Fresh-cut onions: Effects of storage and cut on the shelf-life

Purple onions are primarily consumed fresh in salads and the market of fresh-cut onions is increasing.

In Brazil and in other developing countries where the cold chain is not well established (especially during distribution), and these disruptions have a negative impact on quality and shelf-life of product causing significant economical losses.

Currently, in Brazil, fresh-cut onions are cut into 7 mm thick slices and stored at 2, 4 e 10°C in modified atmospheres, but they show yellowing symptoms, firmness loss and an increase in microbial population growth with increasing temperature.

Brazilian scientists at São Paulo University have investigated the effects of storage temperature and cut type on quality of fresh-cut purple onion cv. Crioula Roxa.
The purple onions were cut testing two cut type:

3-5 mm thick slices
1.0 mm edge cubes. Then, minimally processed onions were put in rigid polypropylene containers and stored in four different cold rooms at 0, 5, 10, and 15°C and 85-90% RU for 15 days.

The shelf-life of fresh-cut purple onions was evaluated by analyzing the pungency (expressed as micromoles of pyruvic acid per gram of fresh matter), total phenolic content, anthocyanin content, quercetin content, respiration rate, color, soluble solids content, titratable acidity, pH, dryness and deterioration index and decay index.

Results showed that storage temperature and cut type affected differently the fresh-cut purple onions shelf-life. The product decay increased by increasing the temperature and cut severity. Thus, low temperatures and lower levels of damage contribute to a longer preservation of quality attributes.

By comparing the fresh-cut purple onions stored at 0°C with those stored at ≥5°C, the former showed the smaller variation in phenolic profile and in respiration rate, thus they showed less pungency and resulted in higher soluble solids content, higher pH, lower acidity, less changes in color.

By comparing the sliced onions with diced onions, the former showed less mechanical damage being the cut surface more reduced in slice than in cube.

Scientists have concluded that fresh-cut purple onions sliced and maintained at 0°C can be stored up to 15 days without significant variations of overall appearance.

Source: Berno N.D., Tezotto-Uliana J.V., Dias C.T., Kluge R.A., ‘Storage temperature and type of cut affect the biochemical and physiological characteristics of fresh-cut purple onions’, 2014, Postharvest Biology and Technology, Vol. 93, pagg. 91-96. http://www.sciencedirect.com/science/article/pii/S0925521414000763