the threshold increased with age, except with citric acid, where a higher sensitivity was observed in young women.
- Bitter: A variety of flavourings were used (up to 30). The most common were caffeine and quinine variants (common in tonics). Also, a correlation with certain genetic profiles were studied in several reports where quinine was used. However, no conclusive results were obtained.
- Sweetness: This was the most discussed flavour, as the studies that used sucrose, half of them did not detect changes with age, while other reported a decrease with age. Also, the age where the decrease was reported was varied.
- Umami: Unlike the previous flavour, there as a large consensus in this case, where an increased umami threshold was detected with age.
The threshold where flavour is perceived and the level of decrease are not the only factors that are of interest, but also the intensity of the flavour perceived in sub-umbral levels. It is precisely this situation that is closer to reality, as the flavouring concentrations found in the foods are generally sub-umbral. The majority of the studies that considered this factor detected a decrease in the intensity of flavour perception, especially for caffeine, citric acid, quinine and NaCl. Again, there was little consensus regarding sucrose at sub-umbral levels.
Considering all the studies as a whole, there is a generalized consensus that flavour threshold and sensitivity decreases with age. However, the level of decrease varies depending on the study. The effect of age in this sensorial perception is complex, not only due to the heterogeneity of the methods used, but also of the samples. Therefore, the main conclusion is that flavour perception decreases with age, although there is little evidence as to what age does this decrease commence.
Understand the factors and level of decrease in perception can be useful for the development of foods especially designed for the elderly, as this loss can be compensated by strengthening certain aspects of the product. However, the method should be carefully considered, as for example the addition of extra salt could compensate the perception loss, but in turn increases the risk for diseases such as hypertension.
Other factors must be considered when evaluating levels of perception, such as the use of dentures, which affect salivation and cover part of the palate; or in smokers, which negatively influences flavour perception.
Despite the fact that the majority of the studies have shown a significant decrease in perception at sub-umbral levels, the degree of decrease, as well as perception threshold, are still under debate, despite being an important factor in the development of foods and beverages for adults. No correlation was detected regarding the individual´s preferred flavouring concentration and its threshold, although there is a negative correlation between sub-umbral perception and concentration, indicating that individuals with decreased perception prefer higher concentrations of the flavour.
Considering all the points commented previously, it can be confirmed that knowing the decrease in flavour perception in the adult is of vital importance in order to prepare meals with strong flavours and smells in order to increase the taste of the elderly for food. This is a strategy to consider in order to avoid malnutrition in this population. The challenge is to find the adequate flavourings in order to avoid any risk in their health.