Food Bioengineering最新文献

The fermented milk mainly consists of Lactobacillus bulgaricus and Streptococcus thermophilus. This research was aimed to investigate the cofermentation characteristics of different L. bulgaricus and S. thermophilus strains. Three strains of L. bulgaricus and S. thermophilus ST-2 were mixed and prepared into the starter (A, B, and C) and applied to milk fermentation for screening of optimal combination, and the commercial starter (D) was used as the reference. The microrheological properties during fermentation were analyzed by using multifrequency diffusion spectroscopy. Meanwhile, the fermented milk's stability, texture, and sensory characteristics were also observed during storage. Microrheology analysis revealed that the time to reach the fermentation endpoint of starters A, B, and C was almost the same during fermentation. Groups A, B, and C showed more elastic solid-state properties and groups A and C had higher elastic factors, indicating that the gel structure of the sample was relatively strong. During storage, the pH value of fermented milk in each group D, A, C, and B was in sequence from high to low, and the titratable acidity was also in sequence from high to low in B, C, A, and D groups, respectively. The viscosity of group A was significantly higher than that of groups B and C (p < 0.05), and there was no change in group D (p > 0.05). The sensory score of fermented milk in group A was higher, and the overall texture was good. Results concluded that group A starter culture produced fermented milk with a firm gel structure and excellent texture and flavor. This study will provide data support and methodology for developing and screening compound starters applied for milk fermentation in the future.

N-acetylneuraminic acid (NeuAc), which has been widely used as a nutraceutical and pharmaceutical intermediate, plays an important role in improving brain development and cognition while enhancing immunity. Bacillus subtilis, generally regarded as a food-safe microorganism, is suitable for developing as a chassis cell for efficient NeuAc synthesis. However, accumulated intermediates can lead to metabolic bottlenecks for NeuAc synthesis. To eliminate the accumulated byproduct N-acetylglucosamine (GlcNAc), the UDP-GlcNAc epimerase pathway without GlcNAc production was first reconstructed and optimized in B. subtilis, resulting in the NeuAc titer increase of 5.9 g/L with GlcNAc elimination. In addition, to reduce another accumulated byproduct N-acetylmannosamine (ManNAc), the directed evolution of N-acetylneuraminic acid synthase and the enhancement of phosphoenolpyruvate supply was implemented. Using this strategy, ManNAc decreased by 46.3%, and the NeuAc titer increased by 54.9%, reaching 7.9 g/L. Finally, the maximum titer of NeuAc in a 3-L fermenter reached 21.8 g/L with a productivity of 0.34 g/L/h.

Hydroxyl radical (•OH)-sensitive carbon dots (CDs) with an excitation wavelength of 390 nm and emission wavelength of 525 nm were synthesized by microwave in one-step. Using CDs as fluorescent probes, an •OH-enhanced fluorescence quenching detection signal based on horseradish peroxidasecatalyzed H₂O₂ was introduced on the basis of enzyme-linked immunoassay, and a •OH-enhanced label-free fluorescence quenching immunoassay (FQIA) was constructed for high-sensitivity detection of six broad-spectrum antibiotics. When used for nitrofuran Q2 metabolites (3-amino-1,3-oxazolidin-2-one, 3-amino-5-(morpholin-4-ylmethyl)-1,3-oxazolidin-2-one, 1-aminohydantoin hydrochloride, semicarbazide hydrochloride), chloramphenicol (CAP) and florfenicol (FLR) detection, FQIAs achieved high sensitivity detection of 0.061, 0.0058, 0.064, 0.045, 0.015, and 0.01 ng/ml, respectively. Compared with ELISA, the detection sensitivity was improved by 2.03- to 7.8-fold. On this basis, the sample pretreatment methods for six targets were optimized, and the simultaneous extraction and high-sensitivity detection of six targets were achieved. The FQIA proposed in this work improved the detection sensitivity, reduced the sample consumption and pretreatment steps, shortened the extraction time, and improved the detection efficiency, which provided support for the development and application of new immunoassay products and the development of the rapid analysis industry.

