Type Of Acidulant Research Articles

Foodborne pathogen inactivation in fruit juices utilizing commercial scale high-pressure processing: Effects of acidulants and pH.

The effects of juice pH, type of acidulant, and post-treatment refrigeration on the high-pressure processing (HPP) inactivation of Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in acid beverages were evaluated. Inoculated apple, orange, and grape juices (at their original pH and adjusted to pH 4.00, 4.50, and 5.00) were treated at 550 MPa for 1 min at 5 °C. In addition, inoculated model solutions acidified to a pH of 5.00 with acetic, citric, malic, and tartaric acids were treated at 400 MPa for 1 min at 5 °C. The effect of refrigerated storage for 24 h after treatment on pathogen inactivation in both experiments was also assessed. A greater than 5-log reduction of the three pathogens inoculated was achieved in all juices immediately after HPP at the juices' original pH, and of L. monocytogenes under all experimental conditions. Refrigerated storage for 24 h after HPP treatment improved the inactivation of E. coli O157:H7, to >5-log reduction, at pH 4.00 in apple juice and of Salmonella in the three juices at pH 4.00. The type of acidulant did not significantly (p > 0.01) affect E. coli or Salmonella inactivation in acidified model solutions but a greater than 5-log reduction after HPP was only achieved for L. monocytogenes when acetic acid was used. The effectiveness of HPP for pathogen inactivation depended largely on product pH and the target pathogen of concern.

Effect of fruit acidulants and storage conditions on the physicochemical, microbiological and sensory characteristics of paneer

Paneer is an unripened soft cheese mainly used by Indians and Pakistans, and it does not require the rennet enzyme. It is prepared by coagulating heated milk with acid. However, fresh paneer has a short shelf life of up to 2 days at ambient temperature. In this study, paneer was prepared from lemon and amla fruit acidulants and stored at room and refrigeration temperatures. Then, the paneer samples were analysed for their physicochemical properties, texture profile, microbiological counts and sensory attributes during storage at room and refrigeration temperatures. The type of acidulant, storage temperature and time significantly affected the paneer's physicochemical properties (p<0.05). However, the changes were rapid in samples stored at room temperature. Moreover, paneer coagulated using fruit acidulants had a higher shelf life and retention of functional properties. Furthermore, the paneer from fruit acidulants had high acceptability, comparable to the control, usually made from citric acid. Therefore, preparing paneer from fruit acidulants with improved functionality, shelf life, and acceptability is possible. Thus, adapting the technology of making paneer with acidulant fruits would reduce milk and fruit postharvest loss, promote a sustainable diet and create market potential for the novel milk product in India and the world at large.

Optimum Physico-Chemical and Processing Parameters for the Preservation of King Coconut Water

King coconut (Cocos nucifera var. aurantiaca) water is a natural, nutritious and healthy beverage. However, it is underutilized in terms of value addition with extended shelf life. Therefore, an attempt was made to develop the physico-chemical and processing parameters for the value addition of King coconut water with extended shelf life. King coconut water was analyzed for sugar, minerals and vitamin C content based on reviewed methods. Studies were conducted to identify the optimum pH, total soluble solid (TSS), type of acidulant and pasteurization conditions based on sensory properties of the product using semi trained panelists. Processed King coconut water was packed in three different packages and stored at refrigerated (4°C) condition for two months. Changes in pH, TSS and titratable acidity were evaluated in two weeks intervals throughout the storage period. The results showed that optimum pH, TSS, type of acidulant and pasteurization conditions were 4.4, 9, malic acid and 70˚C/15 sec., respectively. The product was microbiologically (less than 50 CFU/ml) safe for consumption even after 8 weeks of storage. These storage studies revealed that the changes in pH, TSS and titratble acidity of King coconut water packed in three packaging materials had no significant difference (p<0.05) during refrigerated storage.

Comparison of acids on the induction of an Acid Tolerance Response in Salmonellatyphimurium, consequences for food safety

