Egg vs. Oil in the Cookbook of Plasters: Differentiation of Lipid Binders in Wall Paintings Using Gas Chromatography-Mass Spectrometry and Principal Component Analysis

Wall paintings are integral to cultural heritage and offer rich insights into historical and religious beliefs. There exist various wall painting techniques that pose challenges in binder and pigment identification, especially in the case of egg/oil-based binders. GC-MS identification of lipidic binders relies routinely on parameters like the ratios of fatty acids within the plaster. However, the reliability of these ratios for binder identification is severely limited, as demonstrated in this manuscript. Therefore, a more reliable tool for effective differentiation between egg and oil binders based on a combination of diagnostic values, specific markers (cholesterol oxidation products), and PCA is presented in this study. Reference samples of wall paintings with egg and linseed oil binders with six different pigments were subjected to modern artificial ageing methods and subsequently analysed using two GC-MS instruments. A statistically significant difference (at a 95% confidence level) between the egg and oil binders and between the results from two GC-MS instruments was observed. These discrepancies between the results from the two GC-MS instruments are likely attributed to the heterogeneity of the samples with egg and oil binders. This study highlights the complexities in identifying wall painting binders and the need for innovative and revised analytical methods in conservation efforts.

Quantitative GC-MS Analysis of Artificially Aged Paints with Variable Pigment and Linseed Oil Ratios

In this study, quantitative gas chromatography-mass spectrometry (GC-MS) analysis was used to evaluate the influence of pigment concentration on the drying of oil paints. Seven sets of artificially aged self-made paints with different pigments (yellow ochre, red ochre, natural cinnabar, zinc white, Prussian blue, chrome oxide green, hematite + kaolinite) and linseed oil mixtures were analysed. In the pigment + linseed oil mixtures, linseed oil concentration varied in the range of 10 to 95 g/100 g. The results demonstrate that the commonly used palmitic acid to stearic acid ratio (P/S) to distinguish between drying oils varied in a vast range (from especially low 0.6 to a common 1.6) even though the paints contained the same linseed oil. Therefore, the P/S ratio is an unreliable parameter, and other criteria should be included for confirmation. The pigment concentration had a substantial effect on the values used to characterise the degree of drying (azelaic acid to palmitic acid ratio (A/P) and the relative content of dicarboxylic acids (∑D)). The absolute quantification showed that almost all oil paint mock-ups were influenced by pigment concentration. Therefore, pigment concentration needs to be considered as another factor when characterising oil-based paint samples based on the lipid profile.

Effect of shortening replacement with flaxseed oil on physical, sensory, fatty acid and storage characteristics of cookies

Omega-3 fatty acid imparted good evidence of health benefits. Flaxseed oil, being the richest vegetarian source of alpha linolenic acid (omega-3 fatty acid), was incorporated in cookies by replacing shortening at level of 5 %, 10 %, 20 %, 30 %, 40 % and 50 %. Effect of shortening replacement with flaxseed oil on physical, textural and sensory attributes were investigated. Spread ratio and breaking strength of cookies increased as flaxseed oil level increased. Sensory score was not significantly affected up to 30 % shortening replacement with flaxseed oil as compared with the control cookies. Above 30 % flaxseed oil, sensory score was adversely affected. Fatty acid profile confirmed the enhancement of omega-3 fatty acid from 0 (control) to 14.14 % (30 % flaxseed oil cookies). The poly-unsaturated to saturated fatty acid ratio (P/S) increased from 0.088 (control) to 0.57 while ω - 6 to ω -3 fatty acid ratio of flaxseed oil cookies decreased from 4.51 (control) to 0.65 in the optimized cookies. The data on storage characteristics of the control and 30 % flaxseed oil cookies showed that there was significant change in the moisture content, Peroxide value (PV) and overall acceptability (OAA) up to 28 days of storage at 45 °C packed in polyethylene bags. Flaxseed oil cookies were acceptable up to 21 days of storage and afterwards noticeable off flavour was perceived.