KINETICS OF NONENZYMATIC BROWNING IN CHEDDAR CHEESE POWDER DURING STORAGE

Nonenzymatic browning (NEB) in Cheddar cheese powder during storage was investigated in the water activity (a_w) and temperature ranges of 0.48–0.85 and 20–40C, respectively. The NEB obeyed zero-order reaction kinetics during storage. Activation energies and Q₁₀ values were in the range of 15.1–22.3 kcal/mole and 2.2–3.5, respectively. The NEB increased with increasing temperature and storage time. There was an a_w maxima at 0.63 for NEB at 20C. At 30 and 40C, NEB decreased with increasing a_w. A generalized NEB model for Cheddar cheese powder during storage was developed based on Arrhenius equation to describe NEB as a function of a_w and temperature. Powders stored at 20 and 30C were evaluated for quality aspects. Maximum storage stability was obtained in powders stored at a_w of 0.54 at 20C for five months based on an overall desirability score of 3.5 on a 7-point scale. The average score of fresh powders were 4.7 throughout the storage study 7.     

Water desorption isotherms of two varieties of sweet potato

Water desorption isotherms were determined for New Zealand sweet potato at 25, 40 and 55°C, and for Philippines sweet potato at 28°C. The isotherms were sigmoid in shape and of type II according to the BET classification. The data were fitted to eight two-parameter equations reported in the literature. The effect of water activity, a_w, and temperature, T °C, on the equilibrium moisture content, M _e g water/100g dry solids, was best described for New Zealand sweet potato by: Me = 20.51 T-^0.204 (a_w/(1-a_w)0.39 for a_w= 0.06–0.81     

EFFECT OF CHOCOLATE COATING ON OXIDATIVE STABILITY OF NORMAL AND HIGH OLEIC PEANUTS

Oxidative stability studies were performed on roasted high-oleic acid peanuts (HOP-SunOleic 95) and normal oleic acid peanuts (NOP-Florunner). Peanuts were dry-roasted to a Hunter Lab value of approximately 50. Chocolate-coated peanut bars (6"x4"×1/2") were prepared using milk chocolate, white chocolate, and reduced-fat chocolate (containing salatrim). Chocolate bars were stored at 25C and 0.60 water activity (a_w). Uncoated peanuts were stored at 0.60 and 0.19 a_w at 25C. Samples were removed from storage at 4-week intervals for peroxide value measurement. Oxidation of peanuts with chocolate coatings were higher than the peanuts that were stored uncoated at the same a_w. The peroxide values of NOP were similar for chocolate coated treatments and 0.60 a_w control but the 0.19 a_w control was 2–4 times higher than the others. Chocolate-coated peanuts had higher oxidation rates compared to uncoated peanuts.     

USE of UNIFAC IN the PREDICTION of WATER ACTIVITY VALUES of AQUEOUS POLYOL SOLUTIONS

The water activity (a_w) values of two commonly used aqueous polyoi solutions (xylitol and sorbitol) in the confectionery industry were estimated at 25C by using the UNIFAC (universal functional group activity coefficient) model in the a_w range 0.50–0.99. the comparison between the experimental and estimated a_w values at the high a_w region (a_w> 0.96) revealed very good agreement. However, the predicted values by the UNIFAC model did not fit well to the experimental data at a_w < 0.96, indicating that the UNIFA C method needed to be modified. the agreement between the experimental and predicted values was considerably improved at a_w < 0.96 when the modtfled UNIFAC model was used.     

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 a_w 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 a_w range (p < 0.05), whereas protein solubility was greater at 25°C than 49°C (p < 0.05). TBARS@450nm values at 49°C were generally greatest at low a_w range (p > 0.05). Protein solubility was lowest at medium a_w at 49°C (p < 0.05), while at 25°C low a_w protected protein solubility better than other low or high a_w values.     

