Amaranth, Flax, and Buckwheat Microgreens: Nutritional Quality, Bioactive Diversity, Precision Cultivation, and Health-Functional-Food Potential

Amaranth, flax, and buckwheat were selected as complementary microgreen matrices with distinct botanical origins and research priorities: betalain-associated pigmentation in amaranth, light-responsive quality traits in flax, and rutin- and flavonoid-rich profiles in buckwheat. This narrative review critically synthesizes peer-reviewed evidence on crop-specific nutritional quality, bioactive diversity, precision cultivation, food applications, bioaccessibility, safety, and functional-food potential. Direct evidence from studies explicitly investigating microgreens is distinguished from contextual evidence derived from seeds, sprouts, mature tissues, oils, flours, and processed products; numerical values from these matrices are not transferred to microgreens. Across the three crops, genotype, developmental stage, light spectrum, supplemental UV-B exposure, substrate or hydroponic design, harvest timing, and postharvest management can modify yield and quality-related traits. Pigmented amaranth is especially relevant to betalain- and color-focused applications; flax is a comparatively under-characterized oilseed-derived microgreen with informative light-response evidence; and common and Tartary buckwheat provide strong opportunities for rutin and flavonoid profiling and genotype comparison. The available literature does not support a single numerical ranking across crops, and compositional richness or in vitro antioxidant activity should not be interpreted as evidence of clinical efficacy. Standardized reporting, targeted foodomics, sensory and processing validation, safety control, resource-use assessment, and controlled human studies are priority directions for future research.