Protein and starch in a mash can be centrifuged using water since they are a heavy molecules. The supernatant (top layer) should contain your phytochemicals.

You can use QuEChERS extraction by adding some water (10 mL) and acetonitrile 20-30 mL and shake. You will get a mixture of water and acetonitrile 30-40 mL. You will throw salt (MgSO4 and MgSO4) and shake to separate water and acetonitrile. Starch and protein will be in water side and your compound will be in acetonitrile phase. Protein will also precipitate (solvent crash) and will not be in the acetonitrile phase. You will centrifuge and take the acetonitrile for dispersive cleanup if you need it. Again, please Google and search for QuEChERS method to learn more about the role of solvent, salt, and disperse cleanup.

Dear Sir. Concerning your issue about the extraction of the phytochemicals (like benzoxazinoids, hydroxy cinnamic acid derivates, flavanoids from wheat bran. Optimized extraction of bioactive phytochemicals is of signifi-cant importance to accurately quantify the phytochemicalcontent in foods and plant products. Accurate quantificationallows establishment of proper dietary and safety guidelines.The bioactive phytochemicals exist in multiple forms: soluble(free and conjugated) and insoluble bound forms. It is essen-tialtounderstandvariousformsofthebioactivephytochemicalstoaccuratelyquantifythemandunderstandtheirbioavailabilityand health promoting properties. A wide array of extractionsolvents and technologies have been reported in the peer-reviewed literature (Herrero, Cifuentes, & Ibañez, 2006; Luthria,2012a).The conventional extraction methods include Soxhletextraction, stirring, distillation, manual mixing, and percola-tion. However, in recent decades, several new technologiesincluding, microwave assisted extraction, ultrasound-assistedextractions, pressurized liquid extraction, subcritical fluid ex-traction,solid-phaseextraction,andenzyme-assistedextractionhave been used to automate and/or improve the yields of bioactive phytochemicals. I think the following below links may help you in your analysis:

https://www.academia.edu/16412798/Bioactive_phytochemicals_in_wheat_Extraction_analysis_processing_and_functional_properties

http://onlinelibrary.wiley.com/doi/10.1002/mnfr.201600852/full

Thanks