Salmonella typhimurium inactivation at pH 3.0 in Brain Heart Infusion (BHI) and Meat Extract (ME) was studied using stationary-phase cells grown in non-acidified BHI (pH 7.4) and ME (pH 6.6) and acidified BHI and ME at pH values of 6.4, 5.4 and 4.5 with acetic, ascorbic, citric, lactic, malic and hydrochloric acids. Cells grown in buffered BHI (pH 7.0) were used as non-acid adapted control cells. Acid adapted S. typhimurium cells obtained in both media (BHI and ME) were more resistant to extremely acidic conditions when ME was used as challenge medium, although the ability of S. typhimurium to survive extreme pH conditions also depended on growth medium and type of acidulant used. Acid adapted cells grown in BHI developed a higher Acid Tolerance Response (ATR) than those grown in ME. When cells were grown in acidified BHI, no bacterial inactivation was observed after three hours of acid challenge in ME. Furthermore, when cells were grown in acidified ME at pH values of 6.4 and 5.4, D-values obtained using ME as challenge medium were, respectively, 6–9 and 10–15 fold higher than those found when BHI was used as challenge medium. In all cases, the order of acids in inducing the ATR was citric > acetic > lactic > malic ⩾ hydrochloric > ascorbic. These findings represent a concern for food safety as the increase in the acid resistance of acid adapted cells could allow for S. typhimurium survival in the strong acidic environment of the gastrointestinal tract.

Listeria innocua and Lactobacillus delbrueckii subsp. bulgaricus employ different strategies to cope with acid stress

Responses of Listeria innocua and Lactobacillus delbrueckii subsp. bulgaricus to a rapid change in extracellular pH (pH ex) from pH ex 6 to a range of concentrations down to pH ex 3.0 were examined, using HCl and lactic acid (LA) as acidulants. A new fluorescent probe 5-(and-6)-carboxy-2′, 7′-dichlorofluorescein diacetate succinimidyl ester (CDCFDA-SE) was employed that enabled reliable measurements of intracellular pH (pH i) to a minimum pH i of 4.0. Changes in pH i and H + fluxes from immobilised bacteria were measured using fluorescence ratio imaging microscopy (FRIM) and a non-invasive ion flux measuring technique (MIFE), respectively. L. innocua maintained a relatively constant pH i of 5.5–6.1 at pH ex 4 and 5 via H + extrusion. In contrast, L. delbrueckii subsp. bulgaricus progressively lowered pH i towards pH ex over the entire pH ex range examined. The type of acidulant used influenced pH regulation with both pH i and H +-fluxes being more severely affected by LA compared to HCl. Overall, our data demonstrated different adaptive strategies in these two bacteria. While L. innocua expels protons to maintain a constant pH i, L. delbrueckii subsp. bulgaricus allows proton entry after acidic treatment so that pH i follows pH ex.

Heat resistance of Bacillus cereus spores in carrot extract acidified with different acidulants

The effect of acidification of carrot extract on the heat resistance of Bacillus cereus (ATCC 7004 and 4342) spores was studied. Malic, acetic, citric, ascorbic, lactic and hydrochloric acids were used as acidulants. Thermal resistance experiments were performed over the range 82–108 °C with continuous monitoring of pH. Non-acidified carrot extract (pH 5.2) had a protective effect on the thermal inactivation of spores when compared with the reference McIlvaine buffer at the same pH value. Acidification of carrot extract reduced the D-values obtained for spores, this effect occurring whatever the type of acidulant used. For both strains and all treatment temperatures, as pH decreased the D-values decreased exponentially over the pH range studied (5.2–4.0), yielding straight lines, basically parallel, with an average slope of 0.203 ± 0.023. Significant decreases in survivor counts and apparent D-values were observed when injured spores were recovered using the usual recovery medium containing carrot extract.

Sensitivity of Acid-Adapted and Acid-Shocked Shigella flexneri to Reduced pH Achieved with Acetic, Lactic, and Propionic Acids

Survival and growth characteristics of unadapted, acid-adapted, and acid-shocked Shigella flexneri 2a cells in acidified (pH 3.5 to 5.5) tryptic soy broth with 0.25% glucose (TSB) and tryptic soy agar (TSA) were determined. S. flexneri was grown at 37°C for 18 h in tryptic soy broth without glucose (TSBNG) (unadapted) and TSBNG supplemented with 1% glucose (TSBG) (acid-adapted). Cells grown in TSBNG were acid shocked by adjusting 16-h cultures to pH 5.05±0.05 with lactic acid. Cells were then inoculated into TSB acidified with acetic, lactic, or propionic acids to pH 5.5, 4.5, or 3.5 and incubated at 37°C for 6 h. The order of lethality at a given pH was lactic acid < acetic acid < propionic acid. Significantly (P ≤ 0.05) higher numbers of acid-adapted cells, compared to acid-shocked and unadapted cells, were recovered from TSB acidified (pH 3.5) with lactic or acetic acids. None of the cells survived a 30-min exposure in TSB acidified with propionic acid to pH 3.5. When the three cell types were plated on TSA acidified with lactic, acetic, or propionic acids at pH ≤ 4.5, ≤5.5, and ≤5.5, respectively, visible colonies were not detected. Viable unadapted, acid-adapted, and acid-shocked cells were, however, recovered from TSA acidified with all three acids at pH ≥ 4.5. Acid-adapted and, to a lesser extent, acid-shocked cells survived at lower pH than did unadapted cells, indicating that prior exposure to mild acidic environment results in increased acid resistance. Survival of S. flexneri at a given pH was influenced by the type of acidulant used, a response characteristic exhibited by other gram-negative enteric pathogens.

