| Vegetable oils rich in bioactive substances,such as inoleic acid,α-linolenic acid and γ-tocopherol.And they have the effects of preventing cancer,reducing blood lipid and preventing cardiovascular diseases.Soybean oil,peanut oil,walnut oil and grape seed oil were used instead of milk fat to prepare the solidified probiotic yogurt,because of high unsaturated fatty acids content.Vegetable oil yoghurt was a good functional yogurt for consumers,because it not only containing the nutrient content of milk but also reducing the consumption of saturated fatty acids.In this paper,four kinds of vegetable oils were used instead of milk fat to produce solidified probiotic yogurt.The physicochemical properties,texture characteristics,rheological properties,microstructure,fatty acid composition,volatile flavor,sensory evaluation,antioxidation activity,chemical nutrients and lactic acid bacteria number during the storage period of vegetable oil yogurt were tested to screen for high quality yogurt with good flavor,and provide the basis for the development of the functional vegetable oil yogurt.1.The test used soybean oil,peanut oil,walnut oil,grape seed oil and skim milk powder as experimental raw materials,and Bifidobacteria,Lactobacillus bulgaricus,Lactobacillus acidophilus,and Streptococcus thermophilus were used as the mixed starter,different vegetable oils solidified probiotic yoghurts were prepared through homogenization,fermentation and ripening.And the effects of adding different vegetable oils on physiochemical properties,gel structure,sensory quality,volatile flavor components,fatty acid composition and antioxidant activity of yogurt were explored.The results showed that soybean oil and peanut oil significantly increased the titratable acidity of yogurt(p<0.05),walnut oil and grape seed oil significantly increased the water holding capacity of yogurt(p<0.05),and all four vegetable oils significantly reduced the hardness and consistency of yogurt,and improved cohesion and viscosity index(p<0.05).In yoghurt,many kinds of volatiles flavor compounds such as alkanes,ketones,aldehydes,acids,alcohols,esters,phenols,furans,pyrazines and aromatics were detected,the flavor components and relative content changed with the extension of ripening time.Four kinds of plant oil yogurt were slightly pale yellow,no stratification,because the vegetable oil yogurt has characteristic oil taste,only grape seed oil yogurt was more acceptable.Vegetable oil made the content of unsaturated fatty acids in yogurt increase.Soybean oil and grape seed oil were beneficial to the structural stability of yogurt gel,and the apparent viscosity of grape seed oil yogurt was higher than other groups within a certain temperature range.Peanut oil can significantly reduce the DPPH free radical scavenging ability of skim yogurt(p<0.05),while the other three vegetable oil yogurt had no significant effect(p>0.05).Walnut oil and grape seed oil can significantly decreased the hydroxyl radical scavenging ability of skim yogurt(p<0.05),while soybean oil and peanut oil had no significant effect(p>0.05).2.The grape seed oil,skim milk powder and whole milk powder were used as experimental raw materials,and Bifidobacteria,Lactobacillus bulgaricus,Lactobacillus acidophilus and Streptococcus thermophilus were used as the mixed starter.And different levels of grape seed oil solidified probiotic yoghurts were prepared through homogenization,fermentation and post-ripening.And the effects of adding different levels grape seed oil on physiochemical properties,gel structure,sensory quality,volatile flavor components,fatty acid composition and antioxidant activity of yogurt were explored.The results showed that the physicochemical indexes and sensory indexes of yogurt improved with different degrees when the addition percentage was 3.5%,the titratable acidity was 101.69 °T,the water holding capacity was 56.28%,the hardness was 179.39 g and the viscosity was 4430.90 g.s,the score of color was 16.33,and the score of the tissue state was 30.33.In the four kinds of grape seed oil yogurt,the inherent flavor of the yogurt such as acetaldehyde,2,3-butanedione and 2,3-pentanedione were also detected,the grape seed oil characteristic flavor compounds were detected: 2-octenal.3.0% and 4.0% GOSM had the highest unsaturated fatty acid content,G’(elastic modulus)and G’’(viscous modulus)of 3.5% GOSM were closest to whole milk yoghurt,and its gel structure was the most stable with the temperature changing.Electron microscopy results showed that the fat globules in 3.0% GOSM were filled relatively evenly in the casein gel,and the network voids were uniform and dense.The addition of 2.5% grape seed oil can improve the DPPH radical scavenging of yogurt,adding 3.5% and 4.0% grape seed oil can improve yogurt hydroxyl radical scavenging ability.3.The soybean oil yoghurt,peanut oil yoghurt,walnut oil yoghurt and grape seed oil yoghurt were used as the first test groups,the non-fat yoghurt was used as the first control group.As well as,the grape oil yoghurts with different concentrations were used as the second test groups,the non-fat yoghurt and the whole fat yoghurt were used as the second control groups.The effects of adding different vegetable oils and different adding levels of grape seed oils on the chemical nutrient composition of yogurt and changes of probiotics during storage were studied.The results showed that vegetable oil had no significant effect on crude protein,carbohydrate and water content of yogurt(p>0.05),but it had significant effects on fat and ash content(p<0.05).Grape seed oil,soybean oil and walnut oil were beneficial to the growth of Bifidobacteria,walnut oil and grape seed oil were beneficial to the growth of Streptococcus thermophilus.The number of lactic acid bacteria in grape seed oil yogurt was significantly higher than that of the other four groups during the whole storage period(p<0.05).Additive amount of grape seed oil had no significant effect on the crude protein content of yogurt(p>0.05),but it had significant effect on the fat content of yogurt(p<0.05).Except for the high content of carbohydrate,ash and moisture in the skim yogurt,the other five kinds of yogurt was no significant difference between the three targets(p>0.05).During the whole storage period of yogurt,the count results of bifidobacteria showed an upward trend and a downward trend at first,and 2.5% grape seed oil was more beneficial to the growth and reproduction of Bifidobacterium,Streptococcus thermophilus and other lactic acid bacteria in yogurt. |
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