MICROBIOLOGICAL QUALITY OF CEBRERO CHEESE FROM NORTHWEST SPAIN

Cebrero cheese is traditionally manufactured from raw cow's milk in the Cebrero mountains of Galicia (NW Spain). We report determinations of pH and a_w, and counts of total aerobic bacteria, psychrotrophs, Enterobacteriaceae, Escherichia coli, coagulase-positive Staphylococcus aureus, Listeria, molds and yeasts, in 49 samples. E. coli count exceeded the level permitted by Spanish legislation in 51% of samples. S. aureus count exceeded the level permitted in 20% of the samples. In one sample, with pH 5.06, two species of Listeria (L. monocytogenes and L. seeligeri) were detected. Although the pH of this cheese is fairly low, it does not appear to be sufficient to prevent the occurrence of certain pathogenic microorganisms.     

Thiamin Stability in Solids as Affected by the Glass Transition

The stability of thiamin was evaluated in solid polyvinylpyrrolidone model systems as a function of water activity (a_w) and the glass transition. In the glassy state, thiamin degradation rate constants correlated with the glass transition temperature (T_g), decreasing as T_g increased. Above a_w 0.4, rate constants correlated better with a_w rather than T_g. However, rate constants decreased in the rubbery state above a_w 0.4, which could be attributed to glass transition-induced structural collapse. Glass transition effects (mobility considerations, collapse) have a larger effect on thiamin stability than a_w, which should be recognized during the development of fortified food products.     

EFFECT OF MARINADE AND DRYING TEMPERATURE ON INACTIVATION OF ESCHERICHIA COLI O157:H7 ON INOCULATED HOME DRIED BEEF JERKY

Beef slices were inoculated (5.7–7.5 log CFU/cm²) with a 4-strain composite of E. coli O157:H7, stored (4C, 24 h), marinated (4C, 24 h), dried for 10 h at 62.5C or 68.3C, and stored for 90 days at 21C. Unmarinated beef slices dried for 10 h at 62.5C were used to determine the relative contribution of the marinate versus temperature treatment in the 62.5C trials. Samples were analyzed (bacterial enumeration with selective and nonselective agar media, pH, and a_w) following inoculation, marinating, at 4, 6, 8 and 10 h of drying, and after 30, 60 and 90 days of storage. Marination resulted in slight changes in bacterial populations (−0.3 to + 0.6 log CFU/cm²), but did not enhance bacterial reduction during drying. For all treatments, most bacterial reductions occurred in the first 4 h of drying, with little reduction thereafter. After 10 h of drying, bacterial reductions were 3.2–3.4 log CFU/cm² for unmarinated beef slices dried at 62.5C. Reductions of 2.2 and 3.0–4.6 log CFU/cm² were achieved in marinated jerky slices dried at 62.5C and 68.3C, respectively. No treatment resulted in the recommended 5-log reduction at the end of 10 h drying. However, bacteria did become undetectable by direct plating (<10 CFU/cm²) following 30 days of storage in all treatments except the unmarinated beef slices plated on tryptic soy agar (TSA). Additional work is needed to develop procedures for adequate destruction of E. coli O157:H7 during drying of beef jerky.     

ASSESSMENT of NEAR INFRARED (NIR) DIFFUSE REFLECTANCE ANALYSIS FOR MEASURING MOISTURE and WATER ACTIVITY IN RAISINS

Near Infrared (NIR) Analysis was applied to assess its potential for measuring water activity (a_w) and moisture in California Seedless Raisins in moisture equilibrium and nonequilibrium conditions. Samples covered a wide range of anticipated moisture contents. an NIR calibration for a_w was made for whole raisins that were fully equilibrated. For ground raisins, NIR calibrations were made both a_w and vacuum oven moisture, covering a large range of moisture contents and equilibrium conditions. Direct measurement of a_w by a dewpoint device gave highly repeatable results, especially for ground raisins. Vacuum oven analysis of moisture was less precise than a_w measurements. Full spectrum NIR calibrations indicated that NIR could predict a_w of raisins in ground form, irrespective of their state of hydration beyond three hours following processing. A much larger sample population will be needed to establish precise calibrations for vacuum oven moisture.     

