Firmness of apple tissue in low pH juice and related microstructural analysis

ANDRÉS S.C.; GIANNUZZI L.; ZARITZKY N.E.

SCANNING

JOHN WILEY & SONS INC

Lugar: Chicago, Illinois, USA; Año: 1999 vol. 21 p. 148 - 149

0161-0457

Changes in consumer life-style together with the increasing desire for fresh quality in all food products, has led to the development of fruit products ready to eat without thermal treatments. Texture is an important quality factor of fresh apples. Parenchyma cells and intercellular spaces are loosely arranged in net-like pattern which is inhomogeneous and anisotropic. For preservation, different methods combining refrigeration, addition of natural organic acids and packaging in films with controlled gaseous permeability are adopted. Microstructural changes can be observed by Environmental Scanning Electron Microscopy (ESEM) without fixation and dehydration of the specimens, thus avoiding distortion during observation. The objective of the present work is to analyze in a fresh system of apple cubes (Red Delicious) immersed in pasteurized or natural orange juice, with the addition of organic acids (citric and ascorbic) the effects of plastic film (polyethylene and EVA-SARAN-EVA) permeability on textural changes and the microstructural characteristics using ESEM. Instrumental texture analysis of the apple samples showed that the relative softening observed during storage was significant after 4 days of storage at 10 °C for all tested conditions. Significant differences were also observed when comparing the effects of packaging films; softness was lower in ESE than in Polyethylene. Softening in apples stored in pasteurized juice with citric and ascorbic acids and sucrose were significantly lower than samples stored in natural juice with the same additives. The best tested condition for the storage of Red Delicious apple cubes was the orange pasteurized juice combined with the simultaneous packaging in low oxygen permeability films. Microscopic observations by ESEM did not show significant differences in cellular shape and sizes, and in the cellular arrangements between the fresh and treated apple tissues stored during 9 days. Cellular diameters ranged between 50-500 mm with interconnecting air spaces ranging from 210-350 mm.