The objective of this study was to enhance calcium solubility and bioavailability from calcium-fortified soymilk by fermentation with 7 strains of Lactobacillus, namely, L. acidophilus ATCC 4962, ATCC33200, ATCC 4356, ATCC 4461, L. casei ASCC 290, L. plantarum ASCC 276, and L. fermentum VRI-003. The parameters that were used are viability, pH, calcium solubility, organic acid, and biologically active isoflavone aglycone content. Calcium-fortified soymilk made from soy protein isolate was inoculated with these probiotic strains, incubated for 24 h at 37 degrees C, then stored for 14 d at 4 degrees C. Soluble calcium was measured using atomic absorption spectrophotometry (AA). Organic acids and bioactive isoflavone aglycones, including diadzein, genistein, and glycetein, were measured using HPLC. Viability of the strains in the fermented calcium-fortified soymilk was > 8.5 log(10) CFU/g after 24 h fermentation and this was maintained for 14-d storage at 4 degrees C. After 24 h, there was a significant increase (P < 0.05) in soluble calcium. L. acidophilus ATCC 4962 and L. casei ASCC 290 demonstrated the highest increase with 89.3% and 87.0% soluble calcium after 24 h, respectively. The increase in calcium solubility observed was related to lowered pH associated with production of lactic and acetic acids. Fermentation significantly increased (P < 0.05) the level of conversion of isoflavones into biologically active aglycones, including diadzein, genistein, and glycetein. Our results show that fermenting calcium-fortified soymilk with the selected probiotics can potentially enhance the calcium bioavailability of calcium-fortified soymilk due to increased calcium solubility and bioactive isoflavone aglycone enrichment.

The presence of phytate in calcium-fortified soymilk may interfere with mineral absorption. Certain lactic acid bacteria (LAB) produce the enzyme phytase that degrades phytates and therefore may potentially improve mineral bioavailability and absorption. This study investigates the phytase activity and phytate degradation potential of 7 strains of LAB including: Lactobacillus acidophilus ATCC4962, ATCC33200, ATCC4356, ATCC4161, L. casei ASCC290, L. plantarum ASCC276, and L. fermentum VRI-003. Activity of these bacteria was examined both in screening media and in calcium-fortified soymilk supplemented with potassium phytate. Most strains produced phytase under both conditions with L. acidophilus ATCC4161 showing the highest activity. Phytase activity in fortified soymilk fermented with L. acidophilus ATCC4962 and L. acidophilus ATCC4161 increased by 85% and 91%, respectively, between 12 h and 24 h of fermentation. All strains expressed peak phytase activity at approximately pH 5. However, no phytate degradation could be observed.

A high intake of dietary calcium through out life helps reduce the risk of osteoporosis. The amount of calcium available to the body depends not only on how much is consumed, but on the body's ability to absorb calcium and retain it. As soymilk contains significantly less calcium than cow's milk; calcium is often added as a fortificant, but it is unclear whether this added calcium is well absorbed. Soybeans, like other legumes contain myo-inositol hexaphosphate (IP6), also known as phytate, that can chelate calcium inhibiting its absorption. Fermenting soy milk with certain lactic acid bacteria can reduce the amount of IP6. These microorganisms produce the enzyme, phytase which hydrolyses IP6 to its lower IPs including; myo-inositol pentaphosphate (IP5), IP4, IP3 and IP1. Furthermore, fermenting soy milk with lactic acid bacteria increases the conversion of isoflavones to the biologically active aglycone form. These biologically active soy isoflavones have important actions in decreasing bone loss.Our study objective was to enhance calcium bioavailability from calcium-fortified soymilk by fermenting it with 6 strains of Lactobacillus namely L. acidophilus ATCC 4962, ATCC 33200, ATCC 4356, ATCC 4461, L. casei ASCC 290, and L. plantarum ASCC 276 to measure calcium solubility, IP6 and isoflavone content.Calcium-fortified soymilk, made from soy protein isolate, was inoculated with these bacterial strains, incubated for 24 h at 37ºC then stored for 14 d at 4ºC. Total and soluble calcium were measured using atomic absorption spectrophotometry (AA). IP6 and isoflavone profile were measured using HPLC.Viability of the strains in the fermented calcium-fortified soymilk was > 7.5 log 10 CFU/g at the end of 24 hours of incubation and this was maintained for 14 d storage at 4ºC. After 24 h fermentation, there was a significant increase (P<0.05) in soluble calcium possibly due to a pH decrease in the fermented calcium-fortified soymilk. L. acidophilus ATCC 4962 and L. plantarum ASCC 276 demonstrated 76.6% and 70.3% increase in calcium solubility respectively. The productions of the enzyme phytase during fermentation led to the degradation of IP6 to its lower IPs. Fermentation of calcium-fortified soymilk also increased (P<0.05) the level of conversion of isoflavones into biologically active aglycones by ß-glucosidase activity.Our results show that fermenting calcium-fortified soymilk with L. acidophilus, L. casei and L. plantarum can potentially enhance the bioavailability of calcium from calcium-fortified IUFoST 2006

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