Proceedings of the 7 th International Working Conference on Stored-product Protection - Volume 2

Experimental study on the storage of heat-stabilized rice bran

Hong Qmgci", Hua Well, Zheng Yong! and Chen Chongyr'

Abstract

ThIS paper introduced the stabihzation process of rice branimmediately after rnillmg by added-moisture heating and dry-heatmg, During expenmental storage, we found that theadded-moisture heating was very efficient for the lipaseinactivation by momtonng free fatty acids (FFAs) value andcrude oil content. The FFAs values were all less than 10%for the samples processed at 110 and 120'C for 3 or 5 mm.after 40-days storage. They were 10.5 % and 19.2 % for thesamples processed at 100'C for 5 and 3 min respectivelyafter 30 day's storage While the dry-heated rice bran couldonly be stored for about 15 days with the FFAs value round15% since the lipase activity was gradually recovered Withthe absorption of ambient moisture.

Introduction

Rice bran is a by-product of nee processing It was reportedthat the output of nee bran IS about 8.5 million tons in Chinaevery year. High-qualrty edible oil and nutntious protein'sfeedstuffs can be obtained from rice bran. However, themherent hpase Within the milled rice bran will quickly attackthe rice oil, as a result the FFAs value gradually rises. InChina, refining the crude nee 011 with more than 20% FFAsvalue is considered uneconomical, because the oil will beused only for the industrial purposes.The activity of the lipase is dependent on temperature,

moisture content, and pH value. The optimum actingcondi tion for the lipase IS 30 - 40'C , pH 7 .5 - 8 .0, thus thebaSICpnnciple for nee bran stabilization IS inactivating thelipase enzyme by controlling these conditions'. In thisstudy, the nee bran was treated by added-moisture heatingand dry-heatmg methods and then stored experimentally.FFAs value and content of crude nee oil extracted from theheated samples dunng every 5-days storage interval assessedefficiency of stabilization.

IDepartment of Food Science and Engmeenng , Nanjmg University ofEcononucs, Nanjmg 210003, P R Chma

Material and Determination Methods

Material

Fresh nee bran: obtained from the local rice millImmediately after nee millmg.

Determination methods

MotSture content: GB5497-85, 130'C, 40 mm. drying

methodCrude cnl content: GB5512-85, Soxhlet-extraction

method.FFAs value: GB5530 - 85, Alkahmetnc titration.

Experiments

Ascertaining the treatment conditions for added-moisture heating

When added-moisture heating was used to stabihze therice bran, It should be added With moisture up to the level of16 - 20%, so as to denature the lipase permanently". Forthis purpose, a portable pressure sterilization steamer wasused to generate steams with different temperature andrespective pressures. We set the temperatures at 100, 110and 120'C (pressures at 100, 150, and 200 kParespectively). For each temperature, a sample of 60g freshbran was put in a thin layer on a perforated plate and then inthe steamer for moisture-adding. After 3 or 5 min, wedetermined and found that all the treated barn under threedifferent temperatures was able to have moisture contents of16 - 20%. In order to compare the stabilization efficiency,we set two series of 3 and 5 min heating.Afterwards, the bran samples should be dried to the

moisture content of 10 - 11% for obtaining satisfactorystorage results, because mold growth could be largelyinhibited under this range of moisture contentsSix samples for 100, 110 and 120'C and for 3 or 5 min

respectively were prepared and moisture-added. Then m anoven at 130·C , all the samples were dried for lowering themoisture. After 2 mm drying, the moisture contents of thesamples were all reduced to 10 - 11%. The average resultsof the duplicates were hsted in Table 1.

Ascertaining the treatment time for dry-heating

A simpler dry-heating procedure could inactivate the lipase

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Proceedings of the 7 th International Working Conference on Stored-product Protection - Volume 2

when the moisture content of bran was reduced to 3 - 4%3.The moisture content lowered than tills range will promoteoxidation, ultimately affect the Oil quality and might causespontaneous combustion durmg storage.For detemuning the dry-heating time required, 60g

freshly milled rice bran in a thin layer was put m an oven at120"(. The moisture content of bran was determined atmtervals. Results are listed in Table 2. From the data mTable 2, we found that moisture content of bran could bereduced to 3 - 4% after bemg dry-heated for 12 mm.

