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* ScienceDirect July 2007 Agricultural Sciences in China 2007, 6(7) 890-898

Preparation of Garlic Powder with High Allicin Content

LI Yul. 2 and XU Shi-ying2

1 College of Food Science and Technology. Henun Agricultural University, Zhengzhori 450002, P. R.China 2 The Ke). Laboratory of Food Science & Safety, Mini s rq of EducatiodSouthern Yangrze University, Wuxi 214036, I?R.China

Abstract

Garlic powder with high allicin content was prepared using microwave-vacuum and vacuum drying as well as nucroencapsulation to protect alliinase activity throughout the stomach and improve the ratio of alliin transforming into allicin. The results showed that the optimal drying condition was 376.1 W for 3 min, 282.1 W for 3 min, 188 W for 9 min, and 94 W for 3 min. The thiosulfinates retention after drying was 90.2%. Following drying, the garlic powder was microencapsulated by modified fluidized bed technique. Scanning electron microscope revealed good integrity and core materials that were embedded in the microcapsules. Studies on the release kinetics of microencapsulated garlic granulates in vitro using simulated intestinal fluid indicated that release of garlic powder could be controlled in the intestine by passing stomach conditions.

Key words: allicin, thiosulfinates, microwave-vacuum drying, garlic powder, microencapsulation

INTRODUCTION

Since ancient times, garlic has been used worldwide as a seasoning, spice, and herbal remedy (Ahmad 1996). Garlic is known to possess a vast variety of biological functions. It was reported an antimicrobial (Krest et al. 2000; Kim 2002), antithrombotic (Block et al. 1986), anticancer (Lawson 2000; Mousa 2001), and antioxidant (Farhath 1997; Siems et al. 1996; Yin and Cheng 1998; Sun et al. 1997; Prasad et al. 1996; Wu et al. 2001), and could improve the immune-system (Cheng er al. 1998; Kang et al. 2001), as well as had the capacity to lower serum lipid and glucose levels (Krest 2001; Brewer 2001; Lawson et al. 2001) and blood pressure (Sovova 2000). Since the identification of the thiosulfinate allicin in 1944, many studies have been focused on the thiosulfinates of garlic. The char- acteristic flavors of fresh garlic (Aflium sativurn) are

associated with thiosulfinates (RS(0)SR) and the volatile substances are formed by the action of the enzyme alliinase (EC4.4.1.4) on hydrolyzing S-alkyl-substituted cysteine sulfoxide derivatives with the corresponding alkyl alkane thiosulfinates, ammonia, and pyruvic acid (Krest er al. 2000). This enzyme is separated from its natural substrates until the garlic tissue is disrupted. As the nonprotein amino acid alliin (S-allyl-L-Cysteine Sulfoxide) i s the major substrate in garlic, allicin (diallylthiosulfinate) is the main thiosulfinate and con- stitutes 60-80% of total garlic thiosulfinates (Lawson et al. 1995; Block 1992). The reaction is shown in Fig. 1.

Many studies have recently provided strong evidence that most of these biological functions of garlic are attributed to allicin. In fact, no compound outside the thiosulfinates (of which allicin is about 60-80%) has been found that accounts for a significant portion of the pharmacological activities of crushed garlic at levels

Receiwd 7 August. 2006 LI Yu. Associate Professor, Ph D. Correspondence XU Shi-ying, TeVFax: +86-S10-5884496. E-mail: syxu@sytu,edu.cn

Accepted 22 Januaq. 2007

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Preparation of Garlic Powder with High Allicin Content 891

A Il i tnaEe P 51 2 H2C=CH-CHz- - -CH, -YWCOO - H*C=CH-CH,-S-S-CH~CH=-CH~ + 2CH3-c -coo ~ N H , ' +H20 NH; 8

Alliin Allicin Pyruvate

Fig. 1 Alliinase-catalyzed reaction of alliin into allicin, pyrucic acid, and ammonia.

representing normal human consumption (2-5 g/d). And these biological effects of thiousulfinates can be related to their strong SH-modifying and antioxidant proper- ties (Rabinkov et al. 1998; Prasad et ~1.1996).

