Subcritical Water Extraction Extract Research Articles

Formation and relevance of 5-hydroxymethylfurfural in bioactive subcritical water extracts from olive leaves

Although subcritical water extraction (SWE) has already shown its great potential for the attainment of natural bioactive extracts, concerns still remain on possible unexpected reactions that can arise during the extraction process, usually taking place at high pressure and temperature. It is already well-known that different components might be formed during the SWE extraction protocol due e.g. to Maillard reaction, which can improve the bioactivity of the obtained extracts. On the other hand, the formation of other compounds derived from these reactions, such as 5-hydroxymethylfurfural (HMF), has raised some concerns, mainly related to its safety. In this work, the formation of HMF during subcritical water extraction, at different conditions, from olive leaves has been monitored by using liquid chromatography with mass spectrometry (LC–MS) and diode array detection (LC–DAD). The possible influence of this compound in the overall antioxidant and antiproliferative activities against colon cancer cells has been also studied. Results showed an increase of HMF formation when increasing the extraction temperature, being the maximum concentration achieved at 200°C (3.17μgHMF/mg extract); nevertheless, the HMF contained in the olive leave extracts did not influence the antioxidant capacity or the antiproliferative activity of the natural extracts, thus demonstrating the safety of the SWE process.

Antimicrobial effects of onion (Allium cepa L.) peel extracts produced via subcritical water extraction against Bacillus cereus strains as compared with ethanolic and hot water extraction

In this study, the antimicrobial effects of an onion peel extract prepared using subcritical water extraction (SWE) were assessed for possible development into new bio-functional materials. The extraction temperatures were controlled to 110 and 160°C. At 0.15, 0.3, 0.6, and 1.2 mg extract/mL of broth, the growth inhibition and bactericidal activity of SWE extracts against Bacillus cereus KCCM 40935 and KCCM 11341 were compared with those of ethanol and hot-water extracts. In the case of B. cereus KCCM 40935, it appeared that over 0.6 mg/mL of SWE (110°C) extract exerted a bactericidal effect, and 1.2 mg/mL of SWE (160°C) extract exerted a bacteriostatic effect during culturing, and also that B. cereus KCCM 11341 was more resistant than B. cereus KCCM 40935. Furthermore, our results demonstrated that the death time of 107 CFU/mL of B. cereus KCCM 40935 treated with SWE (110°C) extract at 1.2 mg/mL was 60 min at maximum in 0.8% NaCl. Additionally, the cells damaged by SWE extract were observed with a SEM. It was suggested that an extract of onion peels prepared via SWE (110°C) could be used as a functional biomaterial for the food or pharmaceutical industries.

Antimicrobial and antioxidative effects of onion peel extracted by the subcritical water

The objective of this study was to evaluate the antimicrobial and antioxidative effects of the onion peels extract prepared via the subcritical water extraction (SWE) method. First, the number of cells treated with the extract was reduced by 0.7–1.1 log CFU/mL compared with the control. The SWE extract showed 76.08% scavenging activity and it was more effective than butylated hydroxytoluene (BHT) at 61.3 ppm in lipid peroxidation inhibitory effects. In addition, the antioxidative effect of SWE extract measured via the ferric thiocyanate (FTC) method was 2-fold that of BHT. The results of this study suggest that the onion peels extract prepared via the SWE method may have potential alternative antimicrobial and antioxidative effects as functional substances.