Accelerated natural lactic fermentation of cereal-based formulas at reduced water activity.

Energy required to dehydrate fermented cereal-based food formulas plays a significant part in the production cost. Therefore the effect of reduced moisture content on the fermentation was investigated. Generally, lactic fermentation at reduced moisture content resulted in increased final pH. Significant acidification still occurred at 0.33 kg water/kg dry matter corresponding to either aW = 0.925 in a sorghum-maize-soya (SMS) mixture, or aW = 0.950 in a sorghum-maize-milk powder (SMM) mixture. Acidification adequate for microbiological safety (pH < or = 4.5) was achieved at 0.54 kg water/kg dm in SMS (aW = 0.950) and 0.43 kg/kg dm in SMM (aW = 0.965). In stable accelerated natural lactic fermentations obtained by inoculum recycling ('back-slopping') at 30 degrees C, dominant lactic acid bacteria included Lactobacillus plantarum, L. brevis, L. acidophilus and Lactococcus lactis. Dominating yeasts were Saccharomyces cerevisiae and Candida krusei. L. plantarum isolated from high-moisture (1.5 kg/kg dry matter) SMS fermentations had higher specific growth rates than L. plantarum isolated from reduced moisture (0.54 kg/kg dm) SMS fermentations, when tested under similar aW conditions. This effect was not caused by previous culturing conditions; probably different strains of L. plantarum having different aW-optima dominate at high or reduced moisture conditions.     

Inverse Method to Estimate Kinetic Degradation Parameters of Grape Anthocyanins in Wheat Flour Under Simultaneously Changing Temperature and Moisture

ABSTRACT:  Thermal and moisture effects on grape anthocyanin degradation were investigated using solid media to simulate processing at temperatures above 100 °C. Grape pomace (anthocyanin source) mixed with wheat pastry flour (1: 3, w/w dry basis) was used in both isothermal and nonisothermal experiments by heating the same mixture at 43% (db) initial moisture in steel cells in an oil bath at 80, 105, and 145 °C. To determine the effect of moisture on anthocyanin degradation, the grape pomace–wheat flour mixture was heated isothermally at 80 °C at constant moisture contents of 10%, 20%, and 43% (db). Anthocyanin degradation followed a pseudo first-order reaction with moisture. Anthocyanins degraded more rapidly with increasing temperature and moisture. The effects of temperature and moisture on the rate constant were modeled according to the Arrhenius and an exponential relationship, respectively. The nonisothermal reaction rate constant and activation energy (mean ± standard error) were k _{80 °C, 43% (db) moisture} = 2.81 × 10⁻⁴± 1.1 × 10⁻⁶ s⁻¹ and Δ E  = 75273 ± 197 J/g mol, respectively. The moisture parameter for the exponential model was 4.28 (dry basis moisture content)⁻¹. One possible application of this study is as a tool to predict the loss of anthocyanins in nutraceutical products containing grape pomace. For example, if the process temperature history and moisture history in an extruded snack fortified with grape pomace is known, the percentage anthocyanin loss can be predicted.     

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.     

Thermal syneresis affected by heating schedule and moisture level in surimi gels

ABSTRACT:  The extent of thermal syneresis in protein gelation is indicative of thermal and freeze-thaw stability as well as the network integrity of a protein gel. Thermal syneresis in Alaska pollock surimi gels was examined under different heating schedules (40 °C/20 min to 90  °C/30 min, 60 °C/20 min to 90 °C/30 min, and 90 °C/20 min to 90 °C/20 min) at varying moisture levels (80%, 82%, and 84%). The extent of syneresis and gel firming was monitored by centrifugation expressible moisture and penetration force, respectively. The occurrence of 2 distinct peaks as a function of time for both thermal syneresis and gel firming suggests that a multistage aggregation is involved in the formation of gel network. All syneresis preceded gel firming upon protein aggregation. Increasing the moisture content in the gel delayed the 2nd stage of protein aggregation. The 60 °C/20 min preheating followed by 90 °C/30 min postheating resulted in significantly greater thermal syneresis and gel weakening compared to 40 and 90 °C preheating. Changes of gel structure clearly reflected thermal syneresis when the size of water pores became smaller with initiation of network formation and progressively larger upon further heating. Thermal syneresis history during protein gelation can be used to predict thermal and freeze-thaw stability.     