In Japan and western countries, garlic products have been popular and marketed in recent years as health foods with beneficial physiological effects for humans. Consequently, the majority of the garlic supplements sold today are garlic powder tablets that are standard- ized on allicin (Sovova 2000; Lawson et al. 2001). However, the quality of garlic products is questionable. Many garlic products appear to undergo harsh process- ing (Emiko et al. 1997). Although garlic slices dehy- drated by freeze drying (FD) have excellent quality, it is also one of the most expensive processes for manu- facturing dehydrated garlic slices because of large capi- tal outlays and high operating costs. In recent years, microwave-vacuum drying (MVD) has been investi- gated as a potential method for obtaining high quality dried foodstuffs. MVD combines the advantages of both vacuum drying and microwave drying, and it can improve energy efficiency and product quality. Sev- eral fruits and grains have been successfully dried by MVD (Nidhal and Mohammed 2002; Sham et al. 2001; Erle and Schubert 2001). However, little information is available on garlic slices dried by the use of MVD (Cui et al. 2003). In this article, garlic slices were dried using the new drying method - microwave-vacuum drying combined with vacuum drying (MVDND) to produce high potency allicin-containing garlic powder for health foods.

It has been established that garlic powder and gran- ules can serve as important nutritional supplements. But it has also been found that if garlic powder or granules were stored for long periods, active ingredients present in freshly ground garlic were often eliminated or other- wise rendered inactive. The alliinase is irreversibly de- activated at the pH level in the human stomach. If garlic powder is taken directly, only an insignificant amount of allicin can be produced inside the body.

Therefore, in this study, garlic powder was microen- capsulated and coated with materials, which could re- sist stomach conditions, to prolong the shelf life and protect alliinase activity through the stomach. In this way, allicin could be released only in the intestines, re- sulting in the decreasing of the characteristic odor and aftertaste.

MATERIALS AND METHODS

Materials

Fresh garlic bulbs were obtained from the local market in Wuxi City, China. The garlic bulbs were subjected to gentle pressure by hand to separate them into cloves. The cloves were peeled, cut into two pieces using a kitchen knife, the thickness of each piece was 5 mm, and the slices were dried immediately. L-Cysteine, 5 5 ' - dithio-bis (2-nitrobenzoic acid) (DTNB), and Hepes were purchased from Sigma Chemical Co. (St. Louis, MO, USA).

Methods

Drying The fresh garlic slices were put in a thin layer and dried to a final moisture content of about 5% (wet basis), either by freeze-drying or microwave-vacuum (MVD, made by ourselves) combined with vacuum drying (VD, DZG-6050, Shanghai Senxin Ltd., China). FD was conducted using a laboratory freezing dryer (FD, LGJ-10, Beijing Sihuan, China), with plate tem- perature at 45°C and absolute pressure at 10 Pa.

MVD with VD was performed with 120 g garlic slices each time. There were four levels of output micro- wave power: 376.1,282.1, 188, and 94 W. Following MVD, VD at 40°C was conducted to dry the garlic slices to a final moisture content of 5%. During MVD, the rotation speed of the turntable was 5 r/min.

Response surface methodology (RSM) was used to

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892 LI Yu et al.

design the MVDND method to dry garlic slices. Three levels of drying time were chosen at each output mi- crowave power separately.

RSM data were submitted to the analysis of response surface by using the statgraphic computer program (statistical graphic system by Statistical Graphic Corporation, ver. 5 , 1991). Color measurement Comminion international de I’E classage (CIELAB) L’ (whiteness), a* (red-green), and b’ (yellow-blue) values of dried garlic powder were measured using a colorimeter (WSC-S Ltd., Shanghai, China). The colorimeter was calibrated with a white standard plate. Triplicate measurements were per- formed for each sample. Microencapsulation of garlic powder The garlic slices dried by MVDND were ground into garlic powder by a pulverizer (DFT-200, Dahai Co. Ltd., China), with average diameter in the range of 60 to 80 mesh.

One hundred and fifty grams of dried garlic powder was fluidized in a modified fluid bed coater (FLP-3 Ltd., Jiafa, China). The inlet temperature was adjusted to achieve a product temperature of 30°C. The garlic powder was then sprayed using ethyl cellulose (EC, 3%, w/w) in acetone and isopropanol as solvent at a ratio of 9: 1. The speed of spraying was adjusted to obtain a good and homogeneous film on the garlic powder.

