Rapid identification of black peanut seeds by confocal micro-Raman and near-infrared FT-Raman spectroscopy

Abstract

Confocal micro-Raman spectroscopy and near-infrared (NIR) FT-Raman spectroscopy were used to analyse and identify cotyledons and the skins of black, white, red and ordinary pink peanut seeds. The former method was equipped with a 785 nm semiconductor laser and a 514 nm Ar⁺ laser; the latter method was equipped with a 1064 nm Nd:YVO₄ laser. These methods were also utilised to distinguish black peanut seeds from cheap and imitation coloured black peanut seeds. Significant Raman vibration peaks were detected and assigned by 785 nm Raman and 1064 nm NIR FT-Raman spectroscopy for the black peanut cotyledons. Three bands in the 1064 nm NIR FT-Raman spectra of peanut skins could have critical functions in distinguishing black peanuts from the other three peanut varieties. The two rapid, simple spectral analysis approaches were also demonstrated to distinguish black peanut seeds from coloured black peanut seeds, which is important to ensure food quality and safety.