79-3 |
|
S. L. TAY, H. A. Oh, G. Q. Xu, and C. O. Perera. Dept. of Chemistry, National Univ. of Singapore, Food Science & Technology Programme, Science Dr. 4, S3-06, Singapore, 117543, Singapore There are many technical difficulties involved in working with aggregation of proteins. Atomic force microscopy (AFM) with its high resolution is a powerful tool to study aggregation. The ability to image aggregates means that it is possible to characterize their size and shape. Soybean proteins contain two major globulins - 7S and 11S, which were shown to have different gel-forming properties, possibly, due to the differences in their aggregation patterns. Our objective was to use protein aggregation to explain the differences in the gelation speed, and structure of gels formed by different soy proteins. Protein solutions (4.35% w/v) were heated for 10 min at 100oC, and a freshly prepared glucono-d-lactone (GDL) solution (5% w/v) was added to them. A drop of the resulting solution (30ml) was deposited onto freshly cleaved mica for 1 to 6 minutes. Then argon gas was used to blow-dry the samples and imaged with a Nanoscope III (Digital Instruments) under ambient conditions. All images were acquired in tapping-mode using silicon tips. GDL when mixed with 11S, resulted in the formation of large aggregates within one minute, but, when mixed with 7S, resulted in the formation of small aggregates over a longer time (4-6 min). This showed that 11S forms bigger aggregates faster than 7S, when mixed with GDL. Faster aggregations lead to faster gelation, which result in harder gels. The aggregates of 11S with GDL were spaced far apart while those of 7S with GDL were closed together. This may be the reason for the coarser gel structures seen in the former. AFM measurements allow quantitative analysis of aggregation and growth rate. The aggregation patterns of 7S and 11S provide an explanation for the differences in the rate of gelation and gel structure of these two proteins.
Session 79, Food Chemistry: Protein and enzyme chemistry
|