FSTDESK

Shrimp ammonium smell as an effect of drying

Hello!

We are developing a new shrimp product using vacuum microwave drying. The shrimp is top quality consumer grade shell-on. Nothing special about sulphites or phosphates - everything is below the norm. Cold chain is unbroken. We receive IQF freezed product of 82% moisture. Defrost it in small batches for no more than 10 minutes under microwave, mix it with 1% salt and 1% apple cider vinegar and then use microwave-drying (maximum 80 degrees of heating temp) to bring it to around 20% moisture. All the process is fast, without overexposure to light, oxigen or something else. We work in clean environment, treated with ozone every night.

The problem is that end-product develops strong ammonium smell. Can’t figure out why…

Many factors are involved, mainly the protein content in shrimp is usually high of 20% or more. So what type of shrimp was used and what kind of feed was given to this shrimp- all matters.
Now the drying method that you used - not sure if this is uncontrollable microwave power that is applied (though under vacuum). Different drying methods provide variation in the protein content of the powder or dried product that is obtained.
Something to investigate is the breakdown of the proteins during the heating process.
The difference in protein content before and after drying is something you may want to check, and it can be related to protein denaturation and or browning reactions, where few types/amounts of amino acid is used up.
High amounts of minerals are also present in shrimp, some accelerated reactions can be expected too.
It is also quite known that some (woody) shrimps have ammonia smell more than others and should be avoided for drying.
Not sure if addition of some bicarbonates can help.

2 Likes

Your shrimp when it arrives in your factory is not uniformly fresh.It contains portions that are starting to decompose.Shrimp.is highly perishable seafood as right after being caught, it starts to deteriorate.
If after drying it has ammonical then the shrimp quality is not good…Its a sign of protein degradationwhere ammoniais is one of the product of putrefaction…
Your product is substandard .You should check the quality of your purchased raw material before you even subject it to processing.
There are guides you can see in the web that might be helpful in your system such as this:

2 Likes

Thank you. This new FAO document is nice. In our case we are talking about high-standard shrimp production chain where each player is strictly controlled and minimally GMP and HACCP certified. I work with one of the world’s most trusted (top-10) shrimp processing plant. So in our case the quality is not a question. The question is some chemical reaction caused by something. As we understand (and we have some experience) ammonium smell is coming not only from spoiled products. It is a very common smell in nature that can be generated by different reasons. We are looking for some difficult to come by suggestions…

Thanks!
The microwave energy is controlled and this ammonium smell only comes from shell-on shrimp. Peeled shrimp from the same LOT doesn’t generate it. I also think that the case here is protein denaturation and it’s side effects. Maybe shells accumulate some volatile compounds that in case of peeled shrimp just steam away without a trace.
Sulfites normally are connected with ammonia smell. But they are naturally present in all shrimp and also applied in small amounts at the moment of fishing (30-50 ppm). But again. Peeled shrimp doesn’t generate that aroma under microwave-vacuum drying.
By the way. I was never been anle to discover some good reading on sulfites behaviour under drying. That’s another question, but maybe you’ve heard something about that?

The shrimp internal.organs near its head is the source of that ammoniacal smell as that is the first to deteriorate in the shrimp anatomy.Thats why it comes from the shell not from the shrimp meat.

2 Likes

so you got your answer already: as you stated ‘this ammonium smell only comes from shell-on s shrimp’. Shrimp shells are made of chitin and protein.

Do check why extrusion can produce good shrimp based paste etc? some parameters might be useful for your work.

If one has to go back to bad shrimps being used, then the question of its storage from the moment it is caught (like even the boats use freezer for this purpose), being highly prone to spoilage.

2 Likes

Hello, I also agree that shells could cause retention of volatile compounds, eg. ammonia smell is also formed in vacuum sealed aged cheese. if you are not observing the same (ammonia smell) problem in your untreated IQF shell-on shrimps, you may check if it is due to enzymatic activity during relatively mild drying process. Enzymes like asparaginase may lead to ammonia formation (if asparagine is present) and they are relatively heat tolerant (eg. 50% activity for 60°C/60min)

2 Likes

FAO mannuuals are best to recommend for processing of various seafoods. All in al better concern the type of shrimp used to develop such product

Thank you very much for an idea. Seems like during microwave drying with water boiling temperature set to 40 degrees we first set ideal temperature for enzymatic activity before reaching drastically higher temp kill step. And secondly (not sure) we break the tissues and free up asparaginase (it is present in shrimp) so it acts faster during those low temperature times. Also it seems like chitin in shells accelerates asparaginase activity that provokes more active ammonia formation.

Can you give some hints on asparaginase inactivation by heating/time, by lowering water activity, maybe salt level? What are those border lines?

Also can it be fully inactivated by applying some fast heating to temperatures under 80°?

What role do oxigen plays in reactivation if not fully destroyed?

1 Like

Interestingly enough ammonia smell can be felt on good salami, Spanish chorizos, jamón, hard cheese (i personally always feel it on parmesan outer layer) and many other pretty expensive products. That’s controversial to the general public concerns and pretty straight forward claim that ammonia is always a sign of spoiled product. Seems like this topic is much broader but I can’t get much on it from open resources like research gate and etc. Also (it’s a guess) but sulphites should play some other role in ammonia formation as those light notes (when you work much with it) can be felt in other products and even wines.

1 Like

Thanks, I hope the comments will support your process design. I totally agree some delicatessen products benefit from it. It is very dependant on food substrate and microbial origin but in research papers, commercial ones seem to have good heat stability in lab media (D70 = 60 min, %90 reduction after 70C/60min). As you are using microwave vacuum process, reducing drying time to 15-30 min) can be useful as well. Addition of a blanching pre-step maybe is not feasible for sensory properties, although good for enzyme/bacterial inactivation. My last thought is that final product aw (at 20% moisture) could also allow enzymatic activity to continue (from Labuza curve).

For your reference, [Quality changes in iced shrimps (Pandalus borealis). II Changes in the contents of trimethylamine oxide and volatile nitrogen bases during automatic boiling and peeling (author's transl)] - PubMed

Update. Thank you for the link. What i observe with more and more experiments (also on squid) is that ammonia smell is present in all the samples of seafood if microwave vacuum is applied. I can’t doubt the quality of ingredients we use. Those are the most fresh and strictly controlled samples. What i think is when vacuum is applied and the boiling temperature drops to 35-40 degrees microwaves start to boil water inside the samples and the water rushes out of the product. Seems like we force this volatile compounds out of it and the smell comes more from the drying chamber. Interesting . Seems like we also speed up that TVN formation by vacuum or microwaves.