Bacterial Growth and Histamine Production on Vacuum Packaged Tuna

Vacuum and nonvacuum packaged samples of tuna or tuna spiked with Klebsiella oxytoca T₂, Morganella morganii JM or Hafnia alvei T₈ were stored at 2°C and 10°C and examined for bacterial growth and histamine production on day 3, 6, 10 and 15. Unlike those stored at 2°C, tuna samples stored at 100°C showed significant bacterial growth over time and had high levels of histamine (>200 mg/100g tuna on day 15). Vacuum packaging did not show any beneficial effect in controlling bacterial growth and histamine production on tuna samples at these two temperatures. Low temperature storage was more effective than vacuum packaging in controlling histamine production by the bacteria tested.     

Histamine, Putrescine and Cadaverine Formation in Spanish Semipreserved Anchovies as Affected by Time/Temperature

We studied the changes in counts of mesophilic, psychrotrophic, entera-bacteria, sulphite-reducing and Vibrio microorganisms in commercial samples of Spanish semipreserved anchovies. The influence of NaCl, oxygen concentration and pH on bacterial growth and histamine, putrescine and cadaverine formation were also studied. Notable histamine formation was detected in samples incubated at 20°C and preserved in olive oil (443.68 ppm-3012.13 ppm). This accumulation was probably caused by the conditions of the product, pH 5–6, relatively low NaCl (< 15%), and permissive temperature (product not refrigerated). Correlation between the microorganisms and histamine formation was not clear. Histamine was produced by too high storage temperatures but not by the ripening process.     

Swelling Characteristics of Native and Chemically Modified Wheat Starches as a Function of Heating Temperature and Time

The effects of hydroxypropylation (molar substitution, MS 0.05, 0.12, and 0.18) and cross‐linking (0.03%, 0.1%, and 0.2%) on swelling properties of wheat starch granules at several temperatures and heating times were investigated by laser diffraction particle size analysis. Starch samples were dispersed in water at temperatures ranging from 30 to 90°C, for 1 to 360 min. All starch granules exhibited distinct bimodal size distributions: small B‐granules with mean diameter of 2.3 μm and large A‐granules with mean diameter of 20.4 μm. As temperature increased, the B‐granules swelled more than A‐granules. Swelling of A‐granules sharply increased at 60°C. Swelling was more pronounced with increasing molar substitution of hydroxypropyl groups, while increased swelling was not observed in cross‐linked starches. The dependence of swelling capacity on heating time was different at 60 and 80°C as well as amongst modified starches. As heating time was prolonged, mean granule sizes for native, control, and hydroxypropylated starches at 80°C decreased after reaching maximum size due to loss of granule integrity, while those at 60°C showed no significant change.     

Stability of Apple Polyphenols as a Function of Temperature and pH

The effect of heat treatment on apple polyphenols was investigated at six different temperatures over three different lengths of time. Apple polyphenols, after heat treatment, maintained similar concentrations in solution compared to the control (at room temperature). The effect of pH on apple polyphenols was investigated at 11 different pH levels and at 2 different temperatures. The pH-optimum for apple polyphenols proved to be 5.0. Two apple polyphenol concentrations, three vitamin C concentrations, two sugar concentrations, and two different temperatures were chosen to investigate the effect of apple polyphenols on vitamin C. Apple polyphenols showed good stability and can be used in many types of food products.     

Heterocyclic Amines: 1. Kinetics of Formation of Polar and Nonpolar Heterocyclic Amines as a Function of Time and Temperature

ABSTRACT: The influence of time, temperature, glucose, and creatine on the formation of heterocyclic amines (HAs) in beef was investigated. Kinetic models as a function of time and temperature were used to examine the formation of polar and nonpolar HAs, as described by Arrhenius and Eyring equations. The highest amount of MeIQx was 23.93 ng/g at 220°C for 20 min. However, no formation of 4,8-DiMeIQx was observed at 160°C, 180°C, 200°C, and 220°C for 5 min. Norharman and 4,8-DiMeIQx were more sensitive to temperature change, whereas MeIQx and AαC were less sensitive. The formation of HAs increased with increasing time and temperature. Glucose and creatine decreased at the same pattern with increasing time and temperature. The formation of HAs and the degradation of precursors were inversely correlated. The results provide valuable information toward modulating and inhibiting the formation of HAs in cooked meats.     

Inactivation and Injury of Listeria monocytogenes in a Minimal Medium as Affected by Benzoic Acid and Incubation Temperature

The population of Listeria monocytogenes in a minimal medium (lacking a nitrogen source) at pH 5.5 decreased logarithmically during incubation. Rate of death of the pathogen, indicated by D-values, was greatly affected by changes in the temperature of incubation (4–35°C), but to a much lesser extent by the presence of benzoic acid (3000 ppm). Injury of L. monocytogenes during incubation was equally detectable on tryptose agar containing 6% salt and McBride Listeria Agar containing 0.5% lithium chloride. A greater degree of injury was detected at the lower than the higher temperatures of incubation, but presence of benzoic acid (3000 ppm) did not seem to affect the extent of injury.     