The coated garlic powder using the above-mentioned process was further coated with a second layer of poly- mer solution, cellulose acetate phthalate (CAP, 10’3, w/w) in acetone, and isopropanol as solvent at the ratio of 1: 1 . The ratio of EC/CAP was 2:3. The ratio of garlic powder to wall materials was 4: 1. The encapsu- lation yield and encapsulation efficiency of microen- capsulating garlic powder was 95.0 and 96.8%, respectively. Microstructure determination The microcapsules were placed on SEM specimen holders using a double- coated adhesive tape (Ted Pella Ltd.. Redding, CA, USA) and then coated with a t hn layer of gold in a fine coat ion sputter JFC 1100 (JEOL Ltd., Akishinia, Japan). The surface structure of the microcapsules was observed by a high vacuum JEOL scanning elec- tron microscope (JMS-35, JEOL Ltd., Akishinia. Japan) at 10 kV. The microcapsules were fractured using a razor blade, perpendicularly, through a layer

of capsules attached to the specimen holder with a double-coated adhesive tape (Ted Pella, Redding, CA, USA) to observe. Determination of thiosulfinates Modified Lawson’s method (Lawson et u1. 1995) was used for quantitative determination of total thiosulfinates in fresh garlic, gar- lic powder, and microencapsulated garlic powder.

Fresh garlic cloves were peeled and homogenized in 5 mL g-’ of Hepes buffer (50 mM, pH 7.5). The homo- genate was allowed to stand at room temperature for 5- 10 min to ensure complete enzymatic conversion to thiosulfinates. Garlic juice was obtained by filtrating with the help of a filter paper. The solution of cysteine was freshly prepared in 50 mM Hepes buffer (pH 7.5). The concentration of cysteine was determined by mea- suring the amount of 2-nitro-5-thiobenzoate (NTB) formed after the reaction with 5,5’-dithio-bis (2- nitrobenzoic acid) (DTNB). All the reactions were car- ried out at 26°C. Five milliliters of cysteine solution was added into 1 mL distilled water, and 1 mL reaction mixture was diluted to 100 mL. Four-and-a-half milli- liters of the diluted solution was incubated in a cu- vette with 0.5 mL 50 mM Hepes buffer (pH 7.5) con- taining 1.5 mM DTNB. The absorbance at 412 nm was measured after 15 min (A,,). Five milliliters of cysteine solution was added into 1 mL garlic juice, and the mixture was incubated for 15 rnin. Reaction mixture of 1 mL was diluted to 100 mL. Four-and-a- half milliliters of the diluted solution was incubated in a cuvette with 0.5 mL 50 mM Hepes buffer (pH 7.5) containing 1.5 mM DTNB. The absorbance at 412 nm was measured after 15 min (A).

4 , 2 =A+ Chosulfinates ( D O 1 d - 7 = x loo)@ x 14150) Garlic extract was prepared by homogenizing each

preparation of garlic powder with distilled water (1 g 15 mL-I). Supernatant obtained by centrifugation at 3 000 rlmin was used to determine thiosulfinates as mentioned above.

For microencapsulated garlic powder, 10 mL of ac- etone was added into 1 g of microencapsulated garlic powder and rubbed using a mortar for a few minutes, to break the wall, 5 mL distilled water was added into it, mixed, and allowed to stand at room temperature for 1 min. The mixture was centrifuged at 3 000 r/min and the supernatant was adjusted to determine the

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Preparation of Garlic Powder with High Allicin Content 893

thiosulfinates, the same as above. Release kinetics of thiosulfinates from microen- capsulated garlic powder Simulated intestinal juice was prepared with 9 mL HC1 added to 1000 mL dis- tilled water to adjust pH to 1.2. Simulated gastric juice was prepared with 23.5 mL H,PO, added to 950 mL distilled water and pH was adjusted to 6.8 using 5 mL 4 N NaOH solution distilled to 1000 mL. In v i m thiosulfinates release from microencapsulated garlic powder was determined with a horizontal shaker method. Microspheres were placed in bottles contain- ing simulated intestinal juice, without the digestive en- zymes normally found in intestinal fluid, at a tempera- ture of 37°C. The mixture was shaken in a horizontal shaker at a speed of 100 r h i n . The samples were withdrawn at predetermined time intervals and assayed spectrophotometrically .

RESULTS AND DISCUSSION

Effect of vacuum pressures on inner temperature of garlic slices

Fig.2 shows the average internal temperature of garlic slices under three different absolute pressures during MVD, when microwave output power was 282.1 W. Center point temperature of garlic slices increased as the absolute pressure increased.

Too low vacuum pressure would increase the en- ergy consumption. Adopting low vacuum pressure to reduce evaporation temperature was very efficient. When the vacuum pressure was 4 kPa, the water evapo- ration temperature was about 30°C. When the vacuum pressure was 6 kPa, the water vaporing temperature was only about 35°C (Cui et al. 2003), which could ensure that the temperature of foodstuffs was about 35°C during the former stages of microwave-vacuum drying. It was enough to choose 6 kPa for dry foodstuffs. When the vacuum pressure was 8 Wa, the water vaporing temperature was about 45"C, so the temperature was a little high and alliinase activity could be reduced. Therefore, all experiments were performed with the microwave-vacuum drying at 6 kPa.

