In this work the optimization and application of a dual-amperometric biosensor for simultaneous monitoring of glucose and ethanol content, as quality markers in drinks and alcoholic fermentation media, are described. The biosensor is based on glucose oxidase (GOD) and alcohol oxidase (AOD) immobilized by co-cross-linking with bovine serum albumin (BSA) and glutaraldehyde (GLU) both onto a dual gold electrode, modified with a permselective overoxidized polypyrrole film (PPYox). Response, rejection of interferents, and stability of the dual biosensor were optimized in terms of PPYox thickness, BSA, and enzyme loading. The biosensor was integrated in a flow injection system coupled with an at-line microdialysis fiber as a sampling tool. Flow rates inside and outside the fiber were optimized in terms of linear responses (0.01-1 and 0.01-1.5 M) and sensitivities (27.6 ± 0.4 and 31.0 ± 0.6 μA·M-1·cm-2) for glucose and ethanol. Excellent anti-interference characteristics, the total absence of "cross-talk", and good response stability under operational conditions allowed application of the dual biosensor in accurate real-time monitoring (at least 15 samples/h) of alcoholic drinks, white grape must, and woody biomass.

Benzoic acid and its salts are commonly used additives in the food industry. Their use is not allowed in dairy products even though they can be found naturally. In this work, 100 cheese samples were tested to establish the maximum concentration that can be considered as "natural" and, therefore, permitted in cheeses. Analyses were carried out by a validated ion chromatography method and "positive" samples were confirmed by two other HPLC methods. Benzoic acid concentrations higher than the method LOQ (8.8 mg kg -1) were found in 18 samples, ranging from 11.3 to 28.7 mg kg -1, with a mean value of 20.5 mg kg -1. Taking into account the distribution of benzoic acid concentrations observed in "positive" samples, it is plausible to estimate a maximum admissible limit of 40.0 mg kg -1 for benzoic acid in cheese. Below this value, samples can be considered "compliant". © 2011 Copyright Taylor and Francis Group, LLC.