Effect of temperature and initial moisture content on sorption isotherms of banana dried by tunnel drier

Sorption isotherms of intermediate moisture content (IMC) products are essential to predict shelf-life of packaged moisture-sensitive product by modelling moisture uptake during storage and distribution. The effect of temperature and initial moisture content (MC) of IMC banana on the relationship between MC and water activity were investigated. Raw bananas were dried in a tunnel dryer at 2% relative humidity (RH), 70 °C, and a 3.2 ± 0.2 m s^–1 air velocity. Drying procedure was carried out a number of times until various IMC levels were obtained (5%, 14%, 22% and 33% db for banana). Sorption isotherms of bananas were determined at 10, 20, 30 and 40 °C. The initial MC of IMC banana had no significant effect on the relationship between MC and water activity according to statistical analysis. All the sorption curves were found to be Type II. BET, GAB, modified GAB, Oswin, Halsey and modified Freundlich models were fitted to the data and it was found that the best results were obtained with a modified Freundlich equation. A secondary modified Freundlich model was built accounting for the effect of a _w and temperature on the sample MC.     

Extent of damage to amino acid availability of whey protein heated with sugar.

The effect of heat treatments, at various water activities (aW), on digestibility and on the availabilities of amino acids of whey protein samples in the presence of lactose was estimated by an in vitro digestion method with continuous dialysis. Four aW (0.3, 0.5, 0.7 and 0.97), three temperatures (75, 100 and 121 degrees C) and three heating periods (50, 500 and 5000 s) were selected. The initial lysine:lactose molar ratio was 1:1. Amino acid profiles showed that excessive heating of whey (121 degrees C, 5000 s) destroyed a significant proportion of cystine at all aW, lysine at aW 0.3, 0.5 and 0.7, and arginine at aW 0.5 and 0.7. At aW 0.3, 0.5 and 0.7, protein digestibility decreased (P less than 0.05) as the temperature increased from 75 to 121 degrees C for a heating period of 5000 s, and as the heating time was prolonged, from 500 to 5000 s at 121 degrees C. Excessive heating also decreased (P less than 0.05) the availabilities of all amino acids at aW 0.3, 0.5 and 0.7. The availabilities of lysine, proline, aspartic acid, glutamic acid, threonine, alanine, glycine and serine were particularly affected. Severe heating at aW 0.97 did not seem to favour the Maillard reaction, but the availabilities of cystine, tyrosine and arginine were decreased, probably as a result of structural modifications of the protein upon heating. Heating whey protein concentrates in the presence of lactose not only affected lysine, but also impaired enzymic liberation of other amino acids, according to the severity of heat treatments and aW.     

Growth and Survival of Escherichia coli O157:H7 in Different Types of Milk Stored at 4 °C or 20 °C

ABSTRACT: Samples of ultra heat-treated (UHT) milk (whole, semiskimmed, and skimmed milk, whole milk with cinnamon and lemon flavors, and semiskimmed milk with cocoa) were collected. Growth of E. coli O157:H7 was detected in whole milk at 4 °C (generation time 0.89 d) and in all milks at 20 °C during the first 24 h. Growth of nonpathogenice. coli was detected in milk samples without flavors during the same period of time. The fastest death time of E. coli O157:H7 was detected in whole milk with cinnamon and lemon at 4 °C (−1.35 d) The nonpathogenic strain showed the fastest death time in skimmed milk at 20 °C.     

Comparison of deterioration of rye under two different storage regimes

Deterioration of stored rye samples was studied at different moisture contents and temperatures. Germination, presence of visible and invisible microflora, and free fatty acid values (FAV) were determined for samples at 10.0, 12.5, 15.0 and 17.5% moisture content (wet mass basis) stored at 10, 20, 30 and 40 °C for 16 weeks. Results of deterioration at constant moisture content (case 1) were compared with previously reported results for deterioration under declining moisture content (case 2). Germination rate was almost the same for all the moisture content samples stored at 10 °C for both cases, but a significant decrease was observed at other temperatures with high moisture content. Fatty acid values remained similar in both cases when rye was stored at 10 and 20 °C, whereas at 30 and 40 °C, FAVs of the rye samples in which the moisture content was maintained were high and increased with an increase in temperature and moisture content. Visible mould appeared early in the samples whose moisture content was maintained. Penicillium spp. and Aspergillus glaucus group were the predominant fungal species present in both the cases throughout the study. The rate of deterioration was significantly different between the two cases.     