Tolerance of acid-adapted and non-adapted Escherichia coli O157:H7 cells to reduced pH as affected by type of acidulant.

A study was carried out to determine if three strains of Escherichia coli O157:H7 grown (18 h) in Tryptic Soy Broth (TSB) and TSB supplemented with 1.25% glucose (TSBG), i.e. unadapted and acid-adapted cells, respectively, exhibited changes in tolerance to reduced pH when plated on Tryptic Soy Agar (TSA) acidified (pH 3.9, 4.2, 4.5, 4.8, 5.1 and 5.4) with acetic, citric or malic acids. All test strains grew well on TSA acidified with acetic acid at pH > or = 5.4 or malic acid at pH > or = 4.5; two strains grew on TSA acidified with citric acid at pH > or = 4.5, while the third strain grew at pH > or = 4.8. Acid-adapted and control (unadapted) cells differed little in their ability to form visible colonies on TSA containing the same acid at the same pH. However, on plates not showing visible colonies, acid-adapted cells retained higher viability than unadapted cells when plated on acidified TSA. Growth of acid-adapted and control cells of E. coli O157:H7 inoculated into TSB containing acetic acid (pH 5.4 and 5.7) and citric or malic acids (pH 4.2 and 4.5) was also studied. There was essentially no difference in growth characteristics of the two types of cells in TSB acidified at the same pH with a given acid. Tolerance of acid-adapted and control cells on subsequent exposure to low pH is influenced by the type of acidulant. The order of sensitivity at a given pH is acetic > citric > malic acid. When performing acid challenge studies to determine survival and growth characteristics of E. coli O157:H7 in foods, consideration should be given to the type of acid to which cells have been exposed previously, the procedure used to achieve acidic environments and possible differences in response among strains. The use of strains less affected by pH than type of acidulant or vice versa could result in an underestimation of the potential for survival and growth of E. coli O157:H7 in acid foods.

Modification of Saccharomyces cerevisiae thermotolerance following rapid exposure to acid stress

Thermotolerance was induced in cells of Saccharomyces cerevisiae YPH499 pre-exposed, during 10 min and in the presence of glucose, to a mild acid-stress with HCl at pH 3.5. Thermotolerance was not induced in cells exposed to a severe acid stress by 50 mM acetic acid at pH 3.5, or HCl at pH 2.5 or pH 2.0. Yeast cells pre-incubated under glucose starvation were found to be more tolerant to a lethal heat stress than cells pre-incubated in glucose-supplemented media, despite the pH value of the media (range 2.0–6.5) and the type of acidulant used (HCl or acetic acid). Moreover, the high thermotolerance exhibited by cells pre-incubated at pH 6.5 for 10 min under glucose starvation was not significantly modified by the acidification of the pre-incubation medium. Results are discussed based on the effect that glucose and a mild or severe acid stress have on plasma membrane H +-ATPase activity and on cytosolic pH values, estimated in a previous work.

Heat Resistance of Bacillus subtilis and Bacillus coagulans: Effect of Sporulation Temperature in Foods With Various Acidulants

The influence of the sporulation temperature (35 and 52°C) on the effect of different acidulants on the heat resistance of Bacillus subtilis and Bacillus coagulans in homogenized tomato and asparagus at pH 4 was investigated. Several acidulants (hydrochloric, citric, acetic, lactic, and malic acids and glucono-ä-lactone) currently used by the canning industry to lower the pH of some vegetables before processing were studied. The sporulation temperature determined the response of these microorganisms to the type of acidulant. While the heat resistance of spores sporulated at 35°C was the same at all heating temperatures tried, regardless the type of acidulant, that of spores sporulated at 52°C was two- to fivefold lower when lactic or acetic acids were used. This decrease in heat resistance was the same at every temperature over the whole range of heating temperatures tested. The z values obtained with each microorganism were the same for a given heating menstruum, regardless the type of acidulant used.

