Effect of acidification on the activity of probiotics in yoghurt during cold storage

The viability of Lactobacillus acidophilus LAFTI^® L10, Bifidobacterium lactis LAFTI^® B94, and L. paracasei LAFTI^® L26 and their proteolytic activities were assessed in yoghurt at different termination pH of 4.45, 4.50, 4.55, and 4.60 in the presence of L. delbrueckii ssp. bulgaricus Lb1466 and Streptococcus thermophilus St1342 during 28 days of storage at 4 °C. All strains achieved the recommended level of 6.00 log cfu g⁻¹ of the product with L. acidophilus LAFTI^® L10 and L. paracasei LAFTI^® L26 exceeding the number to 8.00 and 7.00 log cfu g⁻¹, respectively. Lactobacilli strains showed a good cellular stability maintaining constant concentration throughout storage period regardless of termination pH. On the other hand, the cell counts of B. lactis LAFTI^® B94 decreased by one log cycle at the end of storage. The presence of probiotic organisms enhanced proteolysis significantly in comparison with the control batch containing L. delbrueckii ssp. bulgaricus Lb1466 and S. thermophilus St1342 only. The proteolytic activity varied due to termination pH, but also appeared to be strain related. The increased proteolysis improved survival of L. delbrueckii ssp. bulgaricus Lb1466 during storage resulting in lowering of pH and production of higher levels of organic acids, which might have caused the low cell counts for B. lactis LAFTI^® B94.     

Conjugated linoleic acid concentration as affected by lactic cultures and added linoleic acid

Six lactic cultures: Lactobacillus acidophilus (CCRC14079), L. delbrueckii subsp. bulgaricus (CCRC14009), L. delbrueckii subsp. lactis (CCRC14078), Lactococcus lactis subsp. cremoris (CCRC12586), Lc. lactis subsp. lactis (CCRC10791), and Streptococcus salivarius subsp. thermophlius (CCRC12257) were tested for the effects of addition of 1000 and 5000 μg/ml linoleic acid, and incubation time from 0 to 48 h. The levels of conjugated linoleic acid (CLA) formation were determined by gas chromatography. A sharp increase in CLA level was observed in linoleic acid added cultures. Incubation of L. acidophilus in 1000 μg/ml linoleic acid added-skim milk medium for 24 h was most effective in promoting CLA formation. Increasing linoleic acid addition from 1000 to 5000 μg/ml and prolonging incubation from 24 to 48 h did not appear to enhance CLA formation.     

Factors affecting the susceptibility of Staphylococcus aureus CCRC 12657 to water soluble lactose chitosan derivative

In this study, the susceptibility of Staphylococcus aureus CCRC 12657 to water-soluble lactose chitosan derivative as influenced by pH, temperature and cell age were investigated. Besides, the effect of this chitosan derivative on enterotoxin production and cell leakage of S. aureus CCRC 12657 was also examined.It was found that the susceptibility of S. aureus CCRC 12657 to lactose chitosan derivative varied with incubation temperature, pH and cell age. The lactose chitosan derivative exerted a higher antibacterial activity against S. aureus CCRC 12657 at 37°C than at 22 and 5°C. At pH 6.5–7.0, S. aureus CCRC 12657 was more susceptible to the chitosan derivative than at pH 6.0 or 7.5. Besides, cells of S. aureus CCRC 12657 in the late-exponential phase (12 h) were most susceptible to the chitosan derivative followed by cells in the stationary phase (24 h) and mid-exponential phase (6 h). Supernatant of cell suspension showed a marked increase in absorbance at 280 nm after the cells of the test organism were exposed to deionized water-containing lactose chitosan derivative. Furthermore, it was also noted that the lactose chitosan derivative not only caused the death of S. aureus CCRC 12657 but also inhibited enterotoxin production in Brain–Heart infusion broth.     

