12 replies to this topic

[a_andhika]

Dear Forum,

Would you please to share me your knowledge about moisture content testing on foods? What is the main different between using conventional oven (convection system) and the rapid Mousture Analyzer that using infrared or halogen lamp?

I am still relyin on the conventional method to validate the reading of rapid mositure analyzer. But sometimes it gives different result. Example, if I dryin' Chilli Powder on convection oven at 105C for 3 hours (AOAC), I get MC around 3 - 5%. But if I am using the infrared at 110C for 10 minutes I get 6 - 7%. The sample weight is same for both method: 2 grams.

Thanks for the feedback.


Regards,


Arya

[AS NUR]

DEar ARya...

IMEX.. if using Infra red moisture tester.. there are some factors why the result is not the same with conventional one :

1. Your sample thickness in equipment Pan, if the sample to thick theres tend to high moist...
2. Your sample have to flat position in pan...
3. Infra red ussualy have curve that describe the temperature profile... thats can effect to moist content.. so you need to see the profie or you can use literature (ussualy the manual contain the temp. seting for sample) you can use that as refference to set your infra red temp.

Hope can help you...

[Charles.C]

Dear Arya,

Is the infra-red procedure also AOAC approved ?

I hv seen this method routinely used for payment of trucks of incoming product due to speed available but was necessary to calibrate with conventional methods. Even then, results were very sensitive to exact procedure as AS NUR mentions.

No direct experience on chilli powder but for some natural products I had to use a vacuum oven at much lower temperature due breakdown. However if yr method is approved for Chilli, should be the right one.

Rgds / Charles.C

[a_andhika]

Dear AS Nur and Charles C.

Humm, I guess the sample size is not the matter in my case. The sample weight only 2 grams and it distribute properly at the pan. And before it asked by you, the sample position at oven is adjusted with properly, so it wont cause turbulence distraction. The method that used by my supplier also oven, and it dont gives significant difference with mine. And from quick browse I manage to find the percentage also present at 5 - 7% (I assume they are using the oven method too). But if I have to use the oven method on acceptance, I wonder if I can manage the angry driver...

I dunno if Infrared is following the AOAC too. But I guess it already validated through conventional method when it manufactured. Does the heat transfer mechanism between those methods are different ?


Regards,


Arya

[Charles.C]

Dear Arya,

A little more info. here -

 infrared_moisture.jpg   26.29KB   74 downloads

Another ref. I noticed mentioned the need to calibrate against oven data. Maybe it depends on the application.

added - microwave ovens seem quite popular also - advantage of multi-sample handling
added (2) - this brochure by Mettler is quite informative although obviously slightly targetted.

http://www.northshor...ure-methods.pdf

I daresay other people here are using IR routinely and shud hv good idea of pros / cons ??
(added before I saw Hongyun's post, very interesting )

Rgds / Charles.C

[Hongyun]

Hi Arya,

I had the same exact questions on this issue when I was with my previous Company. There are alot of methods used to measure moisture content, (Oven, IR, distillation, Karl Fischer) but why the different results? MC% using the IR method is always higher than vacuum oven method.

Since no one can answer my question, I can only investigate on my own and come up with a most probable answer.

Other than chilli, tomatoes, onion and garlic powders all uses the oven method. And one link is that they all contains sugar.

Vacuum oven method slowly heats up the environment and uses convection as mentioned, thus, maybe it drys them slower, just enough to evaporate the water, but not hot enough to melt/decompose the sugar to give carbon dioxide and water.

Whereas IR heats up very fast initially, I think, more than the set temperature. Once the overall temperature of the sample reaches the set temperature, it weighs the sample and gives the value. But the surface of the sample, which is also the nearest to the halogen lamp, gets burn and most probably, the sugars decomposes to give out water, thus a higher false result...

But the best way to measure moisture content for herbs and spices is still to use the ASTA (American Spice Trade Association) distillation method.

[Hongyun]

Well, thanks Charles for the info.

I guess it substantiate my "theory" that IR uses a higher temperature initially so as to obtain the set temperature within a short period of time or as the attachment mentions: "concentration of heat into the sample being dried."

IR method is most probably useful for raw materials like maltodextrin, modified starches, flour, etc... Helps save a whole lot of time. Very useful indeed.

added:

Oh yes, just read the Mettler brochure and it reminds me that you should avoid testing moisture of ingredients with high VO (volatile oil), as they vaporize easily too and contributes to false readings.

Edited by Hongyun, 28 October 2008 - 01:06 PM.

[AS NUR]

dear Arya...