Lactiplantibacillus plantarum X7022 is a novel strain isolated from stinky tofu brine. Its constipation amelioration potential was evaluated on two different constipation types (acute and subacute) in mice induced by loperamide hydrochloride in present work. L. plantarum X7022 could significantly decrease the first black stool defecation time, and increase black fecal weight, number, and the gastrointestinal transit ratio in both models. High-dose treatment of L. plantarum X7022 (2 × 10¹⁰ CFU/kg BW) was more significant in improving constipation condition than low-dose (2 × 10⁷ CFU/kg BW). Furthermore, 16S rDNA sequencing of the intestinal flora showed that the treatment with the strain X7022 could increase the α diversity in both constipation models. Meanwhile, the abundance of Bacteroidetes increased, and Firmicutes decreased, which was more effective in acute constipated mice. In addition, X7022 treatment could enhance the relative abundance of beneficial flora, such as Bacteroides, Ruminococcus, and depressed Adlercreutzia and Odoribacter in acute model mice. In subacute constipated mice, X7022 treatment could enhance Alloprevotell, Rikenellaceae_RC9, and decreased Lachnospiraceae_NK4A136 and Desulfovibrio. Therefore, L. plantarum X7022 is a prospect probiotic strain for the amelioration of constipation.

In the present study, whey protein was enzymatically hydrolyzed using an ultrahigh-pressure synergistic enzymolysis method. The antioxidant activities and DPP-IV inhibitory activities of the enzymatic hydrolysates were measured. Three-layer isolation and purification were conducted on the enzymatic hydrolysates with antioxidant activity and DPP-IV inhibitory activity by gel filtration chromatography and RP-HPLC. The amino acid sequences were determined by LC-MS/MS. The identified amino acid sequences were then synthesized, and their antioxidants and DPP-IV inhibitory activities were determined. The results showed that 3 of the 14 polypeptides of N3-8 exhibited high antioxidant activity. Among them, peptide DDQNPHSSN had both high antioxidant activity and DPP-IV inhibitory activity. When the concentration was 1 mg/mL, then the ABTS radical scavenging rate, DPPH radical scavenging rate and reducing power were prominent, reaching 91.42%, 88.76%, and 0.637%, respectively, and DPP-IV inhibitory activity reached 66.28%. Whey protease hydrolysates are expected to be commercially developed as functional peptides.

Gluten and gums are usually used in veggie sausage for textural purposes; however, they are not label-friendly for consumers with gluten sensitivity or consumers looking for clean-label foods. Therefore, two commercial egg white proteins (P110 and M200) were studied at different levels (0%–10%) to substitute gluten or xanthan gum. The veggie sausages were subjected to color, texture, length, and weight loss evaluations. M200 significantly improved the texture of sausages and exhibited the most similar texture profile as a commercial meat sausage. The overall texture-enhanced capability of gel materials was ranked in the order of 5% M200 > 5% P110 ≥ 3% Gluten ≥ 1.3% Xanthan Gum. Egg white proteins did not significantly affect the color, length, and weight loss of sausages. Raman spectra revealed that M200 gel had a higher α-helix structure than P110 gel, which indicated that M200 formed an ordered gel by reforming tyrosine at Raman shift 833 and 860 cm⁻¹ inside while P110 formed a disordered gel by exposing tyrosine. This study demonstrated that M200 would substitute both the gluten and xanthan gum for improving the texture of veggie sausages. The findings may also be applied to other meat analogs targeting gluten-free and label-friendly purposes.

Two lactic acid bacteria (LAB) strains were screened in traditional Sichuan sausage, and their nitrite-reducing performance in different production processes was determined in this study. LAB were isolated from traditional Sichuan sausages and identified by 16S rDNA sequencing. The effects of the isolated bacteria on the bacterial community, physicochemical properties, and nitrite-decreasing capacity during sausage fermentation were investigated by comparing nonactivated treatment and activated treatment at 30°C. The results showed that the screened two LAB strains were identified as Pediococcus pentosaceus and Leuconostoc mesenteroides, which adapted well to the new habitat of fermented sausage, reaching a maximum of 7.00 and 7.32 lg CFU g⁻¹ in the nonactivated treatment, 7.65 and 7.52 lg CFU g⁻¹ in the activated treatment, and the two strains had strong acidizing potential, which could inhibit the growth of saprophytic bacteria. Otherwise, the activated treatment was better than the traditional process for nitrite degradation and fermentation time, except for color. Both strains contribute to nitrite consumption while reducing fermentation time and sausage production cycles. In conclusion, these two strains are expected to be the starting point for the improvement of biological safety and nitrite residue control in traditional Sichuan sausage production.

