Enzyme-assisted Aqueous Extraction Of Oil And Protein From Peanut

Enzyme assisted aqueous extraction processing(EAEP) is a promising method for extraction of oil and protein from peanut at the same time. It has the attributes of mild reaction condition, low equipment investment cost, high resource utilization rate and environmental friendly. EAEP has not been industrialized over the course of half a century due to a serious impediment such as principle, process technology, equipment, high investment cost of enzyme and full utilization of resource. In this study, we modified and improved the EAEP and significantly reduced the amount of enzyme to one tenth of the original, 94% of proteins were aviod being overly hydrolysis at the same time. Eventually the industrialization of improved enzyme assisted aqueous extraction processing(IEAEP) from peanut was achieved. The objectives of this study were(1) to evaluate the effect of particle size distribution and the effect of roating temperature on oil and protein extraction;(2) to evaluate the demulsification of cream emulsion from IEAEP;(3) to evaluate the functional properties of hydrolyzed protein which was obtained from cream emulsion demusification process;(4) and to identify possible scaleup issues that may affect oil and protein extraction yields, distribution of extracted oil among the fractions, and total free oil yield when moving from the laboratory to pilot-plant scale and using similar equipment that industry would employ.(5) to determine the volatile flavor compounds and the oxidation stability of peanut oil samples.Firstly, the effect of roasted temperature on oil and protein yield was evaluated. The result show that with the increase of roasting temperature from 130 °C to 210 °C, the free oil yield has a slight increase until the roasting temperature exceeds to 150 °C. The highest free oil yield of peanut(92.2 %) was achieved when using roasted peanut(150 °C). In addition, the protein content in skim fraction was significantly decreased, but in exchange, protein content in insoluble fraction had an increase trend. According to the results of confocal laser scanning microscopy(CLSM) and particle size distribution, roasting treatment was beneficial to peanut comminution. The optimal average particle size(d0.5) for peanut paste in IEAEP was 15.2 ?m which could hardly find intact oil bodies by CLSM. For the insoluble fraction that was obtained from roasted material(150 °C), more oil adhered to the surface of protein bodies. However, these observations were not found in the insoluble fraction of raw material. It was inferred that roasting treatment denatured peanut protein so that amino-acid chains unfolded and exposed more interior hydrophobic amino acids which were likely to combine with oil.The stability of the emulsion is sensitive to the p H, especially at the peanut protein isoelectric point(p H 4.5). All the proteases released more free oil than phospholipase as a result of enzymatic demulsification. The oil recovery yields of enzymatic demulsification decreased in the order of Enzyme E(94.89 %) > Enzyme D(93.10 %) > Enzyme C(86.89 %) > Enzyme A(84.51 %) > Enzyme B(80.76 %). During demulsification, emulsions which were prepared with adding Enzyme D may observe the oil droplets coalescence, but the protein interfacial films were disrupted with further hydrolysis. It is speculated that the addition of protease may hydrolyze proteins to small peptides which were more likely to adsorb at water/oil interface than original proteins and displace original proteins from the interfacial film. The integrity of the interfacial film was undermined so that it was inadequate to prevent oil droplets coalescence.However, the optimal p H of Enzyme E is 4.5 which is near the p I of peanut proteins. Therefore, both p H of the cream emulsion and enzymatic hydrolysis may contribute to the free oil recovery.In this study, the proteins in skim fraction had a better fuctional properties such as emulsifying properties, foaming properties and water(oil) binding capacity than the proteins obtained from cold press which were defated by using organic solvent. In addition, the foaming properties and oil binding capacity indexes were higher than soybean protein isolated. In the case of protein hydrolysis in cream emulsion, the degree of hydrolysis and molecular weight(MW) distribution of proteins were comparable to each other when treating by proteases. Analysis of changes in protein solubility, emulsifying properties, subunit and secondary structure distribution of the protein indicated that all the protein solubility was improved after enzymatic treatment, however, the emulsifying stability indexes(ESI) of all protein were less than control. 70 % of proteins MW in cream emulsion was hydrolyzed to less than 1 k Da. Indeed, a destabilized emulsion was preferred to obtain rather than to obtain a stable emulsion in the present work. Therefore, it is difficult to keep a balance between achieving a high demusification rate and producing a better functional properties protein at the same time.The pilot-scale process of IEAEP which was based on lab scale tests was carried out, the oil recovery yield from pilot-scale process(500 kg) of IEAEP was 89.4 % and the oil contents in insoluble and skim fractions were 1.1 % and 3.4 %, respectively. The results of pilot scale were very close to that obtained from lab scale. A daily capacity of 50 tons of commercial production line of IEAEP which was cooperation with enterprises was build. The IEAEP of peanut was successfully achieved transformation from lab scale to commercial production. The average yields of oil and protein were 92 % and 86.2 %. The quality of peanut oil from IEAEP and screw pressing were evaluated. In the case of peanut oil quality in different extraction methods, the peanut oil from IEAEP had no detectable trace glycidyl ester and 3-chloride propyl alcohol ester. However, it can be detected in the peanut oil which were extracted by using high temperature screw pressing and organic solvent extraction processing. For 0-150 days' preservation without antioxidant, both the peanut oil from IEAEP and cold pressed peanut oil are keep good quality and the peroxidation values were 3.62 ± 0.28 mmol/kg and 4.21 ± 0.38 mmol/kg, respectively. All the test oil samples were at the first stage of oil oxidation.HS-SPME-GC-MS, sensory evaluation and electronic nose(EN) were combined to analyze the effect of roasted temperature on the volatile flavor compounds of peanut oil. A total of 95 volatiles were identified by using HS-SPME-GC-MS. Pyrazine compounds denoted the major flavor for aromatic roasted peanut oil. To compare the pyrazine compounds in peanut oils from IEAEP and screw pressing, the results shown that the content of pyrazine compounds was lower in peanut oil of IEAEP than that from screw pressing process at the same roasting condition. In the case of fried potato chips which was fried by different peanut oil samples(190P, 190 W, 150 W, RW, RP), Pyrazines components were found in all the fried chip samples. The peanut oil which was full of pyrazines components may not retain its unique flavors of roasted peanuts to the fried chips due to their more volatile attribute. The main types and contents of volatile components of five peanut oil fried chips samples were similar. The results of electronic nose and sensory evaluation were correspondent with the results of GC-MS.