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In general, the interest in food that contains a reasonable amount of plant protein is steadily increasing. As a consequence, products with pleasant texture and taste ensuring a high consumer acceptance are needed. The aim of the present study was to develop and characterize structural differences and organoleptic impressions of lactic acid fermented, oatbased gels which could serve as plant protein enriched, non-dairy yoghurt alternatives. Oat protein concentrate, a by-product of cereal processing, was used as plant protein source. It was shown that total solids content had the highest impact on rheological properties. All samples were described as soft fluid gels and their structure was dominated by the heatinduced gelation of starch. Within this mixed food system of starch and protein, swollen starch granules, protein aggregates and residual small fat droplets were embedded in a rough macromolecular network of leached amylose. They acted as filler and increased the rigidity (G') of the system. Native starch content determined the water holding capacity with an increase in water binding with increasing concentration. Overall, rheological characteristics were found to be strongly linked to the products' textural attributes which, in turn, determined consumer acceptability. For the purpose of product development, overall liking was influenced by the quantifiable sensory attributes-sweet, moist, soft, and smooth. Purchase intention, however, was positively influenced by the extrinsic attribute information (on oat protein enrichment). These data, in combination with the impact of the identified ingredients on product structure, are a valuable tool to improve product properties, consumer perceptions and product acceptability. To conclude, lactic fermented, oat-based gels can serve as a plant-based yoghurt-alternative that combines nutritional benefits with good textural properties.

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BACKGROUND During the industrial production of β‐glucan, a protein‐rich fraction remains as a by‐product. Recovery of this protein as oat protein concentrate (OPC) results in a source of cereal protein for food and improves the overall economy of the process. In this study, a yoghurt‐type product is developed by lactic acid fermentation of an OPC suspension after subjection to heat treatment to assure starch gelatinization. RESULTS In detail, the process of yoghurt production involved an initial heating step to 90 °C, followed by 24 h fermentation with a starter culture consisting of Lactobacillus delbrueckii subsp. bulgaricus und Streptococcus thermophilus. The resulting yoghurt‐type product was mildly sour (pH 4.2) with a certain amount of lactic acid (3.3 ± 0.2 g kg−1) and contained 4.9 × 106 cfu g−1 lactobacillus after 24 h fermentation. Scanning electron microscopy revealed a porous network presumably built up from the gelatinized starch fraction containing aggregated structures, between which were assumed to be aggregated oat proteins. Moreover, to a limited extent, proteolysis occurred during fermentation. Thus some of the proteolytic enzymes present in the yoghurt culture cleaved oat protein and released peptides. However, the effect on essential amino acids was small. CONCLUSION The results of this study provide a deeper knowledge into the role of starch and protein in fermented OPC yoghurts. The structure of fermented OPC verifies the applicability of oat protein as an alternative source for yoghurt‐type products. © 2019 Society of Chemical Industry

Foaming ability of oat protein isolate (OPI) was analysed at pH 4 and 7. Foaming properties were influenced by partial hydrolysis with trypsin (OPT) and alcalase (OPA). The viscoelasticity of the protein film, the interactions between the protein molecules, and the network forming within the protein film were analysed by interfacial rheology. At pH 7, foams made of OPI and OPT were found to be stable with OPI having the fastest foaming ability. At pH 4, the foaming properties of OPI were found to be poor due to limited solubility. The specific cleavage behaviour of trypsin improved the foaming properties, especially at pH 4, resulting in a homogenous foam structure, a fast foaming ability and a highly viscoelastic interfacial film. The formation of a thick steric protein layer at pH 7 and the formation of strong hydrophobic interactions at pH 4 were found to be the dominating foam stabilisation mechanisms. In conclusion, oat protein ingredients were developed with targeted functional properties.