| Garlic is a traditional medicinal biologic plant.Its unique flavor made it an indispensable condiment in daily cooking.It has many physiological activities,such as anti-inflammatory,anti-inflammatory,improving the immunity of the body and preventing cardiovascular diseases.In this thesis,fresh garlic was used as the test material and the experiments involved several aspects as follows:First,the influence of sodium sulfite treatment on the main quality indexes of the dehydrated garlic slices was investigated.Then the contact ultrasonic combined with hot air was used to dry garlic slices.Mass transfer model was built and the quality changes of the dehydrated garlic slices before and after drying were analyzed.Finally,the dehydrated garlic slices were ground into garlic powders with different particle sizes.The properties of the powders and their stability during storage were studied.The results are shown as follows:1.The browning problem may decrease the quality of dehydrated garlic during drying process.In this chapter,the effects of concentration of sodium sulfite solution,time and temperature on the color,rehydration ratio,sulfur dioxide content,thiosulfinates content and antioxidant of dehydrated garlic were studied.It was found that sodium sulfite solution had significant effect on the quality of dehydrated garlic.The garlic color was better than control group,when sodium sulfite immerson was performed(500 mg/L,30 min).The sulfur dioxide residue increased with the sodiur sulfite concentration and treatment time.After soaking,thiosulfinates content was significantly higher than that in the control group.2.A self-designed hot-air convective dryer coupled with contacting ultrasound system was used for the dehydration of garlic slices.Contacting ultrasound significantly accelerated the drying process.Compared with non-ultrasound treated samples,the drying time of garlic samples sonicated at 1513.5 W/m 2 was shortened by 35.0%at 50?,48.5%at 60? and 50.0%at 70?.According to moisture transport simulation using a diffusion model considering sample shrinkage,both water effective diffusivity and external mass transfer coefficient were enhanced when garlic samples contacted ultrasound directly during drying.Meanwhile,internal water diffusion was more affected by contacting ultrasound.Furthermore,contacting ultrasound had a positive effect on the preservation of organosulfur compounds in garlic slices during drying.The browning problem of garlic products during hot-air drying was also alleviated if contacting ultrasound treatment was performed properly.Besides,no over-heating problem was observed during contacting ultrasound enhanced drying within the studied experimental range.3.The garlic powders were divided into particle size,namely ?(450-300 ?m),?I(300-150 ?m),?(150-75 ?m)and IV(<75?m).The results showed that the powder properties of the garlic powders changed markedly with the particle size.The pine density,vibratory density,water holding property and oil holding property were all decreased with the decreasing of particle size,while the rest angle and the sliding angle increased with the decrease of the particle size.The color of garlic powder increased with the decrease of particle size changes(p<0.05).Thus,particle size reduction can be improve garlic powder color.In addition,garlic powders were amorphous,and it did not change the structure of garlic powder during pulverization.The main functional ingredient of garlic powder was thiosulfate,which changed significantly with particle size.When the particle size was less than 75 ?m,the thiosulfate content was the highest.The variation trends of organic sulfides and total phenolics were similar,which generally increased with particle size declining.The antioxidant activity was detected.It was found that particle size had no significant effect on antioxidant activity of ABTS,and had significant effect on FRAP antioxidant activity.4.The water adsorption capacity of garlic powders with four particle sizes was studied and their thermodynamic properties were analyzed.The results showed that the GAB model can effectively fit the adsorption isotherms of garlic powder at 20,35 and 50?.Under the same temperature,there was no significant difference in the M0 value of the four samples,and the adsorption specific surface area S0 decreased with the increase of temperature and the decrease of the particle size.Through the analysis of the thermodynamic properties of the garlic powder,it was found that the differential enthalpy of garlic powder was small size was larger at high moisture content,indicating that the energy required for the dehydration was relatively large.Under the low water content,the differential entropy of the sample ? and the sample IV were greater than the sample ? and the sample ?.It revealed that the number of the adsorption sites under the low water content was larger than the size of the sample with the low water content,and the hygroscopicity of the powder with the low water content was stronger under the low water content condition.Besides,the adsorption process of garlic powder was a non spontaneous reaction driven by enthalpy.5.The storage stability of garlic powder under three humidities was investigated.The results showed that the ambient humidity had a significant influence on the quality of garlic powder.The garlic powder stored under the relative humidity of 11%had the best color and lustre color,the best sliding property,the highest retention rate of thiosulfate.Meawhile,the moisture content of garlic powder stored under the relative humidity of 33%exceeded 7.5%,but there was no significant difference(p>0.05)in its color and slipping with the garlic powder before storage.The average retention rate of thiosulfate after 90-d storage was about 70%,and the storage of high humidity could easily lead to the deterioration of the quality of garlic powder.Moreover,its color and fluidity were significantly affected and the retention rate of thiosulfate ester was the lowest. |
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