Effect of vanillin concentration,pH and incubation temperature onAspergillus flavus,Aspergillus niger,Aspergillus ochraceusandAspergillus parasiticusgrowth

The effects of incubation temperature (10–30°C), pH (3.0–4.0) and vanillin concentration (350–1200ppm) on the growth ofAspergillus flavus, Aspergillus niger, Aspergillus ochraceusandAspergillus parasiticuswere evaluated using potato–dextrose agar adjusted to water activity (a_w) 0.98. The radial growth rates after a lag period followed zero-order kinetics with constants that varied from 0 (no growth) to 0.63mmh⁻¹. The lag period depended on vanillin concentration, pH and incubation temperature. The germination time and the radial growth rates were significantly affected by the three studied variables (P<0.001). The inhibitory conditions (no growth after 30 days) depend on the type of mold. A niger, the most resistant species, was inhibited at 15°C, pH 3.0 and 1000ppm. ForA. ochraceus, the most sensitive, the inhibitory conditions in presence of 500ppm vanillin were pH 3.0 and temperature ≤25°C or pH 4.0 with temperature ≤15°C.     

Effect of Sodium Erythorbate on Residual Nitrite, pH and Bacterial Growth in Liver Sausage Formulated with Different Levels of Mechanically Separated Pork

Some microbiological, chemical, and physical characteristics of liver sausage formulated with 0, 25, 50, and 75% mechanically separated pork (MSP), 156 ppm sodium nitrite and 0 or 550 ppm sodium erythorbate were studied during refrigerated storage (5°C, 6 days) and subsequent elevated-temperature holding (20–24°C, 48 hr). Growth of inoculated Clostridium sporogenes was inhibited by 156 ppm nitrite in all sausages even after 48 hr at 20–24°C, regardless of MSP level. Growth of aerobic mesophiles and facultative anaerobes at 20–24°C was also inhibited in sausage formulated with 156 ppm nitrite and 550 ppm erythorbate. Erythorbate addition and increased MSP levels resulted in higher Hunter a color values. Residual nitrite, pH values, and total iron content of liver sausage increased with increasing MSP content.     

COMBINED EFFECTS OF ELECTRICAL STIMULATION AND METHODS OF MEAT PRESERVATION UPON THE SURVIVAL OF BACTERIA1

The synergistic effect caused by electrical stimulation and methods of meat processing on microbial numbers in meat was investigated. Electrical stimulation in all experiments reduced initial bacterial numbers and lowered tissue pH. Under the conditions of this research, no synergistic effect could be proven for electrical stimulation and 3% salt or 3% salt and 200 ppm of nitrite or for storage at -21°C. However, a synergistic effect was observed for electrical stimulation and heating at 60°C. This reduction in thermoresistance caused by electrical stimulation did not appear to be caused by the lowering of pH of the heating media.     

Modeling the Time to Fail of Peach Nectars Formulated by Hurdle Technology

The use of regression with life-data is helpful to observe whether one or more factors affect the failure time (spoilage) of a product, obtaining a model that predicts the time to fail (TTF). TTF models link kinetic (lag time) and probabilistic (growth /no-growth prediction) models for selected formulation/storage conditions. Our objective was to assess the individual and combined effects of pH, a_w, and the incorporation of potassium sorbate (KS) or sodium benzoate (BNa) at selected concentrations on the microbial stability of peach nectar during storage at 25°C, in order to model and predict TTF. Peach nectars were formulated with 40% fruit pulp and the necessary sucrose syrup and citric acid to attain a_w 0.96, 0.97, or 0.98 and pH 3.0, 3.5, or 4.0; while 0, 500, or 1000ppm of KS or BNa were added. Nectars were stored for 180 days in glass jars at 25°C, and periodically analyzed (standard plate as well as yeast and mould counts). The experimental design and analyses were replicated three times. Storage times that revealed microbial populations higher than 10⁴ CFU/mL and signs of spoilage were registered to model TTF by survival analysis. From the 54 combinations tested, 9 formulations (without antimicrobials) exhibited early spoilage (<5 days). For the combinations formulated with 500ppm of BNa, spoilage was detected after 30 days; much longer spoilage times were observed for nectars with 1000ppm of KS or BNa. In general, KS was more effective than BNa in delaying spoilage when 1000ppm were added. TTF models included individual and interaction effects of the evaluated factors and revealed good agreement among experimental and predicted data (R²>0.90). Survival analysis through TTF models can be used to predict spoilage time under specific factor combinations or to select factor levels for a specific shelf-life of peach nectars.     

