TITLE:
A Rapid Method for Measuring Seed Protein Content in Cowpea (Vigna unguiculata (L.) Walp)
AUTHORS:
Yuejin Weng, Ainong Shi, Waltram Second Ravelombola, Wei Yang, Jun Qin, Dennis Motes, David Octor Moseley, Pengyin Chen
KEYWORDS:
Cowpea, Seed Protein Content, Protein Measurement Method, Rapid N Analyzer, Near-Infrared Reflectance (NIR), Vigna unguiculata
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.8 No.10,
September
13,
2017
ABSTRACT: Cowpea (Vigna unguiculata (L.) Walp), a legume crop that is grown in the worldwide, provides beneficial proteins for human consumption and animal
feeding. In comparison, Rapid N analyzer as traditional method, has been widely
used to measure protein content through the percentage of total nitrogen in the
seed’s grounded powder. Near-Infrared Reflectance (NIR) has commonly been used
to measure protein content in soybean seeds using whole grain without the need
of seed grinding, which makes it possible to obtain fast results at a lower
cost-per-analysis than the traditional combustion method. The specific
objective of this study is to test a rapid method for measuring cowpea seed
protein content by the NIR analyzer comparing to the traditional rapid N
analyzer. A total of 240 cowpea genotypes were used in this study, including six
seed coat colors, black, blackeye, browneye, cream, pinkeye, and red with 40
cowpea genotypes. The results showed that a linear relationship exists between
the NIR analyzer and the Rapid N analyzer in the six different color groups. The
correlation efficiency (r) between the seed protein contents from NIR and Rapid N
was higher for pinkeye seed (r = 0.867), blackeye (0.771), cream
(0.729), browneye (0.700), and red (0.623), respectively, but lower for black seeds, indicating that the NIR analyzer can be used to measure protein content for cowpea seeds
with the five types of seed coat except black. Overview, the cowpea seed
protein content measured from the NIR analyzer showed a little higher seed
protein content. A series of regression models with different seed coat color
have been built to adjust to protein content of colorful cowpea seeds from the
NIR analyzer. But, it is not recommended to use for black color seeds due to a
very low correlation efficiency (r) value with 0.184.