Structure and rheology of foams stabilized by lupin protein isolate of Lupinus.angustifolius

Abstract Plant-based protein sources play an important role in sustainable human nutrition but often lack in attractivity compared to animal-derived food products. Aerating is commonly used to increase the appeal of foods and may also improve acceptance for plant-based proteins in consumers' diets. We investigated structure and rheology of foams made from lupin protein isolate. Foamability and foam stability were determined from manual shaking tests. Gas volume fraction, bubble size, yield stress and shear modulus of the foams were determined during aging of pneumatically created foams. The impact of temperature pretreatment, pH and ionic strength on protein size distribution and conformation as well as surface activity in the aqueous solutions was characterized, and its effect on foaming behavior and foam properties is discussed. All foams were stable for at least 1 h. Heat induced denaturation of proteins did not alter foam characteristics much. Foaming capacity, however, strongly increased with increasing pH or ionic strength, but again gas volume fraction and bubble size were hardly affected. Foam rheology was shown to correlate not only to gas volume fraction, bubble size, and interfacial tension but also to the protein solutions’ interfacial elasticity. Protein aggregation decreased foamability but reduced drainage and hence increased foam stability. Blocking of drainage pathways by precipitated aggregates trapped in Plateau channel nodes was evidenced in endoscopic video observations. A “plant milk” made from lupin protein isolate, carboxymethyl cellulose as thickener, and emulsified sunflower oil yielded similar foam volume and texture as cow milk when prepared in a commercial whipper.