Aroma and Flavor in Liquid Beet Sugar Processing

Doctoral thesis, 2000

Production of liquid beet sugar, a product of increasing importance for the food industry, involves many different compounds exhibiting aroma. Aroma compounds are introduced with the raw material, the sugar beets, but also formed as a result of sugar degradation (caramelization and Maillard reaction) or by contamination from process steps, such as adsorbents and ion exchangers. In order to elucidate which compounds are responsible for flavor and aroma in liquid sugar, liquid sugar samples of different purity were produced and analyzed with respect to volatile compounds and these analyses included headspace-GC-MS (gas chromatography-mass spectrometry) analysis, headspace-GC-O (-olfactometry) analysis, sensory analysis, and electronic nose analysis. GC-data were analyzed for correlation with sensory data to find compounds responsible for perceived aromas and flavors using multivariate techniques (PLS). Samples from different parts of the raw sugar production and its subsequent refining were also collected and analyzed to recognize a pattern of the formation and disappearance of volatile compounds in the process. These samples from different parts of the liquid sugar manufacturing process were analyzed with liquid-liquid extraction followed by GC-MS and GC-O and dynamic headspace followed by GC-MS/FID (Flame ionization detector) and GC-O. In addition to these investigations the influence of macromolecules in the liquid sugar matrix on the release of selected aroma compounds was studied. Butanone, heptane-2-one, 2,6-dimethylpyrazine, 2-ethyl-5-methylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,5-dimethylfuran, dimethyldisulfide, and p-methoxyphenol were positively correlated to the analyzed sensory attributes for aroma and flavor. Liquid sugar samples of different purity obtained within normal range of process conditions, were differentiated by the electronic nose. Different patterns of volatile and aromatic compounds were identified at various stages of the sugar manufacturing process. It was shown that compounds giving sour and earthy aromas together with fruity aromas predominated in the early parts of the process and that caramel-like and burnt aromas increased in the process. Aldehydes, ketones, and alkylpyrazines were the groups of compounds that increased the most in the liquid sugar manufacturing process. In the final product the amounts of alkylpyrazines, ketones, aldehydes, cyclotene, and dimethyldisulfide were still high. Some compounds, such as small ketones, even exhibited higher concentrations in the final product than in refinery samples taken further upstream. It was, furthermore, shown that butanal, 2-hexanol, and p-methoxyphenol were significantly less released from the liquid sugar matrix to the headspace when macromolecules of refinery origin were included in the matrix.