High Aw Values Research Articles

Effect of the Application of a Coating Native Potato Starch/Nopal Mucilage/Pectin on Physicochemical and Physiological Properties during Storage of Fuerte and Hass Avocado (Persea americana).

The avocado fruit is an agro-industrial product with high export demand in Peru due to its sensory and nutritional qualities, which can be affected during storage. The study aimed to evaluate the effect of the application of a coating formulated with potato starch (Solanum tuberosum ssp andigena), nopal mucilage (Opuntia ficus indica), and pectin on the physicochemical and physiological properties during the storage of Fuerte and Hass avocados. Samples were taken in their harvest state from the plantation in “Occobamba”, which is cultivated by the Avocado Producers Association in Chincheros, Apurímac, Peru. Physicochemical properties (titratable acidity, pH, total soluble solids) and physiological properties (weight loss, firmness, and color L* a* b*) were determined during 20 days of storage at 20 °C. The elaborated films present high transparency and low aw values. In the coated avocado of the Hass and Fuerte varieties, acidity and total soluble solids decreased significantly (p-value < 0.05) during the storage time. Weight loss and firmness of coated fruits decrease to a lesser extent. Luminosity L*, color index, and color variation showed better attributes for the coated samples. The use of coatings made with potato starch, nopal mucilage, and pectin allows the physicochemical and physiological properties of avocado fruits to be maintained for a longer time during storage.

Crystallization and strength analysis of amorphous maltose and maltose/whey protein isolate mixtures.

Maltose is an essential derivative of starch. To understand the processability and stability of maltose-containing foods, material characterization of the phase and state transition from its amorphous state is required. Although the crystallization of amorphous maltose is well understood, few studies have reported the relationship between the crystallization and the glass transition temperature (Tg )-related molecular mobility. In this study, water sorption, crystallization, Tg -related α-relaxation, and the corresponding time factor for amorphous maltose and maltose / whey protein isolate (WPI) mixtures are measured at various water activity (aw ) levels and 25 °C. The water-additive principle for maltose / WPI mixtures was observed at aw ≤ 0.440 at the molecular level, whereas the crystallization of amorphous maltose occurred at high aw values (≥0.534). The crystal formation and crystallization kinetics of amorphous maltose were affected by water and WPI at aw ≥ 0.534 and 25 °C, as determined by X-ray diffraction. The relationship between Tg and the water content was fitted by the Gordon-Taylor model, and its constant showed a compositional dependence for the maltose / WPI mixtures. The α-relaxation temperature of the amorphous samples decreased due to water plasticization, but increased with an increase in the WPI quantity. The Strength (S) value for amorphous maltose, which was a quantitative estimate of the compositional effects on molecular mobility, was based on the William-Landel-Ferry (WLF) equation. The S concept exhibits considerable potential for application in controlling the crystallization of amorphous maltose and improving the processability and stability of maltose-containing foods. © 2020 Society of Chemical Industry.

Stability of hepatitis E virus at different pH values

Infection with the hepatitis E virus (HEV) can cause acute and chronic hepatitis in humans. The zoonotic HEV genotype 3 is mainly transmitted by consumption of raw and fermented meat products prepared from infected pigs or wild boars. Lowering of pH during fermentation is one of the microbiological hurdles considered to inhibit growth of certain pathogens. However, no data are currently available on pH stability of HEV. As a reliable and reproducible measurement of HEV infectivity in meat products is not established so far, the stability of the cell culture-adapted HEV genotype 3 strain 47832c was analyzed here in phosphate-buffered saline (PBS) at different pH values. Only a minimal decrease of infectivity (up to 0.6 log10 focus forming units) was found after treatment at pH 2 to 9 for 3 h at room temperature. At pH 10, a decrease of about 3 log10 was evident, whereas no remaining virus (>3.5 log10 decrease) was detected at pH 1. The conditions usually achieved during curing of raw sausages were simulated using D/L-lactic acid added to PBS resulting in pH 4.5 to 6.5. After incubation at 4 °C for 7 days at these conditions, no significant differences as compared to a standard PBS solution at pH 7.7 were evident. At room temperature, a 0.8 log10 decrease was found at pH 4.7 after 7 days incubation compared to pH 7.7, but less at the other pH values. In conclusion, only minimal inactivating effects were found at pH conditions commonly occurring during food processing. Therefore, remaining infectious virus might be present in fermented meat products if HEV-contaminated starting material was used. Additional effects of other factors like high salt concentrations and low aw values should be investigated in future studies.