Effect of different time intervals on the viscosity of batter and on the sensory qualities of puras (pancakes) prepared using chhana and paneer whey

The viscosity of pura (pancakes) batter samples prepared with bovine, buffalo and mixed wheys (80 : 20 whey to water) was measured at different time intervals at a temperature of 25  ±  2°C using a Brookfield viscometer (LVT 98534). The viscosity of sweet pura batter samples increased after 1 h, remained constant for another 2 h and then decreased, whereas the viscosity of salty pura batter samples increased from freshly prepared batter to 1 h and then remained constant. Sensory evaluation of both sweet and salty puras at different time intervals from batter preparation was also carried out. The overall acceptability scores for sweet puras prepared using bovine milk chhana whey, buffalo milk paneer whey and mixed milk chhana whey and stored for up to 4 h at 25  ±  2°C and for 24 h at 4–5°C were not significantly different, and the same conclusion applied to salty puras made from bovine milk chhana whey. It was concluded that sweet and salty pura batters can be prepared from any chhana or paneer whey.     

Effect of temperature and fruit-moisture content on discolouration of dried, sulphured Bon Chretien pears during storage

Summary Discolouration of Bon Chretien pears which had been treated with sulphur dioxide and which had moisture contents of either 16, 18 or 20%, was monitored during storage at 4, 7, 10 and 20 °C. Colour was quantified in terms of CIE L*, a*, b*, hue and chroma. L* was used to predict quality retention. Discolouration was categorized as a decrease in all colour parameters, except a* which increased with storage. Measurement of L* showed that only fruit at 16% moisture content and stored at T ≤ 10 °C retained their original colour. The rate of change in overall colour was observed in the following order at 20 °C, 20% > 18 > 16% moisture content. Fruit with 18 and 20% moisture content could be stored at 10 °C for at least 140 weeks without changing their quality grading. Storage at 20 °C shortened this period to 60 and 27 weeks for fruit at 18 and 20% moisture content, respectively.     

Solubilization of wheat gluten with sodium hydroxide

The solubility of wheat gluten may be increased greatly by treatment with 0.25 M sodium hydroxide. At temperatures of 40°C and above, the solubility of the protein exceeds 100 mg/ml in a reaction time of 6 hr or less. The products from the reaction of 60°C and 80°C were darker than the original gluten and had an unpleasant odour of H₂S on dissolution in water. They also contained traces of lysinoalanine. The 40°C reaction product was about the same colour as gluten, and its solutions in water did not smell of H₂S. Reaction of gluten at 20°C also caused a large increase in solubility, but after 24 hr the solubility was only 77 mg/ml. This product was also of the same colour as gluten, and did not smell of H₂S in solution. Neither the 20°C nor the 40°C products contained detectable traces of lysinoalanine. For reasons of flavour, colour, lysinoalanine content and economy of time, the optimum reaction conditions are 6 hr at 40°C.     

The Effects of Marination and Cooking Regimes on the Waterbinding Properties and Tenderness of Beef and Bison Top Round Roasts

ABSTRACT: The combined effect of marination and different cooking regimes on the cooking yield and palat-ability of bison and beef top round roasts was investigated. Semimembranosus (SM) muscles from beef and bison top rounds were injected with a marinade to achieve 20% extension by weight and 0.5% sodium chloride and 0.3% sodium tripolyphosphate levels and then subdivided into 4 roasts and cooked by following 4 cooking regimes: cooking at a constant temperature of 75°C (control; C); similar to the control treatment except that roasts were held at an internal temperature of 55°C for 45 min (Hold45) or 90 min (Hold90) prior to final cooking at 75°C; initial cooking at 55°C with a 5°C increase in oven temperature every hour (Step-up) until the 71°C internal temperature was achieved. Cooking yield, expressible moisture, purge, and shear force of processed roasts were determined. Marination by injection improved the yield and tenderness of beef and bison SM roasts. The cooking yield for injected samples (78%) was significantly (P < 0.05) higher compared with noninjected controls (68%). Injected SM roasts from bison had lower cooking losses than those from beef, whereas control samples from these 2 species did not differ in their cooking yields. Injected beef SM was more tender than bison SM; however, marination significantly reduced the shear force values of SM roasts for both species (i.e., shear force values of 82 N in control samples was reduced to 63 N in injected ones). The cooking regimes, Hold45, Hold90, and Step-up (which allowed a longer time at 55 to 60°C), gave products with lower ( P < 0.05) shear force values than those of the controls. Based on the cooking yield and time involved, the Hold 45 treatment performed the best.     

