Dear Sir. Concerning your issue about the determination of protein in fruits and plants using the spectrophotometer. For the assay to reliability of determination of the protein content in the pectic polysaccharide samples by absorbance in the ultraviolet and visible regions of the spectrum a comparison of the eleven techniques called Flores, Lovry, Bradford, Sedmak, Rueman (ninhydrin reaction) methods, the method of ultraviolet spectrophotometry, the method Benedict's reagent, the method Nessler's reagent, the method with amide black, the bicinchoninic reagent and the biuret method was carried out. The data obtained show that insufficient sensitivity of the seven methods from the listed techniques doesn't allow their usage for determination of protein content in pectic polysaccharide samples. But the Lowry, Bradford, Sedmak methods, and the method Nessler's reagent may be used for determination of protein content in pectic polysaccharide samples, and the Bradford method is advisable for protein contaminants content determination in pectic polysaccharide samples in case protein content is less than 15%, and the Lowry method--for samples is more than 15%. I think the following below links may help you in your analysis:

https://www.ncbi.nlm.nih.gov/pubmed/26165122 https://pdfs.semanticscholar.org/8ea0/34f639c9775d5a8736d3d808239ed798a709.pdf

http://www.ibt.lt/uploads/file/bvtl-2/assays_3.pdf

https://link.springer.com/article/10.1134/S1068162015020119

Thanks

http://onlinelibrary.wiley.com/doi/10.1002/0471142913.fab0103s04/abstract

Zheng Feei Ma, Isam Eldin Hussein Elgailani, Mohamed G. E. Gadallah.

Thank you for your answer, I wish to continue scientific communication.