Effects of pH, Storage Time and Temperature on the Tin Content of Single Strength Canned Grapefruit Juice

Grapefruit juice modified to pH 3.0, 3.5 and 4.0 and stored at 4, 21, 27, 32 and 38°C manifested a consistent two-stage pattern for tin uptake. The first stage consisted of a rapid (3 wk) uptake of tin (from 12 to approximately 100 ppm) and was relatively independent of juice pH or storage temperature. In the second stage, the increase in tin concentrations was extremely temperature dependent and only slightly pH dependent. Canned grapefruit juice should be stored below 27°C to insure tin contents do not exceed the Codex maximum of 250 ppm. In a survey of 55 commercially canned grapefruit juice samples stored 1-8 months under commercial conditions, tin concentrations ranged from 34-180 ppm.     

Quality Changes of Shrimp (Pandalus borealis) Stored under Different Cooling Conditions

The influence of different cooling techniques and storage temperatures (‐1.5 °C or 1.5 °C) to prolong the shelf life of shrimp was evaluated by sensory analysis, physical methods, chemical analysis, and microbial analysis. Storage in liquid ice was more effective than flake ice or brine mixed with flake ice in delaying spoilage of the shrimp by slowing down microbial growth and formation of total volatile basic nitrogen (TVB‐N) and trimethylamine (TMA). Total viable counts (TVC) showed that bacteria grew most quickly in shrimp stored in flake ice and in brine mixed with flake ice, followed by those in liquid ice at 1.5 °C and ‐1.5 °C, respectively. Lowest counts were observed in shrimp stored in liquid ice at ‐1.5 °C where the lag phase of growth was apparently extended at the beginning of storage. Principal component analysis (PCA) showed a good correlation between quality indicators related to microbial growth, TVC, pH, TVB‐N, TMA, responses of an electronic nose and sensory evaluation.     

Escherichia coli O157: H7 Growth in Laboratory Media as Affected by Phenolic Antioxidants

Five strains of Escherichia coli O157:H7 with ATCC 11775 E. coli were grown in brain heart infusion (BHI) broth (pH 5.8, adjusted with citric acid) and treated with butylated hydroxyanisole (BHA), butylated hy-droxytoluene (BHT), tertiary butylhydroquinone (TBHQ), and propyl gallate (PG) individually or combined. Additives ranged from 100–400 ppm with inocula levels between 5 and 104 CFU/mL in tissue culture plates or in flasks; samples were incubated at 4°C or 37°C for 24 hr. Additive antimicrobial efficacy varied with inoculum level and incubation temperature. BHA at <200 ppm was bactericidal on all strains. Poly-hydroxyl additives (TBHQ, PG) were less effective at 4°C. BHA-BHT combinations were synergistic at 4°C.     

Effects of an edible coating, fungicide and cold storage on microbial spoilage of cherries

The effects of an edible coating, i.e., Semperfresh^TM, fungicide, i.e., Imazalil, and cold storage on microbial spoilage of cherries were studied. Two group of cherries (Prunus avium) were coated just after harvest with 1% and 2% Semperfresh^TM fruit coating. Two other group of cherries were treated with 75 ppm and 150 ppm concentrations of Imazalil and then coated with a 1% concentration of Semperfresh^TM fruit coating. Half of the cherries from each of the above groups was stored at ambient temperature (~30Dž °C) and at 40-50% relative humidity, the other half of the cherries was stored at cold storage (0 °C) and at 95-98% relative humidity. Each group was analyzed for the mold and yeast count. The Semperfresh^TM edible coating resulted in a slightly increased fungal spoilage of fruits. Imazalil fungicide treatment clearly decreased and retarded the microbial spoilage of fruits. As a result, low temperature storage was the most effective solution for both microbial spoilage and delay in the ripening.     

