Recovery of sterols from plant based food waste for the development of functional food ingredients

Bioactive compounds recovered from food processing waste can be used for the development of functional food ingredients providing value added products and an alternative solution for environmental problems. The general objective of the thesis is to recover sterols from olive pomace using hydrothermal pretreatments, which also enable recovery of phenolics producing sterol rich pomace oil to be used as a functional food ingredient source and phenolic extract. An in-depth review of the literature data and an overall partitioning study (samples taken from an integral olive milling plant) of pre-dominant lipophilic bioactives (squalene, alpha-tocopherol and beta-sitosterol) were carried out to understand distribution of these bioactives between oil and waste streams during virgin olive oil (VOO) processing. To be used in this study, a rapid in-house GC-FID method was developed to determine lipophilic bioactives (squalene, alpha-tocopherol and beta-sitosterol (BS)) simultaneously, and validated covering; linearity (16.0-700; 12.5; 8.4-500 mg/100g, respectively), recovery (93-95; 93-110; 92-97 per cent) and repeatability. Loss of these lipophilic compounds during VOO processing was determined by analyzing oil in olive fruit, olive oil, pomace and olive mill wastewater samples. The loss of BS (44 per cent) and alpha-tocopherol (42 per cent) were higher than that of squalene (12 per cent) and oil (14 per cent) due to non-recovered bound forms. To recover sterols and phenolics and to increase oil yield, pretreatments hydrolyzing plant cell wall, steam and subcritical water reaction medium was applied to olive pomace at different temperature (160, 180 and 200°C) in a pilot system. While oil recovery was similar to that obtained with acid hydrolysis, 18-32 per cent of the bound BS of the pomace was recovered as free form by hydrothermal pretreatments. Maximum BS recovery was obtained using hydrothermal pretreatment in combination with acid hydrolysis, which might be due to release of bound BS as glycosides from cell membrane structure. Significant increase in phenolic compounds at 200°C and formation of 5-hydroxymethylfurfural (HMF) were indication of lignin decomposition and Maillard/caramelization reactions, respectively.