| During the processing of fermented sausage,moderate lipid oxidation can contribute to the formation of flavor,while high oxidation can result in the loss of flavor and aroma and the shortening of the shelf life of products,thereby leading to negative impact on the nutritional value and sensory quality.Adding antioxidants to sausage can prevent the oxidation reaction.With the improving of healthy consciousness of people,safe and non-toxic natural antioxidants has gradually become the industry prefer to choose compared with synthetic antioxidants.The antioxidant activity of lactic acid bacteria has been confirmed by many experiments in vivo and in vitro.It is rich in fruits and vegetables,dairy products,meat products,as well as various types of fermented food.In addition,many studies have shown that lactic acid bacteria can maintain the balance of intestinal flora,reduce cholesterol levels,lower blood pressure,improve immunity and other physiological functions.As the common starter culture used in fermented sausage,lactic acid bacteria has been reported to improve the sensory properties of fermented meat products in many studies,but there are few studies to investigate the effects of lactic acid bacteria on the oxidant stability of fermented sausage.The main purpose of this thesis is to investigate the effect of Lactobacillus fermentum on the oxidation stability and quality of fermented sausages.The detail content and conclusions are as follows:1.Antioxidant activity of Lactobacillus fermentum in vitroThe cell-free extracts,fermented supernatants and the intact-cells were prepared from the cultured L.fermentum Y4 and Y41.The scavenging effects of three constituents for DPPH free radicals,hydroxyl radicals(OH),ultra-oxygen anion free radicals(O2-),oxygen radical absorbance capacity(ORAC)and the activity of antioxidant enzymes were investigated to evaluate the antioxidant activities of two strains.The Vc was considered as the control.The results show that the cell-free extracts of two strains possessed the higher eliminating effects for O2-· radicals and ORAC,while the fermentation supernatants and the intact-cells fractions could be more efficient for clearing DPPH free radicals and O2-· radicals(P<0.05).Each fraction of L.fermentum Y41 exhibited significantly higher scavenging rate on ·OH and ORAC while lower scavenging effects on DPPH free radicals than those of L.fermentum Y4(P<0.05).As for the scavenging effect for O2-· radicals,the cell-free extracts from strain Y41 showed higher ability to eliminate radicals compared to Y4 while the scavenging effects of fermentation supernatants was lower than Y4(P<0.05).Both strains showed activities of SOD and GSH-Px.2.The effect of Lactobacillus fermentum on the oxidative stability of fermented sausageLactobacillus fermentum Y4 and Y41 were used as starter culture in fermented sausage and the oxidative stability and edible quality of fermented sausage were studied.The results showed during the process of fermentation,the pH and Aw values of the two groups inoculated L.fermentum were significantly higher than those of the two control groups(P<0.05).The rising rate of TBARS and the decrease rate of total thiol value were significantly lower than that of the blank control group(P<0.05).At the end of sausage fermentation,the total content of unsaturated fatty acids and free amino acid of the two groups inoculated L.fermentum were significantly higher than those of the blank control group(P<0.05)indicating that L.fermentum can retard the lipid and protein oxidation of the sausage.The two groups inoculated L.fermentum had significantly higher "a" values than the blank control group.In the aspects of cohesiveness and chewiness,L.fermentum Y41 group had higher value than the other groups.Therefore,L.fermentum can inhibit the oxidation of fermented sausage,which can also ensure the safety of the product and improving the sensory quality of it. |
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