Effects of pH Adjustment and Sodium Ions on Sour Taste Intensity of Organic Acids

ABSTRACT:  Protonated organic acid species have been shown to be the primary stimuli responsible for sour taste of organic acids. However, we have observed that sour taste may be modulated when the pH of acid solutions is raised using sodium hydroxide. Objectives were to evaluate the effect of pH adjustment on sour taste of equimolar protonated organic acid solutions and to investigate the potential roles of organic anions and sodium ions on sour taste perception. Despite equal concentrations of protonated acid species, sour taste intensity decreased significantly with increased pH for acetic, lactic, malic, and citric acids ( P < 0.05). Total organic anion concentration did not explain the suppression of sour taste in solutions containing a blend of 3 organic acids with constant concentration of protonated organic acid species and hydrogen ions and variable organic anion concentrations ( R ²= 0.480, P  = 0.12). Sour taste suppression in these solutions seemed to be more closely related to sodium ions added in the form of NaOH ( R ²= 0.861, P  = 0.007). Addition of 20 mM NaCl to acid solutions resulted in significant suppression of sour taste ( P  = 0.016). However, sour taste did not decrease with further addition of NaCl up to 80 mM. Presence of sodium ions was clearly shown to decrease sour taste of organic acid solutions. Nonetheless, suppression of sour taste in pH adjusted single acid solutions was greater than what would be expected based on the sodium ion concentration alone, indicating an additional suppression mechanism may be involved.     

A Hypothesis for the Chemical Basis for Perception of Sour Taste

ABSTRACT: Sour taste has been considered the simplest of the basic tastes because it is elicited only by hydrogen ions. However, there is not a sufficiently clear understanding of that relationship to allow sour taste intensity to be predicted and rationally modified in foods. On the basis of analysis of sensory data from our laboratory and reanalysis of previously published data, we propose a new hypothesis for the chemical basis for sour taste perception: The intensity of sour taste perception in acid solutions or acidified foods is linearly related to the molar concentration of all organic acid species with at least 1 protonated carboxyl group plus the molar concentration of free hydrogen ions. This hypothesis implies that, on a molar basis, different organic acids will be equally sour, provided at least 1 carboxyl group is protonated. The major effect of pH on sour taste will be to determine the degree of protonation of organic acids. If this hypothesis is confirmed, it will provide a new understanding of the chemical basis for this basic taste perception and have broad usefulness in the formulation of products in which sour taste is an important component of flavor.     

The chemistry and physiology of sour taste--a review

ABSTRACT:  Sour taste is the key element in the flavor profile of food acidulants. Understanding the chemistry and physiology of sour taste is critical for efficient control of flavor in the formulation of acid and acidified foods. After a brief introduction to the main applications of food acidulants, several chemical parameters associated with sour taste are discussed. Special emphasis is given to hydrogen ions, protonated (undissociated) acid species, titratable acidity, anions, molar concentration, and physical and chemical properties of organic acids. This article also presents an overview of the physiology of sour taste and proposed theories for the transduction mechanisms for sour taste. The physiology of sour taste perception remains controversial and significant diversity exists among species with regard to cellular schemes used for detection of stimuli. The variety of mechanisms proposed, even within individual species, highlights the complexity of elucidating sour taste transduction. However, recent evidence suggests that at least one specific sour taste receptor protein has been identified.     

Antioxidant Properties of Edible Basidiomycete Phellinus igniarius in Submerged Cultures