Fig.2 indicated that there are three stages in the MVD process, the first stage is an accelerating drying stage

70

-+- 4 kPa

20

10 0 5 10 15 20 2.5 30

Time (min)

Fig. 2 Average internal temperature of garlic slices under three different vacuity pressure during microwave-vacuum drying at 282.1 W output power.

(preheating period). The second stage is a constant rate drying stage (constant temperature drying stage). The third stage is a falling rate drying stage (temperature increasing drying stage), in turn. The three stages dur- ing MVD, in this study, were consistent with the study conducted by Nidhal and Mohammed (2002). During the initial drying phase, moisture content in the garlic slices was high. Therefore, microwave energy turned into thermal energy and the temperature of the garlic slices increased linearly with the water vapor tempera- ture of the corresponding vacuum pressure. This pro- cess usually lasted for a very short time (about 3 min). As soon as the temperature of the garlic slices reached moisture vapor temperature, the inner and surface mois- ture of the garlic would begin to evaporate. During the second stage, the absorbing microwave energy of the garlic slices was used to supplement the consumed energy of latent heat of vaporization. Therefore, the temperature of the garlic slices was basically kept con- stant during this period. During the falling rate drying stage or temperature increasing drying stage, the interior moisture of the garlic slices was insignificant. Although the dielectric loss constant of the garlic slices and the absorption of microwave energy decreased as the mois- ture content decreased, the total absorption energy was still greater than the energy that was needed by the evaporating moisture. Most of it was used to raise the temperature of the garlic slices, resulting in overheat-

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894 LI Yu et al.

ing of garlic slices. This was attributed to the inactivity of alLiinase.

The optimum drying conditions

Microwave could be more efficiently absorbed by sample. As water was depleted, microwave absorp- tion was reduced, leading to lower values of thermal efficiency. The drying efficiency was lower than the thermal efficiency at all stages of drying, because of the significant contribution of sensible heating during drying. It was reported that it could be as low as 30% at low moisture content at the end of the drying period when moisture content became small, and the heating process was 100% efficient initially when the moisture content was high, even when the vacuum was not ap- plied (Erle and Schubert 2001). As the drying pro- gressed and moisture content decreased, the advantage of VD became more evident because of the enhanced mass transfer of the vapor at reduced pressure. Then, the drying efficiency of VD became similar to MVD. Therefore, although MVD was an efficient method for drying food, it was not so at the latter stage of drying. It should be applied in a controlled environment. Maxi- mum power must be applied at the early stages of dry- ing and the power should be decreased as the drying progresses, to avoid waste of energy and any damage

to the microwave generating equipment, and to get high quality of foodstuffs. Because only a limited amount of water was available during the later stages of the MVD process, the temperature of garlic easily rose and was difficult to control, and the alliinase of garlic be- came very susceptible to temperature. High tempera- ture could lead to alliinase inactivation and so alliinase could no longer hydrolyze alliin to allicin. Therefore, VD would be an alternative way in this period. This combination of MVDND could be an alternative way to obtain high-quality dehydrated garlic. When the moisture content of garlic slices dried by MVD reached a low level, vacuum drying at 40°C would be adopted to continue drying the garlic slices until the moisture content came to below 5%.

Four levels of microwave output power were used to dry the garlic slices with different times. Thiosulfinates retention was determined at the different drying times of each output power variable (Table 1).

The data in Tables 1 and 2 were used to develop the polynomial model shown in eq. (1) according to Table 2. A stands for 376.1 W, B stands for 282.1 W, C stands for 188 W, and D stands for 94 W.

