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Microstructure of Instant Coffee Foam. Confocal Microscopy Method Development and Production Related Parameters Affecting Foam Kinetics

Gustav Nilsson
Göteborg : Chalmers tekniska högskola, 2015. 73 s.
[Examensarbete på avancerad nivå]

Coffee foam is despite being an important parameter for the sensory impressions a cup of coffee provides perhaps the least studied part of this enormous commercial product consumed worldwide. In terms of microstructure and rheology the field is considerably lacking in data. This project aimed to develop a method to study coffee foam from instant coffee, by confocal laser scanning microscopy (CLSM) with the intention of providing data that may be used for production purposes. The instrument setup and operation of the method were defined, efficient dyes identified and common artefacts explained. The average bubble area was measured as a function of time by image analysis, the distribution and movement of particles in the lamellae could be observed and in particular surface active lipids and proteins could be stained and detected. A significant advantage of the method compared to e.g. rheological measurements in a rheometer turned out to be the small sample volumes needed. In addition, a simple method for measuring drainage using a USB-microscope was developed and applied to the foam. The analyzed parameters were filtering (pore sizes of 0.20-0.80 μm), pH adjustment (pH 4.0-6.3), hydrophobic particle addition (~1 μm) as well as the combined effects of filtering and particle addition to the coffee pre-foaming. Growth rate of average bubble area in coffee foam was shown to be virtually linear for at least the first 25 minutes, as oppose to what was described in literature for dynamic liquid foams in general, where growth was described as logarithmic. Extrapolating the growth of average bubble area to minute zero as a measure of foamability proved viable. Previously reported data of increased foamability in the pH range of 5.7-6.3 was confirmed. The results showed that higher pH values (>pH 5.0) had a negative impact on foam stability, and a lower pH increased foam stability. Filtering and particle addition showed that the interaction between various particles in the coffee play an important role for both foamability and foam stability

Nyckelord: Instant coffee, Coffee foam, Crema, Confocal laser scanning microscopy, CLSM, Foam microstructure, Average bubble area, Drainage, Foamability, Foam stability

Publikationen registrerades 2015-06-18. Den ändrades senast 2015-06-18

CPL ID: 218567

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