Soft Ca²⁺-induced pea protein gels through mild heating: Controlling elasticity and fracturing behavior

With the rising demand for plant-based protein, understanding the formation of pea protein gels induced by calcium is important for manufacturing of food products with appealing textural properties. Moreover, the moderate temperature processing is becoming of greater and greater interest, based on conditions used for food fermentation. The objective of this study is to understand the structural and rheology behaviour of calcium-induced pea protein aggregates at moderate plateau temperatures i.e. in the range 30–45 °C with holding times from 0 to 60,000s. Based on the combination of confocal fluorescence microscopy (CLSM) imaging, rheology and IR spectroscopy, our results show that despite the relatively low temperature range, thermal agitation not only allows for partial protein particle dissolution, but also induces interactions leading to soft gel formation. Within a shorter holding time (0–600s) range, higher Gʹ/Gʹ₀ (t) were observed at 40 °C and 45 °C, the end elastic modulus reaching for any parameters tested at least 1000 Pa. As the holding time was extended to 60,000s, the effect of temperature became less pronounced, i.e., all gels reached similar high values of Gʹ even for the low temperature of 30 °C, which is nearly 3–4 times higher than that formed at 600s holding time (at the temperature plateau). IR spectroscopy measurements showed that the protein secondary structure remained stable within the holding time ranging from 0s to 6,000s, while significant but moderate changes were monitored when extending the holding time to 60,000s, which correlated with a more progressive yielding observed in rheology, pointing to the formation of apparently more fragile physical gels. The combination of the techniques shows that the gel formation and strengthening mainly originated from rearrangements at the colloidal level leading to a denser network, while molecular rearrangements only intervened at the longest holding times (i.e, 60,000s).