Infiltration of Tomatoes by Aqueous Bacterial Suspensions

Abstract

Tomato fruit immersed in bacterial suspensions with negative suspension/fruit temperature differentials (fruit warmer than suspensions) became infiltrated by water and bacteria. Increased weight of the fruit was evidence for water uptake. If the increased exceeded approximately 3% of the original weight, cracking and water-soaking of the fruit surface often developed. Isolation of Serratia marcescens (an easily recognizable red bacterium) from internal tissues of fruit previously immersed in suspensions of that organism or the development of bacterial decay in fruit previously immersed in suspensions of Erwinia carotovora ssp. carotovora (Ecc), Pseudomonas marginalis or P. aeruginosa were evidenced for bacterial infiltration. Generally the weight increase of treated fruit was correlated with bacterial infiltration. Disease occurred in fruit that did not have a measurable weight increase (at least 10 mg). Fruits held 1-2 cm below the surface of suspensions of S. marcescens under zero or +2 degree differentials were not infiltrated by S. marcesens and, in similar tests with decay causing bacteria, rarely became diseases. Fruit with fresh stem scars was more vulnerable to infiltration than was fruit with old stem scars. Green and pink fruits immersed in suspensions of Ecc absorbed more water and became diseased earlier than did similarly treated red fruits. Slight weight increases were noted in fruit held 8 cm below the surface of water baths under zero to +2 degree differential conditions, evidence that hydrostatic forces also cause infiltration. These relatively small weight increases were smaller if +11 to +33 degree differentials were used.