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.


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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