The effects of oil-quenching and over-tempering heat treatments on the dry sliding wear behaviours of 25CrMo4 steel

This study, it was aimed to examine the dry sliding wear properties of the tempering and over-tempering heat treatments of 25CrMo4 steel, which is used in the manufacture of parts such as axle shafts, axle sleeves, turbine parts, and turbine blades in the automotive industry Oil-quenched 25CrMo4 steels could be subjected to high temperatures where they are used and may undergo over-tempering period. In this case, there may be changes in many mechanical properties such as wear. For this purpose, microstructural examination, hardness, and dry sliding wear tests were performed on the materials. As a result of the tests, it was observed that the sample, on which we applied the tempering and over-tempering heat treatment, had a martensitic microstructure. The hardness values of the tempered and over-tempered samples increased compared to the raw material and as expected, partially decreased in the over-tempered sample. Dry sliding wear losses decreased significantly in oil-quenched and over-tempered samples compared to the raw material. Even though the hardness decreased in the over-tempered sample, the wear loss was low. The variation between wear losses increased further with the increase in friction forces. While the maximum friction coefficient was highest in the oil-quenched sample, it was lowest in the raw sample.

Acidic water tempering and heat treatment, a hurdle approach to reduce wheat Salmonella load during tempering and its effects on flour quality

The cultivation and processing of wheat render it susceptible to microbial contamination from varied sources. Hence, pathogens such as Salmonella can contaminate wheat grains, which poses a food safety risk in wheat-based products. This risk is displayed by the incidence of foodborne illness outbreaks linked to Salmonella-contaminated wheat flour and flour-based products. The purpose of this study was to assess the effectiveness of combining acidic water and heat treatment in reducing the Salmonella load of hard red spring (HRS) wheat grains during tempering. Effective treatments were then evaluated for their effects on wheat flour quality. Tempering with sodium bisulfate (SBS), lactic acid (LA), and citric acid (CA) at 15% w/v alone reduced (p < 0.001) wheat Salmonella load by 3.15, 3.23, and 2.91 log CFU/g, respectively. Heat treatment (55 °C) reduced (p < 0.001) wheat Salmonellaload by 4.1 log CFU/g after 24 h of tempering. Combining both tempering and heat treatments resulted in a greater reduction in Salmonella load as non-detectable levels (<2 log CFU/g) of Salmonella in the wheat grains were obtained after 12 h of tempering with LA (15%) + heat. A similar result were achieved for both SBS (15%) + heat and CA (15%) + heat treatments after 18 h of tempering. Applying the combined treatments in HRS wheat grains resulted in comparable wheat flour baking (volume, texture, and crumb structure) and physicochemical properties (rheology and composition) relative to the control (tempering with water alone). The results from this study has the potential to be utilized for developing more effective methods for improving the food safety of wheat flour against Salmonella contamination.

Phage Biocontrol Effectively Reduces Contamination of Wheat with Shiga Toxin-producing Escherichia coli O121 and O26 Without Adverse Effects on Flour Quality

Contamination of wheat flours with Shiga toxin-producing E. coli (STEC) is a concern for the milling industry. Milling-specific interventions are needed to address this food safety hazard. The objectives for this study were to determine the efficacy of bacteriophage treatment in reducing wheat STEC contamination during tempering, and assess its effects on flour milling and baking quality. Bacteriophage solutions were prepared by mixing sterile water with the bacteriophage treatment at the following levels: 1 × 106 (0.1%), 2.5 × 106 (0.25%), 5 × 106 (0.5%), 1 × 107 (1.0%), and 1 × 108 (10%) PFU/g wheat dosage. Sterile water (0%) was used as the control. Predried wheat grains were inoculated with STEC (O121 and O26) at 5.0 and 6.0 log CFU/g to restore its original moisture content followed by resting for 24 h. Inoculated grains were then tempered (16% moisture, 24 h) using the prepared bacteriophage solutions. Grains were sampled at 0.5, 1, 2, 6, 12, 18, and 24 h during tempering to determine STEC concentration. The effects of the phage solutions on the flour milling and baking quality were also tested. Tempering time, bacteriophage dose, and their interaction had significant effects on phage efficacy (P < 0.05), with better reductions observed at longer tempering times and higher bacteriophage doses. The use of phage solutions reduced (P < 0.05) wheat STEC concentration after tempering, with the 10% treatment (3.2 logs) achieving ahigher reduction than the 1% (2.4 logs) treatment under similar phage preparation. Phage tempering (including at the highest concentration examined, i.e., 10%) produced wheat flours with comparable quality to the control. Phage-treated wheat flour resulted in breads with finer crumb structure, and comparable texture compared to the control. Phage tempering is a viable intervention for wheat milling as it reduced STEC loads of wheat with no detrimental effects to flour milling and baking quality.