ABSTRACT:  Dried mycelia and mycelia-free broths produced by submerged cultures of  Phellinus igniarius  under optimal culture conditions were extracted using methanol and hot water and investigated for antioxidant properties. Methanolic extracts from dried mycelia (MEM) and mycelia-free broth (MEB) showed significant antioxidant properties for all EC₅₀ values less than 10 mg/mL except for MEB in scavenging effects on DPPH radicals. Hot water extracts from dried mycelia (HWEM) were evidenced by their low EC₅₀ values (<10 mg/mL) to be effective in reducing power, chelating effect on ferrous ions, and scavenging effect on superoxide anions. α-tocopherol was mainly found in MEM and γ-tocopherol in MEB. Ascorbic acid and total flavonoids were abundant in methanolic extracts (MEM + MEB), whereas total phenols were rich in HWEM. An excellent correlation between contents of total phenols and EC₅₀ values was accomplished for antioxidant activity ( R ²= 0.996) and chelating ferrous ions ability ( R ²= 0.922).
Practical Application: In our paper, the products by submerged culture of  Phellinus igniarius  exhibited powerful antioxidant properties. Results told that extracts from fermenting products by  P. igniarius  might be good sources for antioxidant-related functional foods and pharmaceutical industries.     

EXAMINATION OF THE MICROBIAL STATUS OF SELECTED INDIGENOUS FERMENTED FOODS IN NIGERIA

Four Nigerian traditionally fermented foods (wara, nono, ogi and kununzaki) were evaluated for the presence of some microorganisms of public health concern. Among the dairy foods , Staphylococcus aureus and Klebsiella sp. were isolated from wara while Escherichia coli, Salmonella sp. and Klebsiella sp. were isolated from nono. The cereal-based fermented foods (ogi and kunu-zaki) contained Bacillus subtilis, E. coli, S. aureus, Klebsiella sp. and Enterococcus faecalis. The mesophilic aerobic counts were: 5 × 10⁵ for wara; nono, 1.53 × 10⁷; ogi, 3.6 × 10⁶ and kunu-zaki, 2.6 × 10⁶ cfu/mL. The enterobacteriaceae counts on nono, wara, ogi and kunu-zaki were 1.79 × 10⁷, 4.5 × 10⁵, 4.0 × 10⁵ and 1.2 × 10⁶ cfu/mL, respectively. No Vibrio count (detection limit: <10 cfu/mL) was recorded in all the food samples considered. The yeast and mold counts ranged from 1.0 × 10⁵– 3.31 × 10⁷ among the food products. The antimicrobial susceptibility patterns of the organisms isolated from dairy products (nono and wara) revealed that they were resistant to ampicillin (100%) and sensitive to gentamicin (100%) and nalidixic acid (100%). Most isolates from cereal based products (ogi and kunu-zaki) were 100% resistant to penicillin, ampicillin and chloramphenicol. This work highlights the need to maintain hygienic standards in the preparation of our locally fermented cereal and dairy foods.     

Phenolic compound composition and antioxidant activity of fruits of Rubus and Prunus species from Croatia

Two fraction, one containing flavonols, flavan-3-ols, phenolic acids and the other containing anthocyanins, were isolated from Rubus (red raspberry, blackberry) and Prunus (sweet cherry, sour cherry) fruits to study their phenol content by HPLC and antioxidant activity using the DPPH test. Raspberries and blackberries were characterised by catechins and ellagic acid derivatives; sour and sweet cherries by phenolic acids. All fruits had relatively high anthocyanin content. Anthocyanins contributed more to the antioxidant activity of all fruits (∼90%) than flavonols, flavan-3-ols and phenolic acids (∼10%). A biphasic reaction was observed between DPPH^• radicals and phenols, with 'fast' and 'slow' scavenging rates which might be important in the biological activity of these fruits. Sour cherries and blackberries which stand out with the highest total phenol content (1416 and 1040 mg kg⁻¹) had also the strongest antioxidant activity (EC₅₀ = 807 and 672 g of fruit per gram of DPPH) and can be considered as good source of dietary phenols.     

