Search

Vacuum mixing is a new method of dough mixing in noodle industrial production which allows more water in the noodle formula and facilitates gluten development. The quantity and molecular structure of glutenin macropolymer (GMP) governs the gluten strength and dough properties, especially in flour products' processing. In order to learn about the changes of GMP characteristics under vacuum mixing, 3 wheat cultivars with different quality were selected as the material, and mixing experiments were conducted under different vacuum levels (0, 0.06 and 0.08 MPa). GMP content and particle size distributions of freeze-dried noodle doughs were determined, and the free sulfhydryl group (-SH) contents in total protein and GMP were measured respectively using Ellman reagents. The results showed that the vacuum mixed noodle dough at 0.06 MPa had a higher GMP content compared with the non-vacuum mixed dough. However, extremely high vacuum degree (0.08 MPa) could decrease the GMP content. Vacuum mixing at an appropriate vacuum level induced a decrease in the free -SH content in total protein. This result indicated that more unbonded -SH was involved in gluten protein cross-linking. However, in noodle doughs of Jimai 22 and Ningchun 4, extremely high vacuum degree could go against free thiol oxidation and formation of disulfide bonds in protein, leading to the increased -SH content. This could help explain the observed change in GMP quantity. Vacuum mixing significantly influenced the particle size distributions of GMP, and the appropriate level of vacuum could increase the GMP size. The percentages of volume, surface area and number of large-size GMP with diameter >100 fim in Jimai 22 and Ningchun 4 doughs mixed at 0.06 MPa were significantly higher than at 0 and 0.08 MPa (P<0.05), while the volume percentage of large-size GMP in Zhengmai 366 dough was significantly increased when mixed at 0.08 MPa. The certain vacuum degree could induce a reduction in the free -SH content in GMP for Jimai 22 and Ningchun 4; but for Zhengmai 366, the free -SH content in GMP was not affected by vacuum degree. The results also showed that the difference in GMP content between vacuum mixed dough under 0.06 MPa and non-vacuum mixed dough was significant for Jimai 22 (P<0.05); but for Ningchun 4 and Zhengmai 366, the difference was not significant. Furthermore, we found that the size distribution of GMP in Zhengmai 366 dough was less influenced by the vacuum degree compared with the other 2wheat flours. The phenomenon suggested that the polymeric protein size distribution in noodle dough from weak-gluten flour was more susceptible to the degree of vacuum. In conclusion, the potential gluten protein repolymerization in noodle dough is induced by appropriate vacuum mixing, and the effect of vacuum degree on GMP properties for strong-gluten wheat flour is significantly less than that for weak-gluten flour. [ABSTRACT FROM AUTHOR]

Dry processing is a key step for Chinese dried noodle production. It closely related to the energy consumption, production efficient and quality property of the product. Temperature, relative humidity, and air velocity of drying medium are the most important factors that influencing the noodle dry processing, and these factors also have mutual influence. In previous studies the effect of temperature and relative humidity on noodle quality has been investigated. But people know little about the flow of the air in tunnel-type drying chamber, it is very important for noodle drying and energy consumption. No appropriate device that can adapt well the special environment conditions in chamber-high temperature, high relative humidity and easy condensation is the main reason. In order to know the air flow conditions and analyze the effect of air velocity on temperature and relative humidity in actual noodle dry processing, a production line with 5 rows of 60 m in tunnel drying room was chose as the research object. In this study a new experimental instrument, meteorograph (Kestrel NK-4500), was used to research the characteristic of drying medium (air velocity, wind direction, temperature, relative humidity). For the sake of discussion in this paper the drying chamber was divide into four stages by length (equal distance), Istage (0-15 m), IIstage (15-30 m), IIIstage (30-45 m), IVstage (45-60 m). Results showed that there were significant differences in air velocity, temperature and relative humidity among different stages. The air velocity which influenced by the location and density of the ceiling fan, gradually diminished (Istage: 0.95 m/s, IVstage: 0.89 m/s,IIIstage: 0.79 m/s, IVstage: 0.50 m/s) and all were below at 1m/s.The air velocity in middle row (0.54 m/s) was significantly lower than that in left (0.89 m/s) and right (0.90 m/s). Wind direction is analyzed by the wind rose plot. In the drying chamber the wind direction-distribution was prone to the side where the moisture removal mouth located. The temperature in chamber increased during 0-35 m, then decreased. The trend of the relative humidity is similar to the air velocity, increased rapidly in the beginning and then gradually diminished with a average humidity (76.67%). In 4 drying stages, the relative humidity in left side was significantly higher than that in middle and right side, it was mainly influenced by the position of moisture removal mouth. The air velocity significant impacted the temperature and relative humidity in the drying chamber, but in different drying stages the influences were different. During 15-45 m of drying distance, the air velocity had obvious positive correlation with the temperature; but for 0-15 m and 45-60 m, the air velocity and temperature had significant negative correlation. In 0-45 m of drying distance, the air velocity had significant negative correlation with relative humidity. From this study we also find that the meteorograph can adapt well the special environment conditions in chamber with high temperature, high relative humidity and easy condensation. [ABSTRACT FROM AUTHOR]