Inhibition of Red Discoloration in Cooked, Vacuum Packaged Bratwurst

A red discoloration sometimes occurs in vacuum-packaged bratwurst during storage. We attempted to characterize the red pigment and determine the effect of pH, cooking temperature, and sodium lactate on its incidence. Myoglobin was the red pigment in discolored samples. Myoglobin levels were lower in samples at pH (5.5) or cooked to 74°C. Discoloration was associated with microbial growth. Frozen samples had no red discoloration after 4 wks. Discoloration was not observed in bratwurst containing 2% sodium lactate and cooked to 74°C. In preventing red discoloration cooking to 74°C without lactate was as effective as cooking to 68°C with lactate.     

Influence of storage temperature on the quality of beef liver; pH as a reliable indicator of beef liver spoilage

The development of the microbial flora specifically involved in the spoilage of sliced beef livers packaged and stored under aerobic conditions at 0 and 3 °C for 14 days was studied. Changes in the pH value of the product were also determined. The possibility that pH value could be considered as a quick and reliable indicator of incipient spoilage was particularly considered. All microbial groups (except micrococci) showed differences in their rates of growth between 0 and 3 °C. Pseudomonads and lactic acid bacteria were the main components of the spoilage flora. When the 37 °C aerobic plate counts (APCs) reached 10⁵–10⁶ CFU g⁻¹ and the 20 °C APCs and pseudomonad counts reached 10⁶–10⁷ CFU g⁻¹, visible surface colonies (VSCs) were observed. The presence of VSCs is the most important criterion to determine organoleptic beef liver spoilage and has hence enabled us to establish a shelf-life of up to 8–10 and 5.5–6.5 days for samples stored at 0 and 3 °C respectively. Our study shows that the determination of pH, which is simple, economical and rapid, is capable of giving a reliable estimate of the spoilage status of beef livers. pH values lower than 6.15 may be considered as indicative of beef liver spoilage. © 1999 Society of Chemical Industry     

DEVELOPMENT OF A MASHING PROFILE FOR THE USE OF MICROBIAL ENZYMES IN BREWING WITH RAW SORGHUM (80%) AND MALTED BARLEY OR SORGHUM MALT (20%)

Different time and temperature programmes were used to evaluate the production of hot water extract (HWE) and free amino nitrogen (FAN) from mashes containing raw sorghum and either malted sorghum or malted barley in the presence of microbial enzymes. Two malted varieties of sorghum (SK 5912 and Zaria) were used. The former gave higher HWE but lower FAN than the latter. Sorghum malts were unable to provide enzyme activity for starch extraction and exogenous enzymes were always needed. Seventeen commercially available enzyme preparations were assessed. A double-mash process was developed. Inclusion of calcium ions (200 ppm) was beneficial but adjustment of mash pH had little effect. Raw sorghum was gelatinised at 100°C for 30–40 min in the presence of a heat-stable α-amylase followed by mixing with a malt mash (started at B0°C) to give a temperature of 65°C with a total mash time of 167 min (127 min from mixing the mashes). The inclusion of a single commercial enzyme preparation (containing both proteolytic and amylolytic activities) was sufficient to achieve satisfactory HWE and FAN. Addition of different activities or combinations of activities gave no significant advantages. To obtain levels of FAN of 100–140 mg/l however excessive amounts of enzymes were required.     

Thermal Destruction of 5-Methyltetrahydrofolic Acid in Buffer and Model Food Systems

Thermal kinetic data (rate constants, k, and activation energies, Ea) for 5-Methyltetrahydrofolic acid (5-CH₃-H₄PteGlu) were determined in citrate buffers (pH 3-6) and in model food systems between 100° and 140°C. As pH increased from 3.0 to 6.0, the rate constants decreased as the temperature increased from 100° to 130°C, the rate constants increased. Ea values were 19.0, 17.0, 19.7 and 19.8 kcal/mole at pH 3, 4, 5 and 6, respectively. In the model food systems, the Ea values (kcal/mole) were 7.85 in apple juice and 10.6 in tomato juice. When dissolved oxygen content was reduced to 5.3 ppm, the stability of the 5-CH₃H₄PteGlu was increased substantially.     

