Abstract :
[en] Oil plays important role in human daily diet. Global vegetable oil production reaches 211.44 million metric tons in 2021/22. Peanut oil is the most representative oil with better flavor and rich micronutrients. The potential chemical toxicants and characteristic volatiles of peanut oil has attracted research attention. But there is still contradiction on toxicants occurrence and limitation on flavor improvement technology. The aim of this research was to investigate the effect of raw material and processing on safety and flavor of peanut oil.
Firstly, the occurrence of trans fatty acids (TFA) and fatty acid esters of 3-monochloropropane-1,2-diol (3-MCPDE) in different edible oils collected from industrialized production line in China factory were evaluated. Corn oil, soybean oil, peanut oil and palm oil were selected as representative edible oil. TFA is widely present at relatively low levels (0.37-2.61g/100g) in edible oil collected from factory in China. 3-MCPDE are only formed in the deodorization procedure during oil processing. Palm oil has the highest 3-MCPDE content (3750.5±177.3 μg/kg). No 3-MCPDE was detected in peanut oil. The chloride precursor and mitigation method of 3-MCPDE were also studied. The effect of chlorine in different peanut varieties on 3-MCPDE formation was limited. The added salt in baking could significantly promoting the 3-MCPDE formation. Fructose and lactose could remove 35.13% and 36.99% 3-MCPDE, respectively.
Secondly, the characteristic volatile compounds of low- and high-temperature pressed peanut oil were determined by using HS-SPME-GC-MS and e-nose. Seventy-one volatiles were identified in high-temperature pressed peanut oil (HPOs), mainly including pyrazines, pyrroles and ketones, of which characteristic volatiles present nutty and roasty flavor. Fifty-two volatiles were obtained from low-temperature pressed peanut oil (LPOs), mainly consisting of aldehydes, alcohols and carboxylic acids, of which characteristic volatiles show green and fresh flavor. The characteristic volatile of HPOs and LPOs have also been determined. The results indicated that the process method has a significant effect on the flavor components of peanut oil.
Thirdly, the feasibility of using microwaves (MW) pretreatment as an improvement method for cold-pressed peanut oil processing was investigated. The acid value and peroxide value of extracted oil from MW-treated peanuts were slightly increased but far below the limit in the Codex standard. Compared with the untreated sample, a significant (p < 0.05) increase in extraction yield (by 33.75%), free phytosterols content (by 32.83%), free tocopherols content (by 51.36%) and induction period (by 168.93%) of oil extracted from 5 min MW-treated peanut were observed. MW pretreatment formed pyrazines which contribute to improving the nutty and roasty flavor of oil. MW pretreatment is a feasible method to improve the oil extraction yield and obtain the cold pressed peanut oil with longer shelf life and better flavor.
Finally, the key volatile compounds and precursors of high-temperature pressed peanut oil prepared with normal- and high-oleic peanuts were studied. Sensory evaluation results indicated that normal-oleic peanut oil showed stronger characteristic flavor than high-oleic peanut oil. The compounds methylpyrazine, 2,5-dimethylpyrazine, 2-ethyl-5-methylpyrazine and benzaldehyde were considered as key volatiles which contribute to dark roast, roast peanutty and sweet aroma of high-temperature pressed peanut oil. The initial concentration of volatile precursors (arginine, tyrosine, lysine and glucose) in normal-oleic peanut was higher than in high-oleic peanut, which led to more characteristic volatiles forming during process and provided a stronger oil aroma of.
This research will provide data support for raw material screening and quality improvement during peanut oil industrial production.