Thiosulfinates retention= 87.78 - 1.55A - 1.70B + 0. 32C-0.40D- 8.29A2-2.34B2- 1.44C2+0.56D2-2.78AB - 3.35AC - 3.52AD i- 0.70BC + 1.43BD - 0.55CD eq. (1)

Table 1 Resuonse surface analvsis of effect of microwave outDut Dower on thiosulfinates retention

Time under different microwave output power (min) 376.1 W ( A ) 282. I W (B) 188 W (C) 94 W (D) S 3 15 7 I 7 5 7 3 5 5 5 3 5 10 5 3 5 10 3 3 5 15 5 5 7 5 3 3 5 10 5 3 5 10 5 3 5 10 5 3 5 10 5 3 1 10 5 I 3 5 3 5 5 10 5 1 7 15 7 3 3 10 5 5 7 15 3 5 3 5 7 I 5 10 5 1 3 15 3

Thiosulfinates retention

(46. w/w) 69.9 79.1 85.7 89.2 87.9 85.3 74.6 87.8 88.9 88.6 89.4 82.9 71.6 77.1 87.6 86.3 71.3 78.2 80.2 18.9

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Preparation of Garlic Powder with High Allicin Content 895

From Table 2, it can be seen that the model fitted well to the experimental data. The model showed sig- nificant interaction effects between the variables ( P c 0.05), and indicated that the contribution of each vari- able to the yield could be ranked in the following order: B > A > C > D .

Response surfaces for the drying process were shown in Fig.3. Response surfaces study revealed that the optimum drying conditions for thiosulfinates reten- tion were: 376.1 W for 3 min, 282.1 W for 3 min, 188 W for 9 min, 94 W for 3 min, and the thiosulfinates retention was 90.2%.

Among different drying methods, FD was the best drying method, to obtain very high quality dried

Thiosulfinates 80 6942 retention (%) 77 0802

materials. Comparison of MVDND with F D is shown in Table 3. It could be seen that FD was much more time-consuming than MVDND. It was attributed to the fact that the latter was typically two or three times as efficient as the former in terms of water evaporated per unit of energy (Nidhal and Mohammed 2002). Garlic slices that were dried by MVDND were, without sta- tistical significance, a little lighter, with a slightly higher yellow hue than that of FD samples, which might be because of exposure to heat, resulting in the millard reaction. During the later stage of the MVD/VD, the millard reaction could not be totally absent. However, no significant loss of thiosulfinates occurred during the two types of drying and thiosulfinates retention for

88 082 Thiosulfinates 86 3806 retention (%) 84.6791

82 9776 81 2762

5

C: 188 W l 3 15 v6 7 282.1 W

Fig. 3 Response surfaces of effect of different microwave output power on thiosulfinates retention.

Table 2 Analysis of variance for thiosulfinates retention - 3-factor study

Effect Sum of squares df Mean square F-ratio P-value Model 832.82 14 59.49 26.99 0.0003' .4 4.81 1 4.8 1 2.18 0.1903 B 5.78 1 5.78 2.62 0.1565 C 1.02 1 1.02 0.46 0.5209 D 0.32 1 0.32 0.15 0.7163 AB 12.32 1 12.32 5.59 0.0560 AC 89.78 1 89.78 40.73 0.0007' AD 19.88 1 19.88 9.02 0.0239' Bc 3.92 1 3.92 1.78 0.2307 BD 3.25 1 3.25 1.47 0.2703 CD 2.42 1 2.42 1.10 0.335 1 Total error 1.57 4 0.39 Total 846.05 20

Table 3 Comparison of garlic quality dried by different drying method

Drying method

FD MVDND a' b' Thiosulfinates retention (%, wlw) Drying time (h) L' a' b' Thiosulfinates retention (%, w/w) Drying time (h) L'

48 72.24 -0.62 10.98 93.6 3.8 h 73.14 -1.62 11.90 90.2

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896 LI Yu et al.

MVDND was above 90%. This was only slightly less compared to 93% of FD (Table 3). From the above- mentioned, FD has many disadvantages for drying gar- lic slices, such as very expensive equipment, high en- ergy consumption, and high cost. It was obvious that garlic slices dried by MVDND would have a much more powerful market competition than those dried by FD .

Microstructure of microencapsulated garlic

Scanning electron microscope (SEM) was employed to investigate the surfaces and the internal structures of microencapsules (Fig.4).

SEM micrographs showed that the whole surface of the microencapsulated garlic powder granules was continuous and smooth, presenting irregular sphericity. Surfaces of all microcapsules displayed integrity and compactness; therefore the wall of the microencapsu- lated garlic powder could protect the core material from the environment. It could not avoid granulating during preparation of microcapsules when the air suspension method was used.

It is a common characteristic for microcapsules pre- pared with air suspension method to have an irregular form. Therefore. the garlic powder exists as pieces of bigger cohesive solids and not as original fine powder granules. There are two reasons to cause garlic pow- der to assemble and adhere. One reason is that there exist molecular and electrostatic forces among original fine garlic powder granules and they incline to conglo- bate during the fluidization process on the fluid bed.

