Effects of pH and NaCl levels in a beef marinade on physicochemical states of lipids and proteins and on tissue microstructure

- Microstructural changes were assessed by image analysis.
- Protein hydrophobicity and extra-cellular space varied concomitantly with pH.
- Transverse swelling of meat fibres was affected by both pH and NaCl content.
- Dividing the usual NaCl content by two did not affect biochemical changes.
- Acid marinating of salted products is not recommended from a nutritional viewpoint.

Meat slices were incubated for 24 h at 10 °C in marinade solutions so that their pH reached 6.5, 5.4, or 4.3, and their NaCl contents 0.9% or 2%. The histological modifications were assessed by image analysis using two parameters: mean fibre cross section area (FCSA, μm2) and the ratio of the extra-cellular space (ECS, % area). The changes in lipids and proteins were evaluated through oxidation, protein surface hydrophobicity, and protein aggregation by granulometry (size and shape of particles). ANOVA showed that FCSA decreased linearly while ECS increased when pH decreased from 6.5 to 4.3 at either low or high NaCl salt content. Decreasing pH significantly increased TBARS and carbonyl groups, while increasing NaCl level had a significant protective effect on lipids. No marinating effect was observed on free thiols. Protein surface hydrophobicity and aggregation increased significantly with decreasing pH, but were unaffected by NaCl. The effect of these physicochemical changes on the nutritional value of meat is discussed.