Stability of microencapsulated Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris during storage at room temperature at low aw

The effect of freeze drying or spray drying, the use of desiccants to maintain the low a_w and the period of storage (at 25 °C) of Lactobacillus acidophilus and Lactococcus lactis ssp. cremoris on survival, acid tolerance, bile tolerance, retention of surface hydrophobicity and retention of β-galactosidase was studied; an estimation of the maximum storage period was also carried out. Sodium caseinate, vegetable oil, glucose, mannitol and fructooligosaccharides were used as protectant of L. acidophilus and L. cremoris during freeze drying or spray drying and during subsequent storage. NaOH, LiCl and silica gel were used as desiccants during 10 weeks of storage of microencapsulated L. acidophilus and L. cremoris kept in an aluminum foil pouch. The results showed that mainly freeze dried L. acidophilus and L. cremoris kept in foil pouch containing NaOH (a_w 0.07) or LiCl (a_w 0.1) showed higher survival (89–94%) than spray dried bacteria kept under the same conditions (86–90%) after 10 weeks of storage (P = 0.0005). Similar results were also showed by acid tolerance, bile tolerance and surface hydrophobicity of freeze-dried or spray-dried L. acidophilus and L. cremoris. Silica gel was less effective in protecting the functional properties of microencapsulated L. acidophilus or L. cremoris with percentage of survival between 81 and 87% at week 10 of the storage. However, retention of β-galactosidase was only influenced by a_w adjusted by desiccators (P < 0.05). Based on forecasting using linear regression, the predicted storage period for freeze dried L. acidophilus, spray dried L. acidophilus and freeze dried L. cremoris kept in foil pouch containing NaOH would be 46, 42 and 42 weeks, respectively; while spray dried L. cremoris under LiCl desiccant would require 39 weeks to achieve minimum required bacterial population of 10⁷ CFU/g.     

Fermentation of beet juice by beneficial lactic acid bacteria

Red beets were evaluated as a potential substrate for the production of probiotic beet juice by four species of lactic acid bacteria (Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii, Lactobacillus plantarum). All the lactic cultures were found capable of rapidly utilizing beet juice for cell synthesis and lactic acid production. However, L. acidophilus and L. plantarum produced a greater amount of lactic acid than other cultures and reduced the pH of fermented beet juice from an initial value of 6.3 to below 4.5 after 48 h of fermentation at 30°C. Although the lactic cultures in fermented beet juice gradually lost their viability during cold storage, the viable cell counts of these lactic acid bacteria except for L. acidophilus in the fermented beet juice still remained at 10⁶–10⁸ CFU/ml after 4 weeks of cold storage at 4°C.     

Conjugated linoleic acid production by cells and enzyme extract of Lactobacillus delbrueckii ssp. bulgaricus with additions of different fatty acids

The objective of the study was to determine the effect of fatty acid additions to the cells and enzyme extract of Lactobacillus delbrueckii ssp. bulgaricus (CCRC14009) on CLA production. Washed cells of L. delbrueckii ssp. bulgaricus, obtained by cultivation in a MRS broth, were mixed with BSA and each of the three fatty acids: linoleic, oleic, and linolenic acids in sodium phosphate buffer at pH 6.5. After incubation at 37 °C for 108 h, CLA concentration was analyzed by HPLC. Enzyme extract from the culture was also reacted with each fatty acid at 50 °C for 10 min at pH 5 to test for CLA production. Results showed that linoleic acid addition to the culture improved CLA production, indicating the presence of linoleic acid isomerase activity in the culture. The crude enzyme extract from the culture was observed to be capable of oleic and linolenic acid conversions into CLA, demonstrating the possible presence of desaturase activity in the enzyme extract.     

Effects of yogurt starter cultures on the survival of Lactobacillus acidophilus

Recognized to confer health benefits to consumers, probiotics such as Lactobacillus acidophilus are commonly incorporated into fermented dairy products worldwide; among which yogurt is a popular delivery vehicle. To materialize most of the putative health benefits associated with probiotics, an adequate amount of viable cells must be delivered at the time of consumption. However, the loss in their viabilities during refrigerated storage has been demonstrated previously. This study focused on the effects of yogurt starter cultures on the survival of five strains of L. acidophilus, with emphases on low pH and acid production. Differential survival behavior between L. acidophilus strains was further analyzed. To this end, viable cell counts of L. acidophilus were determined weekly during 4 °C storage in various types of yogurts made with Streptococcus thermophilus alone, L. delbrueckii ssp. bulgaricus alone, both species of the starter cultures, or glucono-delta-lactone (GDL). All yogurt types, except for pasteurized yogurts, were co-fermented with L. acidophilus. Yogurt filtrate was analyzed for the presence of any inhibitory substance and for the amount of hydrogen peroxide. Multiplication of L. acidophilus was not affected by the starter cultures as all strains reached high level on day 0 of the storage period. Throughout the 28-day storage period, cell counts of L. acidophilus PIM703 and SBT2062 remained steady (~ 6 × 10⁷ CFU/g) in yogurts made with both starter cultures, whereas those of ATCC 700396 and NCFM were reduced by a maximum of 3 and 4.6 logs, respectively. When starter cultures were replaced by GDL, all strains survived well, suggesting that a low pH was not a critical factor dictating their survival. In addition, the filtrate collected from yogurts made with starter cultures appeared to have higher inhibitory activities against L. acidophilus than that made with GDL. The presence of viable starter cultures was necessary to adversely affect the survival of some strains, as pasteurized yogurts had no effect on their survival. In particular, the inhibitory effect exerted by L. delbrueckii ssp. bulgaricus on L. acidophilus NCFM was highly pronounced than by S. thermophilus, nevertheless, the same effect was not observed on SBT2062. The inhibition against stationary-phase NCFM cells might be caused by the elevated level of hydrogen peroxide produced by L. delbrueckii ssp. bulgaricus. Delineating factors driving the differences in survival trait among probiotic strains will lead to a more efficacious delivery of health benefits in fermented dairy products through targeted technological interventions.     

