Controlling enzymatic browning of fresh-cut eggplant by application of an edible coating and modified atmosphere packaging

摘要

Once cut, some vegetables, such as eggplant, become very perishable due to enzymatic browning of the tissue and loss of firmness. The use of edible coatings combined with antioxidants preserves quality of minimally processed commodities by decreasingrespiration rate, weight loss and enzymatic browning. Moreover, packing under modified atmospheres (MAP) could enhance the shelf life of fresh-cut products. Therefore, the effectiveness of an edible coating with antioxidant activity and MA packaging hasbeen investigated on fresh-cut eggplant. Eggplant pieces were dipped in a coating composed of soy protein isolate (SPI) and 0.5% cysteine, or in water as control. The samples were then packed in trays with air (NA) or two gas mixtures (MA-A: 15 kPa C02 +5 kPa 02; MA-B: 80 kPa 02), sealed with polypropylene films and stored at 5°C for 8 days. In samples packed with air, a control treatment was also performed by macro perforating the polypropylene film (NA-P) to ensure no gas modification in the package. Changes in atmosphere composition in the package, color (CIE L*a*b*), visual quality, texture and weight loss were evaluated during storage. As expected, samples packed in MA and NA showed an increase and a decrease of C02 and 02, respectively. Lower C02 production was detected in the headspace of the trays for coated samples than in the uncoated ones packed under MA-A and MA-B conditions. Coated samples packed under MA-B and NA-P showed the highest L* and the lowest a* values during the first 6 daysof storage. Storage under MA-A did not improve the shelf life of minimally processed eggplant, showing low L* and high a* values. Moreover, this atmosphere increased the weight loss of uncoated samples during storage. Application of the coating without atmosphere modification (NA-P) improved the quality of fresh-cut eggplant and the samples were considered above the limit of commercialization until day 6 of storage. These results suggest that the application of the SPI-based coating can extend the shelflife of minimally processed eggplant. When comparing MA-packaging conditions, a high 02 concentration (MA-B) was more effective than low 02 concentration (MA-A) to preserve the quality of minimally processed eggplant.