Study On The Change Regular Pattern Of Microorganisms Floras For Wheat Flour In Different Storage Conditions

The quality and safety of wheat flour are more demanded along with the development of economy because it is our staple food. There are ample nutritious ingredients including carbohydrate, protein and inorganic salt in wheat flour. These ingerdients provide nutrition to microorganisms. Once the conditions are suitable, microorganisms grow and reproduce, resulting in fever mildew of wheat flour, and even produce harmful mycotoxins. It will impact seriously on the eating quality and safety. This paper aimed to find the ideal storage condition to control the quality of wheat flour based on the impact of temperature and humidity on microorganisms floras for wheat flour in different simulant storage conditions (in humidity of 55%,70%,85% and temperature of 10℃,15℃,20℃,25℃,30℃,35℃). The results showed that:1 Influence of storage humidity and temperature on the moisture contentThe temperature and humidity influenced the moisture content of wheat flour, and then microorganisms growth was affected. The moisture content declined at the humidity of 55% and 70%, and increased at 85% because wheat flour did not have shell to protect and had more hydrophilic substance. At the same humidity, the moisture content was higher in the low temperature than in the high one.2 Influence of humidity and temperature on the bacteria florasThe aerobic bacterial count increased first, and then decreased along with the extension of storage time. The moisture content decreased as the temperature rose, and the aerobic bacterial count also decreased. That was to say, the aerobic bacterial count had negative correlation with the storage temperature. But aerobic bacterial count was more in the temperature of 35℃and the humidity of 85% than in other conditions because this was the best temperature for the growth of bacteria.Escherichia coli were more in the high humidity of 85% and low temperature of 10℃. It is because that the moisture content was higher in low temperature, and the high humidity was befitting to growth of E. coli. And it was more when the humidity was higher. The content of Bacillus cereus in wheat flour increased first, and then decreased. It did not changed obviously except some conditions, and its typical value was 103 cfu/g. This was because the moisture content decreased as the temperature rose, and it restrained growth of Bacillus cereus. And the Bacillus cereus content was restricted because of the competition of other microorganisms.3 Influence of humidity and temperature on the mould florasThe mould content was less relatively in higher temperature along with the extension of storage time in the same humidity. Influence of storage temperature and time on mould content presented a significant nonlinear dependence in the humidity of 55%. The equation was: Y = 41929.04 (lnX1)2 + 9392.83 (lnX2)2 - 155517.73 lnX1 - 39941.44 lnX2 - 4916.65 X1 - 719.10 X2 + 257752.82 (R2= 0.49675, P<0.01). The mould content decreased gradually as the temperature rose and time extended. This because the moisture content decreased as the temperature rose, and the joint action of moisture and temperature was not appropriate to growth of mould. The mould content was especially less in the temperature of 35℃than it was in other temperature. In the humidity of 85%, wheat flour agglomerated after 20 days in the temperature of 30℃and 35℃, or after 30 days in the temperature of 20℃and 25℃worse and worse. Growth of mould was restrained because it was short of oxygen and water. So it was not mildew seriously in 90 days although the wheat flour could not be eaten. And the mould content still did not change in the low temperature of 10℃and 15℃because the moisture content was very high. On the other side, A. candidus always was the dominant mould in different storage conditions.4 The storage humidity and temperature was optimizedIt was compared with other qualities of wheat flour, and the ideal storage condition was found to control growth of microorganisms: moisture<14.0%, humidity<70% and temperature<20℃.5 Microorganisms were not well-proportioned in the hop-pocket in high humidityIn the humidity of 85%, wheat flour agglomerated one after another in the temperature which higher than 20℃. Microorganisms of surface were obviously more than that of interior. They were not well-proportioned in the hop-pocket.6 The preliminary study on the limit of mould countThe wheat flour agglomerated in the high humidity. The mould content was obviously more in surface of the hop-pocket. And the magnitude was increased from 103 to 105. The wheat flour could be stored securely when the mould count was less than 104cfu/g, while wheat flour began to mildew when the count was higher than 104cfu/g, and it mildewed severely when the count was equal to 105cfu/g. It means that the mould content of wheat flour was related to mildew and degree of mildew. The mould content should be controled less than 104cfu/g.7 The microorganisms contamination should be controlled before the storage of wheat flourThe content of microorganisms in wheat flour before storage was related to the safety of storage. The microorganisms contamination before storage and the contamination in processing should be controlled strictly.