Insight into the occurrence of betaines in plant foods for human nutrition.

Betaines are naturally occurring quaternary ammonium compounds derived from amino (or imino) acids through specific biosynthetic pathways involving the exhaustive nitrogen methylation process. Betaines are ubiquitous plant constituents with species-specific distribution patterns in fruits and vegetables. Human dietary intake of exogenous betaines is mainly from plant foods. Scientific evidence has emerged that several betaines found in the human diet play a key role in maintaining health, acting as a defense mechanism against a range of aging-related diseases and disorders. However, the underlying mechanisms remain poorly understood.

In this study, we report LC-ESI-MS/MS quantification of betaines in a variety of fleshy fruits, including drupes (peaches, plums), pomes (apples, pears), and berries (bananas, grapes, strawberries, oranges, lemons, and mandarins), as well as cereals (rice, wheat, millet, and oats) and pseudocereals (quinoa) commonly consumed in human diets.

Betaines were extracted from the samples by homogenization with aqueous formic acid and purified by ion-exchange chromatography prior to LC analysis on a C8 column. Identification of the betaines was based on their retention times, MS² fragmentation patterns, and comparison with authentic standards.

The results of this study agreed with data reported in the previous literature. The analysis of cereal samples revealed a glycine betaine content range of 10 mg/kg in rice to 300 mg/kg in wheat. Notably, it was particularly abundant in quinoa, a pseudocereal belonging to the Amarantaceae family. Conversely, the concentration of this compound was found to be significantly lower in fleshy fruits.

A significantly higher concentration of proline- and 4-hydroxyproline-derived betaines was observed in fruit samples belonging to the Citrus genus when compared to other analyzed samples.

These results provide insight into the associations between dietary intake of plant-based foods and the use of specific betaines as dietary biomarkers.