INFLUENCE OF MODIFIED ATMOSPHERE PACKAGING ON GROWTH OF CLOSTRIDIUM PERFRINGENS IN COOKED TURKEY

Clostridium perfringens containing samples of sterile ground turkey were studied to assess growth under modified atmosphere conditions. Samples were packaged under various atmospheres (CO₂/O₂/N₂: 75/5/20, 75/10/15, 75/20/5, 25/20/55, 50/20/30), stored at 4, 15 and 28C, and sampled periodically for growth. Diluted samples were plated on Shahidi Ferguson perfringens agar (Difco Laboratories, Detroit, MI) to determine vegetative cell counts. Temperature abuse (cyclic and static) of the turkey product was also investigated. The results showed that the growth of C. perfringens was slowest under 25–50% CO₂/20% O₂/balance N₂ at 15 and 28C. There was no growth at 4C for up to 28 days. Temperature abuse (28C storage) of refrigerated products for 8 h did not permit C. perfringens growth. Use of 25–50% CO₂/20% O₂/balance N₂ may extend the shelf-life of turkey, but in the absence of proper refrigeration, it cannot be relied upon to eliminate the risk of C. perfringens food poisoning .     

Role of Moisture in Maillard Browning Reaction Rate in Intermediate Moisture Foods: Comparing Solvent Phase and Matrix Properties

ABSTRACT: In intermediate-moisture foods, a mechanism describing how moisture affects chemical reaction rate is unknown. Previously, research showed glycol addition to model systems allowed high rates of nonenzymatic browning below the monolayer moisture value and an a_w of 0.2. These works were replicated, focusing on a mechanism of either plasticization or reactant dissolution. T_g curves showed plasticization increased with added glycerol and sorbitol. The maximum rate of nonenzymatic browning with glycerol occurred at an a_w= 0.25 and was 1.5 times higher than the control (a_w= 0.65). Sorbitol showed rates similar to the control. Plasticization and aw were poor predictors of reaction rate. Dissolution of glucose in glycerol explained the effect.     

EFFECT OF OXYGEN-ENRICHED ATMOSPHERES ON STORAGE QUALITY OF PACKAGED FRESH MEAT

SUMMARY —The extension of fresh meat shelf-life is important from both practical and theoretical points of view. Color is usually used as a measure of fresh meat quality during storage. Beef top-round slices were prepared using sanitary precautions. Meat slices were enclosed in a thermally sealed semi-rigid polyvinyl chloride tray system of special design. Face-to-face meat samples were used to compare the effects of high oxygen with normal air atmospheres. One package from each pair was evacuated and the atmosphere readjusted to approximately 90% oxygen through a septum. Packages were kept at 4 ± 0.5°C and gas chromatographic readings for CO₂, O₂ and N₂ were conducted daily. Spectrophotometric and bacteriological evaluations were made on selected pack ages during storage to determine pigment oxidation and microbial growth. Three experiments each containing six to eight pairs of samples were conducted. The generation of CO₂ was observed in two periods–the first immediately after packaging and lasting for 1–2 days, after which the CO₂ level remained approximately stable up to 8—9 days, when it again started to increase in correspondence with increased bacterial growth. There was more CO₂ produced than O₂ utilized in the stored samples. In the first stage, samples stored in oxygen-enriched atmospheres had higher O₂ uptake than samples stored in air. Microbial growth was similar in both atmospheres. Under conditions of this study, head space enrichment to about 90% oxygen prolonged acceptable meat color when compared with samples stored in an air atmosphere.     

