RESUMO
Beer is an extremely complex mixture of more than 3,000 different compounds in an aqueous environment. Thus, it is perhaps not surprising that the maintenance of beer quality throughout its lifetime has been a considerable challenge for brewers. Whilst it is inevitable that chemical changes will occur in beer with the passage of time, it is the formation of flavor-active components which is of immediate concern to an overview of beer shelf life stability. Sulfur dioxide has long been recognized by brewers as the most important factor in delaying flavor staling, and prolonging the shelf life of beer. However, nowadays, sulfur dioxide and sulfites are considered allergens and concerns about the safety of their use as food additives have been on the increase. The present review is structured into three main parts. Firstly, the chemical properties of sulfur dioxide are presented, along with the toxic effects and maximum legal levels permitted according to U.S. and EU legislation. As the accurate determination of the free, bound and total sulfur dioxide in beer is essential to ensuring regulatory compliance, several methods have been developed for analyzing sulfur dioxide in beer. Thus, secondly, various types of methods are reported and compared with the officially recommended ones. Finally, the crucial role of sulfite in the control of flavor instability of beer is discussed in light of the current data. Two courses of action have been proposed, which are elucidated in detail relating firstly to the fact that sulfite inhibits beer oxidation during storage by acting as an antioxidant and, secondly, sulfite reacts with the carbonyl staling compounds in beer, and thereby masks stale flavors.
Assuntos
Cerveja/análise , Dióxido de Enxofre , Indústria Cervejeira , Padrão de Identidade e Qualidade para Produtos e Serviços , SulfitosRESUMO
Beer is an extremely complex mixture of more than 3,000 different compounds in an aqueous environment. Thus, it is perhaps not surprising that the maintenance of beer quality throughout its lifetime has been a considerable challenge for brewers. Whilst it is inevitable that chemical changes will occur in beer with the passage of time, it is the formation of flavor-active components which is of immediate concern to an overview of beer shelf life stability. Sulfur dioxide has long been recognized by brewers as the most important factor in delaying flavor staling, and prolonging the shelf life of beer. However, nowadays, sulfur dioxide and sulfites are considered allergens and concerns about the safety of their use as food additives have been on the increase. The present review is structured into three main parts. Firstly, the chemical properties of sulfur dioxide are presented, along with the toxic effects and maximum legal levels permitted according to U.S. and EU legislation. As the accurate determination of the free, bound and total sulfur dioxide in beer is essential to ensuring regulatory compliance, several methods have been developed for analyzing sulfur dioxide in beer. Thus, secondly, various types of methods are reported and compared with the officially recommended ones. Finally, the crucial role of sulfite in the control of flavor instability of beer is discussed in light of the current data. Two courses of action have been proposed, which are elucidated in detail relating firstly to the fact that sulfite inhibits beer oxidation during storage by acting as an antioxidant and, secondly, sulfite reacts with the carbonyl staling compounds in beer, and thereby masks stale flavors.(AU)
Assuntos
Cerveja/análise , Indústria Cervejeira , Padrão de Identidade e Qualidade para Produtos e Serviços , Sulfitos , Dióxido de EnxofreRESUMO
Malus domestica Borkh. cv Bravo de Esmolfe is a typical Portuguese apple cultivar classified as Protected Designation and Origin (PDO). It is a traditional product produced under strict conditions and labelled with a specific law protected designation. This cultivar presents quite good sweetness and flavor. The monosaccharide composition of the pectic polysaccharides from this traditional apple is herein reported for the first time. Based on the molar ratios obtained from the sugar composition, the presumable pectin structure could be inferred. The cell-wall polysaccharides present in the alcohol-insoluble residue (AIR) of unpeeled BE apple were sequentially fractionated. In addition, pectic material was also extracted by citric acid treatment prior to heat extraction at acidic pH. The water soluble pectin, imidazole soluble pectin and sodium carbonate soluble pectin account for 44, 16 and 40 % of the AIR, respectively. The pectic polysaccharides extracted in the presence of citric acid had lower galacturonic acid content and higher neutral sugars content. The homogalacturonan (HG) and less-substituted rhamnogalacturonan (RG) domains are extracted first. Pectin treated with citric acid has been shown to contain more substituted polymers, especially RG-I. In addition, the relatively higher Xylose/Galacturonic acid ratio found in the citric acid extract demonstrates that the xylogalacturonan (XG) domain presumably is present in the pectic material of the unpeeled BE apple.
Assuntos
Malus/química , Pectinas/análise , Ácidos UrônicosRESUMO
Malus domestica Borkh. cv Bravo de Esmolfe is a typical Portuguese apple cultivar classified as Protected Designation and Origin (PDO). It is a traditional product produced under strict conditions and labelled with a specific law protected designation. This cultivar presents quite good sweetness and flavor. The monosaccharide composition of the pectic polysaccharides from this traditional apple is herein reported for the first time. Based on the molar ratios obtained from the sugar composition, the presumable pectin structure could be inferred. The cell-wall polysaccharides present in the alcohol-insoluble residue (AIR) of unpeeled BE apple were sequentially fractionated. In addition, pectic material was also extracted by citric acid treatment prior to heat extraction at acidic pH. The water soluble pectin, imidazole soluble pectin and sodium carbonate soluble pectin account for 44, 16 and 40 % of the AIR, respectively. The pectic polysaccharides extracted in the presence of citric acid had lower galacturonic acid content and higher neutral sugars content. The homogalacturonan (HG) and less-substituted rhamnogalacturonan (RG) domains are extracted first. Pectin treated with citric acid has been shown to contain more substituted polymers, especially RG-I. In addition, the relatively higher Xylose/Galacturonic acid ratio found in the citric acid extract demonstrates that the xylogalacturonan (XG) domain presumably is present in the pectic material of the unpeeled BE apple.(AU)