Radical scavenging activity and phenolic compounds in persimmon (Diospyros kaki L. cv. Mopan)

ABSTRACT:  The Mopan persimmon ( Diospyros kaki L. cv. Mopan) is the major cultivar of astringent persimmon in northern China. This study investigates the radical scavenging activity against ABTS and DPPH radical, and the content of total and individual phenolics (catechin, epicatechin, epigallocatechin, chlorogenic acid, caffeic acid, and gallic acid) with apple, grape, and tomato as controls. The radical scavenging activities against ABTS and DPPH radicals of the Mopan persimmon are 23.575 and 22.597 μm trolox eq/g f.w., respectively. These findings suggest that the Mopan persimmon's antioxidant activity is significantly ( P < 0.05) stronger than that of reference materials. The Mopan persimmon showed the highest content of total phenolics among the 4 materials tested. Significant correlations ( R ²= 0.993, P < 0.05, ABTS radical; R ²= 0.980, P < 0.05, DPPH radical) are found between the total phenolics and the radical scavenging activities. The total content of these 6 kinds of phenolics (catechin, epicatechin, epigallocatechin, chlorogenic acid, caffeic acid, and gallic acid) is significantly correlated ( R ²= 0.831, P < 0.05, ABTS radical; R ²= 0.745, P < 0.05, DPPH radical) with the individual radical scavenging activity of the 4 materials, although the total content of the 6 phenolics accounts for no more than 20% of the total phenolics in the Mopan persimmon. Gallic acid exhibits the strongest antioxidant activity in all 6 kinds of phenolics and its content is the largest in the Mopan persimmon, presumably being responsible for its much higher antioxidant activity as compared to apple, grape, and tomato.     

Nondestructive Analysis of Salt, Water, and Protein in Dried Salted Cod using Computed Tomography

ABSTRACT:  Computed X-ray tomography (CT) was used to determine NaCl, water, and protein levels in dried salted cod. Cod fillets were salted and dried, and CT was conducted several times during the process. Also, homogenized cod samples with a chemical composition covering the typical composition of cod during salting and drying were produced, and CT scanned. Chemical composition of fillet and model samples was predicted from CT images acquired at 80, 110, and 130 kV. The best average prediction errors (RMSECV) obtained for homogenized samples were 0.6% NaCl, 1.3% water, and 1.5% protein; all explained variances were R ²= 0.99 or above. The best RMSECVs and explained variances for cod fillet samples were 0.9% NaCl ( R ²= 0.96), 0.8% water ( R ²= 0.99), and 1.4% protein ( R ²= 0.79). Combining CT values from 2 or 3 voltages gave the best predictions except when predicting salt in cod fillet, where 1 voltage was sufficient.     

YIELD STRESS OF FOOD DISPERSIONS WITH THE VANE METHOD AT CONTROLLED SHEAR RATE AND SHEAR STRESS

The vane method was used to measure yield stresses of 15 commercial food dispersions under controlled shear stress (Cσ) and controlled shear rate (C     ) operating conditions. Magnitudes of yield stress (σ_σ) at Cσ were higher than those of yield stress (σ     ) at C     on tomato products and baby foods. There were good linear correlations ( R ²= 0.96, 0.86) between γ     and σ^σ for food dispersions with undisturbed structure (UDS) and with broken down structure (BDS). Data obtained under Cσ were also used to calculate shear moduli of foods.     

Effect of simultaneous high intensity ultraviolet irradiation and hydrogen peroxide on bacterial spores

High intensity (1.8 × 10³ mW/cm²) ultraviolet light irradiation of spores of Bacillus subtilis in the presence of 2.5% (w/v) hydrogen peroxide resulted in a rapid kill. Higher concentrations of hydrogen peroxide protected spores against the effects of irradiation. The results are discussed in relation to the use of simultaneous ultraviolet irradiation and hydrogen peroxide treatment as a method of sterilization.     

The Synergistic Taste Effect of Monosodium Glutamate and Disodium 5'-Inosinate

SUMMARY— The synergistic phenomenon between the taste of monosodium glutamate (MSG) and disodium 5'-inosinate (IMP) [7.5 H₂O] was studied and the relationship expressed as a mathematical model. The phenomenon could be measured quantitatively by fitting the proposed model to the results of the experiment.
The concentration of MSG equivalent to the taste intensity of that given by the mixture of MSG and the ribonucleotide is represented by the following equation:
y = u +γuv
where y is the equivalent taste intensity of the mixture in terms of g/dl of MSG, u is equal to g/dl of MSG in the given mixture, v is equal to g/dl of sodium 5'-inosinate in the given mixture, and γ is a constant.
The γ value for IMP was calculated from extensive sensory testing as 1.218 × 10⁸.     

