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Spice up your life! Solus Scientific makes testing spices for Salmonella easier to swallowSolus Scientific has recently launched a range of single enrichment pathogen testing immunoassays to the market. The Solus One range, including Solus One Listeria for environmental surfaces and Solus One Salmonella for foods and environmental surfaces, combines the ease of tried and tested ELISA technology with many enhancements to provide a superior pathogen testing system.

AFTER achieving AFNOR and AOAC certification for a selection of matrices we have continued to develop Solus One Salmonella protocols for products that are known to be more difficult to test successfully, such as spices, herbs and flavourings. To date, we believe we offer the only alternative method to successfully test this food category for Salmonella.

CertificationSolus One Salmonella immunoassay achieved AFNOR NF certification in December 2018 in the ready-to-eat, ready-to-reheat (excluding smoked products), heat-processed milk and dairy products, and egg products food categories. The Solus method was compared to the reference method ISO 6579-1 (2017) following the validation protocol ISO 16140 (2016).

This was in addition to the AOAC Performance Testing Methods programme (PTM) certification that was granted to the same product in October 2018. The assay proved to be equivalent to FDA BAM Chapter 5 for the detection of Salmonella in samples of raw salmon fillet, shredded cheddar cheese, romaine lettuce (bagged), non-fat dry milk powder, and selected environmental surfaces.

The assay is also equivalent to the USDA laboratory manual 4.09 Isolation and Identification of Salmonella for detection from raw beef trim and pasteurised eggs.

Media developmentTo successfully detect contamination of food and environmental swabs, samples must be incubated in an enrichment broth to allow the recovery and growth

of potentially stressed and injured Salmonella. In order to facilitate this we developed our own liquid growth media.

Proprietary modified BPWA new liquid growth media was required in order to promote the recovery and healthy growth of Salmonella in a minimal amount of time in herbs and spices. Solus has developed mBPW, which contains a proprietary mix of neutralisers for the Solus One Salmonella assay.

Proprietary selective supplementEnhanced selectivity is also required during our single enrichment step. We therefore developed a proprietary selective supplement to be added to our mBPW for optimum Salmonella recovery and growth. The supplement contains a novel selective component, which is subject to a patent application. We found that this component demonstrates a significant improvement over selective dyes such as brilliant green,

which is used in RVS broth. The supplement as a whole suppresses the growth of the majority of Gram-positive flora whilst allowing the growth of stressed or injured Salmonella. It also allows for the isolation of Salmonella directly from the primary enrichment cultures, thus streamlining the process.

AOAC extension to scopeThrough further development of the Solus One Salmonella protocol we have encouraging results for detection of Salmonella in selected foods, particularly in the herbs, spices and flavourings category. The results show a statistically insignificant difference between Solus One Salmonella presumptive and confirmed results and also between Solus One Salmonella method and reference method at 5 percent level for all matrices evaluated. Table 1 shows a summary of results from the low level (0.2 – 2 CFU/ml) inoculation group of test samples.

APPLICATION NOTE | SOLUS SCIENTIFIC

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Spice protocolsSolus One Salmonella requires only a single step enrichment in modifi ed BPW + proprietary Solus selective supplement. This allows analysis to begin after only 20-24 hours of incubation. In keeping with our user-friendly system, the Solus One Salmonella scheme stipulates only four alternative matrix-specifi c protocols for carrying out spice testing, making it one of the simplest protocol schemes on the market. In each protocol it is only the volume of media or sample size that alters, all other parameters (media composition, level of supplementation, incubation time, and temperature) remain constant.

Protocol 1: Standard protocolFor the majority of spices and blends, including allspice, the standard protocol requires 1:10 sample/broth dilution for a 25g sample. For allspice particularly, this is an enormous improvement over the 1:100 dilution required by the FDA BAM Chapter 5 method.

Protocol 2: Herb and spice blendsLarger sample sizes of herb and spice blends can easily be accommodated by the Solus One Salmonella system, again only requiring a 1:10 dilution for 375g blend samples.

Protocol 3: Oregano and cinnamonCurrently the FDA BAM Chapter 5 methods require a 1:100 dilution for oregano and cinnamon to dilute them beyond their toxic level. The Solus One Salmonella assay only requires a 1:50 dilution for these products, effectively halving the cost of media required for testing.

Protocol 4: ClovesThe Solus method requires only one tenth of the media required for BAM methods with

cloves being diluted at 1:100 sample/broth, greatly surpassing the FDA BAM Chapter 5 method of 1:1000 dilution for cloves.

It is hoped that these extensions to scope will be added to the existing AOAC certifi cation within the next few months.

Further assay developmentWe recognise that the current AFNOR and AOAC certifi cation does not cover all of our customers’ testing needs so we are continuing to work on validating additional food matrices. Our R&D team have already completed an evaluation of 34 representative samples of raw meat, comparing Solus One Salmonella method to the reference method ISO 6579-1 (2017), where we were able to demonstrate that the Solus method meets the acceptability criteria for the raw meat food category.

We are very proud of the Solus One range and as such have been making efforts to introduce an E. coli O157 assay to the collection. To date we have made excellent progress, with incubation times of around nine hours and an assay run time of under two hours. We expect to certify the

Solus One E. coli O157 assay with time to presumptive results of only 11 hours. In this round of testing we have included 375g samples of raw ground beef in 1:4 sample/broth dilution and we will be continuing with matrices to include pasteurised dairy, raw beef trim, leafy greens, and environmental samples.

SummarySolus Scientifi c have developed a new proprietary modifi ed BPW and selective supplement, which enhances the recovery and growth of Salmonella from various food matrices and selected environmental surfaces.

Through these developments, Solus has produced an immunoassay for Salmonella testing that not only reduces time to result but is so effective it is able to detect Salmonella in traditionally diffi cult to test matrices such as spices, herbs and fl avourings.

We are hopeful that AOAC certifi cation for these matrices will be achieved imminently and confi rm Solus as the market leader in this area.

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Table 1: Low Level Salmonella Inoculation Results (20 samples per matrix)

375g samples

Matrix Strain Presumptive positive

Confi rmed positive BAM Ch. 5

Honey MustardOnion Seasoning

Salmonella Typhimurium 9 9 9

Falvoured Ranch Seasoning

Salmonella Seftenberg 9 9 9

25g samples

Matrix Strain Presumptive positive

Confi rmed positive BAM Ch. 5

Cinnamon Salmonella Mbandaka 9 9 9

Paprika Salmonella Tennessee 9 9 7

Black peppercorns Salmonella Seftenberg 8 8 8

NEW FOOD | APPLICATION NOTES SUPPLEMENT 2019 | Volume 22, Issue 03