| Camellia oleifera Abel.is a unique oil tree species in China,from which Camellia oleifera oil being extracted is a kind of edible oil with health-care function.In recent years,with the high-quality development of camellia industry,the planting area,output and combined output value of Camellia oleifera have been steadily improved,but there are still some problems in the camellia industry,including excessive processing,incomplete research on functional values and so on.Moreover,systematic studies on the whole industrial chain of camellia oil are not adequate.This study focused on the key factors and links in the camellia oil industry chain that affect oil quality,discussed the influence mechanism of light refining processing on the quality and thermal stability of camellia oil,investigated the role of lightly refined camellia oil as a functional oil to regulate blood sugar and improve the intestinal flora,aiming to optimize the processing accuracy of the camellia oil production process and to improve the quality and efficacy content of camellia oil,making it be favorably received by Chinese people as a high-quality edible oil.The study also provided some theoretical guidance for a healthy China and scientific oil use.The specific results of the study are as follows.(1)Firstly,the effects of pretreatment,oil making and refining processes on the quality of camellia oil and the content of active lipid concomitants were compared.It was found that hot air and steam pretreatment can increase the phenolic contents of the oil by 76.8% and 59.8% respectively,and there was no significant effect on fatty acid composition of camellia oil(p >0.05).In addition,hot air pretreatment can increase the content of sterols in camellia oil by 7.81%.However,if the temperature during pretreatment process is too high,it would cause an increase in free fatty acids in camellia oil.In the oil making process,the high temperature required for desolvation and evaporation in the leaching process will substantially increase the acid value and peroxide value of camellia oil,and the content of benzo[a]pyrene increased by 158.82%.At the end of the refining process,the acid value of the pressed oil was reduced by65.6%,and refining can remove the benzo[a]pyrene produced during the production process.However,the refining process resulted in the loss of 100%,46.57%,86.18%and 79.19% of the active lipid concomitants such as tocopherols,sterols,squalene and phenolics respectively.However,if the oil is only precipitated by water washing and degumming without decolourisation,deacidification,deodorisation and winterisation,the fatty acid composition of the oil can be kept unchanged,the peroxide value can be reduced by 30.3%,the benzo[a]pyrene produced by the previous production process can be removed,and the retention rate of active lipid concomitants can also be over85%.Therefore,further studies will be conducted on the effects of pretreatment of camellia seed on the antioxidant function of camellia crude oil and the degree of refining on the thermal stability of finished camellia oil as key processes.(2)Secondly,a comparison of the yield,antioxidant functional properties,active concomitant composition and in vitro antioxidant activity of the extracts was carried out on the basis of obtaining optimal conditions for four pretreatment methods: hot air,steam,high-pressure instantaneous puffing and superheated steam.The optimum conditions for the four pretreatment methods were 60 ℃,40 min for hot air pretreatment,800 rpm for high-pressure instantaneous puffing,15 min for steam pretreatment and 15 min for superheated steam pretreatment.It was found that all four pretreatment methods could improve the oil yield of camellia seed,with high-pressure instantaneous puffing treatment being the highest,increasing the oil yield by 19.82%.Pretreatment of camellia seeds can increase the content of active lipid concomitant,among which high-pressure instantaneous puffing treatment increased the content of5.28% tocopherol of the oil,the hot air and superheated steam treatments increased the total sterol content of the oil by 12.52% and 5.18% respectively.The content of free phenolics in camellia oil was increased by 42.86%,82.99% and 94.90% by steam,puffing and superheated steam pretreatment,respectively.The four pretreatments also increased the antioxidant capacity of DPPH,ABTS and FRAP of phenolics from camellia oil.A total of 105 phenolic compounds in 22 classes were identified in camellia oil by metabolomics,among which 8 phenolic compounds may be closely related to antioxidant activity.This indicates that as an important part of camellia oil processing,pretreatment can not only increase the oil yield of camellia seed,but also have a positive effect on the active lipid accompaniments and its antioxidant activity of camellia oil.