Fate of salmonella and shiga-toxin producing Escherichia coli on wheat grain during tempering

Outbreaks of Salmonella and Shiga-toxin producing Escherichia coli (STEC) linked to wheat flour led to increased interest in characterizing the fate of Salmonella and STEC on wheat during processing. Tempering is the stage of wheat processing where water is added to toughen the bran prior to milling, which has the potential to influence pathogen behavior on the kernels. This study aimed to quantify changes in the numbers of STEC and Salmonella inoculated onto soft red winter wheat, and to observe potential changes in the distribution of the pathogens on the surface of kernels during tempering. Lab-scale tempering experiments were conducted to quantify the water activity of and bacterial populations on wheat grain at various time points during 16 h of tempering. The highest water activity observed throughout 16 h of tempering was 0.88. There was no significant change (p > 0.05) in numbers of Salmonella, STEC, or native mesophiles. Using confocal microscopy, observation of Salmonella and STEC cells expressing mCherry on wheat kernels showed an even distribution of inoculated cells, though the localization of cells on kernels did not change significantly after tempering. Even though the environment was not favorable for pathogen replication on grain, the population remained stable, suggesting that disinfection of the kernels prior to milling could reduce food safety concerns in flour.

Impact of Chlorinated Water on Pathogen Inactivation during Wheat Tempering and Resulting Flour Quality

ABSTRACT

Outbreaks of enteric pathogens linked to wheat flour have led the wheat milling industry to seek solutions addressing this food safety concern. Chlorinated water at 400 to 700 ppm has been used in the flour milling industry as a tempering aid to control growth of yeast and mold in tempering bins. However, the effectiveness of chlorinated water for inactivating enteric pathogens on wheat kernels was unknown. Five strains of Shiga toxin-producing Escherichia coli and two strains of Salmonella were inoculated onto hard red spring wheat at 7 log CFU/g and stored at room temperature for 1 month. Inoculated wheat was tempered with four concentrations (0, 400, 800, and 1,200 ppm) of chlorinated water (pH 6.5). The reduction due to chlorine was determined by calculating change in microbial loads at each chlorine level by using the response at 0 ppm as a reference. Uninoculated wheat tempered with chlorinated water was used to measure flour quality parameters. Changes in pathogen population over 18 h ranged from -2.35 to -0.30 log CFU/g with 800 ppm of chlorinated water and were not significantly different from changes at 400 and 1,200 ppm. Significant (P < 0.05) differences in the extent of reduction were observed among strains. However, the effect of chlorinated water at reducing native microbes on wheat kernels was minimal, with an average reduction of 0.39 log CFU/g for all concentrations. No significant (P > 0.05) changes occurred in flour quality and gluten functionality or during bread making for grains tempered at 400 and 800 ppm of chlorinated water. There were small but significant (P < 0.05) changes in flour protein content, final viscosity, and water absorption when tempered with 1,200 ppm of chlorinated water. The data showed that the level of chlorinated water currently used in industry for tempering could reduce enteric pathogen numbers by 1.22 log CFU/g for Shiga toxin-producing Escherichia coli and 2.29 log CFU/g for Salmonella, with no significant effects on flour quality and gluten functionality.

HIGHLIGHTS

Electron microscopy study of carbides precipitated during destabilization and tempering heat treatments of 25 wt.%Cr-0.7 wt.%Mo high chromium cast irons

The effect of a 0.7 wt.%Mo addition on the microstructure and hardness of a heat treated 25 wt.%Cr-2.4 wt.%C cast iron has been studied via comparison with a Mo free reference 25 wt.%Cr-2.4 wt.%C iron. Destabilization led to precipitation of M₇C₃ and M₂₃C₆ secondary carbides in the reference iron, whereas M₂₃C₆ secondary carbide was found in the iron with 0.7 wt.%Mo. Tempering resulted in additional secondary carbide precipitation and formation of ferrite. Secondary hardening was found in the iron with 0.7 wt.%Mo. For the destabilized + tempered condition the macro-hardness of the iron with 0.7 wt.%Mo addition was higher than the reference iron due to a finer and denser distribution of secondary-carbides.

