Effect of olive paste pH during malaxation on virgin olive oil properties

The present study evaluated the influence of olive paste pH adjustment during malaxation on oil yield and quality parameters of virgin olive oil obtained from Olea europaea L. cv. Gemlik. The pH of olive paste was systematically adjusted to 2.7-6.7 using citric acid and NaOH solutions during malaxation. Oil yield, free fatty acidity (FFA), peroxide value (PV), total and individual phenolic compounds, DPPH radical scavenging activity, and color attributes (L*, a*, b*) were determined. Oil yield ranged from 28.67 to 45.11%, with the highest yield observed at pH 6.7. Total phenolic content(TPC)showed a clear pH-dependent pattern, reaching 678 mg GAE kg⁻¹ at pH 2.7 and decreasing to 281 mg GAE kg⁻¹ at pH 6.7. Moderately acidic conditions (pH 4.7) promoted elevated concentrations of secoiridoid derivatives, with oleacein (257 mg kg⁻¹) and oleocanthal (159.7 mg kg⁻¹) attaining their highest levels. Phenolic alcohols exhibited compound-specific pH responses, with tyrosol and hydroxytyrosol acetate reaching maximum levels at pH 4.7, while hydroxytyrosol peaked at pH 3.7 and declined thereafter. Flavonoids, such as apigenin, reached maximum concentrations (16.5 mg kg^-¹) under mildly acidic conditions (pH 3.7). 3,4-DHPEA-EA decreased progressively with increasing pH, from 226 to 103 mg kg^-¹, indicating that pH influences its stability and transformation pathways during malaxation. PV values were highest at pH 3.7 (8.4 meqO₂kg⁻¹ oil) and 4.7 (7.2 meqO₂kg⁻¹ oil). DPPH radical scavenging activity paralleled the phenolic profile, with oils obtained at lower pH exhibiting approximately twofold greater activity than those obtained at pH 5.7 and 6.7. Several quality parameters exhibited significant quadratic responses to pH variation. Color attributes were also influenced by pH, with acidic conditions producing brighter oils with reduced yellowness. These findings indicate that controlled pH modulation during malaxation can influence phenolic composition, antioxidant capacity, and visual characteristics of virgin olive oil, providing mechanistic insight into the pH sensitivity of its extraction and compositional changes.