Proteinase inhibitors content

The inactivation of proteinase inhibitors in the course of food processing has been the subject of many studies. In general, the inhibitors are ther-molabile and can be more or less extensively inactivated by suitable heating processes. In these processes, both the starting material as well as the process parameters are of great importance (time, temperature, pressure, and water content of the sample) (Table 16.16). Steaming of soybeans for 9 minutes at 100 °C causes an 87% destraction of inhibitors (Table 16.17). 

The achievement of a successful analysis depends not only on optimized analytical procedures but also on (1) the ability of the extraction procedure to recover DNA from the sample and to remove potential assay inhibitors, and (2) the quality and purity of the DNA extracted. The analytical technique is useless if the target cannot be extracted from the sample. At this point in time there are no standardized procedures for the extraction of DNA from food samples. The development of DNA extraction procedures is matrix dependent. High fat content and low dry matter seem to explain the decreased extraction efficiency of full-fat soybean flour compared to its defatted counterpart (Gryson et al., 2008). Traditionally, the extraction of DNA has been carried out by treating the sample with detergents such as sodium dodecyl sulfate and proteinases such as proteinase K, followed by the removal of proteins and polysaccharides with phenol-chloroform and precipitation of DNA with ethanol. 

Proteinases in soil extracts have been assayed using casein and substituted amides and peptides as assay substrates. Mayaudon et al. found that the casein hydrolysing activities of soil extracts were directly related to soil organic matter contents and inversely related to clay contents. Specific activities doubled when associated coloured humic compounds were removed from the extracts. The partially-purified proteinases appeared to be of a serine protease type as judged from their responses to inhibitors. Optimal activity occurred at pH 8.5 and at 50 0. The estimated Km value (22mg casein ml was considerably higher than those (0.15 and 0.54mg casein ml reported by Nannipieri et for proteinases of crude extracts from two soils. 

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