The impact of heating and freeze or spray drying on the interface and foam stabilising properties of pea protein extracts : Explained by aggregation and protein composition

The processing of plant protein extracts can affect the protein structure, leading to altered functional properties. In this work, we evaluated the impact of two common processes in pea protein extraction: heating and drying. Non-heated and heated (5 min at 95 °C) samples were compared, which were either freeze- or spray-dried. These processes led to alterations of the proteins, and resulted in changes of their interface and foam-stabilising properties. A mild protein extraction method was used to preserve the native protein structure during aqueous extraction, allowing the extraction of both albumin and globulin proteins. Spray-drying of these fractions led to higher surface hydrophobicity, which resulted in increased surface activity and stiffer interfacial layers at pH 3.8 and 7.0. The heating step induced aggregation of the globulins, while albumins remained soluble. Here, we demonstrated that the albumins had a dominant effect on the interfacial (rheology and ellipsometry) and foaming properties after heating, as the globulin aggregates were too large for effective interface stabilisation. A similar mechanism was also shown at pH 3.8, where the globulins precipitated, as the pH was close to their pI, while albumins remained soluble. Again, the albumins dictated the interfacial properties, leading to highly stable foams after removing the insoluble globulins. We have shown marginal differences in protein functionality after freeze- or spray-drying. More importantly, the changes in soluble protein composition dictate the protein functionality after heating or pH shifts

The impact of wounding and postharvest storage conditions on retention of soluble protein in sugar beet leaves

Abstract: Sugar beet leaves can be a viable and economically interesting source of high-quality protein for the food industry. We investigated how storage conditions and leaf wounding at harvest affect the content and quality of the soluble protein. After collection, leaves were either stored intact or shredded to mimic wounding induced by commercial leaf harvesters. Leaf material was stored in small volumes at different temperatures to assess leaf physiology or in larger volumes to assess temperature development at different locations in the bins. Protein degradation was more pronounced at higher storage temperatures. Wounding accelerated the degradation of soluble protein at all temperatures. Both wounding and storage at higher temperatures greatly stimulated respiration activity and heat production. At temperatures below 5°C, ribulose-1,5-biphosphate carboxylase oxygenase (RuBisCO) in intact leaves was preserved for up to 3 weeks. At temperatures of 30–40°C, RuBisCO degradation occurred within 48 h. Degradation was more pronounced in shredded leaves. In 0.8-m3 storage bins at ambient temperature, core temperatures rapidly increased, up to 25°C in intact leaves and up to 45°C in shredded leaves within 2–3 days. Immediate storage at 5°C greatly suppressed the temperature increase in intact but not in shredded leaves. The indirect effect of excessive wounding, that is, heat production, is discussed as the pivotal factor responsible for increased degradation of protein. For optimal retention of soluble protein levels and quality in harvested sugar beet leaves, it is advised to minimize wounding and to store the material at temperatures around −5°C. Practical Application: To preserve the soluble protein content and quality for at least 3 weeks, sugar beet leaves should be harvested with minimal wounding and stored at temperatures between 1 and 5°C. When aiming to store minimally wounded leaves in larger volumes, it must be ensured that the product temperature in the core of the biomass meets the temperature criterium or the cooling strategy must be adjusted. The principles of minimal wounding and low temperature storage are transferable to other leafy crops that are harvested for food protein