Supplementation with fruit and okara soybean by-products and amaranth flour increases the folate production by starter and probiotic cultures

• All vegetable substrates improved folate synthesis by starter and probiotic strains.
• Okara increased folate levels the most, whereas passion fruit was less effective.
• All strains produced folate after orange by-product and amaranth flour fermentation.
• Folate biosynthesis was strain-dependent.
• BB-02 strain produced the highest folate in the presence of amaranth.

The ability of two starter cultures (Streptococcus (S.) thermophilus ST-M6 and St. thermophilus TA-40) and eleven probiotic cultures (St. thermophilus TH-4, Lactobacillus (Lb.) acidophilus LA-5, Lb. fermentum PCC, Lb. reuteri RC-14, Lb. paracasei subsp. paracasei, Lb. casei 431, Lb. paracasei subsp. paracasei F19, Lb. rhamnosus GR-1, and Lb. rhamnosus LGG, Bifidobacterium (B.) animalis subsp. lactis BB-12, B. longum subsp. longum BB-46, and B. longum subsp. infantis BB-02) to produce folate in a modified MRS broth (mMRS) supplemented with different fruit (passion fruit, acerola, orange, and mango) and okara soybean by-products and amaranth flour was investigated. Initially, the folate content of each vegetable substrate was determined: passion fruit by-product showed the lowest folate content (8 ± 2 ng/mL) and okara the highest (457 ± 22 ng/mL). When the orange by-product and amaranth flour were added to mMRS, all strains were able to increase folate production after 24 h of fermentation. B. longum subsp infantis BB-02 produced the highest concentrations (1223 ± 116 ng/mL) in amaranth flour. Okara was the substrate that had the lowest impact on the folate production by all strains evaluated. Lb. acidophilus LA-5 (297 ± 36 ng/mL) and B. animalis subsp. lactis BB-12 (237 ± 23 ng/mL) were also able to produce folate after growth in mMRS containing acerola and orange by-products, respectively. The results of this study demonstrate that folate production is not only strain-dependent but also influenced by the addition of different substrates in the growth media.