Influence of Processing and Storage Conditions on Quality Stability of Shredded Lettuce

Abstract

Physical, chemical and organoleptic properties of the shredded lettuce (5×5cm) prepared under various conditions were investigated during storage at 5 and 10°C. In processing conditions, a sharp blade slicing or a rotary cutting were superior to either a dull blade slicing or chopping. The shredded lettuce washed with flowing or air-bubbling waters gave 10^-1-10^-2 bacteria number and retained longer storage life than that washed with dipping into water. Chemical treatments such as ascorbic acid and sodium hypochlorite were ineffective. The centrifugal dehydration at 1000rpm for 30 seconds was beneficial. The orientated nylon/low density polyethelene pouch (60μm; ON/PE 60) vacuum-packed at 150mmHg suppressed the browning reaction and/or the ferment-like off flavor formation, which extended storage life of the shredded lettuce. The amounts of ascorbic acid, chlorophill, glucose and fructose and penetrating resistance of the shredded lettuce gradually decreased while the polyphenol content markedly increased after a week during storage. Ethyl alcohol was produced at 2-3% oxygen concentration in the headspace of pouch. The ethyl alcohol content significantly corresponded to the organolep- tic quality during storage. From these results, the preferable processing and storage conditions were developed as follows: slicing with a Sharp blade; washing with cold (5-8°C) and flowing water; dehydrating by the basket-type centrifuge (φ52cm, 1000rpm) for 30 seconds; vacuum-packing at 150mmHg into ON/PE 60 pouch; storing and distributing at 1-5°C.