Dose dependent effects of a milk ion tolerant laccase on yoghurt gel structure

From the paper

Abstract

Fungal laccases with their pH optima in the acidic range may be suitable to improve the physical properties of lactic acid fermented dairy foods, such as yoghurt, by cross-linking of the milk proteins. Ions naturally occurring in milk may inhibit the laccase catalysed reaction. Hence, laccase activity was induced and accumulated in cultures of 20 fungal species and compared to the reference enzyme Laccase C (Lcc C). Laccases of Funalia trogii, Pleurotus flabellatus, Pleurotus eryngii, Pleurotus lampas and Trametes versicolor showed comparable or higher activities than Lcc C in the presence of calcium, chloride, magnesium, potassium, phosphate and citrate. In a cross-linking experiment, P. eryngii laccase (Lcc Per) converted casein completely into protein aggregates with higher molecular masses. A combination of 0.1 U/g Lcc Per and 5 mmol/L vanillin as mediator enhanced all rheological parameters, storage modulus G′, loss modulus G″ and complex shear viscosity η* of a skimmed milk yoghurt by approximately 30%, while a higher dose (1 U/g) resulted in fragmentation of caseins and weakening of the gel. At least 1 U/g of the more strongly inhibited Lcc C was required for measurable cross-linking, but no fragmentation occurred.