Try citric acid to extend shelf life of mushrooms.

Mushrooms are enzymatically very active and highly sensitive when handled or bumped around. This sensitivity can result in a rapid loss of whiteness. Some producers may have high-quality chilling facilities at the farm, packing house and at the transport level. But a large physical distance from market may be a major disadvantage. An extended product shelf life is of paramount importance and hence a key requirement for those involved in mushroom production. The goal of European research is to extend the shelf life of fresh-sliced mushrooms by 50%.

Scientists were able to do this by soaking whole mushrooms in a solution of 40 g/l of citric acid prior to slicing and packaging them. This extended the shelf life by approximately 50% when compared with the control mushrooms. In terms of packaging, a variety of films were tested, but none proved to be more effective at extending the shelf life of fresh mushrooms than the standard perforated viskase film.

A combination of different film types and modified gas compositions also were ineffective. Many of the combinations gave rise to an anaerobic environment unsuitable because it increases the risk of botulinum formation.

Researchers also investigated the placement of dampened pads under sliced mushrooms to control moisture. The small increase in shelf life resulting from the pads was insufficient to warrant the cost of the pads. Antioxidant compounds vitamin E, vitamin C and rosemary extracts were tested as well. Only vitamin C (ascorbic acid) had a beneficial effect on shelf life. However, vitamin C treatments were not as effective as citric acid treatment. Antimicrobial compounds diacetyl and nisin also were ineffective in extending the shelf life of fresh-sliced mushrooms.

Sodium metabisulphite, which has been widely used in the mushroom industry, had deleterious effects on mushroom quality. But citric acid, hydrogen peroxide and EDTA treatments were beneficial in extending shelf life.

Investigators believe citric acid would be the most acceptable compound to use as an additive. A panel of 20 experts failed to detect citric acid in sliced mushrooms soaked whole in a solution of 40 g/l of citric acid for 10 min. The effectiveness of the citric acid, hydrogen peroxide and EDTA treatments varied from batch to batch of mushrooms. These variations were linked to the initial texture of the mushrooms. Softer mushrooms-those with a higher water content-responded better to the treatments than did firmer mushrooms.

Further information. Martine Brennan, the National Food Centre, Castleknock, Dublin 15 Ireland; phone: [phone]; fax: [phone]; email: [e-mail].