Characterization of polymeric substance classes in cereal-based beverages using asymmetrical flow field-flow fractionation with a multi-detection system

Abstract

Cereal-based beverages contain a complex mixture of various polymeric macromolecules including polysaccharides, peptides, and polyphenols. The molar mass of polymers and their degradation products affect different technological and especially sensory parameters of beverages. Asymmetrical flow field-flow fractionation (AF4) coupled with multi-angle light scattering (MALS) and refractive index detection (dRI) or UV detection (UV) is a technique for structure and molar mass distribution analysis of macromolecules commonly used for pure compound solutions. The objective of this study was to develop a systematic approach for identifying the polymer classes in an AF4//MALS/dRI/UV fractogram of the complex matrix in beer, a yeast-fermented cereal-based beverage. Assignment of fractogram fractions to polymer substance classes was achieved by targeted precipitations, enzymatic hydrolysis, and alignments with purified polymer standards. Corresponding effects on dRI and UV signals were evaluated according to the detector's sensitivities. Using these techniques, the AF4 fractogram of beer was classified into different fractions: (1) the low molar mass fraction was assigned to proteinaceous molecules with different degrees of glycosylation, (2) the middle molar mass fraction was attributed to protein-polyphenol complexes with a coelution of non-starch polysaccharides, and (3) the high molar mass fraction was identified as a mixture of the cell wall polysaccharides (i.e., β-glucan and arabinoxylan) with a low content of polysaccharide-protein association. In addition, dextrins derived from incomplete starch hydrolysis were identified in all fractions and over the complete molar mass range. The ability to assess the components of an AF4 fractogram is beneficial for the targeted design and evaluation of polymers in fermented cereal-based beverages and for controlling and monitoring quality parameters.

Influence of malt modification and the corresponding macromolecular profile on palate fullness in cereal-based beverages

“…The cross-flow of the subsequent elution-steps was kept constant (4.0 ml/ min) for 5 min, and then it was decreased linearly to zero within two steps: (1) decrease to 0.2 ml/min within 10 min and (2) decrease to 0 ml/min within the next 10 min. The channel was rinsed for 21 min without an applied crossflow [18].…”

“…The molar mass and molar mass distribution were calculated by Berry's method using scattering angles of 57.0°-126.0°. The fractograms were divided into sub-fractions, which we had previously classified [18]: fraction 1 was assigned to (glycosylated) proteins [refractive index increment (dn/dc): 0.185 ml/g], fraction 2 was assigned to protein-polyphenol complexes (dn/dc: 0.146 ml/g), and fraction 3 was assigned to cell wall polysaccharides (dn/dc: 0.146 ml/g). Dextrins were spread over all fractions.…”

“…The corresponding macromolecular profile and molar masses are shown in Table 3. The indicated fractions represent the different substance classes, which we have previously classified within cereal-based beverages [18]. Differences in the elution behavior were monitored throughout all fractogram fractions for beverages produced from the differently modified malts.…”

“…The macromolecular profile of cereal-based beverages is generally determined by polymeric compounds (proteins, polysaccharides, and polyphenols) and their progress in depolymerization during processing [1,2,[18][19][20]. Since yeasts or specific strains of lactic acid bacteria (LAB) cannot metabolize high-molar-mass substances [21], the macromolecules are solely depolymerized during the malting and mashing process by the malt's intrinsic enzymes.…”

“…Asymmetrical-flow field-flow fractionation (AF4) coupled with multi-angle light-scattering detection (MALS) and refractive-index detection (dRI) has been shown to be a suitable tool to analyze the macromolecular profile of complex matrices in cereal-based beverages [1,2,[18][19][20]. Different substance classes have been identified within the fractogram fractions of cereal-based beverages, namely, proteins (fraction 1), protein-polyphenols (fraction 2), cell wall polysaccharides (fraction 3), and dextrins, eluting throughout all fractions [18]. Using AF4-MALS, a high range of variation within the macromolecular profiles was shown for commercial German lager beers and for non-alcoholic beers, which was attributed to different production methods [1].…”