In situ ultrastructural analyses of proteins and starch in rice, barley, and quinoa during cooking

Abstract

The textural contribution of protein morphology and protein-starch interactions in cooked grains remains limited to correlational analysis and is subject to debate. In this study, in situ ultrastructural analyses of proteins and starch in rice, barley, and quinoa during cooking were conducted using multiple microscopy techniques, including electron microscopy and X-ray tomography. Microscopic analyses revealed that cereal proteins were organized as discrete protein bodies along cell walls of rice and quinoa, whereas barley proteins formed continuous amorphous matrices within the endosperm. While rice protein bodies and the barley protein matrix remained unchanged after cooking, quinoa proteins were transformed from discrete bodies into a continuous matrix. X-ray tomography demonstrated that rice protein bodies contribute to spatial hindrance, barley proteins serve as physical barriers that impede starch gelatinization and leaching, and quinoa proteins shift from hindrance to barrier during cooking. These findings elucidate the ultrastructure of proteins in different cereals, along with protein-starch interactions, and clarify the structural roles of these components, thereby providing insights for developing cereal-based products with desired properties.