Abstract/Summary

The development of a saturated fat replacer for bakery products by formulating a novel nanoemulsion with high content of unsaturated fatty acids can play an important role in addressing the issue of adverse health effects due to a high consumption of saturated fat. However, the formation, physical and chemical stability of nanoemulsions can be influenced by several factors regarding the composition and processing parameters. Therefore, the aims of this research were (i) to investigate the effect of vegetable oils from different origins and the type of stabiliser on the formation and stability of nanoemulsion, (ii) to develop an optimum high-pressure homogenization (HPH) treatment for producing nanoemulsions with lecithin as stabiliser, (iii) to investigate the effect of mixed emulsifiers (lecithin and hydroxypropyl methylcellulose (HPMC)) on the formation, physical and chemical properties of nanoemulsions, and (iv) to evaluate the technological functionality of nanoemulsion made of extra virgin olive oil and stabilised with lecithin and HPMC as a saturated fat replacer on short dough biscuits. The effect of vegetable oil type on the physical and chemical characterisation and stability of nanoemulsion (Chapter 2) showed that the nanoemulsion with higher stability were formulated with oils with lower fraction of unsaturated fatty acids, lower content of free fatty acids and higher value of total phenolic content. The results suggested that extra virgin olive oil (EVOO) could be the most suitable oil to formulate nanoemulsion as a saturated fat replacer because EVOO presented the highest radical scavenging activity and total phenolic content among the oils. The formation and stability of nanoemulsions were affected by the pressure and number of cycles of HPH treatments (Chapter 3). Furthermore, stabilisers’ properties (Tween 20 or soy lecithin) such as interfacial tension, viscoelasticity and molecular structure had also a significant effect on nanoemulsion formation and stability. Although MDD and PDI of Tween 20 stabilised nanoemulsions were influenced by homogenisation pressure and cycles, there was not a significant effect on soy lecithin stabilised nanoemulsions. The most efficient HPH process was at pressures of at least 400 bars and 1 cycle; these conditions produced nanoemulsions with great physical stability when using either Tween 20 or soy lecithin as emulsifiers. Soy lecithin is an interesting surfactant to formulate nanoemulsion for application in clean label food products. In order to improve the technological properties of nanoemulsions as a saturated fat replacer, a stabiliser and structing agent, such as HPMC was studied first in isolation (Chapter 4) and then when incorporated in nanoemulsions (Chapter 5). The molecular structure and concentration of HPMC played a major role in the viscoelastic behaviour, gelation temperature and strength of the gel formed during heating (Chapter 4). The firmness and work of shear of HPMC solutions increased significantly (p < 0.05) with increasing concentration, indicating lower spreadability. HPMC-L, the hydrocolloids with the lowest content of methyl and hydroxypropyl groups of the ones studied, was selected as the most suitable one to formulate fat mimetics because of its higher surface activity and more stable gel structure after heating. Furthermore, the combination of lecithin and HPMC in the formation and stability of emulsions showed an improvement of nanoemulsion physical and oxidative stability in comparison to using lecithin alone (Chapter 5). Addition of HPMC formed a stronger emulsion structure, showed higher lipid oxidative stability and similar physical properties, in terms of firmness and spreadability to butter indicating its potential to be used as a saturated fat replacer in food systems. To formulate short dough biscuits with a healthier fatty acid profile, the nanoemulsion was used to replace 33% of the butter in the dough (Chapter 6). Biscuits made with the novel nanoemulsion presented less oil migration than the control biscuits made with butter. A trained sensory panel did not find significant differences (p > 0.05) in crumb density and hardness on the first bite among the biscuits made with the nanoemulsion and the control. The developed nanoemulsion worked as a saturated fat replacer in short dough biscuits, resulting in a reduction of 30% of saturated fat and 25% of total fat while maintaining high quality physical and sensory attributes. Overall, the development of this nanoemulsion provides a novel strategy for the reduction of saturated fat and total fat content in bakery products. This study will provide useful information about the basis to formulate saturated fat replacers with specific technological functionalities for application in food products.