Pea-Protein Products for Food Applications Methods for Improving Iron and Zinc Availability

Doktorsavhandling, 2001

The thesis deals with some aspects of and possibilities for the production of pea protein with improved nutritional and physiological qualities. The improved pea protein can be used as a beneficial alternative to soya protein in food applications, such as infant formula. Methods for pea-protein dephytinisation by phytase enzymes were examined, in order to obtain pea protein with a high availability of iron and zinc. The removal of oligosaccharides by ultra-filtration was evaluated, to improve the physiological quality of the pea protein. To achieve fast phytate degradation in pea seeds, these have to be milled into flour. The endogenous pea-phytase enzyme can almost completely degrade the phytate in 10 hours, by soaking the pea flour at pH 7.5 and 45°C. The natural synthesis of the phytase enzymes by microorganisms is not sufficient for use in large-scale dephytinisation of pea protein. The expression of phytases in microorganisms is shown to be controlled by complex and hitherto unknown systems. It has not yet been shown whether lactic acid bacteria have the ability to produce phytase. For dephytinisation of pea-protein isolate in industrial production the addition of exogenous phytase enzyme is recommended. Complete phytate degradation was thereby obtained within 1-2 hours. Ultra-filtration by 50 or 100 kD cut-off was an effective method to remove oligosaccharides. Standard pea-protein isolate and dephytinised pea-protein isolate worked well for the production of liquid infant-formula. The new pea-protein infant formulas were evaluated for iron and zinc availability. An ion chromatography method for the simultaneous determination of Cu, Ni, Zn, Co, Mn and Fe in samples of biological origin such as food was developed. The average detection limit is 5 ppb when using 50 µL injection volume. Sample preparations suitable for food and biological samples were also developed and evaluated. The preparation method can be chosen according to the type of sample and the mineral matrix in the sample. A dynamic gastro-intestinal digestion simulation model was used to evaluate the pea-protein infant formulas for the availability of iron and zinc. The dephytinised pea-protein infant formula showed improved iron and zinc availabilities. The availability of iron and zinc in dephytinised pea formula were 70% and 49% respectively, compared with standard pea formula exhibiting 49% iron and 22% zinc availabilities. In this thesis the estimation of iron availability is compared for the first time with iron absorption from identical meals in humans. The results obtained with the digestion model are in agreement with the human absorption results. Furthermore, the possibility of combining the gastro-intestinal simulation model and Caco-2 cells is shown, thereby obtaining an in vitro simulation of both the human digestive and absorption systems. The results for iron availability suggest that pea protein may be a nutritionally beneficial alternative to soya protein for infant-formula application.