D Values of Bacillus stearothermophilus Spores as a Function of pH and Recovery Medium Acidulant

The effect of the pH and the type of acidulant (citric acid or glucono-δ-lactone) of the recovery medium on the thermal resistance of Bacillus stearothermophilus ATCC 12980 was studied. The spores were heated in bidistilled water as a reference substrate and in acidified mushroom extract using citric acid or glucono-δ-lactone as acidulants (pH 6.2) and subcultured in reference (pH 7) and acidified (pH 6.2) media. A period of treatment-dependent pH sensitization was observed in heat-treated spores. In all cases, D values were lower in the acidified recovery medium than those obtained in the reference medium, but the type of acidulant used in the recovery medium had no influence on the D values. No influence on z values was observed as a consequence of the different recovery media, but they changed within a range of 7 to 10°C as a function of the different heating substrates. Glucono-δ-lactone proved to be as effective as citric acid in controlling the microbiological spoilage of foods. The pH has a great influence on decreasing the D values, mainly when acidification of the substrate and acidification of the recovery medium are combined. Consequently, it would be appropriate to take this effect into account in process calculations or validation.

Growth and Heat Resistance of Clostridium SporogenesPA 3679 Spores Heated and Recovered in Acidified Media

The effect of subculture medium composition (pH, type of acidulant, presence of EDTA) on the germination of spores of Clostridium sporogenes PA 3679, both with and without heat treatment in phosphate buffer (30 s at l25°C), was studied. Additionally, the effect of the heating medium substrate and pH and subculture medium pH and composition on the heat resistance of the spores was evaluated. The results indicate that the pH of the recovery medium and the type of acidulant have significant effects (P ≤ 0.05) on counts of PA 3679. Adding EDTA only increases inhibition of this microorganism when the pH is near neutral. For a given pH level, citric acid provided greater inhibiting power than glucono-δ-lactone, although the percentage of undissociated acid was less for citric acid. No growth was observed at pH 5.7, although in the case of glucono-δ-lactone sporadic colony development was seen in some plates. The pH of the heating medium acidified with glucono-δ-lactone did not affect the heat-resistance parameters (D and z) of spores heated to temperatures between 121 and 140°C in relation to the unacidified extract. Nor did we see any significant influence of the composition and pH of the recovery medium on these heat-resistance parameters when comparing the results with those obtained using the usual recovery medium.

Growth and survival of Escherichia coli O157:H7 under acidic conditions

The effect of pH reduction with acetic (pH 5.2), citric (pH 4.0), lactic (pH 4.7), malic (pH 4.0), mandelic (pH 5.0), or tartaric (pH 4.1) acid on growth and survival of Escherichia coli O157:H7 in tryptic soy broth with 0.6% yeast extract held at 25, 10, or 4 degrees C for 56 days was determined. Triplicate flasks were prepared for each acid treatment at each temperature. At 25 degrees C, populations increased 2 to 4 log10 CFU/ml in all treatments except that with mandelic acid, whereas no growth occurred at 10 or 4 degrees C in any treatments except the control. However, at all sampling times, higher (P < 0.05) populations were recovered from treatments held at 4 degrees C than from those held at 10 degrees C. At 10 degrees C, E. coli O157:H7 was inactivated at higher rates in citric, malic, and mandelic acid treatments than in the other treatments. At the pH values tested, the presence of the organic acids enhanced survival of the pathogen at 4 degrees C compared with the unacidified control. E. coli O157:H7 has the ability to survive in acidic conditions (pH, > or = 4.0) for up to 56 days, but survival is affected by type of acidulant and temperature.

Thermal resistance characteristics of PA 3679 in the temperature range of 110–121°C as affected by pH, type of acidulant and substrate

The influence of mushroom extract, acidification and type of acidulant (citric acid or glucono-δ-lactone) on the thermal resistance of PA 3679 spores has been studied. The pH values were 7 (phosphate buffer), 6.7 (non acidified mushroom extract), 6.22, 5.34 and 4.65 (acidified mushroom extract). Spores were less heat resistant in the non-acidified mushroom extract than in phosphate buffer. However, acidification of the extract had an effect on D values which was dependent on the specific pH. At pH 6.22, D values were higher than those in non-acidified extract, for both type of acidulants, but the difference between D values in both substrates was affected by temperature, the higher the temperature, the less the difference. Acidification at other pH levels did not significantly affect D values obtained, neither did the type of acidulant. The z value ranged from 9.79 to 12.09°C for citric acid and from 8.18 to 10.18°C for glucono-δ-lactone. When pH was decreased the z value increased for both acidulants.