Soybean lecithin is often used as a surfactant in food formulation. The aim of this study was to investigate the interactions between soybean lecithin (SL, 0-3%, wt/vol) and whey protein (WP, 10%, wt/vol) or polymerized whey protein (PWP, 10%, wt/vol) induced by heating WP solutions at 85°C for 0 to 20 min at pH 7.0. The samples were evaluated for zeta potential, particle size, morphology, rheological properties, thermal properties, secondary structure, and surface hydrophobicity. Zeta potential of WP increased linearly as SL level increased from 0 to 3%, whereas that of PWP changed with plateau at SL level of 1%, which may be due to the aggregation of SL. The addition of SL increased the particle size and apparent viscosity of both WP and PWP. All the samples exhibited different morphology depending on SL level and heating time according to transmission electron microscopy images. Whey protein showed obviously decreased gelation time and increased storage modulus in the presence of SL. Differential scanning calorimetry curves confirmed the effects of SL on the thermal properties of both WP and PWP. Circular dichroism spectra indicated that SL had effects on the secondary structure of both WP and PWP. The changes in surface hydrophobicity indicated the hydrophobic interactions between WP/PWP and SL. Data indicate that the physicochemical and functional properties of WP and PWP can be altered by adding soybean lecithin.
Fruit juice addition can influence the physiochemical and sensory properties of fermented milk. Effects of adding strawberry juice (15% vol/vol) pre-or postfermentation on particle size, rheology properties, volatile flavor profile, and microstructure of fermented goat milk were investigated. Samples with juice added prefermentation showed larger reinforcement in particle size, apparent viscosity, and storage and loss moduli than samples with juice added postfermentation. Compared with the control, all samples showed improved fruit aroma and reduced goaty flavor; this effect was more remarkable in samples in which juice was added before fermentation. Fermented goat milk with strawberry juice added prefermentation showed the highest levels of 1-hexanol and 2-hexen-1-ol (26.16 and 22.03%, respectively) and the lowest percentage of octanoic acid (2.47%), which are mainly responsible for fruit and goaty flavor, respectively. Microstructure analysis showed that samples with juice added prefermentation had a compact protein network. Results indicated that addition of strawberry juice before fermentation may be a good technology for developing a stirred strawberry fermented goat milk.
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