Glucose Production from Maltohexaose as a Substrate by the Bacterial Alpha-amylase-catalyzed Reaction. Its Time Courses Obtained by a Theoretical and an Experimental Approaches

Based on the subsite structure of an α-amylase from Bacillus subtilis, production of glucose from a substrate maltohexaose in the amylase-catalyzed reaction was theoretically predicted as a function of time. The theoretical time course was found consistent with the experimental results, which were obtained by the determination of a product glucose with a commercial assay-kit. Hence, glucose, product from a substrate maltohexaose, will be a useful probe for the amylase-catalyzed reaction.     

Rate of Hydroxypropylation of Starches as a Function of Reaction Time

To determine the course of the hydroxypropylation reaction as a function of reaction time, waxy corn, normal corn, potato, and wheat starches were reacted with propylene oxide under normal reaction conditions. Amounts of leached material and MS values of both leached and granular molecules were determined over the course of reaction. For waxy and normal corn starches, the extent of reaction increased linearly from 0 to 12 h, after which the reaction proceeded at an ever decreasing rate, reaching zero at about 30 h of reaction. The initial rate of reaction was determined by reacting waxy corn starch with a greater amount of propylene oxide (10×normal concentration) so that there would be no slowing of the reaction due to loss of reagent. Results confirmed that the initial reaction rate was linear. The hypothesis that, as derivatization proceeds, granules are opened up, resulting in ever increasing rates of reaction was not substantiated. Amounts and MS values of leached molecules from waxy and normal corn starches increased continuously over the course of the reaction. For potato and wheat starches, MS values of the granular starch also increased continuously over the entire reaction period. Amounts of leached molecules from potato starch were greater than those from wheat starch, with the amount leached at 30 h from potato starch being slightly more than that from normal and waxy corn starches and that from wheat starch being considerably less.     

Compositional Changes in Brewed Coffee as a Function of Brewing Time

Variations in the composition of brewed coffee as a function of brewing time were monitored using gas chromatography-mass spectrometry. Batches of coffee were produced using flow rates of 50-500 mL/min, which resulted in brewtimes of 4.42-31.07 min. While most components increased in concentration with longer brewing times, several showed significant losses beyond 8 min, indicating an optimum brewtime of 7-9 min.     

Thermophysical Properties of Clarified Apple Juice as a Function of Concentration and Temperature

Effect of concentration and temperature on thermophysical properties of clarified apple juice was studied. Density, viscosity, specific heat, and thermal conductivity were measured at different conditions, ranging from 20 to 90^oC and 12 to 70^oBrix. Experimental data were related to the corresponding properties of water and compared with the behavior of sugar solutions. The results obtained were used to derive mathematical models and correlations for predicting these properties as a function of both concentration and temperature.     

Modeling the Dielectric Properties of Ham as a Function of Temperature and Composition

ABSTRACT The dielectric properties of 19 different ham samples with different moisture (38.2% to 68.9%) and ash contents (1.78% to 6.80%) were measured at −35 to 70 °C at 2450MHz. Equations were developed as a function of temperature, moisture, and ash, and compared to literature equations. The dielectric constant decreased with ash content and increased with moisture content. It increased instead of decreasing with temperature. The dielectric loss factor increased with moisture content for moisture contents lower than 60.7%, then decreased for higher moisture contents. Ash content and temperature increased dielectric loss factor. Frozen samples had low dielectric activity that was increased by ash content above −20 to −10 °C.     

Modeling Growth Rate and Assessing Aflatoxins Production by Aspergillus flavus as a Function of Water Activity and Temperature on Polished and Brown Rice

Abstract: The aim of this study was to model the radial growth rate and to assess aflatoxin production by Aspergillus flavus as a function of water activity (a_w 0.82 to 0.92) and temperature (12 to 42 °C) on polished and brown rice. The growth of the fungi, expressed as colony diameter (mm) was measured daily, and the aflatoxins were analyzed using HPLC with a fluorescence detector. The growth rates were estimated using the primary model of Baranyi, which describes the change in colony radius as a function of time. Total of 2 secondary models were used to describe the combined effects of a_w and temperature on the growth rates. The models were validated using independent experimental data. Linear Arrhenius–Davey model proved to be the best predictor of A. flavus growth rates on polished and brown rice followed by polynomial model. The estimated optimal growth temperature was around 30 °C. A. flavus growth and aflatoxins were not detected at 0.82 a_w on polished rice while growth and aflatoxins were detected at this a_w between 25 and 35 °C on brown rice. The highest amounts of toxins were formed at the highest a_w values (0.90 to 0.92) at a temperature of 20 °C after 21 d of incubation on both types of rice. Nevertheless, the consistencies of toxin production within a wider range of a_w values occurred between 25 to 30 °C. Brown rice seems to support A. flavus growth and aflatoxin production more than the polished rice. Practical Application: The developed models can be used to estimate to what extent the change in grain ecosystem conditions affect the storage stability and safety of grains without the need for running long‐standing storage study. By monitoring the intergranular relative humidity and temperature at different locations in the storage facility and inputting these data into the models, it is directly possible to assess either the conditions are conductive for the growth of A. flavus or aflatoxin production.     

