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Wood hemicelluloses have an excellent capacity to form and stabilize oil-in-water emulsions. Galactoglucomannans (GGM) from spruce and glucuronoxylans (GX) from birch provide multifunctional protection against physical breakdown and lipid oxidation in emulsions. Phenolic residues, coextracted with hemicelluloses using the pressurized hot water (PHWE) process, seem to further enhance emulsion stability. According to hypothesis, phenolic residues associated with hemicelluloses deliver and anchor hemicelluloses at the emulsion interface. This study is the first to characterize the structure of the phenolic residues in both GGM-and GX-rich wood extracts and their role in the stabilization of emulsions. PHWE GGM and GX were fractionated by centrifugation to obtain concentrated phenolic residues as one fraction (GGM-phe and GX-phe) and partially purified hemicelluloses as the other fraction (GGM-pur and GX-pur). To evaluate the role of each fraction in terms of physical and oxidative stabilization, rapeseed oil-in-water emulsions were prepared using GGM, GX, GGM-pur, and GX-pur as stabilizers. Changes in droplet-size distribution and peroxide values were measured during a 3-month accelerated storage test. The results for fresh emulsions indicated that the phenolic-rich fractions in hemicelluloses take part in the formation of emulsions. Furthermore, results from the accelerated storage test indicated that phenolic structures improve the long-term physical stability of emulsions. According to measured peroxide values, all hemicelluloses examined inhibited lipid oxidation in emulsions, GX being the most effective. This indicates that phenolic residues associated with hemicelluloses act as antioxidants in emulsions. According to chemical characterization using complementary methods, the phenolic fractions, GGM-phe and GX-phe, were composed mainly of lignin. Furthermore, the total carbohydrate content of the phenolic fractions was clearly lower compared to the starting hemicelluloses GGM and GX, and the purified fractions GGM-pur and GX-pur. Apparently, the phenolic structures were enriched in the GGM-phe and GX-phe fractions, which was confirmed by NMR spectroscopy as well as by other characterization methods. The frequency of the main bonding pattern in lignins, the β-O-4 structure, was clearly very high, suggesting that extracted lignin remains in native form. Furthermore, the lignin carbohydrate complex of γ-ester type was found, which could explain the excellent stabilizing properties of PHWE hemicelluloses in emulsions.

The incorporation of faba bean flour into wheat-based products is a sustainable way to obtain proteinenriched food items. However, developing breads with a higher content of faba bean flour is challenging due to the poor textural/sensory properties of the final product. A potential solution is to use hydrocolloids as structuring agents to increase the viscoelastic properties of the composite bread. Microbial dextran is a natural hydrocolloid which can be used as a bread texture improver either as a pure food ingredient or by in situ production during sourdough fermentation. The aim of this study was to compare the influence of dextran produced in situ by Weissella confusa VTT E-143403 (E3403) and Leuconostoc pseudomesenteroides DSM 20193 in faba bean sourdoughs on the quality of wheat bread supplemented with 43% faba bean sourdough. The impact of dextran on the rheological properties of dough and textural properties of the final bread were evaluated. Dextran formed by W. confusa and L. pseudomesenteroides reached a level of 5.2 and 3.6% (flour basis), respectively. Incorporation of faba bean sourdough containing dextran synthesized by W. confusa improved the dough viscoelastic properties, and also increased the specific volume (~21%) and reduced crumb hardness (~12%) of the final bread, compared to control breads. Similar positive effects were not obtained with sourdough containing dextran from L. pseudomesenteroides, probably due to its higher acidity. Dextran synthesized in situ by W. confusa is a promising clean label hydrocolloid option to improve the quality of wheat bread enriched with faba bean flour.

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