Interactions in casein micelle - Pea protein system (Part II): Mixture acid gelation with glucono-δ-lactone

Abstract

In our preceding study (Part I), the thermal denaturation and aggregation of enriched pea protein fractions, namely vicilin/convicilin 7S (Vic) and legumin 11S (Leg), were investigated in the absence or in presence of casein micelles (CM) at pH ≈ 7.1. The present report (Part II) focuses on the glucono-δ-lactone (GDL) acid-induced gelation of either co-heated proteins in admixture (namely route 1) or thermally-aggregated pea proteins mixed with unheated CM (route 2), while applying a pea protein (either non fractionated PP or Vic or Leg) - to - CM weight ratio of 1: 1 and total protein concentration of 3.6 wt%. The pea protein thermal aggregates obtained by route 1 were of lower size and less soluble than those yielded in isolation. For route 1, gelation of the heated CM – Vic mixture was triggered at a higher pH value and led to higher final storage modulus G′ than corresponding protein samples in isolation. In contrast, the presence of large and sedimentable aggregates in the case of the CM – PP and CM – Leg mixtures impaired gelation. Concerning route 2, either the PP or Vic aggregates mixed with unheated CM resulted in rapid gelation and higher final G’ values than those measured for their single-protein sample counterparts. Viscoelastic properties of the mixed gel depended on the pea protein fraction used, thermal aggregation route, extent of physical interactions between pea proteins during acidification and further involvement of CM. Hence, route 2 would be more reliable than route 1 to produce a “mixed” dairy-like gelled product containing pea proteins with improved texture properties.