How UK Based Startup Is Putting a Food Preservative Inside the Plastic Itself

PACKAGING

Harleen Singh

7/3/20268 min read

This is an AI generated illustration and does not represent actual product or service.

Every year, roughly one-third of all food produced globally is lost or wasted. For fresh produce, a large share of those losses happen not in the field or at sea, but inside the very containers we use to keep food safe — strawberry punnets, bread bags, sealed trays. Humidity builds up, microbes find a foothold, and a product that passed quality checks on dispatch is unsellable by the time it reaches the shelf. The cold chain helps, but it does not eliminate the problem. Modified atmosphere packaging (MAP) slows spoilage, but it is expensive to implement and still depends on passive gas equilibria rather than active microbial control.

A small Cambridge-based materials company called KluraLabs thinks the answer might already be sitting in your kitchen cupboard.

The Idea: An Old Food Additive, a New Format

Potassium metabisulfite (KMB) has been used as a food preservative and antimicrobial agent for over a century. Winemakers add it to grape must. Dried fruit producers use it to prevent browning. In the food industry it is familiar, approved, and cheap. What KluraLabs has done, according to its recently published international patent application (WO 2026/120294 A1, filed December 2025), is embed it directly into thermoplastic packaging materials — films, stickers, bread bags, and containers — so that it becomes the packaging itself, not something applied to the food.

The core claim is deceptively simple: mix KMB powder with a plastic resin, typically low-density polyethylene (LDPE) or polypropylene (PP), subject the blend to the heat of extrusion or injection moulding (120–200°C), and form a film or carrier that retains antimicrobial activity. The KMB in the finished plastic then releases controlled amounts of sulfur dioxide (SO₂) — the gas that does the actual microbial killing — into the headspace of the container holding the food.

The products named in the patent's process diagram are "KluraFresh sticker" and "KluraFresh Bread bag," suggesting the company already has specific commercial formats in mind.

Why This Should Not Work — And Why It Apparently Does

The counterintuitive aspect of this approach is worth dwelling on, because the patent itself flags it explicitly. KMB is known to decompose at temperatures above 150°C, releasing SO₂ and converting to potassium sulfate. Standard thermoplastic processing — cast film extrusion, blown film extrusion, injection moulding — operates in exactly that range. Incorporating KMB into a plastic melt should, by conventional reasoning, destroy much of the active agent before the product is even formed.

KluraLabs' experimental data (self-generated and not independently verified, as is typical at patent stage) suggests this does not happen to the degree expected. Thermogravimetric analysis (TGA) showed that the onset temperature for KMB degradation in a 20% KMB thin film increased to approximately 202°C — around 57°C higher than in raw KMB powder. The patent attributes this to stabilisation effects from incorporation into the polymer matrix. Whether the polymer physically encases the particles, lowers local moisture activity, or creates some other protective environment is not fully resolved, but the effect appears reproducible across multiple batches tested.

The second counterintuitive observation concerns the comparison between potassium metabisulfite and its more common industrial cousin, sodium metabisulfite (NaMB). Sodium metabisulfite is more widely used as an antimicrobial in various industrial applications, yet KluraLabs reports that when incorporated into the same plastic carriers under the same conditions, NaMB showed very little antimicrobial activity while KMB retained it. The patent suggests this relates to different rates of SO₂ release: NaMB releases SO₂ rapidly and loses its efficacy quickly, while KMB releases it more slowly and in a sustained manner — a controlled-release profile that is arguably more valuable in a packaging application designed to protect food over days or weeks.

What the Experimental Data Shows

The strongest commercially relevant claims in the patent rest on several categories of evidence.

Antibacterial performance. PP films containing 5–20% KMB achieved approximately 6-log reductions (99.9999% kill) against Escherichia coli in direct contact killing assays. Against Staphylococcus aureus — a gram-positive bacterium that is generally harder to kill than gram-negatives — films at 2% and 5% KMB in both PP and LDPE showed complete inhibition in indirect killing assays (designed to capture the effect of volatile SO₂ rather than direct contact). A comparison against a commercially available silver-based antimicrobial formulation at 20% loading showed full inhibition for KMB at 2% and 5%, while the silver product showed no inhibition in the same assay. This is an applicant-generated head-to-head comparison and should be treated accordingly — silver and sulfite-based systems work through different mechanisms and in different conditions — but the data is at least directionally interesting.

Antifungal performance. At 1–2% KMB loadings in PP thick films, the patent reports inhibition of Candida albicans (yeast) and Aspergillus brasiliensis (mould) within 24 hours of contact time.

Strawberry shelf-life trial. The front page of the patent's figures section — Figure 1 — shows the results of what the document describes as a 14-day experiment comparing commercial strawberry punnets lined with control (P) and KluraFresh (K) materials. Rejected punnets — those showing visible spoilage — were counted at Days 3, 5, 7, 10, 12, and 14. By Day 14, the control group showed approximately 3 rejected punnets versus a lower number in the KluraFresh group. The numbers are small and the trial conditions are not described in enough detail in the sections reviewed to make definitive claims about statistical power, but the pattern is consistent with the mechanism proposed. Longer-duration data and independently conducted trials would be needed before this could inform a commercial decision.

