Effects Of Added Components And Lactic Acid Bacteria Starters On The Form And Absorptance Properties Of Calcium In Soybean Milk

Soybean milk,as one of high vegetable protein drinks,has attracted significant attention due to its special nutrients such as essential amino acids,isoflavone and mineral matters,and has become a major source of calcium supplement.In recent years,various kinds of soybean milk appeared,including the normal soybean milk and flavor soybean milk.Additionally,lactic acid bacteria can improve the nutrition content of soybean milk during the fermentation.However,the component of additives and lactic acid bacteria will affect the absorption of soybean calcium.So far,researches about soybean milk all focused on the function of protein,isoflavone and oligosaccharide in soybean.Relatively little information is available on calcium type and bioavailability.Therefore,in this study,soybean milk was chosen as the research object and the study tried to analysis the form and absorption of soybean calcium by Caco-2 cells in vitro.In order to find out the content of calcium in different forms and the distribution of calcium in different forms in normal soybean milk and fermented soybean milk,ICP-AES and HPLC-ICP-MS were used.In addition,the interaction between phenolic acids and soy protein with different subunit,and the complexation of different stabilizer on Ca2+were detected to analyze the effect of interaction between various component in soybean milk on the absorption of calcium.Besides,the calcium absorptivity of soybean milk fermented by different types of lactic acid bacteria was measured to determine the change of calcium forms during fermentation and to provide useful information for producing calcium-soybean products.The major results are as follows:1.The form and bioavailability of calcium in soybean milk were studied.According to the results of ICP-AES tests,Ca2+electrode measurements and HPLC-ICP-MS analysis,calcium could combine with peptide or organic acid in soybean milk,and the molecular weight of the compound was 1-3 KDa.2.The impact of different constituent on the absorptivity of calcium in soybean milk was measured.In this report,we investigated and observed an interaction,which was carried out by binding,between phenolic acids and soy proteins.Further analysis revealed that this kind of interaction was structure dependent and the content of hydroxyl of phenolic acids determine the binding affinity with protein.Interestingly,the interaction between phenolic acids and soy proteins did not affect the protein digestion by pepsin and trypsin,and the phenolic acid-protein compound did not affect the absorption of calcium.Besides,temperature had significant influence on the binding affinity between Ca2+and different stabilizers,among which,gellan gum has the strongest affinity.3.Effect of different types of lactic acid bacteria on the absorptivity of calcium in soybean milk was tested.In this study,one kind of which is hetero-fermentation lactic acid bacteria,from pickled Chinese cabbage and one kind of Enterococcus faecalis were used as starter cultures to ferment soybean milk,respectively.The results of absorptivity of soybean calcium by Caco-2 cells in vitro tests showed that the absorptivity of calcium in soybean milk fermented by Lactobacillus plantarum B2 was higher than the soybean milk fermented by Enterococcus faecalis.4.Effect of different types of lactic acid bacteria on the component of soybean milk was measured.The results showed that all the strains could change the structure of protein and the increment of acid amino acid was the major reason for the enhancement of calcium absorption.Although the lactic acid content of soybean yogurt produced by hetero-fermentation were higher than that of soybean yogurt produced by homo-fermentation,the improvement of calcium absorption was mainly attributed to ion absorption capacity5.The forms of calcium in soybean milk fermented by Lactobacillus plantarum were analyzed.The results of HPLC-ICP-MS tests revealed that calcium could combine with peptides forming compounds with molecular weight of 1500 Da in fermented soybean milk.The amino sequences of indigestible peptides separated and purified by chromatography were identified by LC-MS/MS,including DEDEQIPSHPPR,ESEESEDSELR,GEKEEDEGEQPR,PQHPEREPQQPGEKEED,FVDAQPK.6.Both soybean milk and fermented soybean milk promoted the alkaline phosphatase(ALP)activity of preosteoblast MT3T3-E1,suggesting that both soybean milk and fermented soybean milk could stimulate early differentiation of osteoblast.Compared with normal soybean milk,fermented soybean milk had better effect of proliferation.