Study On The Package Materials Influence On Microorganisms And Qualities Of Stored Wheat Flour

Wheat flour is the main source of food for our people. Wheat flour has small granule,large contact area with the environment,high hygroscopicity and poor thermal conductivity characteristics. Once the conditions that microorganisms may grow and reproduce are suitable,microorganisms cause mildew of wheat flour and even produce mycotoxins which will impact seriously on the eating quality and safety of wheat flour.In a certain temperature and humidity,the stored stability of wheat flour which has or close to safe moisture content is related to packing materials. In this paper,simulated storage of wheat flour was carried out for investigating the influences of all kinds of packing materials that can guanrantee qualities and safety of stored wheat flour.The experimental results showed that:(1)Influence of packing materials on moisture content and qualities of stored wheat flourAt 70%RH and 18～20℃,the moisture content of stored wheat flour in different packing materials had different degree drop and the moisture content of wheat flour in cloth bag declined most because it was worse barrier to water transmission and moisture content was easily volatile.While the moisture content of the wheat flour in high barrier packing bag which had a good wet resistance property had the most stable and the smallest drop,only 0.6%. The moisture contents of the wheat flour in paper-plastic bag and paper -plastic bag with fungicides dropped 0.9% and 1.0% respectively.The change tendency of the moisture content of stored wheat flour at 30℃was the same as at 18～20℃,but lower than the same period of 18~20℃,because the moisture permeability of packing materials was enhanced as storage temperature was high.The variance analysis showed that storage time had very significant influence while packing materials had no significant influence on moisture content of stored wheat flour.At 70%RH,the fatty acid values of stored wheat flour in different packing materials presented a similar rising trend which was concerned with packing materials. In the same packaging material,fatty acid value at 30℃was higher than that of the same period at 18～20℃. At the end of storage,the fatty acid value of wheat flour in cloth bag was the lowest and that of wheat flour in paper-plastic was highest at 18～20℃,while the fatty acid value of wheat flour in paper -plastic bag with fungicides was the lowest and that of wheat flour in high barrier packing bag was highest at 30℃.The variance analysis showed that packing materials and storage time had very significant influence on fatty acid value. The fatty acid value of stored wheat flour had positive linear relationship with storage time and showed positive bivariate linear relationships with moisture content and storage time in a packing material. (2) Influence of packing materials on microbial flora of stored wheat flourAt 18℃,70% RH,as the time prolonged,the arobic bacterial counts of stored wheat flour in these packaging materials descended in varying degrees,and at the end of storage,the arobic bacterial counts decreased from 103 to 102,but had slightly differences which were related with moisture content.In these packaging materials, the arobic bacterial counts of stored wheat flour had negative linear relationship with storage time but in varying degrees.The arobic bacterial counts of stored wheat flour sharply descended from the beginning to 75 days and softly descended after in these four packaging materials at 30℃. The arobic bacterial counts of stored wheat flour decreased faster at 30℃than that of 18～20℃. The variance analysis showed that storage time had very significant influence and packing materials had no significant influence on the arobic bacterial counts of stored wheat flour.The mould counts of stored wheat flour in different packging materials increased first and decreased then in varying degrees.The mould counts of wheat flour stored at the end was decreased compared with at the start.The different decline was related with moisture content. A. candidus was dominant strain from beginning to end,but propotion of it had differences.(3)The correlation analysis between the fatty acid values and microorganism and the moisture content of stored wheat flour in different packing materialsThe fatty acid values of stored wheat flour in these four packing materials presented binary linear relationship with the aerobic bacterial counts and the moisture content,except the fatty acid value in cloth bag had a negative correlation with the aerobic bacterial counts at 30℃. At 18～20℃,the fatty acid values of stored wheat flour in paper-plastic bag and high barrier bag had binary linear relationships with moisture content and the mould count.(4)The choice of packaging materials in different storage conditionsThe cloth bag was the most suitable for stored wheat flour at 70%RH and 18～20℃for the stored wheat flour in cloth bag had the maximum rates of decrease in moisure content,the arobic bacterial counts and the mould counts,and had the minimum rate of increase in fatty acid value,while the paper-plastic bag with fungicides was the most appropriate for stored wheat flour at 30℃through the analysis of the average rate of change on the relevant indicators of the stored wheat flour,microbial flora.