This study aimed to evaluate the effect of cooking (boiling, steaming, and frying) on polyphenols, flavonoids, carotenoids and antioxidant activity of six edible leaves. The total antioxidant capacity of the fresh and cooked leaves was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and singlet oxygen scavenging assays. The results revealed that frying caused a reduction in major bioactives and antioxidant activities in all leafy vegetables tested. However, steamed and boiled leaves of C. auriculata and C. asiatica have shown greater levels of polyphenols, flavonoids, and antioxidant capacity compared with fresh leaves. Polyphenol and flavonoid contents of boiled S. grandiflora and G. lactiferum were higher than that of their fresh form. Boiled and steamed O. zeylanica and S. grandiflora have shown higher carotenoids. Boiled and steamed leaves of P. edulis have shown higher antioxidant activity. The impact of cooking on the changes in bioactive concentrations and antioxidant capacities are dependent on the species and the method of cooking.

Nutritional attributes of flours obtained from five different cultivars of sweet potato roots commonly available in Sri Lanka showed significant differences in the tested parameters. The starch level ranged between 33% and 64% on the dry basis and the extractability from fresh tubers was governed by the quantity of starch. The crude fiber level ranged between 2.1% and 13.6% on dry basis and the highest level was observed in swp7 (CARI 273) and resistant starch ranged from 14.2% to 17.2%. Higher percentage of resistant starch from total starch was found in Wariyapola red (swp1) cultivar resulting in lower digestion level while higher levels of digestion was evident in cultivars with lower levels of resistant starch with high level of total starch. Low levels of calcium and significant levels of iron were found in the five cultivars studied. Crude protein level was in the range of 1.2–3.3% on dry basis and trypsin inhibitor activity level (TIA) was significantly different (P > 0.05) in the cultivars studied while heating resulted in a significantly high reduction in the TIA level than in unheated condition. Polygonal or round shaped starch granules were in the range of 16.8–23.5 μm and low level of starch digestion was shown in cultivars containing larger granules. Total amylose content lies in the range 15.4–19.6% and cultivars having higher percentage of amylose showed higher level of in vitro pancreatic digestion (Pallepola [swp4] and swp7). The starch digestibility of sweet potato flour was in the range of 36–55% and the highest digestion was observed in swp7. Orange fleshed cultivars (swp4 and swp7) were comparatively rich in nutrients and digestibility than the other three studied cultivars.

The aim of the present study was to evaluate the effect of cooking (boiling, steaming, and frying) on anti-inflammation associated properties in vitro of six popularly consumed green leafy vegetables in Sri Lanka, namely: Centella asiatica, Cassia auriculata, Gymnema lactiferum, Olax zeylanica, Sesbania grnadiflora, and Passiflora edulis. The anti-inflammation associated properties of methanolic extracts of cooked leaves were evaluated using four in vitro biological assays, namely, hemolysis inhibition, proteinase inhibition, protein denaturation inhibition, and lipoxygenase inhibition. Results revealed that the frying of all the tested leafy vegetables had reduced the inhibition abilities of protein denaturation, hemolysis, proteinase, and lipoxygenase activities when compared with other food preparation methods. Steaming significantly increased the protein denaturation and hemolysis inhibition in O. zeylanica and P. edulis. Steaming of leaves increased inhibition activity of protein denaturation in G. lactiferum (by 44.8%) and P. edulis (by 44%); hemolysis in C. asiatica, C. auriculata, and S. grandiflora; lipoxygenase inhibition ability in P. edulis (by 50%), C. asiatica (by 400%), and C. auriculata leaves (by 250%); proteinase inhibition in C. auriculata (100%) when compared with that of raw leaves. In general, steaming and boiling in contrast to frying protect the health-promoting properties of the leafy vegetables.

The antioxidant potency of soluble and bound phenolic extracts of freeze‐dried six leafy vegetables was investigated using in vitro systems; singlet oxygen scavenging, hydroxyl radical scavenging, nitric oxide radical scavenging, and ABTS radicals assays. Further rutin, lutein, and β‐carotene content of leaves were analysed. The results revealed that both soluble and bound phenolic extracts have exhibited antioxidant potential toward free radicals and reactive oxygen species concerned. However, soluble extracts showed a higher content of phenolics and flavonoids than the bound counterpart. The highest rutin, lutein, and β‐carotene contents were observed in the leaves of Cassia auriculata, and the leaves of Passiflora edulis showed the highest vitamin C content. Positive associations between phenolics and antioxidant activities except for singlet oxygen radical scavenging ability were observed. Among the leafy types studied, C. auriculata have shown to possess more antioxidant bioactives such as β‐carotene, lutein, and rutin and antioxidant activities. Practical applications This paper will give information about major bioactive compounds such as β‐carotenoids, rutin, and lutein and antioxidant activity in selected green leafy vegetables due to cooking treatments. This is important for the public those concern about the healthy diet in the view of selecting leafy vegetables to combat many oxidative stress‐related chronic diseases.

A study was carried out to determine the levels of starch, protein, crude fat, crude fibre, ash and a few phytochemical constituents (saponins, flavanoids and alkaloids) and mineral elements (Calcium, Magnesium, Iron, Potassium and Zinc) in four cultivars of yams and tubers cultivated under similar agro-climatic conditions in Sri Lanka. Tubers of Dioscorea alata (Rajala and Hingurala), Dioscorea esculenta (Kukulala) and Xanthosoma sagittifolium (Kiriala) were subjected to the above analyses. The total starch percentage in crude flours ranged between 74.66 ± 0.66 to 80.46 ± 0.62% on dry weight basis and no significant difference found in total starch (P <0.05) between the studied varieties. The protein level ranged from 2.66 ± 0.21 to 10.16 ± 0.64% whereas D. alata was found to contain a higher protein level. The crude fat levels in tubers varied ranging from 1.5 ± 0.2 to 2.3 ± 0.1% and the highest level was observed in Xanthosoma sp. The crude fibre content in tubers was found to range from 1.