Survival and activity of selected probiotic organisms in set-type yoghurt during cold storage

The growth and metabolism of two probiotic organisms (L. acidophilus LAFTI^® L10 and Lactobacillus casei LAFTI^® L26) and a regular yoghurt culture (L. delbrueckii ssp. bulgaricus Lb1466 and Streptococcus thermophilus St1342) were studied in yoghurt containing 0.5%, 1.0%, and 1.5% (w/v) of high amylose corn starch powder (Hi-maize^®) or inulin. Viable cell counts of probiotic organisms, their metabolites and proteolytic activities, and viscosity of the yoghurts were determined during refrigerated storage for 28 d at 4 ^oC. In the presence of inulin, cultures showed better retention of viability (8.0 log cfu g⁻¹) in comparison with that of Hi-maize, which had a reduction by one log cycle. Lower concentrations of 0.5–1.0% Hi-maize improved (P<0.05) the production of propionic acid and also increased proteolytic activity of probiotic organisms substantially. A greater release of free amino acids may have sustained better growth of the organisms in yoghurts. Supplementation with either Hi-maize or inulin increased the viscosity of probiotic yoghurts significantly (P<0.05).     

Optimization of the associative growth of novel yoghurt cultures in the production of biomass, β-galactosidase and lactic acid using response surface methodology

The associative growth of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp. bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey was investigated with respect to lactic acid, biomass and β-galactosidase enzyme production using response surface methodology (RSM). The ratio (St 95/2:Lb 77) of the strains and media formulation had significant effect on all responses (p < 0.001). The predicted enzyme activity (2.14 U mL^?1), lactic acid (22.50 g L^?1) and biomass (7.11 g L^?1) production at optimum conditions were very close to the actual experimental values (2.14 U mL^?1, 22.94 g L^?1 and 7.86 g L^?1, respectively). The optimum conditions were to use these cultures in a ratio of 1.66:1.62 (St 95/2:Lb 77) in a medium containing whey (5%), corn steep liquor (4%), potassium phosphate (2%) and peptone (2%) at 43 °C for 8 h. The associative growth provided 6.4% and 39% more β-galactosidase activity and 8.73% and 44% more lactic acid compared with the results obtained using pure St 95/2 and Lb 77 strains, respectively.     

Production of volatile aroma compounds by kefir starter cultures

Production of carbonyl compounds by single-strain cultures, kefir starter (Lactobacillus delbrueckii subsp. bulgaricus HP1+Lb. helveticus MP12+Lactococcus lactis subsp. lactis C15+Streptococcus thermophilus T15+Saccharomyces cerevisiae A13) and kefir grains during fermentation and storage of kefir was studied. The content of carbonyl compounds produced by kefir starter was greater than that produced by kefir grains. The maximum acetaldehyde concentration (18.3 μg g⁻¹) in kefir with starter culture was mainly due to the metabolic activity of Lb. delbrueckii subsp. bulgaricus HP1 isolated from kefir grains. The highest diacetyl production activity was recorded in the starter culture (1.87 μg g⁻¹) and the single-strain culture St. thermophilus T15 (1.62 μg g⁻¹), followed by Lb. helveticus MP12 (0.85 μg g⁻¹) and Lc. lactis subsp. lactis C15 (0.42 μg g⁻¹). The lactobacilli Lb. delbrueckii subsp. bulgaricus HP1 and Lb. helveticus MP12 produced acetone, which was not found in the cocci cultures. The presence of 2-butanone was related to the production ability of Lb. helveticus MP12. In comparison, Lc. lactis subsp. lactis C15 synthesized ethyl acetate more actively than the other single-strain cultures included in the starter. S. cerevisiae A13 produced ethanol and CO₂ in amounts (3975 μg g⁻¹; 1.80 g L⁻¹) that lent cultured kefir distinctive flavour and aroma characteristic of authentic kefir.     