The development of biodegradable packaging materials focuses on their barrier properties and mechanical properties, which are critical parameters for food protection. Synthetic biodegradable material polyamide 4 (PA4) may offer outstanding capacities for packaging due to its rigid molecular structure. The current study originally reveals the various physical properties of PA4 films and explores the influence of its internal structure, molecular weight, and external environment, environmental humidity, on its performance to provide further guidance for PA4 application. PA4 (M_η = 18,000 g/mol) films showed tensile strength (TS) of 47.5 ± 1.3 MPa, elongation at break (EB) of 228% ± 30%, oxygen permeability of 7.83 ± 3.32 × 10⁻¹⁷ cm³ m⁻¹ s⁻¹ Pa⁻¹, and water vapor permeability of 4.34 ± 0.06 × 10⁻¹¹g m⁻¹ s⁻¹ Pa⁻¹. The TS and EB of PA4 improved slightly with increasing molecular weight, while the barrier characteristic remained unchanged. The moisture adsorption capabilities of PA4 films were similar to natural hydrophilic polymers. The mechanical characteristic of PA4 changed from brittle to ductile with the increase in relative humidity. Overall, PA4 can be considered to be a promising food packaging material since it presented better mechanical and oxygen barrier properties than those of commercial food packaging polymers.

Mannosyl compounds have been widely used in nutrition, fodder, and vaccine adjuvant industries. In our previous study, the engineered strains for the biosynthesis of three mannosyl compounds including β-1,2-mannobiose (M2-β-1,2), β-1,2-mannotriose (M3-β-1,2), and mannosylglycerate (MG) have been developed. However, their biological activities have not been reported. Here, those three compounds were successfully purified after fermentation of the engineered strains, and their potential immunomodulatory activities on RAW264.7 macrophages were investigated with commercialized β-1,4-mannotriose (M3-β-1,4) as control. Our results showed that M3-β-1,2 and MG promoted the viability and phagocytic function of RAW264.7. Meanwhile, the cytokine TNF-α and interleukin-6 (IL-6) level of RAW264.7 macrophages were significantly enhanced upon the stimulation of M3-β-1,2 and MG compared with M3-β-1,4. Moreover, MG significantly stimulated macrophages to secrete IL-10 compared with other mannan oligosaccharides. Finally, this study proved that the immunomodulatory activity of M3-β-1,2 and MG on RAW 264.7 cells was mainly through mitogen-activated protein kinases and myeloid differentiation protein 88 (MyD88)-dependent signaling pathways. All these findings suggested that M3-β-1,2 and MG exhibited immunomodulatory activities in the innate and adaptive immune systems, thus facilitating the application potential in developing of mannosyl compounds as an immunomodulator available for food and pharmaceutical area.

Vitamin B₆ is an essential nutrient, which is widely used in food products, feed additives, pharmaceuticals, disease diagnosis, and other fields. Pyridoxal-5′-phosphate (PLP), the active form of vitamin B₆, is an important coenzyme participating in a variety of enzyme reactions. At present, the oxazole method is mainly used for the production of vitamin B₆, but toxic and corrosive intermediates produced in the synthesis process, which does not conform to the green manufacturing. Therefore, there is considerable interest in shifting from chemical processes to sustainable fermentation techniques and research on PLP metabolism of other valuable compounds. In this review, we will briefly describe the enzymes that PLP participated and focus on the advances in vitamin B₆ biosynthesis and discuss its application to engineering bacteria that overproduce other commercially valuable substances including cadaverine, 3,4-dihydroxyphenylacetate-l-alanine, γ-aminobutyric acid, and l-phosphinothricin. It will provide a reference for the biosynthesis of vitamin B₆ or other valuable compounds in which PLP participates in the reaction, and we also look forward to the future development prospect of PLP.