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This study evaluated the antimicrobial activity of tea polyphenols (TP) against 4 Cronobacter sakazakii strains with different sequence types (ST) isolated from powdered infant formula (PIF). The results showed that in normal saline, 5mg/mL of TP (pH 3.44) could eliminate approximately 7.0 log cfu/mL of C. sakazakii within 1 h; in rehydrated PIF, after acidification with HCl (pH 3.55), TP showed a stronger antibacterial activity compared with the controls (malic acid, ascorbic acid, and citric acid). Further, some differences were obvious in tolerance to TP between C. sakazakii strains with different ST. The tolerance of C. sakazakii CE1 (ST4) to TP was found to be greater than that of the other 3 C. sakazakii strains (ST1, ST8, and ST64). The results of recovered test and transmission electron microscope analysis revealed that the action of TP against C. sakazakii was an irreversible bactericidal process caused by leakage of cytoplasm. Taken together, these results indicated that TP had an effective bactericidal effect against C. sakazakii, and provided a new idea for preventing and inactivating C. sakazakii in PIF., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Most γ-aminobutyric acid (GABA)-producing microorganisms are lactic acid bacteria (LAB), but the yield of GABA is limited in most of these GABA-producing strains. In this study, the production of GABA was carried out by using Lactobacillus plantarum NDC75017, a strain screened from traditional fermented dairy products in China. Concentrations of substrate (l-monosodium glutamate, L-MSG) and coenzyme (pyridoxal-5-phosphate, PLP) of glutamate decarboxylase (GAD) and culture temperature were investigated to evaluate their effects on GABA yield of Lb. plantarum NDC75017. The results indicated that GABA production was related to GAD activity and biomass of Lb. plantarum NDC75017. Response surface methodology was used to optimize conditions of GABA production. The optimal factors for GABA production were L-MSG at 80 mM, PLP at 18 μM, and a culture temperature of 36 °C. Under these conditions, production of GABA was maximized at 314.56 mg/100 g. Addition of Lb. plantarum NDC75017 to a commercial starter culture led to higher GABA production in fermented yogurt. Flavor and texture of the prepared yogurt and the control yogurt did not differ significantly. Thus, Lb. plantarum NDC75017 has good potential for manufacture of GABA-enriched fermented milk products., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

On the basis of our previous results on potential immunoregulation of Lactobacillus acidophilus NCFM, the immunoregulatory effects of exopolysaccharides (EPS) isolated from L. acidophilus NCFM and their regulating mechanisms are further investigated in the current research. Stimulated by EPS preparations, four immune-related genes in the human colorectal adenocarcinoma cell line Caco-2 cells, namely, interleukin-1α (IL-1α), chemokine C-C motif 2 (CCL2), tumor necrosis factor α (TNF-α), and pentraxin 3 (PTX3), first showed an increase at 2-4 h, peaked at 4 h, and then decreased at 4-12 h. Similar trends were observed in vivo: four genes showed transient expression (highest on the 4th day) in the cecum and colon of mice. Meanwhile, the organ coefficient, clearance index and phagocytic index all significantly increased with time extension and dose increase of EPS stimulation. EPS triggered NF-κB and p38 mitogen-activated protein kinase (p38 MAPK) signaling pathways in Caco-2 cells, and the activated pathways initiated the genes expression. EPS compounds from L. acidophilus NCFM may play an important role in host immunoregulation and might be applied as a new type of immunoregulatory agent in functional foods.