Gamma irradiation would be a method of choice, if you have access to the adequate facility.

Thank you Pierre.

I have looked into this - unfortunately consumer levels of knowledge are not great (mostly they perceive irradiated food is "radioactive") and, as the "Radura" symbol needs to be applied to finished goods & this tends to deter consumers from purchasing irradiated products. Plus there are only so many countries that allow irradiation & then only in some products (not all) but I'm going to keep looking as I don't think cold plasma is at the industrial stage (yet!). My problem is that our raw materials arrive frozen, making wet treatments impractical & this is why we are considering dry decontamination techniques.

Lesley

Dear Lesley,

You can test the treatment of fruit pieces by SO2 gas. This method is widely applied for many varieties of fruits such as apricot and grape when fruit drying is considered. The SO2 possesses two advantages in this treatment: decontamination and antibrowning effect. It is important to remember here that we have to control the residue of SO2 in the product. Some countries limit its residue for several hundreds of ppm.

Duried

Hi Duried

Many thanks for your response - our customer is very picky indeed & I believe the allergen residue might be a deal breaker as the sulphite limit is currently 10ppm for allergen declaration (Europe/USA)

We either need to perform this treatment on frozen fruit or post drying as it is very important to keep pieces separate during drying.

Do you know of any literature sources that might be worth looking at?...

Lesley

Dear Lesley,

Can you tell me what is the final product expected to produce from these frozen fruit pieces. I try to help you better?

For sulfur dioxide treatment, please refer to the following article:

https://onlinelibrary.wiley.com/doi/full/10.1002/jsfa.6584?casa_token=9Awa1G_i1W4AAAAA%3AnwVKWnRuabxB7NIfvwIZeqEfD5LDODqWAYXjZLxfR3vTR8H-WSdG41U7uGpmInq5VAAuOhW2Nhhow2fA

Duried

Hi Duried

Thank you for your reply. The process is very simple - it starts with frozen IQF fruit pieces which are freeze dried to produce freeze dried fruit pieces for use in food products. However the lyophilization process operates at a lower temperature than pasteurization & throughout the process water is continually sublimated - gradually lowering water activity in each piece - so no effective microbiological log reduction is noted.

The lyophilization process starts with the frozen fruit pieces, so any process that either thaws or raises the temperature of pieces will adversely affect the freeze drying process & cause the pieces to stick together (affecting quality of the finished product).

Cold plasma technology isn't really fully industrialised yet...so I'm currently looking at UV, IR & gas applications.

The challenge is really to retain end product quality (colour, vitamins, polyphenols, piece integrity) but still apply an effective microbiological log reduction step.... so, quite a challenge?!.

Lesley

Hi Lesley Roberts,

In your process system, can we act on the quality of raw materials of frozen IQF fruit pieces? if we can start the decontamination process in the early stages, this would be more effective?

The freeze-dried fruit pieces contain a high load of microorganisms compared to traditional thermally dried ones because the freezing process protects the microorganisms, while the lyophilization (freeze-drying) process concentrates the contamination microorganisms by keeping their viability especially the spore-forming bacteria, yeast, and molds. In this case, the decontamination process will confront a high level of microbial load in the dried food product. For decontaminating dried foods, the irradiation and gas processes are the most used.

Concerning the treatment of products with SO2, it is generally applied for fresh fruits. Assays must be performed to validate its effectiveness as a decontamination process for frozen products or maybe for dried ones.

We are working now on a novel drying method called RAD, i.e. "Reducing Atmosphere Drying", as an alternative to the freeze-drying method. The results obtained for RAD-dried apple and apricot fruits were highly attractive concerning the preservation of the color and antioxidant properties of fruits. Unfortunately, the RAD method is only applicable to fresh products (non-frozen ones). For more information about the RAD technique, please refer to the following paper:

https://rdcu.be/bGzLi

Duried

Hi Duried

If only that were possible!!.... this was investigated at the start of the process, but unfortunately we have diverse suppliers from all over the world (and there are probably more than 300 pack houses where the fruit vegetables are packed), many of these are in developing countries so don't have surplus capital. If we were to insist that they implement a decontamination step before we accept their fruit we would quickly have no suppliers.... and in fruit like raspberries, which are very fragile when dehulled, decontamination is not possible by the cheaper (traditional) methods (such as chlorine wash/peracetic acid).

Irradiation & SO2 are not acceptable to our customers (as you observed in the conclusion of your paper) so are not possible for us.

Your paper on RAD is very interesting - congratulations on a great piece of work!.

Lesley