Effect of Palm Oil (PO) and Distilled Mono-Glycerid (DMG) on Oil Separation and Rheological Properties of Sesame Paste

Abstract

Sesame oil separation from sesame paste is viewed as a quality defect during sesame paste processing and storage. Palm oil (PO) and distilled mono-glycerides (DMG) were added to sesame paste at (0–2%) and (0–8% [w/w]), respectively, to reduce sesame oil separation. Results showed oil separation was reduced by 12.5% at 2% PO and by 50% at 8% DMG. Most oil separation occurred during the first 40 days of storage for DMG. Rheological behavior was modeled with a typical thixotropic model. A progressive structural breakdown and decrease in viscosity. Addition of DMG to sesame paste was responsible for increasing the viscosity of colloidal system as compared to PO. It was observed that emulsifying properties of both PO and DMG were responsible for retarding oil separation. The study concluded that addition of 8% DMG to sesame paste was effective in reducing oil separation in sesame paste. Practical Applications A common problem with sesame paste (tahini) and halva (made from tahini and sugar) is sesame oil separation during storage. After grinding of de-hulled and roasted sesame seeds, oil is released and separates into an oily layer above a relatively dry mixture of sesame solids and a little oil. This results in contamination of the containers, reduction of marketability and formation of a tough and nonsmooth texture. Mono-glycerides are food additives which act as both emulsifiers and binders. They were used in this study to prevent or reduce natural oil separation taking place in sesame paste. Mono-glycerides were added to sesame paste at three concentrations (0%, 2%, 4% and 8% [w/w]) while palm oil (PO) was added at two concentrations (1% and 2%). The standard oil diffusion test was used to simulate real life oil separation.