Influence of the degree of hydration on the thermal expansion of muscle tissue

The variation of expansivity, α, of beef M. semitendinosus with moisture content was determined by measurement of the temperature change induced by adiabatic compression over the moisture content range 2 to 90%, at temperatures (T) of 1, 8 and 15°C. At low levels of hydration, α increased with moisture content, reached a maximum around 35% water, and thereafter decreased. The data suggested that thermal expansivity is related to water binding, and the application of a simple expansivity model based on 'free' water, 'bound' water and dry-solids, gave a value for the expansivity of 'bound' water at 8°C of 8.9±1.7x10-⁴°C-¹, about seventeen times that of 'free' water.     

Improved Sanitizing Treatments for Fresh Tomatoes

ABSTRACT:  Fresh tomatoes repeatedly have been associated with major outbreaks of salmonellosis; however, efforts to disinfect them with chlorine or other sanitizing agents have had only mixed success. Our objective was to determine whether hydrogen peroxide (H₂O₂) treatments would be more efficacious than conventional methods in disinfecting tomatoes containing human pathogens and, at the same time, be noninjurious to quality. Tomatoes were dip inoculated with Escherichia coli NRRL B-766 or a Salmonella cocktail and then held for 0, 24, or 48 h at 4 or 24 °C prior to treatment. Treatments included 200 ppm chlorine (Cl₂) at 20 °C for 3 min, water at 20 °C for 3 min or at 60 °C for 2 min, 1% H₂O₂ at 20 °C for 15 min or at 60 °C for 2 min, and 5% H₂O₂ at 60 °C for 2, 3, or 5 min. In tomatoes held 48 h postinoculation, the chlorine treatment was only marginally more effective than an equivalent water rinse in reducing the target bacterial population, while the hot water and 1% H₂O₂ treatments achieved reductions no greater than 1.3 logs. However, application of 5% H₂O₂ at 60 °C resulted in larger reductions. Efficacy of all treatments decreased as the time interval between inoculation and treatment increased. Greater reductions could not be achieved with 5% H₂O₂ at 60 °C by increasing the contact time or addition of surfactants, and these treatments caused some quality loss.     

Dietary fibre content of table olives processed under different European styles: study of physico‐chemical characteristics

Some European varieties of olive fruit (Douro, Hojiblanca, Cassanese, Conservolia, Taggiasca, and Thasos), processed under different conditions (black oxidised, fermented in brine or dried by different methods) were analysed, their contents of moisture, fat and dietary fibre being quantified. The percentages of moisture and fat were very different between varieties due to the different processing conditions, although differences between samples of the same variety were much less. The content of dietary fibre was around 12% of the fresh weight, although in dried samples this percentage increased to around 20%. Some physico‐chemical characteristics (water holding capacity, cation exchange capacity, and ion retention capacity) were measured. The water holding capacities were related to moisture content, dry samples having the lowest values. Processed olives had very low cation exchange capacity in comparison to other vegetables, exhibiting the same relationship between this characteristic and moisture content. Olive fibre retained more iron than calcium under the assay conditions. © 2000 Society of Chemical Industry     

