A comprehensive review on wheat phytochemicals: Chemistry and distribution, field management and processing effects, bioaccessibility, and health benefits

Authors: TIAN, WENFEI - Kansas State University; ZHENG, YI - Kansas State University; WANG, WEIQUN - Kansas State University; WANG, DONGHAI - Kansas State University; Tilley, Michael - Mike; ZHANG, GUORONG - Kansas State University Agricultural Research Center-Hays; HE, ZHONGHU - Chinese Academy Of Sciences; LI, YONGHUI - Kansas State University

Submitted to: Comprehensive Reviews in Food Science and Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2022
Publication Date: 5/23/2022
Citation: Tian, W., Zheng, Y., Wang, W., Wang, D., Tilley, M., Zhang, G., He, Z., Li, Y. 2022. A comprehensive review on wheat phytochemicals: Chemistry and distribution, field management and processing effects, bioaccessibility, and health benefits. Comprehensive Reviews in Food Science and Food Safety. 21:2956-3009. https://doi.org/10.1111/1541-4337.12958.
DOI: https://doi.org/10.1111/1541-4337.12958

Interpretive Summary: Epidemiological studies have found that consumption of whole grain products may reduce risk of chronic diseases such as obesity, type 2 diabetes, cardiovascular diseases, and cancer. The health-promoting effects of whole grain products can be attributed to their dietary fibers and phytochemical constituents. Driven by consumers’ desires for healthy food ingredients and products, wheat breeders and producers are becoming interested in phytochemicals as another parameter in the evaluation of wheat quality in addition to the conventional targets such as grain yield and end-use properties. The past two decades has witnessed significant progress on research of wheat phytochemicals in the whole wheat chain, e.g., from farm to fork. Changes of wheat phytochemicals during grain processing and food-making are investigated. Various processing technologies have been developed for increased nutraceutical values of whole wheat flour and whole wheat products. However, a considerable number of questions remains to be addressed. For example, the in situ linkages between phytochemicals and major wheat components (starch, protein, and cell wall polysaccharides) are poorly understood. Also, the change of phytochemicals during long-term storage is not been thoroughly investigated. Even among areas that have been extensively reported, there are some limitations in the extraction and characterization methods, which often led to inconsistent results and inappropriate data interpretations. In this review, we begin with an introduction of the fundamental chemistry and occurrence of wheat phytochemicals which are essential but not covered in detail in previous reviews. We highlight the importance and future research opportunities of ester and/or glycoside forms of carotenoids, tocopherols, and phytosterols that have not been well recognized and investigated. We comment on different extraction protocols of wheat phytochemicals and in vitro antioxidant assays that sometimes lead to difficulty in data interpretation. Then, we critically select and describe recent progress on health-promoting properties of wheat phytochemicals. We further cover literature on the effects of genotypes (G), field managements (M), environments (E), and grain and food processing including milling, germination, fermentation, enzymatic treatments, thermal treatments, and other processes. Studies that shed light on bioaccessibility and metabolite pathways of wheat phytochemicals are also reviewed. This article covering wheat phytochemical from farm to fork will serve as a useful reference for both experts and non-experts in the field.

Technical Abstract: Phenolic acids, flavonoids, alkylresorcinols, carotenoids, phytosterols, tocopherols, and tocotrienols are major wheat phytochemicals. Health benefits of whole wheat consumption are partially attributed to its phytochemicals. It is of increasing interest to produce whole wheat products rich in bioactive phytochemicals. We reviewed fundamentals on chemistry, extraction and occurrence of wheat phytochemicals and addressed several long-lasting key issues and pitfalls in this field that need to be further resolved: 1) commonly used nomenclature on distribution of wheat phenolic acids, namely soluble-free, soluble-conjugated and insoluble-bound phenolic acids; 2) different extraction protocols for wheat phytochemicals; and 3) chemistry and application of in vitro antioxidant assays. We also discussed recent advances on health benefits of wheat phytochemicals and effects of genotypes, environments, field managements, and processing techniques on the health benefits. Bioaccessibility of wheat phytochemicals were also covered in this review. We believe that this comprehensive and critical review will be beneficial to both the researchers and the general public who are concerned about the bioactive compounds of cereal grains.