Isolation and characterization of the microbial population of different South African kefir grains

Kefir, a slightly acidic fermented milk, is produced by adding lactic acid bacteria and yeasts, in the form of grains, to milk. The bacteria and yeasts present in the kefir grains are known to vary widely. Selective growth media and morphological and biochemical characteristics were used for the isolation and identification of the microbes present in the grains from eight different sources in South Africa. The kefir grains were activated in milk for only 24 h to prevent any changes in the microbial population of the grains. The microbial numbers varied between 6.4 × 10⁴ and 8.5 × 10 ⁸  cfu/g on the media selective for the bacterial species and between 1.5 × 10 ⁵ and 3.7 × 10 ⁸   cfu/g on the media selective for the yeast species. The bacterial genera that were identified included Lactobacillus , Leuconostoc and Lactococcus and the yeast genera included Zygosaccharomyces , Candida and Saccharomyces . The distribution frequencies of the microbes in the different grains were determined and most of the grains were dominated by two microbial species. No pediococci, acetic acid bacteria or propionibacteria were detected.     

Control of Listeria monocytogenes in ready-to-eat meats containing sodium levulinate, sodium lactate, or a combination of sodium lactate and sodium diacetate

ABSTRACT:  This study investigated the use of sodium levulinate to prevent outgrowth of Listeria monocytogenes in refrigerated ready-to-eat (RTE) meat products. Turkey breast roll and bologna were formulated to contain 1%, 2%, or 3% (w/w) sodium levulinate, 2% sodium lactate, a 2% combination of sodium lactate and sodium diacetate (1.875% sodium lactate and 0.125% sodium diacetate), or no antimicrobial (control). Samples of the RTE products were sliced, inoculated with 10² to 10³ CFU/cm² of a 5-strain cocktail of L. monocytogenes , vacuum packaged, and stored at refrigeration temperature for 0 to 12 wk. Counts reached 10⁸ CFU/cm² on control turkey roll product after 8 wk, and over 10⁷ CFU/cm² on control bologna after 12 wk. Addition of 2% or more sodium levulinate to turkey roll and 1% or more sodium levulinate to bologna completely prevented growth of L. monocytogenes during 12 wk of refrigerated storage. A consumer taste panel with pathogen-free samples found no differences in the overall liking among the preparations of turkey roll or among preparations of bologna. These results show that sodium levulinate is at least as effective at inhibiting outgrowth of L. monocytogenes in RTE meat products as the current industry standards of lactate or lactate and diacetate, and levulinate addition does not alter the overall liking of the RTE meat products.     

Enhancement of Fermentation Process in Pu-Erh Tea by Tea-Leaf Extract

ABSTRACT:  Pu-erh tea is known as a fermented tea and longer storage enhances its flavor and taste. Recently,  Aspergillu s,  Blastobotrys , and  Streptomyces  are found to play important roles in nutritional enhancement of Pu-erh tea by fermentation. Since water and temperature affect the microbial growth, we therefore explored the factors that might enhance the Pu-erh tea fermentation. The results showed that the addition of fresh tea-leaf extract (TLE) enhanced the withered tea fermentation (at 37 °C, 80 to 85% RH) as compared with the water only. Contents of statin, GABA, gallic acid, DPPH scavenging and polyphenol oxidase (PPO) activities were increased, whereas polyphenols and caffeine were decreased over 6 mo. TLE dose-dependently enhanced some of the qualities (that is, statin, PPO) of Pu-erh tea significantly as compared with the water only. The effect was related to the increase population of  A. niger  and  A. carbonarius  at 6 mo (from 7.6 ± 1.2 × 10¹ and 3.2 ± 1.3 × 10¹ to 3.1 ± 1.2 × 10⁶ and 2.4 ± 1.1 × 10⁵ colony forming units [CFU]/g, respectively). After drying process (90 °C, 30 min), the total microbial count from these samples returned to background level (3 ± 0.5 × 10² CFU/g). None of ochratoxin and fumonisin, toxins from  Aspergillus , was detected in the final products. The flavor and taste were also enhanced by treatment with TLE. The inoculation with  S. cinereus  Y11 with 2% TLE further enhanced these functional contents (about 2-fold increase of statin level) in the experimental Pu-erh tea. Therefore, this result may add a new process for Pu-erh tea manufacture.     