NITROGEN EXTRACTABILITY AND MOISTURE ADSORPTION CHARACTERISTICS OF SUNFLOWER SEED PRODUCTS

Diffusion-extracted (DE) sunflower meal and protein isolate were compared with untreated samples for their nitrogen extractability and moisture adsorption. Nitrogen extractability values of 90% were found at pH 7 or above in the untreated meal, whereas a maximum solubility of only 70% was achieved at pH 9.0 in the DE meal prepared at 60°C. DE meal prepared at 80°C had low solubility over a pH range of 1–11 which indicated substantial denaturation of the sunflower proteins. The untreated isolate showed a sharp minimum solubility point in contrast to the law solubility of the DE isolate over a pH range of 3–7. Moisture adsorption values for the samples held at 5, 20 and 30°C indicated little difference in moisture contents at relative humidities of 11–55%. At higher levels, however, the untreated meal adsorbed more moisture than the DE meal. A reverse trend was noticed for the isolates as the moisture content of the DE isolate was higher than the untreated sample. The rate of moisture uptake by sunflower kernels was slower than that observed with rapeseed or soybean meats and lower total moisture contents were observed after a 4 hr soaking period.     

Processing Properties of Extruded Corn-Soy Blends

ABSTRACT: Extruded corn-soy blend (CSB), is a nutritious, fully cooked product that rehydrates at room temperature. CSB, at 10, 13, and 19% moisture was extruded at 115 °C and dried at 45, 65, and 85 °C. The porosity of the lower moisture samples was higher and dried more rapidly at all temperatures. These samples also exhibited a lower breaking strength that could facilitate grinding and color that approximated that of the standard CSB. Most of the chemically available lysine was retained during processing. There were no differences among the peroxide values (PV) of the extruded and dried products. Extruding at low moisture content, the extrudate can be dried rapidly and provide better storage stability.     

Effects of Vacuum Hydration on the Incidence of Splits in Canned Kidney Beans (Phaseolus vulgaris)

Dry red kidney beans were canned using two different pretreatments: soaking for 12 hr at 20°C, and vacuum hydration for 5 min followed by soaking for 2 hr at temperatures from 45-59.1°C. Samples were then packed, processed to commercial sterility, and tested for percentage of split beans after processing. Vacuum hydration pretreatments greatly decreased the incidence and severity of splitting in the canned product and accelerated water uptake while retaining the same moisture content after soaking as the conventional soak treatment. Vacuum-hydrated beans gained less moisture during retorting than conventionally treated samples.     

Characterization of Thermal Properties of Potato Dry Matter–Water and Starch–Water Systems

ABSTRACT: Potato dry matter samples of varying moisture contents were analyzed by differential scanning calorimetry (DSC). One endothermic and one exothermic transition were observed when the moisture content was < 50% (w/w) in the dry matter–water system. Both endothermic and exothermic transitions of potato dry matter were influenced by moisture content. One endothermic transition at about 66 °C was observed when the samples were reheated after 2 wk of storage at 5 °C. Gelatinization and retrogradation of starch are chiefly responsible for the endothermic transitions in the potato dry matter. The exothermic transition may originate from chemical reactions such as Maillard and caramelization during heating of a potato dry matter–water system when water is limited (< 50%, w/w) and at temperatures > 120 °C     

Measurement of the oxidation-reduction potential of cheddar cheese

ABSTRACT:  The objective of this study was to develop a method to measure the oxidation–reduction (redox) potential of hard cheeses such as cheddar and to investigate the impact on this parameter of measurement temperature, and factors associated with electrochemical cell design such as distance between reference and working electrodes and depth into the cheese of the platinum electrodes. For this purpose, a novel, self-sealing, platinum working electrode was constructed which was thin and flexible enough to be inserted directly into the cheese sample. A calomel electrode was used as the reference electrode and the circuit was completed with a 3 M KCl salt bridge. The physical orientation of electrodes, such as distance between reference electrode and working electrode, had a substantial effect on equilibrium time for redox potential measurement. The time required for redox potential to reach equilibrium was 2 d in cheddar cheese and the optimum distance between the platinum and calomel electrodes was 2.5 cm. The fastest equilibration time was obtained when the working electrode was inserted 5 or 6 cm into the cheese. Temperature also had an important effect on redox potential. The shortest time to reach equilibrium of potential was at room temperature (20 °C), but it was not practical to keep cheese at this temperature for a period of 2 d. Therefore, redox measurement at 12 °C was recommended in spite of the longer equilibration time compared with room temperature. The results of this study suggest that the novel platinum working electrode allows reproducible measurement of the oxidation–reduction potential of cheddar cheese.