Acceptability of Water, Selected Beverages and Foods as a Function of Serving Temperature

In Experiment 1 the consumer acceptability of water, four fruit-flavored beverages and tea was examined at five serving temperatures (38°, 52°, 74°, 97° and 120°F). Results showed significant main effects of beverage and temperature on acceptability ratings and a significant beverage × temperature interaction. Pure water, which was moderately acceptable at low serving temperatures, was the most unacceptable of all samples at high temperatures. In Experiment 2 the acceptability of three beverages and ten solid foods was examined at five serving temperatures (40°, 55°, 70°, 100° and 135°F). Results showed that the acceptability of each food item was greatest in the temperature range at which the food is normally served; except for foods normally served at ambient temperatures. The importance of temperature/acceptability functions for food and beverage selection under conditions where heating and/or cooling is not feasible, and the relationship of the present data to data on temperature/intensity functions in taste were discussed.     

Kinetics of Ascorbic Acid Autoxidation as a Function of Dissolved Oxygen Concentration and Temperature

The kinetics of ascorbic acid autoxidation was studied at pH 6.1 (μ= 0.08) using a buffered model system. Oxygen replenishment in the solution was accomplished by shaking the reaction vessel in a shaker water bath or by bubbling oxygen-nitrogen gas mixtures through the solution. Using the former system, a second order rate constant of 58.19 ± 11.92 min^?1 M^?1 was calculated (45°C), Since the shaker bath did not assure oxygen replenishment and dissolved oxygen levels could not be varied, the latter system was developed. The second order rate constants in the gas mixture experiments ranged from 20.80 ± 2.28 min^?1 M^?1 (30°C) to 176 ± 6.93 min^?1 M^?1 (55°C). Activation energies measured under different conditions ranged from 9.47 to 16.43 kcal mole^?1.     

Histamine and Other Biogenic Amines and Bacterial Isolation in Retail Canned Anchovies

ABSTRACT: Histamine and biogenic amine contents in retail canned anchovies were determined. Bacterial strains were isolated, and their histamine-producing capability was determined. The majority of canned anchovy products (80%) had histamine levels below the FDA guideline of 50 ppm. The sensory quality of products was relatively good. A few samples contained high levels of histamine (>1000 ppm). Overall, histamine contents in the products showed great lot-to-lot variations. Spermine and tyramine were commonly detected in all samples analyzed, regardless of their histamine contents. Bacterial counts in the products were mostly below the detection limit (10² CFU/g), and bacteria were frequently recovered with the enrichment of test samples in tryptic soy broth supplemented with 0.5% or 5% NaCl. Only Bacillus spp., the nonhistamine formers, were isolated from these test products. Prolific histamine-forming bacteria were not detected in these canned anchovies.     

Content and Profile of Isoflavones in Soy-Based Foods as a Function of the Production Process

Soy has been traditionally incorporated in diet as processed foods, such as soymilk, tofu, miso, tempeh, etc., and the consumption is commonly associated with a reduction of the development of chronic diseases due to their antioxidant, anti-inflammatory, and anti-allergic properties, among others. Many of the health benefits of soy have been attributed to isoflavones. They comprise a group of naturally occurring flavonoids consisting of heterocyclic phenols. Soy contains three types of isoflavones in four chemical forms: the aglycones daidzein, genistein, and glycitein; the β-glucosides daidzin, genistin, and glycitin; their 6″-O-malonyl-β-glucosides (6OMalGlc); and their 6″-O-acetyl-β-glucosides (6OAcGlc) conjugates. Industrial processing methods of soy-based food products commonly lead to the loss of isoflavones through removal of undesirable fractions. On the other hand, isoflavones can be transformed into different conjugates, which may have significant effects on the food texture and on the bioavailability and pharmacokinetics of the isoflavones. This article reviews the effect of a number of soybean processing treatments on the isoflavone content and profile. The preparation and manufacturing of different soy-based food and food ingredients, fermented and non-fermented, has been analyzed in terms of content and distribution of the three major isoflavone derivatives, daidzein, genistein, and glycitein, and their respective conjugates.     

适当延长制曲中挺温度时间对制酒生产的影响

曲药培养过程中适当延长中挺温度时间,对曲药酶活力有适当的抑制作用,从而减小白酒中因酶活力过高而给生产和产酒质量带来的不利影响。适当延长中挺温度时间,有利于对曲药中微生物的驯化,增加微生物对生产环境的适应性;控制曲药的酶活和发酵力,更加有益于生产;增加曲药的复合香。(孙悟)