The effect of NaCl substitution with KCl on proteinase activities of cell-free extract and cell-free supernatant at different pH levels and salt concentrations: Lactobacillus acidophilus and Lactobacillus casei.

The aim of this study was to investigate the effect of substitution of NaCl with KCl at different pH levels and salt concentrations on proteinase activity of cell-free extract and cell-free supernatant of the probiotics Lactobacillus acidophilus and Lactobacillus casei. de Man, Rogosa, and Sharpe broth aliquots were mixed with 2 pure salts (NaCl and KCl) and 2 salt concentrations at 2 concentration levels (5 and 10%), inoculated with Lactobacillus acidophilus or Lactobacillus casei, and incubated aerobically at 37°C for 22 h. The cultures were then centrifuged at 4,000×g for 30 min, and the collected cell pellets were used to prepare cell-wall proteinases and the supernatants used as a source of supernatant (extracellular) proteinases. The proteolytic activity and protein content of both portions were determined. After incubation of both portions with 3 milk caseins (α-, ß-, κ-casein), the supernatants were individually subjected to analysis of angiotensin-converting enzyme (ACE)-inhibitory activity and proteolytic activity using the o-phthalaldehyde method. Significant differences were observed in ACE-inhibitory and proteolytic activities between salt substitution treatments of cell-free extract and cell-free supernatant from both probiotic strains at the same salt concentration and pH level.

The effect of NaCl substitution with KCl on Akawi cheese: chemical composition, proteolysis, angiotensin-converting enzyme-inhibitory activity, probiotic survival, texture profile, and sensory properties.

The effect of partial substitution of NaCl with KCl on Akawi cheese with probiotic bacteria was investigated during 30 d of storage at 4 °C. Chemical composition, the survival of probiotic and lactic acid bacteria, proteolytic activity, and texture profile analysis were analyzed and sensory analysis was carried out to determine the effects of substitution. No significant differences were observed in moisture, protein, fat, and ash contents among the experimental Akawi cheeses at the same storage period. Significant differences were observed in water-soluble nitrogen and phosphotungstic-soluble nitrogen between experimental cheeses at the same of storage period. No significant difference was observed in the growth of Lactobacillus delbrueckii ssp. bulgaricus between experimental cheeses at the same storage period. However, the growth of Streptococcus thermophilus, Lactobacillus casei, and Lactobacillus acidophilus was significantly affected among experimental cheeses. A significant difference was observed in soluble Ca among experimental cheeses at the same storage period. In general, no significant differences existed in hardness and adhesiveness among experimental cheeses at the same storage period. No significant differences existed in sensory attributes, including creaminess, bitterness, saltiness, sour-acid, and vinegar taste among experimental Akawi cheeses at the same storage period.

The impact of NaCl substitution with KCl on proteinase activities cell-free extract and cell-free supernatant at different pH levels and salt concentrations: Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus.

UNLABELLED: The effect of NaCl substitution with KCl at different pH levels (6.0, 5.5, and 5.0) and salt concentrations on proteinase activities of cell-free and supernatant of Lactobacillus delbrueckii ssp. bulgaricus 11824 (L. bulgaricus) and Streptococcus thermophilus MS (ST) was investigated. MRS broths were separately mixed with 4 salt treatments (NaCl only, 1NaCl:1KCl, 1NaCl:3KCl, and KCl only) at 2 different concentrations (5% and 10%) and incubated at 37 °C for 22 h. The cell pellets were used to prepare proteinase of cell-free extract and the cell-free supernatants were used as source of extracellular proteinases. The proteolytic activities and protein contents of both fractions were determined. The supernatants after incubation of both fractions with 3 milk caseins (α-, ß-, κ-casein) were subjected to angiotensin-converting-enzyme inhibitory (ACE-inhibitory) activity and proteolytic activity by ortho-phthalaldehyde (OPA) method. Significant differences were observed in ACE-inhibitory activities and proteolytic (OPA) between salt treatments of cell-free extract and cell-free supernatant of L. bulgaricus and S. thermophilus at same salt concentration and same pH level. There was a significant effect of pH level and salt treatments interaction on ACE-inhibitory activity, OPA activity and azocasein activity. PRACTICAL APPLICATION: To reduce sodium concentration in cheese by substituting of NaCl with KCl, it was important to study the effect on starter culture proteinases which play a vital role in ripening and texture profile of cheese.