Storage stability of pineapple slices preserved by combined methods

Storage stability during 3 months was evaluated for pineapple slices preserved by combined methods (blanching for 1 min with saturated vapour, a_w reduction by osmotic concentration in sucrose syrup, pH reduction by addition of citric acid, and the addition of 1000 parts per million (ppm) of potassium sorbate and 150 ppm of sodium bisulphite). Pineapple slices were microbiologically sound and their moisture content, °Brix, pH and a_w remained almost constant during storage with mean values of 71.8%, 26.1, 3.65 and 0.978, respectively. Total sulphite and potassium sorbate concentrations of the pineapple slices were reduced during storage at 5 and 25 °C, being final concentrations 51% and 38% and 63% and 48% of the initial concentrations, respectively. Colour, texture and sensory evaluation revealed that there were no significant (P < 0.05) changes between samples stored at 5 or 25 °C. Good overall acceptability (initial mean score 7.21) of preserved pineapple slices even after 3 months storage at 25 °C (final mean score 7.02) was observed.     

Phytate Reduction in Brown Beans (Phaseolus vulgaris L.)

Brown beans (Phaseolus vulgaris L.) were subjected to treatments to evaluate effects of pH, temperature, CaCl₂, tannase and fermentation on degradation of phytate. Soaking was performed at 21°C, 37°C and 55°C at pH 4.0, 6.0, 6.4, 7.0, and 8.0. Optimal conditions for phytate degradation were pH 7.0 and 55°C. After soaking 4, 8 or 17 hr at these conditions 79%, 87% and 98% of phytate was degraded, respectively. Addition of tannase enhanced reduction of phytate. Fermentation of presoaked whole beans resulted in reduction of 88% of phytate after 48 hr.     

Inhibition of Salmonella by Sodium Nitrite and Potassium Sorbate in Frankfurters

All beef frankfurters and beef-pork frankfurters containing various levels of sodium nitrite (0, 50, or 156 ppm) or potassium sorbate (0, 0.26, or 0.39%) alone or in combination (50 ppm nitrite + 0.26% sorbate) were prepared. Frankfurters were inoculated with nalidixic acid resistant Salmonella and incubated at 15°C and 27°C for up to 21 days. Frankfurters formulated with 50 or 156 ppm nitrite and incubated at 27°C, or 50 ppm nitrite and incubated at 15°C failed to inhibit the growth of Salmonella. Sorbate alone and sorbate in combination with 50 ppm nitrite were equally effective in inhibiting Salmonella at either temperature and were equivalent to 156 ppm nitrite in inhibiting Salmonella at 15°C.     

Antioxidant effect of turmeric powder,nitrite and ascorbic acid on stored chicken mince

This investigation was carried out to evaluate the antioxidant effect of turmeric (turmeric 1000 ppm, turmeric 5000 ppm), nitrite (nitrite 200 ppm) and ascorbic acid (ascorbic acid 500 ppm) on raw minced chicken stored at 4 ± 1 °C. Physicochemical properties [pH, water activity, cooking loss, thiobarbituric acid (TBA) value, peroxide value (PV), free fatty acid (FFA)] were evaluated on 0, 2, 4 and 6th day of storage. Highly significant differences (P < 0.01) in pH, TBA value, PV and FFA value were noticed between treatments and between storage periods. TBA values were observed to be lowest for nitrite 200 ppm and then turmeric 5000 ppm, and there was no significant difference between nitrite 200 ppm and turmeric 5000 ppm, and both were superior to ascorbic acid 500 ppm and turmeric 1000 ppm. Among different treatments, PV was found to be lowest in turmeric 5000 ppm and highest in nitrite 200 ppm. FFA value was found to be lowest in turmeric 5000 ppm and highest in ascorbic acid 500 ppm among all treated samples. It can be concluded that turmeric has potential to replace synthetic antioxidants presently used in meat processing with many added advantages.     

