11 replies to this topic

[MRios]

I´ve been determining fat acidity in corn grits with a method from the AACC 02-01A. In this method, you have to extract the fat using a Soxhlet. The fat that stays behind in the flask is dissolved in a toluene-alcohol-phenolphthalein solution, and titrated with KOH. However, when we have more than 1.5% fat in a sample, the fat acidity goes way up.
This method helps us make sure that the grits are not rancid. However, if we wanted to do this for whole corn, to check if the corn is OK or for the corn subproduct which includes the outer "skin" of the corn, plus its germ, the fat acidity value would be off the charts. What other method can I use?
Can anybody here help me? Maybe someone who works with snacks?

[Charles.C]

Dear MRios,

I presume yr problem is not able to easily handle the increased titration quantities involved for yr expanded sample? If I hv misunderstood the problem, pls correct / clarify.

If understood correctly, can offer one (or two) suggestions which are typical shortcuts of yr existing official procedure. Of course, the result is no longer exactly "official" which may influence yr flexibility (?). I hv used these methods for foods of various types with varying acidity levels (but not for corn as such!).

The usual first try adaptions are to either (a) reduce the sample size, from memory this analysis, is typically sample weight 5-10g, can say halve or whatever as still considered reasonable with respect to sampling error. Or (b) can appropriately modify/increase the concentration of the titrating agent assuming that the endpoint is still sharp (should be no problem, normally problem is only for too low acidity to measure). Or © can take an aliquot of the extract but IMEX, © may be less easy in practice.

There may be other techniques which can readily handle higher acidities (??) but yr basic procedure (although slow) is well time-tested and very commonly used IMEX.

Rgds / Charles.C

added - as discussed in a parallel thread here on FFA, options like potentiometric methods are available but obviously, money and expertise is also involved.

[MRios]

Dear Charles C.,
Thank you for your answer. I´ll apply this method when I have high fat samples.
However what worries me is that we have a limit of 40 mg KOH/100g sample. To tell you the truth, this is a value we received as a specification from one of our clients, that buys corn grits to make extruded snacks. When we have higher levels of fat, our fat acidity is higher. The real question is, would this producto be "more rancid" than a lower fat product, even if they came from the same raw material?
I´ve looked all over the internet and I haven´t found any information to back up this 40 mg KOH / 100 g value, or any other value for that matter. Maybe I´m not using the correct procedure or maybe this procedure isn´t really telling me anything about the rancidity of the product?
Also, I have to measure shelf life for different corn milling products, one of which has a certain amount of corn germ, so it has a high fat level. I was thinking of using this analysis to determine if the product was still OK after a certain amount of time, but now I´m having second thoughts.
Could you please help me out? How do you determine rancidity of a product in other types of settings?

[SaRaRa]

Hello MRios! I looked abit in my uni notes and I found these stuff... I hope they can be helpful. I didnt find anything about corn grits but I found something about cornoil.

Cornoil contains a big amount of linoleic acid and very small amounts of linolenic acid and arachidonic acid. According to Weiss (1970) the composition of cornoil in fatty acids is the following:

Palmitic 11,5%
Stearic 2,2%
Oleic 26,6%
Linoleic 58,7%
Linolenic 0,8%
Iodine number: 124,4
Melting point: -12 C to -10 C



There are 2 kinds of rancidity that can occur in oils:

A) Hydrolysis which could be:
- microbial hydrolysis
- enzymatic hydrolysis (phospholipase)

and it can be clarifired by measuring the acidity (free fatty acids) of the sample.

B) Oxidation which could be:
- auto-oxidation
- photo-oxidation
- enzymatic oxidation

and it can be clarified:

- by measuring the prime products of oxidation (Wheeler method, Lea method, Official
American Method and others)
- by measuring the conjugated double bonds of the peroxides that are being formed (measuring absorbance in 232 nm in pure iso-octane)
- by measuring the 2nd products of oxidation with Kreis method.
- with the TBA test.
- with the carbonyl compound test.


Cheers!

[Charles.C]

Dear MRios,

Your supplier has effectively given you a max. “acid value, AV” which can be recalculated into a max. FFA% value. I suggest you look up these terms on IT. My text book states that with most oils, rancidity is noticeable to the palate when the acidity (=FFA) calculated as oleic acid is about 0.8 – 1.5pct. Many processors of oil-fried products use the lower end as a routine oil quality control parameter.
Rancidity can variously result from factors as per previous post however I presume that the more fat which is present, the greater the relative likelihood of degradation of the product. There is a variety of other parameters which can be used to estimate rancidity, eg peroxide value etc. Suggest having a look in a food analysis textbook.