The effect of substitution of NaCl with KCl on chemical composition and functional properties of low-moisture Mozzarella cheese.

The effect of NaCl substitution with KCl on chemical composition, organic acids profile, soluble calcium, and functionality of low-moisture Mozzarella cheese (LMMC) was investigated. Functionality (meltability and browning), organic acids profile, and chemical composition were determined. Chemical composition showed no significant difference between experimental cheeses at same storage period, and same salt treatment. Meltability of LMMC salted with 3NaCl:1KCl, 1NaCl:1KCl, and 1NaCl:3KCl was higher compared with only NaCl (control). The amount of soluble Ca and P increased significantly during storage, with no significant difference between salt treatments. Organic acids profile did not differ between salt treatments at the same storage time.

Proteolysis of low-moisture Mozzarella cheese as affected by substitution of NaCl with KCl.

The proteolytic and ACE inhibitory activities of low-moisture Mozzarella cheese (LMMC) as affected by partial substitution of NaCl with KCl were investigated. Experimental LMMC were made and salted with 4 salt mixtures: NaCl only (control), 3NaCl:1KCl, 1NaCl:1KCl, and 1NaCl:3KCl, and then proteolytic activity and angiotensin-converting enzyme inhibitory activity were determined. Salt treatment significantly affected angiotensin-converting enzyme inhibitory activity and phosphotungstic acid-soluble N of LMMC during storage. Water-soluble N, trichloroacetic acid-soluble N, lactic acid bacteria population, and total free amino acids were unaffected during storage. Nonetheless, water-soluble N and trichloroacetic acid-soluble N increased significantly during storage within a salt treatment. Peptide profiles and urea-PAGE gels did not differ between experimental cheeses at the same storage time.

The effect of substituting NaCl with KCl on Nabulsi cheese: chemical composition, total viable count, and texture profile.

The effect of substituting NaCl with KCl on Nabulsi cheese characteristics was investigated. Nabulsi cheese was made and stored in 4 different brine solutions at 18%, including NaCl only (A; control); 3NaCl:1KCl (wt/wt; B); 1NaCl:1KCl (wt/wt; C); and 1NaCl:3KCl (wt/wt; D). Chemical composition, proteolysis, total viable count, and texture profile analysis were assessed at monthly intervals for 5 mo. No significant effect was found among experimental cheeses in terms of chemical composition or texture profile. Proteolytic activities were higher in cheeses kept in brine solutions that contained higher KCl (B, C, and D) compared with the control. At the end of the storage period, water-soluble nitrogen in Nabulsi cheeses stored in B, C, and D was higher than that in the control cheese (A). In addition, total viable count increased significantly after 1 mo of storage for all salt treatments. Hardness and gumminess generally decreased significantly during storage within the same salt treatment.

The effect of sodium chloride substitution with potassium chloride on texture profile and microstructure of Halloumi cheese.

The effect of partial substitution of NaCl with KCl on texture profile and microstructure of Halloumi cheese was investigated. Four batches of Halloumi cheese were made and kept in 4 different brine solutions (18%, wt/wt), including A) NaCl only, B) 3NaCl:1KCl, C) 1NaCl:1KCl, and D) 1NaCl:3KCl and then stored at 4°C for 56 d. The texture profile was analyzed using an Instron universal machine, whereas an environmental scanning electron microscope was used to investigate the effect of NaCl substitution on the microstructure of cheeses. No significant difference was found in hardness, cohesiveness, adhesiveness, and gumminess among experimental cheeses at the same storage day. Hardness, cohesiveness, and gumminess decreased significantly during storage period with the same salt treatment, whereas adhesiveness significantly increased. Environmental scanning electron microscope micrographs showed a compact and closed texture for cheeses at the same storage period. The microstructure of all cheeses became more closed and compact with storage period. Calcium content negatively correlated with hardness and Na and K contents during storage with the same salt treatment.

