Advances in research on calf rennet substitutes and their effects on cheese quality.

Milk coagulation is an important step in cheese production, and milk-clotting enzymes (MCEs) play a major role in this process. Calf rennet is the most widely used MCE in the cheese industry. The use of calf rennet substitutes is becoming necessary due to the limited availability of calf rennet and the increase in cheese consumption. The objective of this review is to summarize the latest findings on calf rennet substitutes (animal MCEs, plant-derived MCEs, recombinant MCEs and microbial MCEs) and their application in cheese production. Special emphasis has been placed on aspects of the effects of these substitutes on hydrolysis, functional peptides, cheese variety and cheese yield. The advantages and disadvantages of different calf rennet substitutes are discussed, in which microbial MCEs have the advantages of less expensive production, greater biochemical diversity, easier genetic modification, etc. In particular, some of these MCEs have suitable characteristics for cheese production and are considered to be the most potential calf rennet substitutes. Moreover, challenges and future perspectives are presented to provide inspiration for the development of excellent calf rennet substitutes.

Characterization and Selection of Lactobacillus plantarum and Lactobacillus paracasei for prevention of oral bacterial infections from Chinese pickle.

The oral infections were mainly caused by Streptococci and Staphylococcus aureus. Antibiotic therapies can eliminate these harmful bacteria. However, it can break beneficial microbes and lead to the persistence of resistant strains. The objective of our study was to select potential probiotic strains for the prevention of oral bacterial infections and evaluate their potential probiotic properties in oral cavity. AR113 (Lactobacillus plantarum) and AR340 (Lactobacillus paracasei) with significantly antimicrobial ß-hemolytic streptococci and Staphylococcus aureus activity were isolated from Chinese pickle through agar well diffusion assay. Through the analyses of probiotic properties in antibiofilm, lysozyme and hydrogen peroxide tolerance, bacterial surface properties, adherence ability, tooth degradation and anti-inflammatory activity, the AR113 and AR340 showed anti-adhesion activity of 45.2-71.1% and 20.3-56.8% against ß-hemolytic streptococci and 15.4-52.6% and 30.7-65.9% against Staphylococcus aureus, respectively, at different concentration. The two strains with high hydrophobicity, autoaggregation and survival rate adhered strongly to FaDu cells. AR113 and AR340 exhibited low calcium released from teeth (0.04 µg/mL and 0.03 µg/mL, respectively). ELISA analysis showed that AR113 and AR340 significantly inhibited the LPS-induced increase of NO and TNF-α expression. Strains-fermented skim milk inhibited the growth of ß-hemolytic streptococci or Staphylococcus aureus. AR113 and AR340 were considered as probiotic candidates because of their higher antibacterial activity against some oral pathogenic bacteria, no potential of primitive cariogenicity. These candidates were expected as new probiotics with potential oral health benefits and no harmful effects.

Human-origin Lactobacillus salivarius AR809 protects against immunosuppression in S. aureus-induced pharyngitis via Akt-mediated NF-κB and autophagy signaling pathways.

Lactobacillus salivarius AR809 is a newly discovered probiotic strain from a healthy human pharynx and has potential ability to adhere to the pharyngeal epithelium and inhibit Staphylococcus aureus (S. aureus)-induced inflammatory response. Pharyngeal spray administration of AR809 exhibited protective effects in a S. aureus-induced mouse model of pharyngitis. The inhibitory effect and underlying molecular mechanism of AR809 on S. aureus-stimulated pharyngitis were further investigated. AR809 significantly increased phagocytosis and bactericidal activity, reduced the production of inflammatory mediators (intracellular reactive oxygen species (ROS), prostaglandin E2 (PGE2), cyclooxygenase-2 (COX-2), nitric oxide (NO), inducible NOS (iNOS)) and the expression of inflammatory cytokines (tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß)), and induced macrophages to adopt the M2 phenotype. AR809 also attenuated S. aureus-induced phosphorylations of protein kinase B (Akt) and rapamycin (mTOR), and elevated the autophagic protein (light chain 3 from II (LC3-II) and Beclin-1) level. Furthermore, AR809 inhibited nuclear transcription factor kappa-B (NF-κB) activation by suppressing the nuclear translocation of NF-κB p65. Likewise, 740Y-P (a PI3K activator) decreased the anti-inflammatory effect of AR809 against S. aureus-induced inflammatory response, while AR809 treatments with wortmannin (a PI3K inhibitor) markedly reversed this inflammatory response. AR809 prevents S. aureus-induced pharyngeal inflammatory response, possibly by regulating TLR/PI3K/Akt/mTOR signalling pathway-related autophagy and TLR/PI3K/Akt/IκB/NF-κB pathway activity, and therefore has potential for use in preventing pharyngitis and other inflammatory diseases.

A lateral flow immunochromatographic strip test for rapid detection of hexoestrol in fish samples.

A lateral flow immunochromatographic strip test was developed for rapid and sensitive on-site detection of hexoestrol (HES) residues in fish samples with colloidal gold labelling of the anti-HES monoclonal antibody. The strip is composed of a sample pad, a conjugate reagent pad, an absorbent pad and a test membrane containing a control line and a test line. The sensitivity (half inhibitory concentration, IC50) of the strip in the detection of fish extract samples was confirmed to be 1.86 µg kg-1, and the limit of detection value was 0.62 µg kg-1. For intra-assay and inter-assay reproducibility, recoveries of HES-spiked samples ranged from 86.3% to 92.3% and 85.8% to 93.4%, coefficients of variation were 2.91-4.64% and 4.24-5.17%, respectively. High-performance liquid chromatography was employed to confirm the performance of the strip. The strip test takes less than 10 min, and thus provides a repaid method for on-site detection of HES residues.

Rapid and sensitive detection of ß-agonists using a portable fluorescence biosensor based on fluorescent nanosilica and a lateral flow test strip.

A portable fluorescence biosensor with rapid and ultrasensitive response for Clenbuterol (CL) has been built up with fluorescent nanosilica and a lateral flow test strip. Quantitative detection of CL was realized by recording the fluorescence intensity of fluorescent nanosilica captured on the test line. The sensing results indicated that the sensitivity of the fluorescent nanosilica-based strip was better than that of conventional colloidal gold-based strips. The visual limit of detection of the strip for qualitative detection was 0.1 ng/mL while the LOD for quantitative detection could down to 0.037 ng/mL by using fluorescence biosensor. The recoveries of test samples were from 89.3% to 97.7%. The assay time for CL detection was less than 8 min, suitable for rapid testing on-site.