Measuring and modeling the hygroscopic growth of two humic substances in mixed aerosol particles of atmospheric relevance

Abstract. The hygroscopic growth of atmospheric particles affects atmospheric chemistry and Earth's climate. Water-soluble organic carbon (WSOC) constitutes a significant fraction of the dry submicron mass of atmospheric aerosols, thus affecting their water uptake properties. Although the WSOC fraction is comprised of many compounds, a set of model substances can be used to describe its behavior. For this study, mixtures of Nordic aquatic fulvic acid reference (NAFA) and Fluka humic acid (HA), with various combinations of inorganic salts (sodium chloride and ammonium sulfate) and other representative organic compounds (levoglucosan and succinic acid), were studied. We measured the equilibrium water vapor pressure over bulk solutions of these mixtures as a function of temperature and solute concentration. New water activity (aw) parameterizations and hygroscopic growth curves at 25 °C were calculated from these data for particles of equivalent composition. We examined the effect of temperature on the water activity and found a maximum variation of 9% in the 0–30 °C range, and 2% in the 20–30 °C range. Five two-component mixtures were studied to understand the effect of adding a humic substance (HS), such as NAFA and HA, to an inorganic salt or a saccharide. The deliquescence point at 25 °C for HS-inorganic mixtures did not change significantly from that of the pure inorganic species. However, the hygroscopic growth of HA / inorganic mixtures was lower than that exhibited by the pure salt, in proportion to the added mass of HA. The addition of NAFA to a highly soluble solute (ammonium sulfate, sodium chloride or levoglucosan) in water had the same effect as the addition of HA to the inorganic species for most of the water activity range studied. Yet, the water uptake of these NAFA mixtures transitioned to match the growth of the pure salt or saccharide at high aw values. The remaining four mixtures were based on chemical composition data for different aerosol types. As expected, the two solutions representing organic aerosols (40% HS/40% succinic acid/20% levoglucosan) showed lower water uptake than the two solutions representing biomass burning aerosols (25% HS/27% succinic acid/18% levoglucosan/30% ammonium sulfate). However, interactions in multicomponent solutions may be responsible for the large variation of the relative water uptake of identical mixtures containing different HSs above a water activity of 0.95. The ZSR (Zdanovskii, Stokes, and Robinson) model was able to predict reasonably well the hygroscopic growth of all the mixtures below aw = 0.95, but produced large deviations for some multicomponent mixtures at higher values.

Effect of dioxane on the binding of competitive inhibitor proflavin and catalytic activity of bovine pancreatic α-chymotrypsin

The binding of competitive inhibitor proflavin by α-chymotrypsin in water-dioxane mixtures over the entire range of thermodynamic activities of water a w was studied. The data on the degree of binding of proflavin were compared to the results on the catalytic activity of the enzyme preliminary incubated in water-dioxane mixtures. An analysis of the behavior of the concentration dependences of these characteristics demonstrated that, at low a w values, the behavior of the interprotein contacts in the enzyme formed during its drying largely governs its functional properties, while at high a w values, they are determined by the interaction of the enzyme with the organic solvent. Interplay of these two factors is responsible for the observed complex shape of the isotherm of binding of proflavin, with the maximum degree of binding being attained at moderate a w values.

