Effects of variable grain hydration during steeping on the content and physicochemical properties of non-starch polysaccharides in malt and wort

Relationship Between Physical Characteristics of Cereal Polysaccharides and Soft Tribology-The Importance of Grain Source and Malting Modification

Starch and non-starch polysaccharides ((N)SPs) are relevant in cereal-based beverages. Although their molar mass and conformation are important to the sensory characteristics of beer and non-alcoholic beer, their triggering mechanism in the mouth is not fully understood. Soft tribology has emerged as a tool to mimic oral processing (drinking). The contribution of each (N)SPs to the friction coefficient can be determined when they are enzymatically isolated and characterized by chromatography techniques. Thus, this work aimed to study the relationship between the physical characteristics of isolated (N)SPs and their possible contribution to oral processing through soft tribology (friction). To accomplish this, this research analyzes the effect of grain source (barley, wheat, and oats) and its modification (by steeping degree at two levels) to the (N)SPs´ physical characteristics in wort produced on a laboratory scale. Different characteristics were present in the (N)SPs due to the grain source and the degree of modification. When comparing the impact of the grain source, the malted oats showed the highest molar masses. A higher modification degree produced smaller and more compact structures except for wheat's arabinoxylans and dextrins. The conformation ratio (r rms / r hyd ) values indicate the existence of sphere and micro-gel structures within each (N)SPs, with branches in arabinoxylans and dextrins. Subsequently, soft tribology was measured on all the worts and their correlation to the (N)SPs' data was performed by multivariate analysis. The wort produced with high modification grains generated higher friction responses. However, this was only statistically significant in barley samples. The multivariate analysis showed that within the mouth (tongue) velocity, the apparent density of the (N)SPs, and the molar mass of arabinoxylans and β-glucans may influence the friction response and, hence, the oral processing in the mouth during oral processing (drinking).

Influence of the malting conditions on the modification and variation in the physicochemical properties and volatile composition of barley (Hordeum vulgare L.), rye (Secale cereale L.), and quinoa (Chenopodium quinoa Willd.) malts

The traditional malted cereal used primarily for beverages is barley (Hordeum vulgare L.), while rye (Secale cereale L.) is mainly used in baked goods. In contrast, quinoa (Chenopodium quinoa Willd.) is a gluten-free pseudocereal, rich in starch and high-quality proteins, that can be used similarly to cereals. Their physicochemical properties and volatile compositions (e.g., aroma compounds) directly influence the finished food products. The sharp bitterness of unprocessed rye and the earthy aroma of native quinoa can interfere with the development and acceptance of food products. Malting is known to improve the processing and sensory properties of barley. A face-centered, central composite design was used to investigate the individual and interactive effects of three malting parameters (i.e., steep moisture (SM), germination temperature (T), and germination time (t)) on malt quality indicators (e.g., extract) and volatile formation (e.g., 3-methylbutanal) in rye and quinoa, and were compared to barley. The malt modification predictive models were then used to determine standard malting regimes for brewing quality malts. The malting parameters for the steeping and germination stages were: 43 %, 15 °C, and 6 d for barley; 45 %, 12 °C, and 8 d for rye; and 46 %, 16 °C, 6 d for quinoa. Malt modification and volatile formation were primarily associated with the interactive effect of germination temperature and time. Conversely, steep moisture had limited impact on malt modification but strongly regulated the formation of 34 known (pseudo)cereal volatile compounds. Principal component analysis (PCA) of the volatile data identified (pseudo)cereal specific volatile patterns. Aldehydes were characteristic in the cereal malts, particularly barley, whereas phenyl compounds and pyrazines were abundant in rye and quinoa malts, respectively. Controlling (pseudo)cereal modification and volatile development through the malting process could help deliver targeted sensory properties and improve the acceptance of malt-based food products.

Impact of barley selection and mashing profile on the arabinoxylan content and structure in beer

Non-alcoholic and low-alcoholic beers often suffer from inferior foaming quality and lack palate fullness, both of which are positively influenced by arabinoxylan. This study aimed to identify factors during brewing that most affect arabinoxylan content and structure. Analysis showed that malting and mashing had the most significant impact on arabinoxylan, increasing its extractability and reducing its molecular weight. Given that arabinoxylan was most affected at the initial stages of brewing, barley malt selection and mashing profile adjustments were further investigated. Barleys (n = 21) were micro-malted, exhibiting a wide range of endoxylanase activity (6-63 U/kg dm malt) and water-extractable arabinoxylan content (0.54 %-1.04 % dm malt). Malts with extreme values for these parameters were subjected to two mashing profiles, with only one allowing endoxylanase activity, to evaluate the impact of both barley selection and endoxylanase activity on the arabinoxylan profile in beer. The resulting beers had total arabinoxylan content ranging from 1.0 to 2.0 g/L and high-molecular-weight arabinoxylan from 0.4 to 1.2 g/L, levels that significantly contribute to palate fullness and foam stability. The negligible impact of endoxylanase activity highlighted the importance of barley selection. Therefore, brewers should make informed barley (malt) choices to optimize arabinoxylan content and structure in beer.

Characterization of molar mass and conformation of relevant (non-)starch polysaccharides in cereal-based beverages

Arabinoxylans, β-glucans, and dextrins influence the brewing industry's filtration process and product quality. Despite their relevance, only a maximum concentration of β-glucans is recommended. Nevertheless, filtration problems are still present, indicating that although the chemical concentration is essential, other parameters should be investigated. Molar mass and conformation are important polymer physical characteristics often neglected in this industry. Therefore, this research proposes an approach to physically characterize enzymatically isolated beer polysaccharides by asymmetrical flow field-flow fractionation coupled to multi-angle light scattering and differential refractive index detector. Based on the obtained molar masses, root-mean-square radius (rrms from MALS), and hydrodynamic radius (rhyd), conformational properties such as apparent density (ρapp) and rrms/rhyd can be calculated based on their molar mass and size. Consequently, the ρapp and rrms/rhyd behavior hints at the different structures within each polysaccharide. The rrms/rhyd 1.2 and high ρapp values on low molar mass dextrins (1-2·105 g/mol) indicate branches, while aggregated structures at high molar masses on arabinoxylans and β-glucans (2·105 -6·106 g/mol) are due to an increase of ρapp and a rrms/rhyd (0.6-1). This methodology provides a new perspective to analyze starch and non-starch polysaccharides in cereal-based beverages since different physical characteristics could influence beer's filtration and sensory characteristics.

Non-starch polysaccharides in beer and brewing: A review of their occurrence and significance

It has become apparent that beer (both alcoholic and nonalcoholic) contains appreciable amounts of non-starch polysaccharides, a broad subgroup of dietary fiber. It is worth noting that the occurrence of non-starch polysaccharides in alcoholic beer does not imply this should be consumed as a source of nutrition. But the popularity of nonalcoholic beer is growing, and the lessons learnt from non-starch polysaccharides in brewing can be largely translated to nonalcoholic beer. For context, we briefly review the origins of dietary fiber, its importance within the human diet and the significance of water-soluble dietary fiber in beverages. We review the relationship between non-starch polysaccharides and brewing, giving focus to the techniques used to quantify non-starch polysaccharides in beer, how they affect the physicochemical properties of beer and their influence on the brewing process. The content of non-starch polysaccharides in both regular and low/nonalcoholic beer ranges between 0.5 - 4.0 g/L and are predominantly composed of arabinoxylans and β-glucans. The process of malting, wort production and filtration significantly affect the soluble non-starch polysaccharide content in the final beer. Beer viscosity and turbidity are strongly associated with the content of non-starch polysaccharides.