91. Determination of alpha- and
beta-acid concentrations in type-90 hop pellets by near infrared (NIR)
spectroscopy and chemometric analysis
James Redwine (1), Jacob Gallimore (1); (1) Kalsec, Inc., Kalamazoo, MI, U.S.A.
Analytical
Poster
Accurate information regarding the potency and quality of hops is of
utmost importance to the quality of the resulting beer. Two of the most
important potency parameters for hops are the concentrations of alpha-
and beta-acids (humulones and lupulones). Current methods for
determination of these values include UV/Vis spectrophotometric analysis
and HPLC analysis. While highly accurate and precise, these techniques
require substantial training and generate hazardous waste that must be
disposed of properly. In the presented work, diffuse reflectance NIR
spectroscopy with quantitative chemometric analysis is explored as an
option to determine the potency of type 90 hop pellets with minimal
sample preparation and no solvent usage. Two instrument technologies
were used. First, a research-grade Fourier transform NIR (FT-NIR)
instrument equipped with a diffuse reflectance sampling stage was used
to explore a wide wavelength regime at high resolution. Second, a
dispersive grating-based NIR instrument intended for at-line usage was
utilized to determine the applicability of NIR analysis of hops near the
site of pelletizing. Models for both alpha-acid and beta-acid content
were developed on both instruments with acceptable accuracy and
sensitivity. Chemometric models were developed using various
pretreatments of the data and utilizing partial least squares (PLS)
quantitative analysis. Resulting models for alpha-acid showed an R2
of 0.986 and root mean squared error of full cross-validation (RMSECV)
of 0.72% alpha-acid for the dispersive instrument and an R2 of 0.997 with RMSECV of 0.69% alpha-acid on the FT-NIR instrument. The resulting models for beta-acid had an R2 of 0.940 with RMSECV of 0.55% beta-acid on the dispersive instrument and R2
of 0.990 with RMSECV of 0.55% beta-acid on the FT-NIR instrument. The
presented work will highlight strategies that are most successful for
this application of NIR spectroscopy, including sample selection, sample
presentation, sampling methods, and mathematical pretreatments of the
spectral data.
James Redwine received a B.S. degree in chemistry from Michigan
State University in 2008, followed by a Ph.D. degree specializing in
analytical chemistry from Purdue University in 2013. That same year he
started employment in the Analytical group at Kalsec, Inc. in Kalamazoo,
MI, a producer of natural colors, natural flavor extracts,
antioxidants, hop extracts and nutritional ingredients for the food,
beverage and pharmaceutical industries.
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