Rgds / Charles.C

[MRios]

Thank you Sarara and Charles for the info. I´m kind of in a hurry now. But I´ll take some time in the afternoon to slowly read this and digest it!! so much fat takes a while to digest.

[Charles.C]

Dear MRios,

A quick assist, hopefully no decimal point screw-ups -

Acid value (AV) of fat or oil = number of mg of KOH required to neutralise the free acid in 1g sample

you have max 40mg / 100g sample

So AV = max 0.4

Or perhaps more usefully -

Free Fatty Acid (% FFA) = (weight (g) of titratable "acid") / (weight (g) of sample) x 100

the acid is (here) conventionally chosen to be oleic acid and some manipulation then gives -

%FFA = AV /2 = max 0.2 for yr spec

Offhand, seems quite demanding for a raw material but maybe typical for this product (no personal experience). Hopefully corn grits is a standardised commodity ??

Rgds / Charles.C

[MRios]

Thank you Charles C for your help.
What is a standardised commodity? Sorry, English isn´t my first language.
One of the problems I have is that this specification, like I mentioned before, came from one of our clients, and , like you mentioned, sounds like it´s quite demanding. But I can´t find any reference anywhere. Do you know if there are any other IFSQN members that have experience with corn grits, or maybe even with milling oats or other cereals that have a risk of rancidity?
Maybe this specification is way out of line, though somewhere I did read that for wheat flour, the fat acidity limit was 50 mg KOH / 100 g sample.

[Charles.C]

Dear MRios,

The term “standardised commodity” is used in various ways but I meant = something that has a typical specification, eg given by codex or other commercial standards (and therefore often available on the IT). Many agricultural products are like this so as to facilitate buying / selling contracts.

I did notice a few references to corn grits chemical characteristics by their users on the IT but nothing specifically for FFA. You need to do some searching unfortunately (first time I hv ever seen this product on the forum!)

The most common values I hv seen for wheat flour specs relate to the protein, ash, fat, carbohyrate, fibre contents. FFA is not so common IMEX.

Rgds / Charles.C

[MRios]

Thank you Charles C. According to the definition, corn grits are a standardised commodity. What changes from one type of grits to another is the size of the particles (granulometry? is that a word in English?), but specifications for other aspects are all the same.
I looked it up in the Codex and there is in fact no mention of FFA.
Which makes me think: this isn´t important at all for corn grits, otherwise it would be in the Codex.
Then how can I measure shelf life? Simply by detecting off odors / flavors in the product? Changes in color?
At this moment, we´re giving the product 4 months of shelf life, but we want to change it to 6 months at least. I´ve had samples in a warehouse that´s located in a hot and humid area that have not had any color, odor, flavor changes in a year. Is this enough to back up the decision to extend the shelf life?

[Charles.C]

Dear MRios,

I think you hv the right understanding. You typically hv to (a) define yr quality requirements / limits then (b) do a controlled evaluation with time. Then © make a conclusion. Step (a) is often the hardest

Try this document (original credit to Jean) -

 shelflife1_2_2.pdf   459.91KB   187 downloads

and maybe this link for some ideas (there are many threads here on this topic)

http://www.ifsqn.com...?showtopic=9678

Rgds / Charles.C

added -

a practical example from another post and for a different product (Caz) -

we recently had a similar request from a retailer. albeit we have a shelf life of 23 days, they wanted us to extent it to 26 days, so that they could guarentee 21 days into their stores.
i am making a product that is pH controlled.

what we did was an extended shelf life trial, and conducted this trial over 3 separate runs.

so, on day 22, 23, 24, 25, 26, 27 and 28 we tested the product for our usual range of micro, plus listeria & salmonella.
We also coducted taste panel's to see if there was any deterioration in flavour profile.
and we also checked the chemical properties of the product.

we also ran these trials in duplicate with an external laboratory.

[MRios]

Once again, thank you Charles C.
Indeed, the first part is the toughest! I checked the links and most of them refer to microbiological testing, which, because of the low humidity of our product, is not a problem. Still, it sure helped me to have a better idea of what I should do.