Want to extend shelf life without adding too much preservative? Take a look at the effects of these five processing methods

FoodMate News: Consumer demand for clean labels is forcing companies to reformulate, reduce preservatives, and still maintain shelf life. But reducing preservatives is not easy. The absence of microbial growth does not mean quality indicators will not deteriorate; oxidation, color fading, separation, and purge loss can each cause problems during shelf life. So the topic we are sharing today is: after removing preservatives, what can make up for shelf life? There is actually considerable measured data in the journals, and this article summarizes the effects of five process categories for your reference.

01.

High pressure processing

The principle is to use water as the medium and pressurize packaged products to several hundred megapascals, killing bacteria with essentially no temperature rise. Flavors and vitamins are retained better than with thermal sterilization.

In a lettuce juice trial published in Food Science in 2023, treatment at 600 MPa for 2 minutes, followed by 30 days of storage at 0, 4, and 8 °C, kept total aerobic bacteria below 100 CFU/mL and molds and yeasts below 10 CFU/mL throughout. Shelf life was 25 days at 4 °C and 15 days at 8 °C, with the best overall performance at 0 °C.

Overseas results are similar. In a trial with raspberry juice, above 400 MPa reached the level of commercial sterilization; juice treated at 600 MPa kept for 28 days under refrigeration.

But the cost is also quite high: equipment requires investment on the scale of tens of millions of yuan, and production is batch-based, one batch at a time, so capacity cannot be increased; packaging must also withstand pressure and leave compressible headspace, and any packaging material that would swell cannot be used—all of this adds cost.

02.

Modified atmosphere packaging

The air in the package is replaced with a gas combination; the common approach is CO2 to inhibit bacteria, N2 to support the package, and O2 to protect color.

A comparative trial on yellow-feathered broilers was published in LWT: at the same 4 °C, ordinary air packaging reached the 7.0 lg (CFU/g) limit for total bacterial count in 4 days, while 80% CO2 plus 20% N2 lasted 10 days, at least 6 days longer. But the higher the CO2 concentration, the more obvious the purge loss.

Another dataset for chilled beef showed that modified atmosphere storage with 45% O2, 50% CO2, and 5% N2 gave a 12-day shelf life, which increased to 16 days after combination with clove and cinnamon extracts. The combined effect of packaging and natural preservatives is quite good.

Of course, for modified atmosphere packaging, seal airtightness is also key.

03.

Irradiation sterilization

Electron beams or gamma rays pass through food and break microbial DNA. With no temperature rise and no residue, it is one of the lower-cost types of cold sterilization.

The 2009 chilled pork trial in the Journal of Radiation Research and Radiation Processing gave very specific parameters: a dose of 3.23–4.0 kGy reduced the initial bacterial count by 2 log units, extended shelf life at 4 °C by about 12 days compared with the control, and by about 9 days at 7–10 °C.

Another fresh pork trial compared five doses from 1 to 9 kGy: above 7 kGy, sterilization was indeed powerful, but color and sensory quality began to suffer, and fat oxidation was accelerated; on day 12, the TBARS value of the 9 kGy group was significantly higher than that of the blank control. Overall, 3 kGy had the most balanced effect.

Irradiation has dedicated regulations; check the applicable scope before use.

04.

Biopreservation from natural sources

Nisin, ε-polylysine, chitosan, and the like come from microbial fermentation or natural extracts, but all are still food additives.

Data on chilled pork dipped in nisin showed that soaking in a 0.05 g/L preservative solution for 120 seconds extended shelf life by 6 days, with no significant difference from 0.05 g/L potassium sorbate. Equivalent replacement: this is the starting point for many companies changing formulations.

More practical is combined use. For chitosan combined with ε-polylysine, a 2026 report in Food and Fermentation Industries stated that the fractional inhibitory concentration (FIC) of the two was 0.5, judged as synergistic; after combined use, the inhibitory concentrations of the two components dropped by 75% and 94%, respectively. With lower dosage, cost and flavor concerns are both halved.

But excessive combination also has side effects. If the nisin concentration is increased too much, the synergistic effect instead declines; this kind of rise-then-fall curve has appeared in several papers, so more lab-scale trials are needed to determine how much to add.

05.

Secondary sterilization

Passing vacuum-packaged products through pasteurization afterward is the most commonly used extension method for low-temperature meat products and can be done without adding equipment.

The roast chicken trial compared water bath and microwave methods after vacuum packaging at 85, 90, and 95 °C for 30 minutes each; the conclusion was that water bath was clearly superior to microwave, and practice recommends 85–90 °C for 30 minutes.

A study on spiced lamb concluded that sterilization at 85–90 °C for 30 minutes, performed twice with rapid cooling for 30 minutes in between, kept the total bacterial count at 3.99 lg (CFU/g) after 6 months of refrigerated storage.

But there is also a problem: secondary heating brings a cooked flavor, the texture becomes loose, and it consumes labor hours. Products sensitive to heat need extra attention.

06.

How to interpret the study numbers

Putting five sets of numbers together does not mean they can be directly compared horizontally; for example, saying HPP is better than MAP because it lasts 25 days is incorrect. The matrix, initial bacterial count, and storage temperature of each group are all different.

Take the MAP group: yellow-feathered chicken in air packaging at 4 °C maxed out at 4 days. If your workshop hygiene is better and the initial bacterial count is half, the same packaging lasting several more days is normal; conversely, if the raw material total bacterial count is high, even the best packaging is useless.

So interpretation requires three steps: first, check whether the study matrix and your product are the same category; second, see how much the initial bacterial counts differ; finally, align the study temperature with the actual temperature of your cold chain. Only when all three steps pass do the numbers have reference value.

There is another variable that is easy to miss. Reaching the end of shelf life does not mean microbial counts exceed the limit. Color, purge, and flavor often go wrong first. Groups with impressive microbiological results in the literature may not have equally impressive quality indicators; the table deliberately retains both types of indicators.

07.

Costs and validation

HPP is expensive, MAP makes demands on packaging, irradiation is subject to regulations, natural preservatives make demands on the matrix, and secondary sterilization makes demands on the product. Choosing a method is really about matching your product's weak points against the option with the smallest trade-off.

The validation sequence is: first run lab-scale trials to establish the parameters, recording the initial bacterial count, total bacterial count at each testing point, and quality indicators; confirm the trend is stable. Then move to pilot scale. Copying literature parameters directly onto a production line often leads to problems. When problems occur, they are mostly due to two variables: initial bacterial count and temperature fluctuation.