| Oil provides energy for human race, and it is one of the three major nutrients of humans. Edible oils and fats not only provides the essential fatty acids which is necessary for human life and activity, but also play a crucial role in improve the food color, smell and taste of food. Flavor and oxidative stability are two important indicators to evaluate the quality of edible oil, and oil processing and storage conditions have a significant effect on oil’s flavor and oxidative stability.The content of unsaturated fatty acid up to 80% in flaxseed oil’, and the content of α- linolenic is about 54%, it has lots of function, such as: prevented cardiovascular disease, lowering blood pressure, lowering blood pressure, anti-aging, enhance intelligence, protect eyesight and anticancer etc.. But because of its high unsaturated acids and especially the high content of linolenic acid, the improper processing or storage conditions can cause it have a special “green taste or fishy smell”, and reduce its storage stability. This research aims to study the effect of processing and storage conditions on linseed key flavor compounds and oxidative stability, and to explore the rules between key flavor compounds and oxidative stability, for improve the flavor of linseed oil and improve storage stability provided a theoretical basis. The main findings are as follows:First, Study the effects of heat and cold-pressed extra on linseed oil key flavor compounds, found flavor compounds included: alcohols, aldehydes, ketones, furans, dimethyl sulfide and so on. The evaluation of key flavor compounds of linseed by OAVs and found the key flavor compounds in order was: dimethylsulfide, hexanal, propionaldehyde, 2-butanol, 1-hexanol, 3-methyl-1-butanol, 3-pentyl alcohol, 2-methyl-propanol, 2-methyl-butanol and the like. The content of dimethyl sulfide which is the most critical flavor compound in hot-pressed linseed oil is 2.1 to 3 times than cold-pressed sample. The content of aldehydes substance which is the second key flavor compound in hot-pressed linseed oil is 1.5 to 2.3 times than cold-pressed sample. These two types of substances mainly presented green, grassy, fishy, and the earthy smell of the soil, speculated that hot-pressed linseed oil’s "green taste or fishy smell" smell heavy than cold-pressed linseed oil. The Speculated result is consistent with the results of sensory evaluation. In addition, the study found that peroxide value and content of secondary oxidation products of hot-pressed linseed oil samples showed an increasing trend relative to the cold-pressed linseed oil, indicating that hot-pressed to promote the primary oxidation and secondary oxidation of linseed oil. For hot-pressed and cold-pressed linseed oil, the “green taste or fishy smell” has a very close relationship of the oxidation stability. There is a negative correlation between the “green taste or fishy smell” and oxidation stability, ie linseed oil presented stronger “green taste or fishy smell” when oil had a poor oxidative stability, linseed oil presented lighter “green taste or fishy smell” when oil had a good oxidative stability.Second, Study the effects of Broiling conditions(moisture content of flaxseed, Broiling time, Broiling temperature) on linseed oil key flavor compounds and oxidative stability. Broiling conditions(moisture content of flaxseed, Broiling time, Broiling temperature) has a significant impact on the flavor of linseed oil, and directly affects the types of key flavor compounds formation and the content. So control Broiling Conditions can control dimethyl sulfide and other key flavor compounds’ generated, and further more can regulation and control the "Green taste" and "fishy smell" of linseed oil. Especially when Broiling temperature rises to 160 ℃, the key flavor compounds in linseed oil has changed, linseed oil’ flavor mainly reflects 2-methyl-butanal, 3-ethyl-2,5-dimethyl-Pyrazine. 15 linseed oil samples can be divided into three categories by sensory evaluation, namely 1) a strong "green taste or fishy smell "; 2) a slight "green taste or fishy smell"; 3) grilled flavor. Compared the sensory evaluation results and the results of the cluster analysis can be found some relevance between in the two ways. In addition, the study found moisture has a minimal impact on the primary oxidation of linseed oil; when broiling time reaches 50 min or the broiling temperatur e reaches 160 ℃, the peroxide value of linseed oil has significantly increased, indicating broiling time and broiling temperature had an significant effect on primary oxidation of linseed oil(but peroxide value of all samples were below the national standard level of linseed oil which is 6mmol/kg). The secondary oxidation products are hexanal and propanal in different moisture content and broiling time samples, but its content significantly changed with Broiling conditions changed. When broiling temperature reaches 140 ℃ and 160 ℃, nonanal, 2-methyl-butanal and other oxidation products has appeared linseed oil, indicating broiling temperature is an important factor on secondary oxidation products’ generated. In the heat-pressed, the flavor changes is closely related to the content of secondary oxidation product: hexanal and 2-methyl-butanal. When content of hexanal greater than 6.83mg/kg, the sample showing strong "green taste or fishy smell". When the content of hexanal less than 6.26mg/kg, the sample showing a lighter "green taste or fishy smell". When the secondary oxidation products 2-methyl-butanal appear in the sample, the sample showing a "roast flavor"Third, study the effects of storage conditions on linseed oil key flavor compounds and oxidative stability. By studying the changes of cold-pressed sample(samples a), broiling temperature 120℃(samples b) and broiling temperature 160℃(samples c) during storage. Found that three processes sample’s key flavor compounds did not have a significant change during storage. But with the extension of storage time, the amount of the key flavor compounds’ OAVs undergone significant changes. The dimethyl sulfide’ OAVs has a small changes in a sample and the sample c, but showing increasing trend at first and lower trend at last of sample b. Relative to samples of 0 day, aldehydes and alcohols’ OAVs have significantly increased in both sample b and sample c. At accelerated oxidation process of 70 ℃, the primary oxidation products were measured of sample a, sample b and sample c, results showed that: the induction time of three samples were samples a> sample b> sample c, illustrate cold pressed sample have a longest oxidation induction and sample c have shortest oxidation induction. At accelerated oxidation process of 70 ℃, the content of secondary oxidation products of sample a, sample b and sample c were measured. Found that during 1 day-3 day, increased rate of the content of secondary oxidation products in three samples is sample c> sample b > sample a. Therefore its preservation of were sample a> Sample b> Sample c, which are consistent with the Racimat results. In addition, by measuring the phenolic content, the content of phenolic compounds were samples a> sample b> sample c, explained the content of phenolic compounds is one reason of the different shelf of three sample. This conclusion is verified of this paper. During storage, when linseed oil have higher content of hexanal, the sample showing stronger "green taste or fishy smell" and have a poor oxidative stability. When linseed oil have lower content of hexanal, the sample showing lighter "green taste or fishy smell" and have a good oxidative stability. When linseed oil occurs 2-methyl-butanal, the samples showed roasted flavor and have a worst oxidation stability. |
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