Improved reliability of mechanical behavior for a thermal tempered lithium disilicate glass-ceramic by regulating the cooling rate

Traditional thermal tempering was applied to lithium disilicate (LD) glass-ceramic specimens with bar-like and disc-like shapes. The tempering process was conducted by heating the specimens to a temperature below the dynamic softening point, and then rapid cooling in silicone oil with different temperatures ranging from room-temperature to 300 °C to regulate the cooling rate. Effect of the oil-temperature on mechanical behavior of the tempered glass-ceramic was investigated. For the tempering at the lower oil-temperature (e.g., at room-temperature), it was found that the LD glass-ceramic specimens with both the bar-like and disc-like shapes could be remarkably strengthen and toughen, however, obvious anisotropy in fracture toughness was displayed by the specimens with the bar-like shape. With increasing the oil-temperature up to 250 °C, the mechanical anisotropy of the bar-like specimens could be significantly alleviated without much loss of the strengthening effect. The results can provide references for improving reliability of mechanical behavior for the tempered LD glass-ceramic by regulating the cooling condition according to specimen geometry.

Determination of the effect of high energy ultrasound application in tempering on flour quality of wheat

This research has been carried out under laboratory conditions. To determine the effect of soaking with ultrasound application to dampen hard wheat samples at one stage in tempering process was the prior goal. In the experiments, Bezostaya-1 wheat samples in different hardness levels (45, 65 and 75%) are used as material. The milling quality and qualitative properties of the flour were investigated. Results compared with the classic tempering process which has two stages tempering for hard and semi-hard wheat at the industrial applications. Ultrasonication of the samples has been applied by a probe-type ultrasound device. Because of experimental deviations, inevitable positive effect of ultrasonic tempering had not seen in the quality parameters of milling experiments like flour yield and energy consumption. But tempering with ultrasound application increased the speed of water intake and diffusion into the grain center. In the study, the wet gluten rates of the flour obtained by classical tempering process were 24.52% and the gluten index rate was 87.17%, while the results obtained by ultrasonic tempering were 22.70% and 93.33%, respectively. Thus it raised flour quality a little, possibly, due to low amount but better quality gluten coming from central endosperm in the flour obtained. Other analysis results in flour showed significant differences in some values of classical and ultrasonic tempering processes. As a result of ultrasonic tempering, the fineness rate (granulation) increased from 73.27% to 79.77%, ash content decreased from 0.61% to 0.55%, Zeleny sedimentation value decreased from 25.0 mL to 23.67 mL, flour stability increased from 9.76 min to 12.06 min, water absorption 59.1% decreased from 61.28%, softening resistance increased from 400.33 BU to 504.50 BU, maximum resistance increased from 420.50 BU to 536.16 BU. In bread trials, bread volume increased from 328.3 mL to 347.3 mL, and specific volume increased from 2.39 mL / g to 2.57 mL / g. These issues have been confirmed by some analysis such as fine granulation, low ash content, high gluten index, some farinogram, and extensigram properties, and finally better performance in bread making was observed.

Pre-crystallization process in chocolate: Mechanism, importance and novel aspects

Pre-crystallization is an important step in the production of chocolate, which is defined as tempering of cocoa butter through primary and secondary nucleation. The goal of tempering is to obtain a sufficient amount of β_V polymorph of the right size. The pre-crystallization process has a great impact on the quality and production cost of final product. Development of chocolate technology requires the use of the most appropriate techniques and ingredients without negatively affecting the quality characteristics. Applications of novel technologies within the confectionery industry have allowed production of chocolate in sufficient quantities to meet the public needs. In order to provide and investigate the potential and usage of novel technologies, the present review focused on different pre-crystallization methods and factors affecting the processing conditions. Seeding and ultrasound-assisted pre-crystallization can be used as alternatives to conventional tempering process. However, in both methods, optimization of experimental conditions is required.