Linoleic acid Isomerase Activity in Enzyme Extracts from Lactobacillus Acidophilus and Propionibacterium Freudenreichii ssp. Shermanii

Enzyme extracts from Lactobacillus acidophilus (CCRC14079) and Propionibacterium freudenreichii ssp. shermanii (CCRC11076) were reacted with linoleic acid at 50 °C for 10 min at pH 5, 6, 7, and 8, and the levels of conjugated linoleic acid (CLA) formation were determined by high performance liquid chromatography. CLA formations were observed in all the reactions catalyzed by the retentates using ultrafiltration membranes with 100 kDa nominal molecular weight cutoff, indicating the presence of the activity of linoleic acid isomerase with nominal molecular weight higher than 100 kDa in the retentates from two cultures. More CLA was formed at pH 5 of L. acidophilus treatment and t10c12, c11t13, and c9t11 CLA were 3 major CLA isomers produced. Results demonstrate a potential for CLA production through linoleic acid isomerase.     

Fermentative ability of alginate-prebiotic encapsulated Lactobacillus acidophilus and survival under simulated gastrointestinal conditions

Lactobacillus acidophilus was encapsulated in alginate-inulin-xanthan gum and its ability to grow in carrot juice and survive 8 weeks of storage at 4 °C and subsequent exposure to artificial gastrointestinal conditions were assessed. Encapsulation significantly enhanced cell viability after fermentation and storage (6 × 10¹² and 4 × 10¹⁰ cells/ml versus 4 × 10¹⁰ and 2 × 10⁸ for free cells, respectively). Encapsulation protected L. acidophilus from exposure to simulated gastric conditions; minor alterations in viability and the protein profile occurred after incubation in pancreatic juice. For free cells, viability decreased significantly and the expression of numerous proteins was lost after incubation in gastric and pancreatic juice. Thus, encapsulation preserved probiotic bacterial viability and activity; the addition of inulin as a prebiotic component could enhance the functional properties of food products containing this formulation.     

High hydrostatic pressure processing on microstructure of probiotic low-fat yogurt

The effect of milk processing on the microstructure of probiotic low-fat yogurt was studied. Skim milk fortified with skim milk powder was subjected to three treatments prior to innoculation: thermal treatment at 85 °C for 30 min, high hydrostatic pressure at 676 MPa for 5 min, and combined treatments of high hydrostatic pressure (HHP) and heat. The processed milk was then fermented by using two different starter cultures containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus, and Bifidobacterium longum. The microstructure of heat-treated milk yogurt had fewer interconnected chains of irregularly shaped casein micelles, forming a network that enclosed the void spaces. On the other hand, microstructure of HHP yogurt had more interconnected clusters of densely aggregated protein of reduced particle size, with an appearance more spherical in shape, exhibiting a smoother more regular surface and presenting more uniform size distribution. The combined HHP and heat milk treatments led to compact yogurt gels with increasingly larger casein micelle clusters interspaced by void spaces, and exhibited a high degree of cross-linking. The rounded micelles tended to fuse and form small irregular aggregates in association with clumps of dense amorphous material, which resulted in improved gel texture and viscosity.     

Edible methylcellulose-based films containing fructo-oligosaccharides as vehicles for lactic acid bacteria