Survival and growth of Cronobacter species (Enterobacter sakazakii) in wheat-based infant follow-on formulas.

AIMS: To determine the survival and growth characteristics of Cronobacter species (Enterobacter sakazakii) in infant wheat-based formulas reconstituted with water, milk, grape juice or apple juice during storage. METHODS AND RESULTS: Infant wheat-based formulas were reconstituted with water, ultra high temperature milk, pasteurized grape or apple juices. The reconstituted formulas were inoculated with Cronobacter sakazakii and Cronobacter muytjensii and stored at 4, 25 or 37 degrees C for up to 24 h. At 25 and 37 degrees C, Cronobacter grew more (>5 log(10)) in formulas reconstituted with water or milk than those prepared with grape or apple juices (c. 2-3 log(10)). The organism persisted, but did not grow in any formulas stored at 4 degrees C. Formulas reconstituted with water and milk decreased from pH 6.0 to 4.8-5.0 after 24 h, whereas the pH of the formulas reconstituted with fruit juices remained at their initial pH values, c. pH 4.8-5.0. CONCLUSIONS: Cronobacter sakazakii and C. muytjensii can grow in reconstituted wheat-based formulas. If not immediately consumed, these formulas should be stored at refrigeration temperatures to reduce the risk of infant infection. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study will be of use to regulatory agencies and infant formula producers to recommend storage conditions that reduce the growth of Cronobacter in infant wheat-based formulas.

Effect of desiccation, starvation, heat, and cold stresses on the thermal resistance of Enterobacter sakazakii in rehydrated infant milk formula.

Enterobacter sakazakii is an opportunistic foodborne pathogen that has been isolated from powdered infant milk formula. This study determined the effect of desiccation, starvation, heat and cold stresses on the thermal inactivation of E. sakazakii in rehydrated infant milk formula (RIMF). Stressed cells were mixed with RIMF at 52, 54, 56, and 58 degrees C for various time periods. The D- and z-values were determined by using linear regression analysis. D-values for unstressed E. sakazakii at 52, 54, 56, and 58 degrees C were 15.33, 4.53, 2, and 0.53 min, respectively. Desiccation and heat stresses, but not starvation or cold stress, caused significant (P < 0.05) reduction in D-values. The z-values of desiccated, starved, heat stressed, and cold stressed E. sakazakii were not significantly different from unstressed cells (4.22 degrees C). Thermal resistance of E. sakazakii in RIMF is affected by the environmental stresses; that is, desiccation and heat stresses that may surround the bacterium prior to the contamination of infant formula. The results of this study may be of use to regulatory agencies, infant milk producers, and infant caregivers to design heating processes to eliminate E. sakazakii that may be present in infant milk formula.

Inactivation of Enterobacter sakazakii in infant milk formula by gamma irradiation: determination of D10-value.

Enterobacter sakazakii is an emerging foodborne pathogen that has caused several cases of meningitis and necrotizing enterocolitis in infants and has been associated with infant formulas. Five strains of E. sakazakii were inoculated individually into brain heart infusion broth and rehydrated or dehydrated infant milk formula and exposed to ionizing radiation. E. sakazakii strains in brain heart infusion broth and rehydrated infant milk formula (RIMF) were exposed to irradiation dose of up to 1 kGy while strains in dehydrated infant milk formula (DIMF) were exposed to irradiation dose of up to 9 kGy. The D(10)-values were determined by using a linear regression model. Average calculated D(10)-values ranged from 0.21 to 0.29 kGy, 0.24 to 0.37 kGy, and 1.06 to 1.71 kGy in brain heart infusion broth, RIMF, and DIMF, respectively. The results obtained from this study will be useful for powdered infant milk formula industries to reduce the risk associated with E. sakazakii.