Effect of Water Activity and Temperature on Growth and the Relationship between Fumonisin Production and the Radial Growth of Fusarium verticillioides and Fusarium proliferatum on Corn

The two major fumonisin-producing Fusarium species are Fusarium verticillioides and Fusarium proliferatum. The growth and fumonisin production of these two isolates on corn was studied at water activities (aw) between 0.860 and 0.975 and at temperatures between 15 and 30°C. Growth rates (g, mm/day) were obtained by linear regression during the linear phase of growth. In general, growth rates for both isolates increased significantly (P < 0.05) with increases in aw and temperature. Both fumonisin production and radial growth (mycelial development) for both isolates increased with aw at all temperatures investigated, but the effect of temperature on this relationship was not obvious. The effect of temperature on fumonisin production at high aw values optimal for growth was only marginal, whereas at lower aw values the effect of temperature was more pronounced, with more fumonisin production occurring at temperatures not optimal for growth. The optimum temperature for fumonisin production was between 15 and 25°C. For F. proliferatum, the optimum temperature for growth at all aw values, 30°C, resulted in the poorest fumonisin production. For both isolates, the slowest initial rate of fumonisin production was at 15°C, the temperature at which the slowest growth rates were obtained.

Effect of Water Activity on Lipid Oxidation and Protein Solubility in Freeze‐dried Beef during Storage

ABSTRACT: Ground beef patties (15% fat) were freeze‐dried to different aw endpoints and stored at 25°C or 49°C. Water activity, total moisture (%), lipid oxidation (TBARS@450nm), and protein solubility were evaluated. TBARS @450nm was favored at 49°C, but not at 25°C except at high aw range (p &lt; 0.05), whereas protein solubility was greater at 25°C than 49°C (p &lt; 0.05). TBARS@450nm values at 49°C were generally greatest at low aw range (p &gt; 0.05). Protein solubility was lowest at medium aw at 49°C (p &lt; 0.05), while at 25°C low aw protected protein solubility better than other low or high aw values.

Water Vapor Barrier Properties of Zein Films Plasticized with Oleic Acid

ABSTRACTWater sorption, water vapor permeability, and tensile properties were evaluated for zein films plasticized with oleic acid. The effect of relative humidity on water vapor permeability and tensile properties of films was investigated. Samples were produced by two different methods: casting from a zein solution and stretching from a zein‐fatty acid resin. Films were also coated with linseed oil. Results indicated that preparation method affected water sorption and permeability of zein films. Resin films showed lower water sorption than cast films, especially at high Aw values. Water vapor permeability was also lower for resin films. Coating with linseed oil further improved water vapor barrier ability of resin films. Permeability was affected by environmental relative humidity; higher relative humidity resulted in increased permeability. Environmental relative humidity also affected tensile properties of resin films. Toughness and elongation were improved when relative humidity increased from 50 to 85% rh. Tensile strength showed a maximum at 75% rh. Coating improved elongation and toughness of films. Maximum elongation and toughness were observed for coated samples at 85% rh. Zein resin films showed good tensile and water barrier properties that were maintained through environmental humidity levels from 50 to 98% rh.

Biochemical characteristics of two types of unripe Spanish cow's milk cheese (Cebreiro and Pasiego varieties)

A detailed study of two varieties of unripe Spanish cheeses (Cebreiro and Pasiego) has been carried out for the first time. The overall chemical composition, the most relevant physicochemical parameters and the classical nitrogen fractions were determined in 24 batches of each variety. The chemical compositions of both varieties are fairly similar to those described in the literature for other unripe cheese varieties. Their low NaCl and ash contents are, above all, outstanding. The low pH of Cebreiro cheese (4.29 ± 0.20) is worth noting. The pH value of Pasiego cheese (5.59 ± 0.60) is similar to that found in other unripe cheeses obtained by enzymatic coagulation. Both varieties show very high Aw values which is to be expected in cheeses with a high moisture content, low NaCl content and very little protein degradation. The values determined for the different nitrogen fractions in both types of cheese indicate a very slight proteolysis. Linear discriminant analysis was applied to analytical data in order to differentiate both varieties. According to this statistical technique, d-lactic acid, NaCl, Ca, P, and ammonia nitrogen contents and pH and Aw values were the major discriminating variables involved in the differentiation. The correctly classified cases were 100%.