The goal of this work was to investigate the physicochemical properties of methylcellulose (MC) based films as stabilizers of two strains of lactobacilli: Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 and Lactobacillus plantarum CIDCA 83114. The incorporation of 3% w/v fructo-oligosaccharides (FOS) into the MC film formulation improved the viability of L. delbrueckii subsp. bulgaricus CIDCA 333 after film preparation. L. plantarum CIDCA 83114 was intrinsically more resistant as no viability loss was observed upon preparation of the films in the absence of FOS.Scanning electronic microscopy images also showed a good incorporation of microorganisms without affecting the homogeneity of the films. FTIR spectroscopy provided structural information about the bacteria-loaded films. Water sorption isotherms showed an impervious behavior at low a_w but on exceeding 0.7 of a_w the film started to dissolve and form syrup, causing a drastic drop of bacterial viability (log N/N₀ ≤ − 5). Dynamic mechanical analysis (DMA) demonstrated that the incorporation of microorganisms into the MC films had no effect on vitreous transition temperatures. FOS incorporated into the MC films had a plasticizing effect.Microorganism-loaded films were stored at relative humidities (RH) ranging from 11 to 75%. Both strains could be stored at 11% RH for 90 days. At 33 and 44% RH L. delbrueckii subsp. bulgaricus CIDCA 333 could be stored up to 15 days and L. plantarum CIDCA 83114 up to 45 days. At 75% RH only L. plantarum CIDCA 83114 could be equilibrated (log N/N₀: − 2.05 ± 0.25), but CFU/g films were undetectable after 15 days of storage.The results obtained in this work support the use of MC films containing FOS as a good strategy to immobilize lactic acid bacteria, with potential applications in the development of functional foods.     

Viscosity of model yogurt systems enriched with barley β-glucan as influenced by starter cultures

The effect of barley β-glucan (BG) on the growth of two yogurt starter cultures (SCs) each consisting of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus was investigated. Model yogurt systems were prepared with or without the incorporation of barley BG and lactose to mimic natural levels in milk and allowed to ferment for 8 h at 42 °C. The fermentation efficacy of the SCs was monitored through pH measurements. Samples were collected and analyzed for pH and viscosity at 0, 2, 4, and 8 h. Viscosity was determined using a rotational viscometer at shear rates of 1.29–129 s⁻¹ and 20 °C. The pH measurements indicated no adverse effect on the growth of SCs as the acidification process was consistent with normal pH development, but viscosity measurements suggested that BG was depolymerized by SCs when lactose became a limiting nutrient during fermentation.     

Probiotic viability and storage stability of yogurts and fermented milks prepared with several mixtures of lactic acid bacteria

Currently, the food industry wants to expand the range of probiotic yogurts but each probiotic bacteria offers different and specific health benefits. Little information exists on the influence of probiotic strains on physicochemical properties and sensory characteristics of yogurts and fermented milks. Six probiotic yogurts or fermented milks and 1 control yogurt were prepared, and we evaluated several physicochemical properties (pH, titratable acidity, texture, color, and syneresis), microbial viability of starter cultures (Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus) and probiotics (Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus reuteri) during fermentation and storage (35 d at 5°C), as well as sensory preference among them. Decreases in pH (0.17 to 0.50 units) and increases in titratable acidity (0.09 to 0.29%) were observed during storage. Only the yogurt with S. thermophilus, L. delbrueckii ssp. bulgaricus, and L. reuteri differed in firmness. No differences in adhesiveness were determined among the tested yogurts, fermented milks, and the control. Syneresis was in the range of 45 to 58%. No changes in color during storage were observed and no color differences were detected among the evaluated fermented milk products. Counts of S. thermophilus decreased from 1.8 to 3.5 log during storage. Counts of L. delbrueckii ssp. bulgaricus also decreased in probiotic yogurts and varied from 30 to 50% of initial population. Probiotic bacteria also lost viability throughout storage, although the 3 probiotic fermented milks maintained counts ≥10⁷ cfu/mL for 3 wk. Probiotic bacteria had variable viability in yogurts, maintaining counts of L. acidophilus ≥10⁷ cfu/mL for 35 d, of L. casei for 7 d, and of L. reuteri for 14 d. We found no significant sensory preference among the 6 probiotic yogurts and fermented milks or the control. However, the yogurt and fermented milk made with L. casei were better accepted. This study presents relevant information on physicochemical, sensory, and microbial properties of probiotic yogurts and fermented milks, which could guide the dairy industry in developing new probiotic products.     

Some low homogenization pressures improve certain probiotic characteristics of yogurt culture bacteria and Lactobacillus acidophilus LA-K

