DEVELOPMENT OF FUNCTIONAL FOODS AND COMBINED HERBAL NUTRACEUTICALS USING PLANTS, Psidium guajava (GUAVA), Garcinia quaesita (GARCINIA), AND Cinnamon verum (CINNAMON), WITH POTENTIAL ANTI-DIABETIC PROPERTIES

Sri Lanka has a long history of utilizing medicinal plants for disease management, healthcare, and culinary applications. However, the transformation of these plant resources into value-added functional foods and nutraceuticals remains limited. Therefore, this study aimed to evaluate the bioactive properties, particularly antidiabetic potential, of selected medicinal plant extracts, develop innovative functional foods and nutraceuticals, and evaluate their physicochemical, functional, sensory, and commercial potential. Initially, a consumer survey was conducted to evaluate awareness and preferences on antidiabetic functional foods. The findings revealed that 85.43% of respondents were interested in novel food products incorporating plant materials with diabetes-reducing potential, with a higher  preference for food-based products than nutraceutical forms. Three medicinal plants, namely guava leaves (Psidium guajava), Ceylon cinnamon (Cinnamomum verum), and Garcinia (Garcinia quaesita), were used in this study. Four extraction techniques, such as ultrasonication bath (USB), ultrasonication probe (USP), maceration (Mce), and warm maceration (HS), using water and methanol as solvents, were compared to find the best technique and best extracting solvent. Accordingly, aqueous  ultrasonication bath extraction (USB-aq) was found to be the most effective, economical,  safe, and environmentally sustainable technique, producing extracts with significantly higher antioxidant and antidiabetic activities (p < 0.05). Guava leaf extract exhibited the highest total phenolic content (136.88 ± 1.42 mg gallic acid equivalents/g dry weight) and strong 2,2 Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (IC₅₀ = 8.33 ± 0.34 ppm), followed by cinnamon bark extract (136.17 ± 4.18 mg gallic acid equivalents/g dry weight; IC₅₀ = 8.89 ± 0.31 ppm). A strong positive correlation was observed between ferric reducing antioxidant power and total phenolic content (r = 0.998), while phenolic-rich extracts showed enhanced α-glucosidase inhibitory activity. Based on these findings, aqueous extracts of guava leaves and cinnamon bark obtained  through USB extraction were used to develop a combined herbal nutraceutical. The selected  nutraceutical formulation (C. verum: P. guajava crude extracts - 2:25 ratio) demonstrated  enhanced bioactivity, with total phenolic content of 140.20 ± 2.64 mg gallic acid equivalents/g dry weight, ferric reducing antioxidant power of 194.65 ± 4.65 mg Trolox equivalents/g dry weight, DPPH radical scavenging IC₅₀ value of 7.22 ± 0.36 ppm, and α - glucosidase inhibitory IC₅₀ value of 38.06 ± 1.72 ppm, indicating synergistic antioxidant and antidiabetic effects. Four functional foods: plant-based sausage, Nutri Cracker, guava herbal tea, and cinnamon -based kombucha, were developed and evaluated for antioxidant activity, antidiabetic  potential, nutritional composition, sensory properties, texture characteristics, glycaemic  response, and storage stability. The plant-based sausage formulation showed significantly higher taste, aftertaste, and overall acceptability (p < 0.05), with low fat content (3.07 ± 0.10%), high dietary fibre (6.70 ± 0.83%), and six-month frozen storage stability. The Nutri Cracker exhibited significantly lower hydrolysis index (0.56 ± 0.01) and predicted glycaemic index (59.84 ± 0.02) compared with commercial products (p < 0.05), confirming its low-glycaemic potential. The guava herbal tea demonstrated high phenolic content, antioxidant activity, and superior α-glucosidase inhibition exceeding acarbose. Fermentation enhanced the functional properties of cinnamon-based kombucha, with the selected formulation showing high flavonoid content, improved antioxidant activity, favourable sensory attributes, and increased SCOBY biomass growth (94.03%). Overall, this study successfully developed innovative functional foods with desirable sensory characteristics, enhanced nutritional value, strong bioactive properties, and promising commercialization potential. 

Keywords: Bioactive compounds, functional Foods, herbal Plants, nutraceuticals, product 
development