Table 1. Ascertammg the treatment condition for added-moisture heatmg.

Steam temp.cae)

Steam pressure(kPa)

Moisture content" ( % )First steaming for 3 min FIrst steaming for 5 mm

then drying at 130°C for 2 mm then drying at 130°C for 2 mm

100

110

120

100

150

200

15.4 - 10.3 17.9 - 10.8

16.0 - 10.5 18.2 - 10.8

16 . 8 - 11. 0 20 . 0 - 11. 1

* The ongmal moisture content was 13 5%

Table 2. Ascertaining the treatment time for dry-heatmg at120"( .

TIme (nun. ) 6 8 10 12 14

(%) 7.3

*(%) 7.6

9.1

5.8

10.2

4.7

11.6

3.3

13.2

1.7

* the origmal moisture content was 14.9 % .

Stabilization procedure and storage experiments

The Oil in freshly milled bran would quickly be hydrolyzedto form FFAs Without stabilization processing. However thedally handhng capacity of our small steamer was lmuted. Fortills reason, we sampled two batches of fresh bran separatelyfor two-days handlmg. The first batch was treated for thecontrol and 3 nun. added-moisture heating samples (at 100,110 and 120°C separately) and the second one was for 5 min.added-moisture heating (at 100, 110, and 120°C separately)and dry-heatmg. The treated amount for each sample was200g.The added-moisture heatmg and dry-heatmg samples were

all in the thickness of 0 . 5 em and processed according to thetreatment conditions descnbed above. All the treatedsamples and the control were then mdividually put mto 8small sacks made of two-layer's gauze. They were placed

under cool and good ventilation condition for storageexpenments. At every 5-days interval, cakmg and moldmgphenomena were checked, and FFAs values and crude oilcontents were determined.

Results and Discussions

The sample of fresh nee bran had some brilliant color andgood smell. After added-moisture heating, its color wasslightly darkened and its smell became better During 40days' storage the color of them did not change apparently,in particular the samples treated at 120°C always had slightgood smell and kept m a loose condition The control wasgradually losmg its color and becoming lumped With off-smell In comparison with the control, the dry-heatedsample slowly lost its smell and colorThe ambient temperature of our storage test was m the

range of 13 - 24°C The FFAs values of the crude oilsextracted from the processed samples and the control atevery 5 days' intervals were listed m Table 3. The FFAsvalues of the control and the added-moisture heatmg for 3min. were shown m Fig. 1; wlule the FFAs values of thedry-heating sample and added-moisture heating samples for 5mm. in Fig. 2

Table 3. FFAs value's vanation of the samples durmg experimental storage.

Days III storage

0 5 10 15 20 25 30 35 40

Control 5.1 30.1 40.4 51.0 61.6

100°C 5.1 9.4 12.1 13.9 15.0 17.3 19.2 21.7 21.8

Steaming for 3 min. 110°C 5.1 6.4 6.6 8.0 8.6 8.8 8.8 9.2 9.7

120°C 5.1 5.9 5.9 5.9 6.0 6.0 6.1 6.1 6.2

100°C 5.1 6.2 7.7 8.7 9.4 9.6 10.5 10.5 10.9

Steaming for 5 min. 110°C 5.1 6.4 6.8 7.5 7.6 7.8 8.1 8.4 8.7

120"C 5.1 5.5 5.9 6.0 6.0 6.1 6.1 6.1 6.1

Dry-heating 5.1 7.4 11.3 15.1 29.5 39.5

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Proceedings of the 7 th International Worktng Conference on Stored-product Protection - Volume 2

It was shown from Table 3, Fig. 1 and Fig. 2 that thehpase enzyme within the added-moisture heated samples (3nun. or 5 min. at 120"() was almost permanentlydenatured, so that made the samples stabilized. After 40days' storage, their FFAs values were stabilized at the levelof about 6%. The lipase m the samples processed at 1l0oefor 3 or 5 min. was effectively inhibited. The FFAs valuesincreased slowly and were not over 10% in 40 days.Meanwhile, the FFAs values of the samples processed at100"( for 5 and 3 nun. were 10.5% and 19.2%respectively after 30 days' storage (it was reported, therice bran still can be used to produce edible 011 With FFAsvalue less than 20% ) . However, the FFAs value of thecontrol was up to 30% after 5 days and exceeded 50% after15 days. The amount of crude 011 extracted from it graduallylowered (Table 4), its color became darker and its smellwas off-flavor.

