Among the 20 proteinogenic amino acids, 19 can exist in two stereoisomeric forms, D- and L-enantiomers except glycine. According to conventional theory, L-amino acids are the main body involved in life activities, while little attention has been paid to the existence and physiological activity of D-amino acids in organisms. With the development of analytical technologies for chiral amino acids, a large number of D-amino acids and bioactive peptides containing D-amino acids have been found in various organisms, including mammals, plants, microorganisms and humans. D-amino acids possess unique physiological activities such as neural signal transduction, hormone regulation, antibacterial effect and immune regulation. Daily diet is an important source of D-amino acids for humans, and the daily average supply of D-amino acids for humans is about 100 mg. D-amino acids in foods mainly origin from processing conditions such as fermentation, high temperature and certain pH, along with a small amount from food raw materials. At present, emerging functional foods with D-amino acids as the major component have begun to appear in the market. D-amino acids hold great potential that deserves to be explored further and are expected to be an important ingredient for the development of new functional foods in the future.

Mitochondrial dysfunction is proposed to be substantially associated with ageing and ageing-related diseases like Alzheimer's disease (AD). However, it is unclear whether different mouse models with mitochondrial-related diseases have similar changes in mitochondrial morphology of the same tissues. Moreover, whether similarities in mitochondrial morphology can be a suitable marker for screening and/or discovering mitochondrial-protective substances remains unknown. Mitochondria morphology in different tissues of a novel mitochondrial outer membrane protein Slc25a46 knockout mouse and a traditional APP_SWE/PS1ΔE9 transgenic mouse were examined using transmission electron microscope (TEM). Both young Slc25a46 knockout mice and aged APP_SWE/PS1ΔE9 mice models showed similar mitochondrial damage in cerebellum tissues. The results indicated that different mitochondrial-related diseases shared similar alteration and defects in mitochondrial morphology. Furthermore, Lycium ruthenicum Murr. extract, a bioactive food substance with cognition-improving property, could effectively improve muscle strength and increase body weight in the Slc25a46 knockout mice. These findings suggest that mitochondrial morphology defects in mice models, particularly in the mitochondrial compartment, represent a unified and effective marker for screening and validating natural product-derived functional substances with mitochondrial protective properties. It also holds potential application in mitochondrial-impaired senile neurodegenerative diseases, especially in AD.