Isolation And Physicochemical Characterization Of Peanut Oil Bodies

Oilseeds store energy as triacylglycerides during periods of dormancy in preparation for germination and the early stages of development.The triacylglyceride is stored in discrete organelles termed oil bodies.Oil bodies are formed during the synthesis of neutral lipids within the bilayer of cellular endoplasmic reticulum(ER);as lipid is synthesised it forms droplets of oil that swell distending the ER membrane and at a critical diameter separate from the ER by vesiculation forming independent organelles.These organelles are structurally stabilized by a phospholipid monolayer originating from the ER and the addition of highly amphiphilic oleosin proteins.Oil bodies have been shown previously to be extremely stable organelles that can be easily extracted and purified from oilseeds;our aim was to develop an understanding of the physical and chemical properties of peanut oil bodies ex-vivo prior to their subsequent use in commercial products.Several novel findings were elucidated through this work: the optimum condition for high quantity and quality of oil bodies besides their phytochemical composition,their physical and oxidative stability and their main macro and minor components.Generally,our work decomposed into five small chapters;Firstly,a simple aqueous extraction method was used to extract peanut OBs and its effect on the properties and the stability of the resulted emulsions was evaluated.The abovementioned method involves successive mechanical steps in order to release OBs from their cell networks,followed by purification using different recovery pHs and washing.Results showed that crude OBs had a high amount of extrinsic proteins and low physical stability.Washing OBs twice with the increase in recovery pH decreased the extrinsic proteins,the lipid oxidation and improved the storage stability.The physical and the oxidative stability of all OBs emulsions was significantly enhanced by heating.These results suggest that peanut OBs extracted using this aqueous extraction method,can be used to prepare natural emulsions with improved longterm stability.In the second part,we have used the same above mentioned extraction method to study the macro and micro elements of peanut OBs.in vivo OBs are well-organized structures in the form of capsules dispersed throughout the whole seed.As we cited earlier,the protein fraction represents the special part of OBs,therefore,we had to study their propertied Ex vivo.The Tricine SDS PAGE of peanut OBs recovered using the aqueous extraction method at different pH,revealed the presence of two oleosin isoforms of 14 and 16 kDa besides one calseosin,one steroleosin and some other extrinsic proteins.Moreover,OBs essential amino acids are 1.52 higher than those in the PPI indicating the nutritional benefit that can be provided by these natural capsules.Oleic acid and linoleic acid are the major fatty acids in both,cold press peanut oil and OBs regardless of pH.It was hypothesised that tocopherol is tightly associated with plant oil bodies,as a result,we have tested by recovering oil bodies from peanut seed and washing them by increasing the pH recovery to remove extraneous proteins and associated phenolic compounds.Tocopherol content went from 270,76 to 278,2 ?g/g when pH got increased which hypothesized that this high tocopherol concentration and its intrinsic association to oil bodies structures would contribute to an increased level of oxidative stability.?-Tocopherols appeared tightly associated with peanut OBs as it was resistant to the alkaline washing,however,?–tocopherols were discovered to be weakly associable.on the contrary,phytosterols content decreased when pH got increased,with 631,49 ?g/g for pH 6.8 and 614,96 ?g/g for pH 11.0.The third part of the research was dedicated only to TAGs matrix of oil bodies isolated from peanut.The ultra-performance liquid chromatography coupled with quadrupole time-offlight mass spectrometry(LC-Q-TOF-MS)was used to separate and identify the TAGs in cold press oil and in the OBs in goal to reveal the differences and the similarities between the oil protected inside OBs and the oil extracted from the whole seed.Generally,both samples showed a similar TAGs profile with 2 extra TAGs identified in CPO in very low content.23 different TAGs were identified in the peanut OBs and 25 TAGs in the CPO.The most abundant TAGs were OOO,OOL,POO,POL and OLL in both samples.Furthermore,oleic acid,linoleic acid and palmitic acid were the major fatty acid in peanut oil bodies and in CPO.To the best of our knowledge,this is the first research that studied the TAGs matrix of an oil body revealing no major difference between the TAGs profile of the TAGs protected by the peanut OBs membrane and the oil extracted from the whole seed.The fourth part was kind of application of all the knowledge we got from the previous parts.We have selected one successful food product based on OBs to evaluate the behaviour and the interaction of OBs inside a complex system.Peanut milk was the product we have selected,and we used the same method described for OBs isolation but without centrifugation because we want to prepare a full-fat peanut milk.In the previous part of the present research we studied the effect of pH,heat treatment and NaCl(not mentioned in the thesis part mentioned in the list of publication)on the OBs behaviour and stability,but now we want to evaluate the effect of roasting,high-pressure homogenization and heat treatments on physicochemical properties,physical stability of peanut milk through the OBs behaviour.Vegetable milks were obtained and homogenized by applying,150 and 300 MPa,then thermal treatment(pasteurization or sterilization).The conclusion we could get from this part was that OBs contribute directly to the peanut milk physicochemical properties and stability.Moreover,a positive interaction between OBs and milk proteins can donate a stable product with high organoleptic quality.The results showed that unroasted peanut milk was very sensitive to sterilization and it getting more sensitive in case of previous homogenization regardless the pressure used.The degradation of the product was seen visually but the reason was not understood.Therefore,a microscopic visualization was needed where it showed that after sterilization or after a combination of homogenization and sterilization,a severe aggregation coalescence took place between the OBs.Moreover,the light scattering values confirm these results where the OBs size increased dramatically.This degradation of the unroasted peanut milk happened because the OBs oleosin didn't resist to high thermal treatment under highpressure,moreover,the protein of unroasted peanut had weak emulsifying properties.After roasting,the results were completely different.Homogenization and thermal treatment worked together to enhance the peanut milk properties,stability and viscosity.The reason behind this change is principally related to the Maillard reaction and its effect on the protein solubility.The results showed that roasting did increase the protein solubility and consequently their emulsifying properties.The Tricine SDS PAGE of OBs showed that their oleosin isoforms where intact regardless the treatment applied indicating that the OBs were protected by another layer(roasted peanut proteins).The last part was kind of opening to another area of research but directly related to oil bodies and their intrinsic proteins.In the previous chapter of the present research,we get to know that OBs intrinsic proteins have a great emulsifying properties also they provide a strong stability to OBs,therefore there is an increasing interest to use them as emulsifying agents in the food,cosmetics and pharmaceutical industries.From our side,we tried to use these proteins as wall material to encapsulate other oil with high nutritional value and more sensitive to oxidation.We have found some interesting results such as oleosin can recognize the oil used of the formulation of AOBs,where,they react perfectly with their oil of origin(peanut oil)also with chia oil which is considered as a foreign oil however they didn't well reformulate with the flaxseed oil.