A single-step microdistillation procedure for the determination of total vicinal diketones in beers

Abstract

Vicinal diketones (VDK) strongly affect the quality of beers, as they are responsible for off-flavors and deterioration markers, which are recognized as safe for humans when ingested but are toxic when inhaled. Thus, their determination is required in both the production process and the final beverage. A novel approach for determining the total VDK content in beers using microdistillation as a simple approach for sample pretreatment is proposed. The lab-made microdistillation apparatus consists of a capped Falcon® tube with the sample at the bottom and the acceptor solution inside a suspended Eppendorf® tube. The sample is heated (90 °C, 20 min) to volatilize the analytes, which are collected from the headspace by an acceptor-derivatizing solution (o-phenylenediamine in acid medium), and the product is determined by ultraviolet spectrophotometry. Under conditions optimized by experimental design, a linear response was achieved from 0.05 to 1.00 mg L-1 diacetyl, with a coefficient of variation (n = 11) and limit of detection (95 % confidence level) estimated at 4.3 % and 0.01 mg L-1 diacetyl, respectively. The procedure requires as low as 40 μg of o-phenylenediamine, 1.7 μL of 37 % (v/v) hydrochloric acid, and 5000 μL of sample, generating only 5400 μL of waste per determination. It allows for the simultaneous analysis of 10 samples, a capability not previously reported in the literature. Results obtained for Ale and Lager beers using the proposed and reference procedures agreed at a 95 % confidence level. Therefore, the current proposal is a reliable and environmentally friendly alternative for the rapid determination of VDKs in beer, contributing to improved quality control in both the process and final products of the brewing industry.