A simultaneous infrared dry-blanching and dehydration (SIRDBD) method utilizes infrared dry heat to blanch fruits and vegetables and simultaneously remove a certain amount of moisture. This study investigated the effects of three processing parameters, e.g. distance between infrared emitter and material (9.5, 12.5 and 15.5 cm), thickness (0.8, 1 and 1.3 mm, and the diameter was 6 cm) and processing time which was determined based on the complete inactivation of polyphenol oxidase (PPO), on blanching and dehydration of potato slices. The measured performance parameters were temperature, moisture ratio (MR), drying rate, relative residual PPO and surface color change (ΔE). In the test, the surface temperatures of all samples increased to predetermined temperatures within 1 min and then were kept at those temperatures for the rest of processing. In general, the tests showed that the radiation distance decreased from 15.5cm to 9.5 cm and the thickness of samples decreased from 1.3mm to 0.8 mm, which would lead to an increase of the maximum dehydrating rates of potato slices from 0.24 g/(gos) to 0.59 g/(gos), a decrease of the reduction time of PPO inactivation from 364 s to 152 s, and a reduction of the color difference value ΔE from 5.26 to 1.66. Therefore, the test results indicated that the thin slices and narrow distance between the infrared emitter and sample were desirable for the quick moisture reduction, fast inactivation of enzymes and less color change. The residual PPO activities after application of various processing conditions were between 0-8.51%, which corresponded to a moisture reduction from 37.96% to 55.42% (w.b.), and a processing time from 150 s to 420 s. This indicated that infrared heating could blanch fruits and vegetables and simultaneously remove a certain amount of moisture. In addition, when the thickness of potato slices increased, the activation energies of potato slices decreased, but the effective moisture diffusivities increased. The reduced distance between infrared emitter and sample improved effective moisture diffusivities of potato slices. The effective moisture diffusivities of potato slices under different processing conditions were between 3.37×10-10 m2/s and 6.36×10-10 m2/s (R2=0.974-0.983), and the activation energies of potato slices ranged from 20.34 kJ/mol to 32.59 kJ/mol (R2=0.951-0.996). First-order kinetics fitted well for PPO inactivation (R2 was from 0.926 to 0.988), and the predicted kinetic parameters provided useful information for the blanching processing. The rate constants of PPO inactivation under different infrared radiation conditions were between 0.0063 s-1 and 0.0151 s-1, and the reduction times ranged from 152 s to 364 s. The best processing parameters for the infrared heating mode were 9.5 cm radiation distance, 0.8 and 1 mm potato slice thickness and 150 and 180 s corresponding processing time, which resulted in 8.51% and 2.44% residual of PPO, 55.44% and 61.49% moisture content (w.b.), 1.66 and 2.24 ΔE, respectively. It has been concluded that SIRDBD method can be used as an alternative to manufacture blanched and partially dehydrated fruits and vegetables. For infrared dry-blanching, a narrow distance between infrared emitter and material with high temperature should is recommended. [ABSTRACT FROM AUTHOR]