Study On The Effect Of Shelf Life Of Additing Carbon Dioxide To Yogurt

There is always some problems in the producing,storing and transporting of yogurt,for example,it is difficult to control the growth of the microorganism completely in yogurt at low temperature.The yogurt is putrefactive easily during the course of growing on molds and yeast,so it can't achieve the requirement of production.Carbon dioxide is a kind of safe and natural preservative and it can be removed from raw milk.The purpose of this study is to find out the best level of carbon dioxide together with temperature to prolong yogurt storage period.1.The effect of temperature on embient pressure carbonation of yogurt was determined by addition carbon dioxide through the materials at various temperatures for 45 min.As temperatures decreased,more dissolved carbon dioxide in yogurt.At 4℃,maximum dissolved carbon dioxide is 42.29mmol/L.At 8℃,maximum dissolved carbon dioxide is 34.69 mmol/L.At 17℃,maximum dissolved carbon dioxide is 22.03 mmol/L.2.The sensory quality,pH value,titration acidity and structure sensory of yogurt by adding carbon dioxide was studied.When the yogurt was added carbon dioxide,dissolved carbon dioxide was less than 24.09mmol/L,there was no effect on the sensory quality,titration acidity increased significantly,and pH value decreased significantly.The carbon dioxide was nonlinear correlation with pH value and titration acidity,and while carbon dioxide was removed,the sensory quality,pH value,titration acidity and structure sensory were all normal.3.The effect of antibacterial on,E.Coli,Fluorescens,Molds and Lactobacillus Bulgaricus, Streptococcus thermophilus by carbon dioxide was studied.The results showed that carbon dioxide dissolved in degreasing milk culture medium inhibited growth of E.Coli and Pseudomonas with the initial concentration less than 5×10³cfu/ml,and the higher the concentration of carbon dioxide,the more significant the effect of antibacterial;the concentration of carbon dioxide with 33.5mmol/L can inhibit the growth of Lactobacillus Bulgaricus and Streptococcus thermophilus with the initial concentration less than 5×10⁷cfu/ml.While the concentration of carbon dioxide was 24.09mmol/L,the lag phase of growth for E.Coli with the initial concentration less than 5×10²cfu/ml and 5×10³cfu/ml increased prolong 2 days,the lag phase of growth for Pseudomonas of which the initial concentration was 5×10²cfu/ml,increased 3 days,and the lag phase of growth for Pseudomonas with 5×10³cfu/ml increased 2 days,and the lag phase of growth for Molds of which the initial concentration was 5×10²cfu/ml,increased 4 days.There was no significant effect on growth parameter of Lactobacillus Bulgaricus and Streptococcus thermophilus. 4.The effect of combination the carbon dioxide and low temperature to preservation of yogurt was studied.Microorganism,pH value and sensory quality were tested in this research.At 4℃,and the storage life of groups,which were treated by carbon dioxide from 18.58mmol/L to 24.09mmol/L, were 3 to 5 days.At 7℃,the storage life of groups,which were treated by carbon dioxide from 24.09mmol/L to 33.5mmol/L,were all 2 days.The best combination was 4℃/24.09 mmol/L CO₂.5.The effect of combination in the condition of the low pressure carbon dioxide together with 0.1～0.5MPa and low temperature to extend the storage life of yogurt were studied.Microorganism, pH value and sensory quality were tested in this research.The results showed that,at the condition of 4℃/0.1MPa CO₂,4℃/0.2MPa CO₂,4℃/0.3MPa CO₂,7℃/0.2MPa CO₂ and 7℃/0.3MPa CO₂,yogurt could stored for 3 days at least.The best combination was 4℃/0.2MPa CO₂ at low pressure.