Determination of total polyphenol from walnut kernel pellicle and the effect of walnut kernel pellicle on walnut storage quality

To establish an assay method, Folin-Ciocalteu colorimetric was used to determine the total polyphenol in walnut kernel pellicle (WKP) and study the influence of polyphenol on walnut kernel quality during the process of storage. WKP and gallic acid were used as raw material and standard, respectively. The results indicated that the optimum conditions for determining total polyphenol were as following:1.0mL of the WKP extract polyphenol, 1.5mL of Folin-Ciocalteu reagent dosage and 1.0mL of 20% sodium carbonate solution, treatment at 60℃ for 60min and 60% ethanol as extract solvent, the average spiked recovery was 99.86%, with a RSD of 2.87%. There was a good linearity between the absorbance and gallic acid concentration from 4.4 to 30.8μg/mL (R2=0.9994) in 765nm. This method was easy to operate, accurate, sensitive, stable and high recovery rate. It could be used as an appropriate method to measure the polyphenols in WKP. The distribution of polyphenol in walnut was WKP (21.73%) >walnut peel (6.37%) >walnut shell (2.92%) >walnut kernel (0.77%) . During the process of walnut storage, the polyphenol content of WKP increased quickly and then tended to be stable while the acid and peroxide value was increasing all the time. WKP had little effect on the quality of walnut.