Characterization and solubility properties of pumpkin seed flour for functional beverage development : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Food Technology, Massey University, Palmerston North, New Zealand

Abstract

The rise in demand for plant-based protein beverages has given opportunities to explore various alternatives protein rich sources like pumpkin seed flour (PSF). This research mainly focuses on the functional and structural properties of PSF which originated from hull less pumpkin seeds. The aim of the study was to check the suitability of pumpkin seed flour in beverage applications. The initial proximate on the pumpkin seed flour, determined high crude protein (53%) and crude fat (15.9). In addition to this, PSF also contains notable ash and carbohydrate levels which making PSF a strong potential nutritional source. By eye it was evident that the commercial pumpkin seed flour studied was comprised of heterogenous particles – some dark green and others light green. The functional impact of this visual variation was evaluated via a sieving experiment performed across standard mesh sizes. The darker green particles concentrated in the larger mesh size while the lighter green particles tended to be smaller. The ash and the protein content in the various particle sizes however showed minimal variation, which justifies the usage of whole flour for solubility studies. Water solubility was conducted at different pHs (3, 6.6 and 8) and temperatures (30ºC, 60ºC and 80ºC). The result showed that the solubility of PSF improved with rising temperatures and with alkaline conditions. The proximate analysis of the solubility sediments, resulted in lower amounts protein and fats, when comparing with the supernatants. The colour analysis of the sediments showed significant variations in L*, a* and b* values which mostly depend on the application of heat and pH. It also shows potential colour degradation and Maillard reaction during varying conditions. SDS – PAGE analysis confirms the solubilization of certain protein bands mostly on higher temperatures and under alkaline conditions. The notable soluble bands are Cucurbitin, 11S basic subunits and 7S globulins. Confocal laser studies gave evidence of protein and fat interactions in varying conditions. The fat and proteins were more dispersed and mixed structures in supernatant during high solubility conditions meanwhile, dense protein aggregates were visible in the sediment fractions. Generally, this study indicate that alkaline conditions are necessary to manufacture a beverage. However, the properties are highly depended on varying processing conditions, mainly certain temperature and pH. These findings help to give an idea for developing a high protein content plant-based drink with the use of pumpkin seed flour as a sustainable and functional ingredient.