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Polyphenols, including extractable polyphenols (EPP) and non-extractable polyphenols (NEPP), are natural and secondary metabolic substances in plants that have beneficial properties to human health. However, NEPP associated with dietary fiber and protein are not taken into account in most literature data. In this paper, NEPP were released from blueberries with acid or alkaline hydrolysis methods, and the related extraction conditions were determined and optimised by response surface methodology (RSM). The results showed that NEPP yield obtained with alkaline hydrolysis was much higher than that obtained with acid treatment. The NEPP yield in alkaline hydrolysis process was significantly affected by the NaOH concentration and liquid/solid ratio, while in the acid hydrolysis process, the NEPP yield was significantly affected by the temperature, time and liquid/solid ratio. The second order polynomial models were developed for predicting NEPP content in blueberries. The optimisation of the extraction process of NEPP in blueberries would provide a good idea and basis for the application of non-extractable fractions.

The total polyphenol (TP), flavonoid, proanthocyanidin (PAC) content, and antioxidant capacity of both onion varieties (red and yellow) were compared. The content of TP, flavonoids, and PAC was determined by Folin-Ciocalteu colorimetric method, AlCl3, and by DMAC colorimetric method, respectively. The results showed that the contents of TP and flavonoids decreased from the outer to the inner layers in both onions, but there was no significant difference in PAC content. The outer layers had the highest antioxidant activity of extracts followed by a continuous decrease towards the inner layers in both varieties. The contents of phenolic acids and flavonoids were quantified by HPLC. Gallic acid, ferulic acid, and quercetin, as the main compounds in polyphenols, were detected in each layer of both onions. The red variety showed better antioxidant activity than yellow onion according to the linoleic acid system and DPPH assay. The higher contents of TP and flavonoids were associated with higher antioxidant activity.

The contents of extractable polyphenols (EPP), non-extractable polyphenols (NEPP), extractable proanthocyanidins (EPAC), non-extractable proanthocyanidins (NEPAC) and extractable anthocyanidins (EAC) in blueberry leaves were investigated. An experiment was conducted to analyse the effect of solvent types (methanol and ethanol), concentration (50 and 70%) and pH (2 and 6) on the extraction of bioactive compounds. Total extractable polyphenols (TEPP), total extractable proanthocyanidins (TEPAC), and total extractable anthocyanidins (TEAC) were analysed in methanol/ethanol/water extracts, NEPP were determined in acidic hydrolysates and NEPAC were quantified by depolymerisation in HCl/butanol. The results showed that ethanol and methanol did not affect the extraction of TEPP, while methanol was better for TEPAC and TEAC. The contents of TEPP and TEAC in 50% solvent were higher than those in 70% solvent. When solvent pH dropped to 2, the contents of EPP and EPAC were increased, while the EAC content was decreased.