Phillips, Jade B.
(2019)
Processing to valorise green biomass side streams to create new food ingredients.
PhD thesis, University of Nottingham.
Abstract
The aim of the work presented in this thesis was to investigate differing conversion routes on pea biomass in order to make it a functional food ingredient with differing properties than it has in its native form. These would then have differing microstructures and properties to enable the pea biomass to have alternative structures and functions, which mirror starch functions. These modifications were made to formulate a powder-like material similar to that of a flour and to make a dispersion with added fibre, which is to be used within a composite model system. Thereby replacing a high calorific ingredient with a zero digested calorific one.
Firstly the composition of pea biomass was assessed in order to understand the complexity of the compositional matrix.
Then pea biomass was successfully ball milled for different periods of time. Ball milled pea biomass, which had a reduced crystallinity, degree of polymerisation and degradation temperature, was rehydrated and re-crystallised. No glass transitions were determined through thermodynamic measurements. Upon swelling amorphous ball milled pea biomass particulates doubled in hydrated volume. Rheological measurements showed that with various methods of swelling, the rehydrated ball milled pea biomass (at solid contents of 25 % and 33 %), provided visco-elastic properties similar to starch but at much higher solid contents. Methods of swelling showed that once the powder was successfully mixed with water for a period of time, more coherent pastes were apparent, rather than the alternative method of subsequently quenching the powders in water for a 24 hour period, without continuous mixing.
Fibrillated pea biomass was created through a combination of various conversion routes. Fibrillated pea biomass with a mixed diameter of fibrillated masses were engineered through hydrothermal and various chemical/mechanical treatments. The mechanical methods showed that microfluidisation was advantageous for creating a high NFC:MFC, and that sonicated fibres were advantageous for creating a mainly MFC system with larger macro-fibres still present. The chemical pre-treatment of a sodium hydroxide wash successfully reduced the amount of hemicellulose content, however this did not have advantageous yields of MFC/NFC and or properties in terms of rheology and microstructure than without the treatment. Ethanol washes had no effect in reducing the concentrations of polysaccharides and lignin proportionally to the overall composition. These results indicated that other polymers and lignin within plant cell wall materials may have a synergistic effect on the fibrillation of cellulosic materials, with ethanol washed samples having the most desired fibrillated properties, for example producing the greatest expanded structure to be used in a model snack product. As a control Solka floc was successfully fibrillated through the mechanical means, without heat and chemical pre-treatments. These fibrillated masses provided stable dispersions with visco-elastic properties at low solid concentrations of 1 %, within an aqueous dispersion and were shown to be stable. Furthermore, fibrillated samples showed a strong network structure with suspected high reinforcement capabilities through the creation of new structures with varying levels of crystalline fractions.
Ratios of all starch commodities in model snack products were replaced by using modified pea biomass in the form of a ball milled powder and fibrillated masses, which contained a mixture of fibre diameters and lengths. Results showed that up to 30 % starch commodities could be replaced by pea biomass and the resulting composite would have similar properties of texture, viscosity, fried expansion and structure, but visually aesthetic aspects of the resulting product such as colour were different, with low added biomass concentrations of as much as 10 % starch replacement.
Thereby indicating that valorised pea biomass can successfully be utilised and partially replace starch commodities, benefiting the nutritional content of a composite snack product and provide advantageous health benefits over the traditional snack product.
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