Impact of the acid-hydrolyzed phenolic extracts of parsley (Petroselinum crispum L.) leaves on soybean oil-in-water emulsions

Parsley (Petroselinum crispum L.) is a rich source of polyphenols, making it a potential option for extracting natural antioxidants. However, not all these compounds are easily extractable in their aglycone form and when they exist in glycoside forms their antioxidant activity is limited. Acid hydrolysis post-treatment is a reliable method to break glycosidic bonds and release the aglycone form of polyphenols. This study aims to develop an effective extraction method coupled with acid hydrolysis to determine if the formation of aglycones can increase the antioxidant activity of parsley extract to inhibit lipid oxidation in soybean oil-in-water (O/W) emulsions. Various HCL concentrations (0.3, 0.6, and 1.2 M) and hydrolysis durations (1, 2, and 3 h) were employed in acid hydrolysis to optimize total phenolic content (TPC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity in parsley extract. The emulsion consisted of 2% (w/v) stripped soybean oil, and 0.2% (w/v) Tween 20 in a 10 mM sodium acetate-imidazole buffer (pH 7.0). Acid-hydrolyzed and unhydrolyzed extracts were added to the emulsion, achieving final phenolic concentrations of 400 and 800 µmol gallic acid equivalent (GAE)/L. An emulsion without the addition of extracts was used as a control. Oxidation stability was assessed by monitoring primary (hydroperoxide) and secondary (hexanal) oxidation products. Under optimal acid hydrolysis condition (0.6 M HCl, 2 h at 80 ℃), TPC increased to 716.92 ± 24.43 µmol GAE/L from 490.44 ± 0.89 µmol GAE/L, and DPPH scavenging activity rose to 66.89 ± 1.63% from 42.93 ± 0.36%. Acid hydrolysis could transform the glycosidic phenolic compounds into aglycones, causing an increase in the content of individual polyphenols and the release of myricetin and gallic acid. The emulsion prepared with 400 µmol GAE/L TPC of the acid-hydrolyzed extract showed the highest oxidative stability with an 11-day lag phase for the headspace hexanal, while the control group had a 0-day lag phase. The results highlighted that acid-hydrolyzed extracts are a potential tool to increase the shelf life of emulsion-based foods.