Revised PEC method for measuring water activity

The Proximity Equilibration Cell (PEC) method of Lenart & Flink (1983) for measuring water activity (a_w) in foods was revised by improving equilibration cell design and cell handling procedures. Calibration methods were changed to eliminate time and temperature variation effects on measured (a_w). The PEC cells are inexpensive, easy to use and can measure a_w over the range 0.4–1.0, although accuracy is greatly improved above 0.6. In a study of osmotic concentration of apple (Palacha & Flink, 1987) over 1000 a_w measurements were made over a 3-month period. Values of a_w for raw apple (0.985) and sucrose osmosis solutions were in good agreement with literature values.     

DEVELOPMENT OF STRESS AND SURVIVAL OF SALMONELLA TYPHIMURIUM ATCC 7136 IN A TAPIOCA SOYSTARCH PRODUCT CONTAINING POTASSIUM SORBATE

The effects of reduced water activity and 0.1% sorbate on Salmonella typhimurium ATCC 7136 in a soy-starch product were examined. The formulated product (final pH 6.7), was inoculated with cells to give a final concentration of approximately 2 × 10⁶ cells/g. Ten gram samples were placed in a series of desiccators over saturated salt solutions and stored at either 22°C or 40°C. Water activities ranged from 0.79 to 0.97. Samples were withdrawn at prescribed intervals and appropriate dilutions made. A dual plating procedure was used to monitor growth (tryptic soy agar) and development of injury (Levine's Eosin Methylene Blue Agar supplemented with 2% NaCl and 0.05% sodium desoxycholate). Cells stored at 22°C remained viable longer at an a_w of 0.79 than at a_w values of 0.96 to 0.97. As storage time increased, cells were stressed at a faster rate at higher a_w values. This effect was accelerated at 40°C and as storage time increased.     

SURVIVAL AND GROWTH OF SELECTED MICROORGANISMS IN KHOA DURING PREPARATION AND STORAGE

The survival of Escherichia coli and Staphylococcus aureus during the production of khoa, a heat concentrated Indian milk-based product, was investigated. Heat processing of milk containing from 3.6 to 6.5% fat at either 63 or 73C eliminated all E. coli. Under similar processing conditions , S. aureus was recovered, but only when heated in milk at 63C containing 6.5% fat. Potassium sorbate (3000 ppm) appeared more effective in inhibiting the growth of selected yeast and molds in khoa at 7C, compared to ascorbic acid (3000 ppm). Reducing the water activity (a _w) of khoa from 0.97 to 0.93 did not appear to enhance the preservative effect. The reduction of E. coli or S. aureus in khoa during prolonged storage at 6–7C, was less than one log cycle, regardless of a _w or preservative type. Survival of S. aureus in khoa appeared to be enhanced with a decrease in a _w. The potential for pathogens to survive in khoa during processing should be taken into consideration when formulating heating protocols.     

EFFECT of WATER ACTIVITY ON VITAMIN A DEGRADATION IN WHEAT FLOUR (ATTA)

ABSTRACT. The effect of water activity (a_w) on the stability of vitamin A palmitate adsorbed onto wheat flour, starch, gluten, enzyme inactivated wheat flour and micro-crystalline cellulose was investigated. In wheat flour the rate of vitamin A degradation was lowest at 0.0 a_w. In gluten, starch and enzyme inactivated wheat flour, the rate was highest at 0.0 a_w and decreased with rise in a_w. the rate of lipid oxidation in wheat flour was lowest at 0.0 a_w whereas in enzyme inactivated wheat flour it was highest at 0.0 a_w and decreased with rise in a_w. In micro-crystalline cellulose system vitamin A degradation was least at 0.33 a_w and the rate of degradation increased both below and above this a_w. Among the wheat flour constituents, gluten provided better protection to vitamin A than starch. the role of lipoxygenase enzyme in accelerating the rate of degradation of vitamin A in wheat flour at higher a_w has been suggested.     

Water activity of culture media used in food microbiology

An improved gravimetric method was used to simultaneously determine (in a single assay) the water activity ( a_w ) of 30 solid and liquid culture media covering the entire useful range of a_w in food microbiology, including media recommended for osmophilic, halophilic and xerophilic organisms. The water activities of the media ranged between 0.999 and 0.739. As could be expected, the water activities of the solid media were not affected significantly by the presence of agar. No significant differences were observed either between the gravimetric (20°C) and the cryoscopic measurements (below 0°C) of liquid media of very high a_w .     