Equivalent processing for pasteurization of a pineapple juice–coconut milk blend by selected nonthermal technologies

Identifying equivalent processing conditions is critical for the relevant comparison of food quality attributes. This study investigates equivalent processes for at least 5-log reduction of Escherichia coli and Listeria innocua in pineapple juice–coconut milk (PC) blends by high-pressure processing (HPP), pulsed electric fields (PEF), and ultrasound (US) either alone or combined with other preservation factors (pH, nisin, and/or heat). The two blends (pH 4 and 5) and coconut milk (pH 7) as a reference were subjected to HPP at 300–600 MPa, 20°C for 0.5–30 min; PEF at an electric field strength of 10–21 kV/cm, 40°C for 24 µs; and US at 120 µm amplitude, 25 or 45°C for 6 or 10 min. At least a 5-log reduction of E. coli was achieved at pH 4 by HPP at 400 MPa, 20°C for 1 min; PEF at 21 kV/cm, 235 Hz, 40°C for 24 µs; and US at 120 µm, 45°C for 6 min. As L. innocua showed greater resistance, a synergistic lethal effect was provided at pH 4 by HPP with 75 ppm nisin at 600 MPa, 20°C for 5 min; PEF with 50 ppm nisin at 18 kV/cm, 588 Hz, 40°C for 24 µs; and US at 45°C, 120 µm for 10 min. The total soluble solids (11.2–12.4°Bx), acidity (0.47%–0.51% citric acid), pH (3.91–4.16), and viscosity (3.55 × 10⁻³–4.0 × 10⁻³ Pa s) were not significantly affected under the identified equivalent conditions. HPP was superior to PEF and US, achieving higher ascorbic acid retention and lower color difference in PC blend compared to the untreated sample.     

Thermophysical and Dielectric Properties of Salsa Con Queso and its Vegetable Ingredients at Sterilization Temperatures

Aseptic processing of a low-acid multiphase food product using continuous flow microwave heating system can combine the advantages of an aseptic process along with those of microwave heating. The objective of this study was to determine the thermophysical and dielectric properties of salsa con queso and its vegetable ingredients (tomatoes, bell peppers, jalapeno peppers, and onions) at a temperature range of 20 to 130°C to design a safe process for aseptic processing of salsa con queso using a continuous flow microwave system. The influence of temperature on apparent viscosity of salsa con queso was described by an Arrhenius-type relationship. Second order polynomial correlations for the dependence of thermophysical and dielectric properties (at 915 MHz) of salsa con queso and its vegetable ingredients on temperature were developed. The results showed that the dielectric constant decreased with an increase in temperature and the dielectric loss factor increased with an increase in temperature.     

Microbial and enzymatic changes in natural soursop puree during storage

Microbial and enzymatic comparisons were made on natural soursop puree stored at 15, 4 and −20°C without pasteurisation and with pasteurisation at 79°C for 69 s. Results showed that pasteurisation caused significant decrease in microbial count in soursop puree from 6.4×10³ to 8.5×10¹ cfu per g. Generally, storage at −20°C exhibited greater stability of samples as compared to those kept at 4 and 15°C. In contrast to microbial reduction, pasteurisation caused significant increase in cloud from 0.318 to 0.529 and completely inactivated the pectinesterase enzyme. The puree packed into foils kept at 4°C exhibited decreased cloud loss as compared to others packed in cans and bottles kept at 15 and −20°C. No pectinesterase enzyme regeneration was observed for pasteurised puree in this study during 12 weeks of storage time.     

Viscosity Behaviour of the Mucilage Extracted from Ruredzo (Dicerocaryum zanguebarium)

The concentration of metal ions in the mucilage that is extracted from Ruredzo (Dicerocaryum zanguebarium) was determined by atomic absorption spectroscopy. Calcium, magnesium, potassium, iron, copper, lead and zinc were found to occur in concentrations ranging from 0.01 ppm for lead to 15 ppm for calcium. Cations were removed from solutions of the mucilage using Dowex 50W-X12 resin and the viscosity of the decationized mucilage studied. Addition of CaCl₂, NaCl and sucrose decreased the viscosity of the decationized mucilage but addition of sucrose resulted in an increase in viscosity. The effect of incubating the mucilage at various temperatures for up to 30 min before measuring the viscosity at 25°C was investigated. No change in viscosity was observed for samples incubated at 40°C and 60°C. 80°C incubation resulted in reduced viscosity. Solutions of the decationized mucilage exhibited maximum viscosity at pH 5.