08 April 2022

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Effects of soy and bovine milk beverages on enamel mineral content

Lara Figini

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Soy-based beverages are increasingly being promoted as healthy alternatives to cow's milk, but literature data highlight their different anticariogenic and tampon-based properties compared to bovine milk. The anticariogenic properties of bovine milk have been recognized for many years and have been attributed to its major protein casein and bioavailable calcium and inorganic phosphate ions. Milk casein contains phosphoseryl residues in cluster sequences (-Ser(P)-Ser(P)-Ser(P)- Glu-Glu) that stabilize amorphous calcium phosphate. These complexes bind to the tooth surface providing a source of bio-available calcium and phosphate ions to help maintain saturation of the enamel mineral thereby inhibiting demineralization and promoting remineralization. Soy beverages are a stable emulsion of water, oil, protein and mineral salts,  are a source of lecithin, isoflavones (non-steroidal oestrogens) and vitamin E, do not contain lactose, have less saturated fat and have approximately the same protein content as milk. However, they usually have added sucrose and/or glucose to improve organoleptic (taste) properties [Dashper 2012].

Materials and methods
In a double-blind, randomized, crossover clinical trial accepted and available online from June 22, 2019 on Journal of Dentistry (will be coming soon published), the authors compared  enamel mineral content after consumption of bovine milk or a soy beverage. Human enamel slabs with subsurface lesions were prepared and inserted into intra-oral appliances worn by volunteers who consumed 200 ml of either bovine milk or a soy beverage over a 60 s period once a day for 15 days. Enamel lesion depth and mineral content were measured using transverse microradiography. Saliva samples were collected immediately after consuming the beverages and calcium, inorganic phosphate and fluoride levels analysed. Data were statistically analysed using a linear mixed model.

Results
Depth of the enamel subsurface lesions increased by 7.1 ± 2.0 µm and mineral content decreased by 47 ± 22 vol% min.µm after consumption of the soy beverage indicating demineralization. However, after consumption of bovine milk the depth of the lesions decreased by 7.6 ± 3.5 µm and mineral content increased by 202 ± 43 vol% min.µm indicating remineralization. The changes were significantly different (p < 0.001) between the two beverages. Fluoride levels were similar in the saliva samples for both beverages, however the calcium and inorganic phosphate levels for the bovine milk group were significantly higher (p < 0.02) than those for the soy beverage group.

Conclusions
From the data of this study, which must be confirmed with other similar studies, it can be concluded that regular and prolonged consumption  of a soy beverage demineralized enamel whereas bovine milk produced remineralization.

Clinical implications
Although soy beverages are promoted as healthy alternatives to bovine milk the added sugar and low calcium bioavailability of the soy drink makes frequent consumption a caries risk.