Food migration testing. Arguably the most commercially important data in the filing concerns food safety. Films containing 5% and 8% KMB were tested for overall and specific migration using European Food Contact Materials testing methodology (TES-AC-501 and TES-AC-812). Overall migration of both formulations was below 0.3 mg/dm² (well under the EU regulatory limit of 10 mg/dm²). Specific migration of potassium from the 5% KMB film was below 0.01 mg/kg, against a Specific Migration Limit (SML) of 0.01 mg/kg; sulfites migrated at roughly 0.005 mg/kg against an SML of 10 mg/kg. The testing used Tenax (a dry food simulant) rather than aqueous simulants, which is relevant — the choice of simulant affects whether worst-case food contact scenarios are captured. The patent notes that these tests were performed by a UKAS-accredited laboratory, which adds methodological credibility, but regulatory dossier requirements for novel food contact applications in EU or UK markets will require considerably more data.

The Particle Size Detail That Actually Matters

One of the more technically precise elements of the patent — and one that may prove commercially significant — is the treatment of KMB particle size. The patent specifies that KMB is jet-milled to a D95 of approximately 22–27 microns for the input powder, and that after compounding into the plastic carrier the particles should be approximately 5 microns. The target particle size in the final product is described as an "ideal" for achieving the preferred SO₂ release rate, particularly when used with LDPE at a low melt flow index (MFI around 0.5) and at a 20% w/w loading.

This is not a minor formulation detail. Particle size in embedded antimicrobial systems directly governs surface area exposure, release kinetics, and mechanical performance of the film. Too coarse and the SO₂ release may be too slow or uneven; too fine and you risk accelerated release that exhausts the antimicrobial reservoir early or compromises the film's physical properties. The fact that the patent specifies a preferred combination of KMB loading (20% w/w), polymer grade (LDPE, MFI ~0.5), and particle size (5 microns in the carrier) as a preferred embodiment suggests that KluraLabs has done significant optimisation work in this area — and that would likely form a meaningful part of any manufacturing defensibility, even if the broad chemical concept faces prior art challenges.

Commercial and Regulatory Implications

The format strategy in this patent is worth noticing. KluraLabs is not primarily pitching a new antimicrobial chemical — KMB is already approved and familiar. What it is pitching is a new delivery format for a known preservative, one that integrates into existing packaging supply chains without requiring reformulation of the food product itself. The compounding process described (jet milling KMB, blending with plastic resin, extruding into pellets, then forming films via cast or blown film extrusion) is compatible with existing plastic film manufacturing infrastructure. That is a meaningful commercial advantage over technologies that require specialised deposition, coating, or surface treatment steps.

For retailers and fresh produce suppliers, the most attractive commercial proposition would be the sticker format — a small antimicrobial disc placed inside an existing punnet or container, rather than replacing the container itself. This reduces capital requirements for adoption (the retailer or packer does not need to change their packaging line) and allows trialling at small scale. The bread bag format is a different commercial conversation, requiring the packaging converter to adopt a new film specification, which typically involves longer qualification cycles.

On the regulatory side, the path is not straightforward. In the UK and EU, materials intended to be in contact with food that release active substances (including SO₂) are regulated as "active food contact materials" under EU Regulation 450/2009 and its UK equivalent. Approval requires demonstrating that the released substance is safe at the levels reaching food, that the migration data meets the relevant SML, and — critically — that the use of the active material does not mislead the consumer about the condition of the food. The migration data in the patent, while promising, covers a limited range of food simulants and concentrations. A full regulatory submission would require substantially more, including data on aqueous food simulants (relevant for high-moisture produce like strawberries), compliance at elevated temperatures, and potentially a review of SO₂ allergenic potential for sulfite-sensitive individuals.

Sulfite allergies affect a small but clinically significant portion of the population, and sulfite compounds already carry mandatory labelling requirements in the EU and UK when present in food above 10 mg/kg. The extent to which SO₂ released from packaging into food headspace — and subsequently absorbed by the food — triggers labelling obligations is a question that will need regulatory clarification. The patent's migration data shows very low levels of KMB and sulfites migrating into food simulants, which would need to be confirmed across the relevant food matrix types if a labelling exemption is to be argued.

What Industry Professionals Should Watch

KluraLabs' approach occupies an interesting niche: it is technically credible enough to generate substantive experimental data, uses a regulatory-familiar active ingredient, and targets a packaging format that does not require upstream food reformulation. Those are meaningful advantages for commercial uptake.

The near-term questions are practical ones. Does the antimicrobial performance hold across the full range of pathogens and conditions relevant to specific food categories? Listeria, in particular, is conspicuously absent from the published experimental data — an important gap for any fresh produce application. How does performance vary as a function of temperature, humidity, and MAP gas composition, all of which vary significantly across chilled food supply chains? And what happens to the film's mechanical properties — tensile strength, seal integrity, tear resistance — as KMB loading increases? At 20% w/w, you are displacing a significant fraction of the polymer matrix with a crystalline inorganic salt, and the structural consequences of that are not addressed in the sections of the patent reviewed.

For ingredient and packaging suppliers evaluating this space, the key strategic question is whether KMB-in-plastic represents a genuinely defensible platform or whether the prior art landscape will constrain KluraLabs to narrow claims that can be designed around. The outcome of prosecution — particularly how the applicant responds to the category X citations — will be worth monitoring.

For food producers and retailers considering active packaging solutions more broadly, KluraLabs is at least asking a sensible question: if you already trust KMB as a food additive, why not trust it as a packaging component? The answer may ultimately come down to regulatory pathway clarity and consumer perception of sulfite-containing packaging as much as the underlying technical performance.