What i mean is to see profiling the temperature during process using IR Moisture tester.. IMEX.. i have same problem with you before.. so i try to set the profiling temp. (how many time the temp. to increase, and what the max temp., how long the max temp remain and how many percent different that the equipment decide to stop measure, and how many grams of samples), and after some trial we found that our setting that gave us the result relative no siginificant difference with the Oven methode..

And dont forget to calibrate your equipment first .. to see the unceratinty of your measurement..

Edited by AS NUR, 29 October 2008 - 01:40 AM.

[a_andhika]

Dear All,

Interesting comments... Your thoughts might become a scientific journal someday:)

You might as well look to this PDF link:
http://www.nobleligh..._vs_ir_heat.pdf

Although I think the content is much more promoting the infrared oven, but I guess what has been figured by Hongyun and AS Nur is correct: "With infrared emitters a far greater flexibility in heat up rates and temperatures can be
achieved using different energy densities and wavelengths" as quoted from the document. Perhaps, I need to use a different program for the spices and other fresh-dried material, because they may contain volatile substance that gives false readings.

I am interested to using method just like AS Nur said. I've been doin that at my previous company, which has more "sophisticated" moisture analyzers using Halogen Lamp. The heating scenario can be adjusted, whether a constant heating or step by step. It so difficult to find the setting at that time. And just like Hongyun mentioned, the sample near the Halogen Lamp is oftenly burnt when we adjust the program. But once it settled, it gives relatively constant reading.

Unfortunately, the MA that I am using right now is a little bit "special", which is the last of it's kind... So what can I do now I guess just re-tune the program for the spices. Maybe lower than 110C, about 100C for 10 minutes. Any other suggestions? To gives you a little more clear figure, this is the brochure from Sartorius. Mine is MA 30, earlier edition of MA35, also using a Metal tubular-shaped heating element (infrared dark radiator) as heating element. I wonder if this kind of "metal" is may gives different reading than the lamp (although they declare it as infrared)?

https://no.vwr-cmd.c...21/BRO-MA-e.pdf


Regards,


Arya

[Charles.C]

Dear Arya,

Perhaps you need the 300P.

I suppose all these comments are the reason why AOAC approval is apparently not so easy.

This link gives a (few) AOAC approved moisture methods for use in meat industry.

http://www.anslab.ia...MethodsUsed.ppt.
(10MB)

Includes only one fast method for moisture (microwave) which looks quite impressive. Stated to be suitable for powders etc also. I saw a second hand unit advertised at $6000 on the IT.

Some impressive manufacturer moisture data (meat again) near the end of this link –

http://www.meatscien...00_sebranek.pdf.

Rgds / Charles.C

[a_andhika]

Dear Arya, Perhaps you need the 300P. Rgds / Charles.C

Dear Charles,

Tell it to my boss:)

Although it seems meat can be measured by other method, I personally choose the conventional method. The rapid testing IMO only able to measure the water content on the surface of the meat. Plus, they heat it with so fast and high temp, wonder if other substance might vaporize at that time too. BUt the NIR and GMS sounds so promising to get accurate measurement (and expensive...).

Thank you Charles, its a very good reference. We're in the middle of developing meat extraction. It surely needed by me.


Regards,


Arya

PS: The woman at Denver Instrument advertise is remind me to "The Black Dahlia" movie... It shockin me for a while..

[engan20]

Hope this helps you. I learned from colleague.

1) to assume the result from oven method is correct.
2) with fixed time, to adjust the infra-red temperature accordingly, the result compared with OM.Select the temperature setting which give you the nearest result to OM. Repeats few times, in order to get consistent and reliable result.
3) Ensure that your moisture analyzer was calibrated periodically on weight and temperature

Besides, i think that the sample weight is less. Suggest that 5-10g.

engan20

[a_andhika]

Dear Engan,

Welcome to the club!!:) Its an honour for me that you put your first post on my topic..:)

Yes, as figured by the other member too, I think the best way to measure the moisture content of the spices by using infrared is comparing it to the OM, and re-tune my setting. Do you have any suggestion what temperature that I should use? Or time? I'll try to havin' trial at 100C, and perhaps 105C (same like my oven). And yes, we already calibrate it on last April. It still work with well.

BTW, the reference of 2 g is using the AOAC. On my previous company, we are using 5 gram for the halogen lamp. Do you have any particular reason why it has to be 5-10 g? If the quantity of the sample is getting large, does it need a longer time? Besides, if the sample was mounted, does the heat air may able to reach the deepest part of the sample?


Regards,


Arya