Effects of tempering (annealing), acid hydrolysis, low-citric acid substitution on chemical and physicochemical properties of starches of four yam (Dioscorea spp.) cultivars

The effects of tempering (annealing), acid hydrolysis and low-citric acid substitution on chemical and physicochemical properties of starches of four Nigerian yam cultivars were investigated. Crude fat and protein contents of the native starches decreased significantly after the modifications, while nitrogen-free extract increased significantly with acid hydrolysis and citric acid substitution. Acid hydrolysis and low-citric acid substitution reduced the least concentration for gel formation of the starches from 4 to 2% w/v, but tempering had no effect. Swelling power of the starches reduced significantly, and water solubility increased significantly at 75 and 85 °C, especially with acid hydrolysis and low-citric acid substitution. However, tempering significantly reduced starch solubility in the four cultivars. Paste clarity of starches of white (29.17%), water (18.90%), yellow (30.90%) and bitter (10.57%) yams reduced significantly with tempering to 14.43, 11.83, 16.93 and 7.27%, but increased significantly with acid hydrolysis to 41.40, 35.37, 28.77 and 32.33%, and low-citric acid substitution to 36.60, 44.17, 50.67 and 14.33%, respectively. Pasting properties such as peak, trough, breakdown, final, and setback viscosities and peak time of native starches reduced significantly with acid hydrolysis and low-citric acid substitution, however, tempering significantly increased their pasting temperature, peak time, setback and final viscosities.

Production of sn-1,3-distearoyl-2-oleoyl-glycerol-rich fats from mango kernel fat by selective fractionation using 2-methylpentane based isohexane

High-purity isohexane containing 88.12% 2-methylpentane, which has a higher polarity than industrial hexane, was selected to selectively fractionate mango kernel fat to produce 1,3-distearoyl-2-oleoyl-glycerol (SOS)-rich fat. The three-stage fractionation process was optimized by considering the stearin yield and its SOS content to obtain a third stearin (TS). This fat contained a high percentage of SOS (69.2%) with only 0.8% diacylglycerol. Mass spectra and sn-2 fatty acid analyses further revealed that the TS was mainly composed of symmetrical monounsaturated triacylglycerols. Compared with cocoa butter (CB), the unique composition of the TS improved its thermal properties (35.6% and 0% solid fat content at 35°C for the TS and CB, respectively). In particular, tempered binary fat blends, which were composed of 20-50% TS and 50-80% CB, showed acceptable compatibility at 20-28°C. The TS could be utilized by chocolate manufacturers to make products suitable for sale and consumption in tropical conditions.

Effect of tempering methods on quality changes of pork loin frozen by cryogenic immersion

The quality characteristics of pork loin frozen by cryogenic immersion were examined, such as the drip loss, cooking loss, water holding capacity, moisture content, protein solubility, lipid and protein oxidation, color, and microstructure, and compared after different tempering methods: radio frequency (27.12MHz), water immersion, forced-air convection, and microwave tempering. Forced-air tempering was the most time-consuming process, whereas electromagnetic energy methods (radio frequency and microwave) were the shortest. The tempering rate of radio frequency at 400W was 5 and 94 times greater than that obtained with water immersion and forced-air tempering, respectively. The drip loss, water holding capacity, moisture content, color, and microstructure of pork samples all declined as a result of microwave tempering. By contrast, the least degree of changes in the drip loss, microstructure, and color of the pork loin samples was obtained with radio frequency tempering, suggesting its potential application in providing rapid defrosting without quality deterioration in the frozen meat industry.

Effect of Aspergillus niger xylanase on dough characteristics and bread quality attributes

The present study was conducted to investigate the impact of various treatments of xylanase produced by Aspergillus niger applied in bread making processes like during tempering of wheat kernels and dough mixing on the dough quality characteristics i.e. dryness, stiffness, elasticity, extensibility, coherency and bread quality parameters i.e. volume, specific volume, density, moisture retention and sensory attributes. Different doses (200, 400, 600, 800 and 1,000 IU) of purified enzyme were applied to 1 kg of wheat grains during tempering and 1 kg of flour (straight grade flour) during mixing of dough in parallel. The samples of wheat kernels were agitated at different intervals for uniformity in tempering. After milling and dough making of both types of flour (having enzyme treatment during tempering and flour mixing) showed improved dough characteristics but the improvement was more prominent in the samples receiving enzyme treatment during tempering. Moreover, xylanase decreased dryness and stiffness of the dough whereas, resulted in increased elasticity, extensibility and coherency and increase in volume & decrease in bread density. Xylanase treatments also resulted in higher moisture retention and improvement of sensory attributes of bread. From the results, it is concluded that dough characteristics and bread quality improved significantly in response to enzyme treatments during tempering as compared to application during mixing.