(3)Subsequently,in order to explore the effect of refining degree on thermal stability of camellia oil,the changes of oxidation degree and lipid changes of crude oil,lightly refined oil and refined oil during heating were compared.The oxidative stability of the three types of camellia oils was in descending order of lightly refined oil > crude oil > refined oil,which may be related to the active lipid concomitants such as tocopherols and phenolics in camellia oil.Through untargeted lipidomics,a total of1598 lipids were identified in camellia oil before and after heating.Using value importance in projection(VIP)and fold change(FC)as thresholds to screen different forms of lipids in camellia oil before and after heating,a total of 83 differential lipids were screened in crude oil,90 in lightly refined oil and 94 in refined oil.The upregulation fold was significantly greater in crude oil and lightly refined oil than in the refined oil.Pathway analysis identified glycerophospholipid metabolism as one of the key oxidative pathways,which included five lipids: PE(34:2),PE(40:0),PE(42:5),PE(44:0),PS(38:4).Refining and heating accelerated the conversion of PS to PE.It indicates that light refining is beneficial to retain the antioxidant lipids in camellia oil.In conclusion,light refining has a positive effect on the quality of camellia oil in terms of oxidation stability,active lipid concomitants and lipid changes.Light refining should be carried out according to the quality of the crude oil to maximize the content of active lipid concomitants in the commercial oil when refining and processing oil from camellia seeds.(4)The effects of exogenous addition of four active lipid concomitants with relatively high content in camellia oil,α-tocopherol,β-sitosterol,squalene and quercetin,on thermal stability of camellia oil were studied.Results showed that the addition of α-tocopherol and β-sitosterol reduced the production of hydroperoxides by30% in camellia oil during heating and protected the = C-H,C = C and C-O-C bonds in the triglyceride molecule,they also can increase the initial decomposition and oxidation temperature of camellia oil respectively,adding α-tocopherol could increase the initial decomposition temperature of camellia oil by 16 ℃,that is,can delay the thermal oxidation of camellia oil.Squalene and quercetin were less effective in retarding oxidation,but had protective effects on the = C-H and C-O-C bonds in the triglyceride molecule.Molecular dynamics simulations revealed that the antioxidant mechanism of all four active substances was to provide hydrogen protons to the lipid oxide radicals and prevent free radical chain reactions.(5)In order to broaden the application scenarios of lightly refined camellia seed oil and explore its physiological functions,mice with type II diabetes were fed with high and low doses of lightly refined camellia oil to reveal its effects on regulating blood glucose and improving intestinal flora.The group of mice fed with high-dose lightly refined camellia oil could reduce the amount of food and water intake,and had a significant effect on reducing fasting blood glucose from 29.5 mmol/L to 23.7mmol/L.After 4 weeks of intervention,it had a similar hypoglycaemic effect as metformin,and the high-dose lightly refined camellia oil also improved the glucose tolerance and insulin resistance of mice after gavage of glucose.The lightly refined camellia oil intervention group and the metformin positive group showed a significant decrease in the abundance of the firmicutes,a significant increase in the abundance of the Bacteroidetes,a significant decrease in the F/B ratio and a significant decrease in the abundance of Thermodesulfobacteria compared with the model group.The intervention with high dose of lightly refined camellia oil could increase the abundance and diversity of intestinal flora,change the species composition of intestinal flora in db/db mice and improve intestinal health.Further studies found that the high dose lightly refined camellia oil intervention group differed in species of Clostridiales at the order level and Clostridiaceae at the family level,the beneficial effect of camellia oil may be attributed to the increased abundance of Clostridiales.In addition,differential metabolites in the intestine and liver of diabetic mice were analysed by metabolomics and most were related to carbohydrate metabolic pathways.The results of this study may provide a theoretical basis and guidance for the development of hypoglycaemic function of camellia oil. |
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