Lactobacillus delbrueckii ssp. bulgaricus, Streptococcus salivarius ssp. thermophilus, and Lactobacillus acidophilus are dairy cultures widely used in the manufacture of cultured dairy products. Commonly used homogenization pressures in the dairy industry are 13.80 MPa or less. It is not known whether low homogenization pressures can stimulate bacteria to improve their probiotic characteristics. Objectives were to determine the effect of homogenization at 0, 3.45, 6.90, 10.34, and 13.80 MPa on acid tolerance, bile tolerance, protease activity, and growth of L. delbrueckii ssp. bulgaricus LB-12, S. salivarius ssp. thermophilus ST-M5, and L. acidophilus LA-K. The cultures were individually inoculated in cool autoclaved skim milk (4°C) and homogenized for 5 continuous passes. Growth and bile tolerance of samples were determined hourly for 10 h of incubation. Acid tolerance was determined every 20 min for 120 min of incubation. Protease activity was determined at 0, 12, and 24 h of incubation. All homogenization pressures studied improved acid tolerance of L. delbrueckii ssp. bulgaricus LB-12 but had no beneficial effect on protease activity and had negative effects on growth and bile tolerance. A pressure of 6.90 MPa improved acid tolerance, bile tolerance, and protease activity of S. salivarius ssp. thermophilus ST-M5, but none of the homogenization pressures studied had an effect on its growth. Homogenization pressures of 13.80 and 6.90 MPa improved acid tolerance and bile tolerance, respectively, of L. acidophilus LA-K but had no effect on protease activity and its growth. Some low homogenization pressures positively influenced some characteristics of yogurt culture bacteria and L. acidophilus LA-K. Culture pretreatment with some low homogenization pressures can be recommended for improvement of certain probiotic characteristics.     

Probiotic-loaded microcapsule system for human in situ folate production: Encapsulation and system validation

This study focused on the use of a new system, an alginate | Ɛ-poly-l-lysine | alginate | chitosan microcapsule (APACM), able to immobilize a folate-producing probiotic, Lactococcus lactis ssp. cremoris (LLC), which provides a new approach to the utilization of capsules and probiotics for in situ production of vitamins. LLC is able to produce 95.25 ± 26 μg·L^− 1 of folate, during 10 h, and was encapsulated in the APACM. APACM proved its capacity to protect LLC against the harsh conditions of a simulated digestion maintaining a viable concentration of 6 log CFU·mL^− 1of LLC. A nutrients exchange capacity test, was performed using Lactobacillus plantarum UM7, a high lactic acid producer was used here to avoid false negative results. The production and release of 2 g·L^− 1 of lactic acid was achieved through encapsulation of L. plantarum, after 20 h. The adhesion of APACM to epithelial cells was also quantified, yielding 38% and 33% of capsules adhered to HT-29 cells and Caco-2 cells, respectively.     

Exploring the industrial potential of Lactobacillus delbrueckii ssp. bulgaricus by population genomics and genome-wide association study analysis

Lactobacillus delbrueckii ssp. bulgaricus is one of the most commonly used starter cultures for yogurt production. However, how its genetic background affects acid production capacity is unclear. This study investigated the industrial potential of L. delbrueckii ssp. bulgaricus using population genomics and GWAS analysis. To meet our goal, population genetics and functional genomics analyses were performed on 188 newly sequenced L. delbrueckii ssp. bulgaricus strains isolated from naturally fermented dairy products together with 19 genome sequences retrieved from the NCBI database. Four distinct clusters were identified, and they were correlated with the geographical sites where the samples were collected. The GWAS analysis about acidification fermentation results with sucrose-fortified reconstituted skim milk revealed a significant association between l-lactate dehydrogenase (lldD; Ldb2036) and the bacterial acid production rate. Our study has broadened the understanding of the population structure and genetic diversity of L. delbrueckii ssp. bulgaricus by identifying potential targets for further research, development, and use of lactic acid bacteria in the dairy industry.     

Production of cured meat color in nitrite-free Harbin red sausage by Lactobacillus fermentum fermentation

Lactobacillus fermentum was substituted for nitrite to produce cured pink color in a Chinese-style sausage. Treatments included inoculations (10⁴, 10⁶, and 10⁸ CFU/g meat) followed by fermentation at 30 °C for 8 h and then at 4 °C for 16 h. Control sausage (with sodium nitrite, 60 mg/kg meat) was cured at 4 °C for 24 h without L. fermentum. The UV–Vis spectra of pigment extract from L. fermentum-treated sausage were identical to that of nitrosylmyoglobin (NO-Mb) formed in nitrite-treated control. The NO-Mb concentration and the colorimetric a¹ value of sausage treated with 10⁸ CFU/g meat of L. fermentum essentially replicated those in nitrite-cured meat. Free amino acid content in sausage treated with L. fermentum was greater and the pH slightly lower compared with the nitrite-cured control sample. This study showed that L. fermentum has the potential to substitute for nitrite in the sausage production.