Study on the modification of whey functional properties by enzymatic hydrolysis of its residual fat | Etude de la modification des proprietes fonctionnelles du lactoserum par hydrolyse enzymatique de sa matiere grasse residuelle

The aim of this work was to investigate the potential of a new treatment to improve whey interfacial an functional properties, and hence to promote its incorporation in foods. The process was based on the lipase-catalyse hydrolysis of the remaining fat fraction in whey in order to produce surfactants which enhanced the emulsifying and foaming properties of whey proteins. The interfacial properties of whey were considerably modified by the transformation of triglycerides into fatty acids and monoglycerides by Mucor miehei lipase. The results on adsorption kinetics at the air-water interface emphasised a better ability of modified whey in reducing surface tension. Differences between native and modified whey were less pronounced during adsorption at oil-water interfaces. Compression isotherms obtained with a Langmuir film balance showed a distinct mechanical behaviour for the films of native and modified whey spread on an aqueous subphase. In general, the fat modification allowed to reach higher surface pressure at the end of compression. Moreover, the modified whey formed more elastic films which therefore possessed a better resistance to mechanical disturbance. The triglycerides hydrolysis improved emulsifying and foaming properties of whey. This enzymatic modification enhanced the foam capacity, increased the emulsifying capacity, improved the emulsifying activity index and delayed the emulsion creaming. Some correlation aspects were studied and relationships between functional and interfacial properties were established. Equilibrium surface pressure (air-water interface) can provide a good prediction of the ability of a product to stabilise foams and emulsions. However, for emulsion systems, a higher degree of correlation indicates that equilibrium interfacial pressure (oil-water interface) is a better indicator of stability. The emulsifying activity index is correlated to the film elasticity. The more elastic interfacial film, the best is its ability to protect fatty globules against destabilisation. Nevertheless, no correlation is observed in our study between film elasticity and foam stability. In order to explain functional properties such emulsifying and foaming capacity, it is necessary to consider the entirety of interfacial properties (adsorption rate at interface, film elasticity and capacity). There may be some limiting factors