Prevalence of Salmonella in Broiler Flocks: Effect of Litter Water Activity, House Construction, and Watering Devices

Litter samples from 24 flocks of broilers and four flocks of broiler breeders were evaluated for Salmonella contamination, water activity (Aw), and total moisture content (MC). The drag swab (DS) monitoring system was used to collect samples to detect Salmonella contamination. Simultaneously, representative samples of the uppermost surfaces of dry (loose) litter and wet (caked) litter were collected for Aw and MC analyses. On dry litter surfaces, high Aw values (0.90-0.95) were associated with flocks Salmonella-positive using DS; low Aw values (0.79-0.84) were associated with flocks Salmonella-negative by DS; and transition Aw values (0.85-0.89) were associated with flocks having an increased risk for the presence of Salmonella. The association of high Aw values with Salmonella risk was not observed for wet (caked) litter surfaces. Observations suggest that limiting Aw in the litter base of broiler houses may create a less favorable environment for the multiplication of Salmonella and thus a more hygienic environment for broiler production.

WATER ACTIVITY and PHYSICAL STATE EFFECTS ON AMORPHOUS FOOD STABILITY

Water-adsorption data and glass transition temperatures (Tg) of maltodextrins with dextrose equivalent (DE) values ranging from 4 to 38, horseradish roots, and strawberries were used to establish relationships between water activity (aw), water content (m), and Tg. Critical m values were considered as those depressing Tg to 25C. Corresponding values of critical aw were obtained from GAB isotherms that were used to model water adsorption. the use of BET isotherms was tested, but the model showed poor correlation with experimental data at high aw values, especially for low DE maltodextrins. Critical m and aw values were lowest for strawberries (1.5 g H2O/g solids; 0.07 aw). the values increased with decreasing DE, ranging from 7.2 (0.44 aw) to 11.2 g H2O/g solids (0,70 aw). Understanding of water-sorption properties and Tg is valuable in controlling processability and stability, and for determining of food-packaging requirements.

Determination of water activity of canned fish using gravimetric, hygrometric and psychrometric methods

SummaryThe water activity (aw) of canned mackerel, tuna and sardine was determined using three methods: a gravimetric and two instrumental methods. The aw values obtained by the gravimetric method, which only requires simple laboratory apparatus, were not significantly different from the values obtained by the other two methods, and can be used to determine high aw values.

An improved simple gravimetric method for measurement of high water activities

SummaryA previously reported gravimetric method for measurement of water activity (aw) has been simplified and improved, to determine aw in the range from about 0.700 to 0.999. Extrapolated aw values above 0.990 gave average underestimates of –0.001 aw units with the improved method. Comparative results on various dairy products were in good agreement with those found by a reference method (thermocouple psychrometer). The differences between the results provided by both methods were smaller for products with very high aw values than for products with high and intermediate aw values.

Prevention of Mold Growth and Toxin Production through Control of Environmental Conditions

Environmental conditions influence mold growth and mycotoxin production. Such things as water activity (aw), temperature, pH and atmosphere can strongly affect and profoundly alter patterns of growth and mycotoxin production. Generally, maintenance of low temperatures will prevent aflatoxin production in stored products, whereas other toxins such as penicillic acid, patulin, zearolenone and T-2 toxin may be produced at low temperatures. Toxic Penicillium and Fusarium species are generally more capable of growth at low temperatures than are toxic species of Aspergillus. Temperature interacts with aw to influence mold growth and mycotoxin production. Aflatoxin B1 can be produced at conditions of aw and temperature which are close to the minimum aw and temperature for growth. On the other hand, patulin, penicillic acid and ochratoxin A are produced within a narrower range of aw and temperature, compared with those for growth. In fact, production of patulin and penicillic acid by Penicillium species appears to be confined to high aw values only. In optimal substrates, the minima of aw and temperature for growth and toxin production may be lower than in other substrates. It appears that pH and substrate composition have no great effect on growth of toxic molds, but may have a great influence on toxin production. Presence of CO2 and O2 influences mold growth and mycotoxin production. A 20% level of CO2 in air depresses aflatoxin production and markedly depresses mold growth. Decreasing the O2 concentration of air to 10% depresses aflatoxin production, but only at O2 levels of less than 1% are growth and aflatoxin production completely inhibited. With patulin- and sterigmatocystin-producing molds, concentrations of 40% CO2 depress growth and toxin production, but a level of 90% CO2 is needed to completely inhibit production of these toxins. Decreasing O2 concentration to 2% depresses production of patulin and sterigmatocystin but does not affect fungal growth. Only at levels down to 0.2% are growth and toxin production completely inhibited. Controlled atmospheres with increased CO2 (above 10%) and decreased O2 (2%) can be used to retard mold growth. Exclusion of O2 by vacuum packaging in materials with low O2 permeability will depress or even prevent aflatoxin production. Presence of other microorganisms may also restrict fungal growth and mycotoxin production. Aflatoxin production by Aspergillus flavus in mixed cultures with Aspergillus niger is less than in pure culture. Mixtures of fungi growing in grains and nuts in competition with A. flavus seem to prevent aflatoxin production. Other organisms including Rhizopus nigricans, Saccharomyces cerevisiae, Brevibacterium linens and some lactic acid bacteria have been shown to reduce growth and aflatoxin production by Aspergillus parasiticus. In general, mold growth and mycotoxin production can be prevented by employing various measures based on knowledge of the factors involved. Choice of the measures depends upon the type of product, storage period and available techniques.

