Antioxidant Activity and Oxidative Stability of Flaxseed and Its Processed Products: A Review

Flaxseed (Linum usitatissimum) is one of the most important crops worldwide due to its nutritional and functional properties. Given the diversity of flax and its processed products, this review aimed to systematize and analyze data on their antioxidant properties, oxidative stability, and content of biologically active substances. The literature search was conducted using the following databases: Scopus and The Lens. This review examines the approaches to studying the antioxidant properties, oxidative stability, and content of biologically active substances of flax and its processed products, which are used in the food industry, highlighting the advantages and limitations of the methods employed. For the analysis of AOA and OS in flaxseeds and their processing products, the most common approach is the in vitro model. For AOA assessment, non-standardized methods such as DPPH•, FRAP, and ABTS•+ are most frequently used, while standard methods for determining OS (PV, AV, p-AnV, CDs, CTs, TBARSs, OSI) are employed. However, these parameters are integral and cannot fully explain the underlying processes. In our opinion, the most promising directions for further research are the standardization of methods for analyzing the antioxidant activity (AOA) of flaxseed and its processing products. Furthermore, expanding the methodological framework will lead to a better understanding of the mechanisms of oxidative processes and how to inhibit them. An expanded set of AOA assessment methods will allow researchers not only to study the action of antioxidants but also to predict it. This is particularly relevant since the same antioxidant can exhibit both antioxidant and pro-oxidant effects.