Identification of Resistant Starch-rich Sources from Selected Plants and Development of Low-calorie Food Products with Functional Properties

<p dir="ltr">A large portion of the global population suffers from non-communicable diseases (NCDs) such as diabetes, cardiovascular diseases, cancer, and obesity, often due to unhealthy eating habits. A major dietary contributor is the overconsumption of carbohydrate-rich foods. However, resistant starch (RS), a type of starch that escapes digestion, has gained attention for its health benefits, including lowering blood glucose levels, reducing cholesterol, exerting prebiotic effects, and potentially preventing cancer. Incorporating RS into foods helps reduce the glycaemic index (GI) and glycaemic load (GL), offering a functional strategy for improving food quality and health outcomes. This study focused on identifying RS-rich food sources and using them to develop low-calorie, functional food products. Initially, 14 plant-based sources such as tubers, cereals, pulses, root crops, and fruits were identified by resorting to an exploratory survey and subsequently analysed for RS content. Finally, potatoes, arrowroots, chickpeas, oats, and unripe bananas were found to be richest in RS within their respective categories. These samples were then subjected to different thermal-based cooking treatments (boiling and pressure cooking) at varying times to assess the degree of RS degradation. Results revealed a general increment in RS content with increased cooking time, except in chickpeas, where cooking to courses elevated RS content due to the starch retrogradation process.</p><p dir="ltr">Based on the phenomenon of RS retention over the different cooking processes, potatoes and arrowroots were selected for further study. Specific boiling and pressure-cooking times were employed for each source, and subsequently, these sources were freeze-dried into powders. Six types of freeze-dried powders were obtained from the raw samples and cooked samples (FDRA, FDRP, FDBA, FDBP, FDPA, FDPP). Raw freeze-dried powders of potatoes (FDRP) and arrow roots (FDRA) tend to retain higher RS percentages than their cooked counterparts. Raw samples also exhibited finer particle size and lower solubility compared to cooked powders. These six freeze-dried powders were then incorporated into low-fat Greek yoghurt formulations to evaluate their functional impact. Thirteen yoghurt variants were developed using 1% and 3% flour concentrations, alongside a control without flour. Physicochemical characteristics such as whey separation, texture, colour, protein content, ash content, syneresis, viscoelastic properties, gelation, and microstructure were analysed. Shelf-life analysis was also conducted over 21 days at 5°C in 7-day intervals. Yoghurts with 1% flour addition showed improved texture, gel strength, and viscosity, attributed to enhanced water-binding capacities and protein network development, and these were facilitated by the added flour. In contrast, the 3% flour incorporated yoghurt formulations exhibited excessive syneresis and lower gel strength, as confirmed through confocal laser scanning microscopy. The 1% formulations demonstrated better shelf-life stability, making them suitable for further development.</p><p dir="ltr">In the final stage, synbiotic Greek yoghurts were developed by incorporating both probiotics (Lactobacillus acidophilus) and RS-rich prebiotics (from the freeze-dried flour). The viability of probiotic cultures, including LAB strains (L. delbrueckii subsp. bulgaricus and S. thermophilus), was assessed throughout shelf life and during simulated digestion. While RS did not significantly improve probiotic survival during storage, it positively influenced bacterial survival during digestion, indicating enhanced functionality under gastrointestinal conditions.</p><p dir="ltr">In conclusion, this study highlights RS as a promising functional ingredient for food applications. The incorporation of RS-rich flours into Greek yoghurt improved textural and structural properties while offering potential digestive health benefits. The optimal incorporation level was 1%, which contributes to balancing the technological advantages while compromising sensory acceptability. The resulting synbiotic yoghurt represents a nutritious, low-GI food product with valuable commercial potential in addressing diet-related NCDs.</p>