CAROTENE OXIDIZING FACTORS IN RED PEPPER FRUITS (Capsicum annuum L.): OLEORESIN‐CELLULOSE SOLID MODEL

ABSTRACTAn oleoresin‐cellulose model was used for studying the interacting processes which influence carotene bleaching in powdered paprika. Special attention was given to the effects of water activity and the addition of aqueous pepper extracts, copper and ascorbic acid. The stability of carotenoids in the model system increased slightly with increasing water activity, but the effect of moisture become considerable when the system also included ascorbic acid and copper sulfate. When aw in powdered paprika exceeded 0.32, carotenoid bleaching proceeded in three stages. After an initial bleaching, there was a prolonged period of stability, after which oxidation resumed. The intermediate period of stability was absent in the dry product. Results obtained with the oleoresin‐cellulose model showed that the three‐stage carotenoid bleaching at high aw values was characteristic of the combined action of copper and ascorbic acid. It is concluded that these two materials, by becoming soluble at high water activities, play an important part in the stabilization of carotenoids in powdered paprika. Under conditions of high water activity, the prooxidant effect of a water‐soluble protein is overcome by the marked antioxidant action of the ascorbic acid‐copper system. However, in the dry product the decisive factor in carotenoid bleaching is the proteinous fraction which was previously shown to have peroxidase activity.

The heat resistance of bacterial spores at various water activities.

SUMMARY: The heat resistance of the spores of six species of bacteria varied with water activity (aw) at which the spores were heated, although the magnitude of the changes differed greatly between species. At all aw values there was an approximately linear relation between the logarithm of the number of viable spores and the time of heating. The slopes of these straight lines were used to describe the observed death-rates as the time (D value) required to decrease the population by one log. unit. For all six species the greatest heat resistance was manifest at aw values of about 0.2–0.4, the maximum D values at 110° now varying from about 2 to 24 hr. At aw values less than 0.2 the heat resistance decreased; for spores rigorously dried over P2O5 (0.00 aw) the D values at 110° now varied between about 30 sec. and 30 min. When the spores were heated at aw values above 0.4 the resistance of 4 species decreased considerably, being lowest at 1.00 aw; with spores of Bacillus coagulans and B. stearothermo-philus the heat resistance decreased less at the high aw values; at 1.00 aw their D values were slightly greater than at 0.00 aw. At the high aw values the D values at 110° varied from less than 0.1 sec. for Clostridiuum botulinum type E to about 40 min. for B. coagulans and B. stearothermophilus. The Q10 for thermal death was about 10 at high aw values, decreasing to about 2 at aw values below 0.3. Under very moist conditions spores of B. stearothermophilus were about 50,000 times more heat resistant than were spores of C. botulinum type E; but at aw values less than about 0.5 this ratio fell to about 10. The convergence of this ratio resulted from more than a 100,000-fold increase in the resistance of the type E spores, and only a 20-fold increase in the resistance of the spores of B. stearothermophilus.