Effect of MAP with argon and nitrous oxide on quality maintenance of minimally processed kiwifruit

The shelf-life of minimally processed (MP) kiwiftuit is principally limited by softening and colour degradation, caused by increased enzymatic activities as a consequence of wounding. Modified atmosphere packaging (MAP) with non-conventional gas mixtures was tested on the maintenance of some physico-chemical characteristics of MP kiwifruit slices, during refrigerated storage. Kiwiftuit slices were sealed in polypropylene boxes that were stored in air (control) and in three different modified atmospheres: N-2 (90%), O-2 (5%), CO2 (5%); Ar (90%), O-2 (5%), CO2 (5%) and N2O (90%), O-2 (5%), CO2 (5%). The packed kiwifruit samples were stored at 4 degrees C for 12 days and the following quality parameters were monitored during storage: soluble solids content, weight loss, carbon dioxide and oxygen levels in the package headspace, texture changes and surface colour by a reflectance colorimeter (lightness, hue angle and chroma) and by image analysis (percentage of browning area). MA with 90% of N2O was the best mixture of tested gases in order to maintain the quality of kiwiftuit slices. The initial firmness value of kiwifruit slices (about 13 N) decreased only by 10% after 8 days in the sample packed in N2O, while about 70% firmness loss was detected in the control sample after just 4 days of refrigerated storage. Kiwiftuit slices in N2O also maintained a better initial colour, in particular in terms of L* and hue. Moreover, the use of image analysis showed less browning in both the pericarp, and core surfaces of the samples in N2O, compared to the control. Correlation analysis between texture and all colour results showed that the application of an image analysis technique allowed a good recognition of chromatic changes related to fruit softening. Score plots of principal component analysis (PCA) showed slight modifications in the most important discriminated quality factors for the sample in N2O, a rapid quality loss for samples in air and in N2 and an acceptable quality maintenance until the 8th day of storage for the sample in Ar.