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The nutritional and bioactive content of banana and red beetroot peels was investigated. The basic macrocomponent composition was determined using standard AOAC (Association of Official Analytical Chemists) methods, while the recovery efficiency of bioactive compounds was investigated using conventional and innovative extraction techniques (subcritical water extraction, ultrasound- and microwave-assisted extraction). Extracts were analyzed for biological effects in vitro on human hepatic, tongue and colon cancer cell lines. A macrocomponent analysis revealed a notable amount of dietary fiber in banana and beetroot peels (39.0 and 33.6% dmb) and a relatively high content of protein in beetroot peel (18.3% dmb). Regarding the micronutrients-minerals, banana and beetroot peels were shown to be a very good source of potassium (75.06 and 41.86 mg g−1 dmb). Both extracts of banana and beetroot peels obtained by conventional extraction - decoction (100 °C, 20 min) exhibited the highest total phenolic content and antioxidant capacity. Additionally, in banana peel, these extracts were the richest in dopamine content (12.63 mg g−1 dmb). Extraction by infusion (80 °C, 30 min) yielded a beetroot peel extract with the highest total betacyanin content (9.80 mg g−1 dmb). Biological effects in vitro were dose- and time-dependent, as well as influenced by the presence of polysaccharides.

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Native Crocus taxa are abundant in regions with moderate and dry climate; however, their potential in the food industry has thus far been neglected. The objective of this study was to compare the quantitative and qualitative flavonoid content and antioxidant and cytotoxic activity in organs of several populations of Croatian native taxa and assess their potential for application in the food industry. The dominant flavonoids in the native Crocus taxa were kaempferol and quercetin. Tepals contained similar or higher concentrations of flavonoid-glycosides than other organs. Tepals from Cvv1 and Cvv2 populations contained more flavonoid-glycosides than the commonly used spice saffron (C. sativus stigmas). The FRAP antioxidant activity of Cvv1 and Cvv5 tepals was similar to that of standard Trolox. DPPH inhibition of Cvv1 and Cvv3 tepals was within the range of that recorded for saffron. Cvv1 tepals significantly reduced reactive oxygen species in the broadest concentration range (50-1000 μg/ml), and showed considerable antioxidant activity in the ABTS assay, equal to 82% of standard Trolox antioxidant activity. A significantly higher concentration of kaempferol-rutinoside was recorded in this than in other taxa. The flavonoid showed a very strong or strong correlation with antioxidant assays results, and a negative correlation with cellular reactive oxygen species concentration. We therefore presumed that kaempferol-rutinoside is one of the main antioxidant phenolics in Crocus tepals. None of the tested extracts showed cytotoxicity toward Caco-2 cells. The results revealed that Cvv tepals have potential as a food supplement and are a promising material for further food safety tests.