Marek Szmigielski
Influence of thermal processing on selected factors of quality soybean seeds and their products
zeszyt 364, ss. 72
Due to the beneficial chemical composition, soybeans are demanded component of a food or feed. However, the use of soybeans is limited by the number of anti-nutritional substances that reduce the nutrient absorption within a consumer’s organism.
Heating is one of the basic, commonly used in food processing, methods of transforming the raw materials such as soybean, essential to obtain a product with the required usefulness for consumers. Heating the food or feed raw materials is aimed at reducing the activity of anti-nutritional factors and microbial contamination contained, as well as it contributes to the increase in absorption of nutrients from the product and to formation of desirable rheological and sensory features.
However, to provide with the appropriate quality of soybean products, requires the application of a proper form, manner, and time of raw material heating, due to which it is converted to a product with imposed properties controlled by a sensitive and accurate quality assessment system. Nevertheless, the lack of a versatile, simple, quick, and at the same time sufficiently sensitive method of assessment, is noticeable.
The study aimed at determining the effect of various forms of thermal processing on selected quality indicators of soybean grains, high-fat soybean meal, and post-extraction soybean meal, as well as developing the mathematical models of these indicators changes in soybean products as a result of thermal processing applied.
The object of the research consisted of soybeans of Polish cultivar ‘Aldana’ as well as high-fat and post-extraction soybean meal, that were subject to thermal processing in forms of various heating manners. The most frequently used thermal processing forms and heat carriers applied in agricultural and food industry processes as well as pressure and thermal variants (extrusion and granulation) were taken into account during selection of these methods.
Samples from every variant of soybean grains, high-fat meal, and post-extraction meal heating were subject to the quality assessment by determining the bromocresol purple indicator (BCPI), trypsin indicator activity (TIA), urease activity (UA), and cresol red indicator (CRI).
All samples from each heating variant were verified in terms of the interdependence of results from BCPI vs. CRI, BCPI vs. TIA, and BCPI vs. UA tests by means of calculating the appropriate linear correlation coefficients (r), and if these factors appeared to be high and statistically significant, the regression equations CRI = f (BCPI), TIA = f (BCPI), and AU = f (BCPI) were developed by fitting curves (the least squares method) to the actual experimental data. Applying statistical procedures SimReg, it was examined whether pre-heating method had a similar impact on changes in UA, TIA, and CRI depending on the bromocresol purple indicator (BCPI). Then, using the F test, the hypothesis on the significance of differences between the developed regression relationships was verified, or the convergence of experimental data related to industrial samples (extruded, granulated) with previously developed models: UA = f (BCPI), TIA = f (BCPI) and CRI = f (BCPI) was tested.
All compared methods (BCPI, CRI, TIA, AU) proved to be useful in assessing the impact of thermal treatments on the qualitative changes in the protein fraction of soybeans and its products. However, due to the high sensitivity, precision, distinctness, and relatively low time-consumption, the BCPI method seems to be the most appropriate for this purpose.
Similarity of the regression equations CRI = f (BCPI), TIA = f (BCPI) and AU = f (BCPI) indicates the versatility of these functions and the similarity in quality variations of soybean protein during analyzed processes. The results also point to the usefulness of regression equations developed for the assessment of soybean products obtained by industrial methods (extrusion, granulation).
The practical application of the research may consist in the use of BCPI method to evaluate the effectiveness of soybean grains and products thermal processing at least in three cases:
– in addition to previously used methods of assessment,
– as a replacement of up-to-date used methods (CRI, TIA, UA) with the possibility of converting the results with a help of regression equations developed,
– complete replacement of the existing methods in feed and food industry laboratories.
Each of the proposed variants of BCPI method contributes to decreased time and labor-consumption of analyses, does not require any complicated and expensive laboratory equipment, is based on easy implementation of analytical procedures, and at the same time, is characterized by high sensitivity and promotes reduction of costs associated with the soybean processing of on an industrial scale.