FFA Value(%)

45

35

25

100"('

15

___----e----- 110'C

120'C

o 5 10 IS 20 25 30 35 40Storage Days

Fig. 1. FF As values of the samples processed for 3 mm andthe control.

From Table 3, Fig. 1 and Fig. 2, it was also shown thatthe treatment for 5 nun was more favorable than for 3

mm., particular at 100oe. The dry-heating treatment wasable to inactivate the hpase to some extent The enzymeactivity could be recovered With the ambient moistureabsorbed into bran. As a result, the FFAs value wasgradually increased

FFA Value(%)

50

Dry-heatmg

45

40

35

30

25

20

IS___ ---100"('

~>_::::::::::::=----....q---- 110"('5 I~~=:o- --o--04----(l--120"('

10

o 10 15 20 25 30 35 40 Storage Days

Fig. 2. FFAs values of the samples processed for 5 mm andthe control.

The vanation of the crude 011 contents was listed in Table4 The color of oil from the control and dry-heated sampleswere from light yellow to heavy yellow as the storage penodprolonged On the other hand, the oils' color of the added-moisture heatmg samples was always light yellow duringstorage. The crude 011 contents of the control and the dry-heated sample were slightly lowered and all of the moisture-added heating samples kept almost constant contentsthroughout the storage.Table 5 showed the vanation of the FFAs values With the

moisture contents for the dry-heated sample. Therein thesample gradually absorbed the ambient moisture and thehpase activity was recovered, as indicated in an increasingFFAs value.

Table 4. Variation of the sample' s crude 011 contents during expenmental storage.Days m storage

0 5 10 15 20 25 30 35 40Contral 16.1 16.0 15.9 15.8 15.0

1000e 16.1 15.8 15.8 15.8 15.6 15.7 15.8 15.6 15.7Steaming for 3 nun. uoc 16.1 16.0 15.5 15.4 15.6 15.6 15.6 15.6 15.6

1200e 16.1 16.1 15.9 15.7 15.7 15.7 15.8 15.8 15.71000e 18.8 18.8 18.6 18.6 18.6 18.7 18.8 18.7 18.7

Steaming for 5 min. nne 18.8 18.8 18.3 18.6 18.2 18.7 18.2 18.7 18.21200e 18.8 18.8 18.6 18.7 18.4 18.5 18.8 18.2 18.2

Dry-heating 19.1 19.1 18.8 18.9 18.6 17.51687

Proceedings of the 7th Internatumal Working Conference on Stored-product Protection - Volume 2

Table 5. The FFAs value variation of dry-heated sample withthe moisture content.

Days stored 0 5 10 15 20 25

Moisture content/ % ) 2.6 5.1 5.7 6.7 7.1 8.1

FFAs valuet % ) 15.1 7.4 11.3 15.1 29.5 39.5

Conclusion

As for the inactivation efficiency of the lipase enzyme, theprocessing for 5 min. IS better than 3 min.j the steam atnot: IS better than lOOt: and 120°C than not:. TheInactivating factors seemed to include both temperature andmoisture.For economical reason, If fresh rice bran is to be

stabilized for 30 days, a moisture-added heatmg treatment atlOOt: for 3 min FFAs value less than 20% can be used. Ifthe stabilization period is longer a moisture-added heatingtreatment at more than lOOt: or at lOOt: for much time must

be adopted.The dry-heating treatment is simpler to use and do not

need a boiler But It can inactivate the hpase m only one ortwo weeks, so it IS only suitable for the rice branstabilization in a shorter period.

References

Chen Huawen, et al. , Study on the technology for nee branstabilization, China OIls and Fats, Issue No. 61, 25 - 29.Barber, S., et aI., 1974, Process for the stabilization ofnee bran. I. Basic research studies Page 49 m:Proceedings of Rice By-products Utilization InternationalConference, II. Velencia.Yokochi, K., et aI., 1974, Rice bran processing for theproduction of rice bran 011 and characteristics and uses ofthe oil and defatted bran, Page 1 in: Proceedings of RiceBy-products Utihzation International Conference, III.Velencia.

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