Oxidation in fish-oil-enriched mayonnaise 1. Assessment of propyl gallate as an antioxidant by discriminant partial least squares regression analysis

A number of different analytical techniques (HPLC, GC-MS, sensory analysis, laser diffraction droplet size determination, confocal laser scanning microscopy and rheological measurements) were employed to elucidate both chemical, sensory, structural and rheological aspects of the oxidation process in mayonnaise containing 16% fish oil. The primary focus of the study was on the antioxidative effect of two different types of commercial propyl gallate mixtures: an oil-soluble and a water-soluble preparation. The effect of adding extra emulsifier (Panodan TR), used to manipulate the physical structure of the fish-oil-enriched mayonnaise and in turn affect the antioxidative activity of the propyl gallate mixtures, was also investigated. Mayonnaise with fish oil did not oxidise faster than mayonnaise without fish oil when judged from the chemical parameters tested. However, the fish-oil-enriched mayonnaises developed unpleasant off-odours and off-flavours much faster than the mayonnaise without fish oil. Addition of the two different propyl gallate mixtures not only influenced negatively the sensory qualities but also affected the structure and the rheological properties of the mayonnaise, Propyl gallate thus, in particular, promoted the development of fishy and rancid off-flavours during the storage of mayonnaise with fish oil, and this effect was especially pronounced for the water-soluble propyl gallate mixture, Four volatile oxidation compounds, namely 3-furaldehyde, a,4-heptadienal, 2,4-decadienal and ethyl benzene, appeared to correlate to the fishy and rancid off-flavours that developed in mayonnaises with propyl gallate, Addition of propyl gallate also resulted in increased peroxide values, and a less viscous mayonnaise with bigger droplets. The data thus demonstrated that the propyl gallate mixtures employed did not protect mayonnaise with fish oil against flavour deterioration due to oxidation during storage. In addition, the data showed that several structural and rheological parameters were affected by the addition of propyl gallate.