The other reason is that after wall solution has some degree of viscosity sprayed to garlic powder, they would adhere together with a liquid bridge.

With volatilization of the solvent, the adhesive gran- ules would adhere to each other with a solid bridge of wall material. Hence, the core of the granules formed first, and then the core became larger in two ways: aggregation and coating. Through aggregation, garlic powder and wall material adhered together forming granules. This caused the surface of the final products to be rough and the shape of the final products irregular. Coating was where the core grew up with fine garlic powder sedimentation on the core, layer by layer, mak- ing the surface of the final products smooth and the shape of the final products round. From the micro- graph it could be seen that the microcapsules of garlic powder were smooth on the surface and presented ir- regular sphericity (Fig.4). Perhaps at the beginning aggregation predominated in the process of growing larger granules and coating followed the growing process.

Controlled release of microencapsulated garlic powder

After microencapsulated garlic powder was incubated in simulated gastric juice at 37°C for 2 h, thiosulfinates retention was still above 98% (Fig.5). Fig.5 shows that the microencapsulated garlic powder in simulated gastric juice did not release within 60 min, and fol- lowed zero-order linear release from 60 min to 120 min. The regression equation was y =0.03 17x - 2.0296, where

Fig. 4 Microstructure of microencapsulated garlic powder. Outside structure (left), inside structure (right).

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Preparation of Garlic Powder with High Allicin Content 897

80 - E

s - O *

d

3 2 60

p 4 0 - -J

20

x was the incubated time and y was the release content of thiosulfinates. The correlation coefficient was R2 = 0.9864, and the release rate constant was 0.0317 g min-'. This result demonstrated that the wall of the product could resist the low pH and preserve alliinase activity in the gastric cavity.

Then the same microencapsulated garlic powder, which had been incubated in simulated gastric juice for 2 h, was incubated in simulated intestinal fluid at 37°C for 1 h. Under ideal conditions, controlled release of core materials could follow zero order, one-half order, or first order of the kinetics equation.

Figs.6 and 7 showed that the release of microencap- sulated garlic powder in simulated intestinal fluid fol- lowed zero-order linear release within the first 2 min. The regression equation was y = 14x, where x was the incubated time and y was the release content of thiosulfinates. The correlation coefficient was R2 = 0.998, and the release rate constant was 14 g m i d . From 2 to 50 min, release followed the first-order, and the regression equation was y = -0.0089~ - 0.2081. The correlation coefficient was R2 = 0.9809, and the release rate constant was 0.0089 g min-'. From 50 min to 60 min, the release rate increased suddenly. This could be because of the disappearance of the rate-determining step, where the solvent of the aqueous solution of the core inside the capsule diffused from high concentra- tion to surrounding the outside capsule as a result of CAP wall material crumbling. In this period, release followed zero-order, and the regression equation was y = - 1 . 6 ~ - 1.4667, with correlation coefficient R2 = 0.9992. The release rate constant was 1.6 g m i d .

.

* * * * -

** -

2.0

1.8

1.6 - 1.4 - 1.2 - 1.0 - 0.8 - 0.6 -

- J' = 0.03 17.r - 2.0296 R' = (1.9864 t -

0 1 - g -0.2 c

5 -0.3.

s - -0.4 3 2

-0.5 0

3 A -0.6

-0.7-

v

SO 60 70 80 90 100 110 120 130

Time (min)

-

-

-

-

Fig. 5 Release kinetic curve of microencapsulated garlic powder in simulated gastric juice.

* *

0 4 I

0 10 20 30 40 50 60

Time (min)

Fig. 6 Release kinetic curve of microencapsulated garlic powder in simulated intestinal fluid.

10 20 30 40 50 hn " I

: I -0.1

y =-0.0089x- 0.2081 R2 =0.9809

Time (min)

Fig. 7 Release kinetic curve of microencapsulated garlic powder.

CONCLUSION

Garlic powder was prepared by MVDND technology. This technology could provide high allicin content with the quality of the finished product as good as the prod- uct prepared by FD. The optimal drying condition was microwave output power at 376.1, 282.1, 188, and 94 W, for 3, 3, 9, and 3 min, respectively. The thiosulfinates retention after drying was about 90.2%. The structure of the microencapsulated garlic powder made by the modified fluidized bed technique showed good integrity and the core materials were embedded in microcapsules. The microencapsulated garlic powder could resist stomach condition and be control-released in the intestine.

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(Edited by ZHAO Qi)

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