Phytochemicals are valuable non-nutritive molecular entities in various nutrient-rich plants, including fruits, vegetables, grains, legumes, and nuts (Jimenez-Garcia et al., 2018). The molecules are also present during metabolic processes, from seed germination to plant growth and development, and as self-defence against pests (Jimenez-Garcia et al., 2018). Polyphenols embody the largest group of phytochemicals, where carotenoids and vitamins are high-value supermolecules with remarkable antioxidative properties against reactive oxygen species (ROS) (Santhiravel et al., 2022). Phytochemicals, such as carotenoids, have also substantially impacted human disease treatments, including cancer, cardiovascular, atherosclerosis, rheumatoid arthritis, and muscular dystrophy, due to their intrinsic protective features (Lauritano et al., 2016). The minute amounts of carotenoids and vitamins recovered from land resources and their growing demand have prompted the generation of their synthetic counterparts in bulk by employing inexpensive manpower and chemicals (Novoveská et al., 2019). Nevertheless, consumers are more inclined towards natural nutraceuticals than their artificial counterparts due to increased health cognisance (Li et al., 2018). The preference shift in consumers has led to interest in microalgae as a potential substitute carotenoid source (Li et al., 2018).

Neutral lipid sourced from microalgae is a premier source for producing green biodiesel. The biodiesel is obtained through transesterification, with the carbohydrate fraction as an alternative feedstock in manufacturing bioethanol via fermentation (Suparmaniam et al., 2019). Microalgae also secrete various secondary metabolites, such as antioxidants and allelochemicals (Martínez-Francés and Escudero-Oñate, 2018). Mass microalgae farming for high-value phytochemicals (HVPCs) is profitable (Gauthier et al., 2020) due to their metabolic versatility over terrestrial crops, including exceptional growth rates and highly efficient photosynthesis (circa 6–8%) (Suparmaniam et al., 2022b). Consequently, classifications of microalgae-sourced phytochemicals and detailed biological applications have been extensively documented (Coulombier et al., 2021). Fig. 1 illustrates the multifaceted contributions of phytochemicals to human health.

Remarkable advancements and technological progress in algal biotechnology during the recent Anthropocene led to numerous reports of various microalgae species accumulating copious HVPCs under diverse stress environments (Ambati et al., 2019). Under harsh conditions, microalgae undergo chlorophyll withdrawal from their nitrogen reservoir to support crucial cellular component synthesis for survival. Nonetheless, the process negatively affects the metabolic flux required for cell proliferation and overall biomass productivity, which has often been overlooked in previous studies (Suparmaniam et al., 2022a). The present review provided a holistic assessment of stress-integrated microalgae farming, focusing on the growth and productivity of microalgae species and their high-value products, such as carotenoids and vitamins. Suggestions and an in-depth possible amalgamation of manifold cultivation methods, metabolic pathways, plausible stress conditions, and crucial physiochemical parameters for efficacious cultivation systems to maximise biomass and the selected HVPCs were also discussed. Furthermore, a novel concept of utilising abiotic stress as a reliable method for generating phytovitamins from microalgae was provided in this review. The present study also comprehensively analysed the technological and economic aspects of microalgae-derived HVPCs production routes.