RADIATION STERILIZATION OF SPICES FOR HOSPITAL FOOD SERVICES AND PATIENT CARE

A survey of the commercial spices used by food services in a typical hospital environment revealed high contamination with microorganisms, i.e., 10⁴ to 10⁷ counts per gram. The predominant microorganisms were as followed (in colony counts/gram): (1) heat-resistant bacterial spores in black pepper, 1 × 10⁷; thyme, 2 × 10⁶; anise, 7 × 10⁴; curry powder, 4 × 10⁵; poultry seasoning, 8 × 10⁴; pickling spice, cardamom, and cumin, 1.5–3 × 10⁴; (2) mixed populations of vegetative cells and bacterial spores in cumin, 1 × 10⁶; (3) molds in cream of tartar, 2 × 10⁴. Sterility of food may be important in a hospital setting, especially in the care of immunocompromised patients. To eliminate the organisms, we recommend radiation treatment, accompanied by appropriate microbiological quality control. On the basis of radiation survival data, the composite natural flora would be reduced to the level of "commercial sterility" (defined as less than 10 organisms per gram((Kiss 1982) by the following minimum radiation doses (in kGy): black pepper, 13; thyme, 13; cumin, 12; anise, 10; curry, 7.3; pickling spice, 7; poultry seasoning, 6; cardamom, 9.4; cream of tartar, 4. For practical purposes, two dose levels can be recommended for treatment of spices in the hospital environment, low = 6–10 kGy and high = 10–15 kGy.     

Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products

ABSTRACT:  The impact of sodium nitrite (NaNO₂) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO₂) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 × 10³ L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 °C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 °C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 × 10⁴ to 1 × 10⁵ CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO₂ (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX^® System (DuPont™ Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria -positive food samples and were consistently superior to and significantly different ( P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.     

IDENTIFICATION AND CHARACTERIZATION OF MATRIX METALLOPROTEINASES FROM THE SARCOPLASMIC FRACTION OF COMMON CARP (CYPRINUS CARPIO) DARK MUSCLE

Two gelatin hydrolyzing proteinases in the sarcoplasmic fraction of common carp muscle were detected using gelatin zymography. A comparative study shows that the gelatin hydrolyzing activity in dark muscle is obviously higher than that in white muscle. The enzymes can transform to their active forms after treated by aminophenylmercuric acetate, an activator of matrix metalloproteinases. Optimum pH and temperature of these enzymes were around 8.0 and 40C using gelatin as substrate. Metalloproteinase inhibitors (ethylenediaminetetraacetic acid and ethylene glycol-bis (2-aminoethylother)-N, N, N', N'-tetraacetic acid) completely suppressed the activities and 1,10-phenanthroline also showed great inhibitory effects. However, other proteinase inhibitors, such as soybean trypsin inhibitor, benzamidine, E-64 and pepstatin A, did not show any effect. Metal ions Ca^{2 +} and Zn^{2 +} are essential for these gelatinolytic activities. All these facts indicate that these proteinases are matrix metalloproteinases. Furthermore, these enzymes hydrolyze collagen effectively and maybe thus proposed to be responsible for the tenderization of fish muscle during the postmortem stage.