APPLICATION OF CORRELATION BETWEEN BIOT AND DINCER NUMBERS FOR DETERMINING MOISTURE TRANSFER PARAMETERS DURING THE AIR DRYING OF COROBA SLICES

The moisture mass transfer parameters characterizing the air drying of coroba slices were determined using the correlation between Biot and Dincet numbers. The air drying was carried out at temperatures of 71, 82 and 93C and velocities of 0.82, 1.00 and 1.18 m/s. Experimental moisture content data for coroba slices were collected. The drying coefficient and lag factor were calculated from the experimental data and were incorporated into the correlation. The moisture diffusion coefficient, Biot number and mass transfer coefficient ranged between 1.147  ×  10 ^{− 12} –3.740  ×  10 ^{− 12}  m²/s, 0.097–0.114 and 0.903  ×  10 ^{− 4} –1.729  ×  10 ^{− 4}  m/s, respectively. The predicted dimensionless moisture content profiles showed adequate agreement with the experimental observations, with the mean relative error between 0.98 and 4.61%.

PRACTICAL APPLICATION

As drying is an energy-intensive operation, it has become the prime concern of the researchers to optimize process conditions that lead to energy savings. Moisture transfer parameters are important transport properties needed for accurate modeling in food drying applications. Therefore, accurate determination of these parameters for the drying operation is essential. There is a large amount of studies available in the literature to determine and calculate these parameters for the products subjected to drying. But limited studies have been carried out to determine these parameters using the drying process parameters in terms of lag factor and drying coefficient as first introduced by Dincer and Dost.     

MEASUREMENT OF THE HARDNESS AND MOUTHFEEL OF CHEESE USING A SLIDING PIN CONSISTOMETER

A sliding pin consistometer (SPC) was used to differentiate between six commercial cheese products, including a hard, mature Cheddar and a soft, cream cheese, at a number of temperatures in the range 0.8 to 25.0°C. Average force values (F_f) decreased with increasing temperature and with decreasing relative cheese hardness. Measurements were also made on six Cheddar cheeses with a range of salt to moisture (s/m) ratio (2.95 × 10^-2 to 5.57 × 10^-2) at a sample temperature of 16°C at maturation periods of 22, 58, 100 and 183 days. A panel of 27 adults scored the hardness and mouthfeel of these samples at these maturation periods using 9-point scoring scales. The SPC discriminated between samples and maturation periods and was more discriminating than the subjective evaluation of panelists. Mean F_f values decreased with maturation and increased linearly with increasing s/m. Panelists' hardness scores increased with s/m but were not influenced significantly by maturation. Mouthfeel increased with maturation and was a maximum at a s/m of between 4.36 × 10^-2 and 4.57 × 10^-2. The SPC provides objective information that could be useful in assessing the effect of treatment on cheese.     

Separation of Immunoglobulin G from Cheddar Cheese Whey by Avidin-Biotinylated IgY Chromatography

High-purity immunoglobulins (Ig), which may be useful for immunologic supplementation of food products, were isolated from Cheddar cheese whey in a one-step process using avidin-biotinylated yolk immunoglobulin (IgY) column chromatography. Yolk antibodies specific to bovine IgG (IgY_IgG) were biotinylated with biotinyl amido-hexanoic acid-N-hydroxy-sulfo-succinimide ester without any notable effect on antigen-binding activity, and coupled to immobilized avidin columns. The resulting avidin-biotinylated IgY_IgG columns, with binding capacity of 50–55% (w/w percent ratio of IgG to immobilized IgY_IgG), were used for specific binding of IgG from cheese whey. Elution with a commercially available eluent (Actisep) or 0.1 M glycine-HCl buffer at pH 2.8 yielded IgG with purity of 99% by radial immunodiffusion.