Hot Water Treatment of Tomatoes Ploy Kurdmongkoltham Hi, my name is Ploy Kurdmongkoltham. My postharvest project is using hot water to reduce decay during postharvest wash of tomatoes. 1
Introduction Postharvest loss is a worldwide problem FAO estimated 1.3 billion tons of food are wasted annually through (Gustavasson et al. 2011) Decay is one of the major factors in food loss Mismanaged handling and storage step can increase decay incidence Decay can occur by: Product mishandling Inadequate storage Internalized pathogen from field Postharvest loss is a worldwide problem for both developed and developing countries. 1.3 billion tons of food are wasted annually. Loss can happen at farm, retail, and consumer level. Food loss caused by decaying organisms is one of the major factors in food loss. There are multiple stages between farm to consumer supply chain, however proper handling and storage of commodity is an important factor in reducing decay incidence. Decay can be caused by mishandling of products which introduces pathogens, lack of adequate storage facility, or pathogen that is already present in the commodity during preharvest and produces symptoms during postharvest. 2
Objective Chlorine solution is generally used in dump tanks ph must be maintained Organic matter accumulation reduce free chlorine (Zhou et al. 2013) Formation of trihalomethanes Chemical free treatment can be a better alternative Determine whether hot water treatment can reduce decay incidence in tomatoes While chlorine solution is normally used for pathogen reduction in dump tanks for tomatoes, there are many factors to be considered for maintaining its effectiveness. ph must be kept between 6 7.5 to keep the active ingredient (HOCl) at a high concentration. Organic matter that will naturally accumulate in the dump tank can reduce free chlorine in the tank Trihalomethanes can form using chlorine which is a health concern Finding an alternative to chlorine treatment may be beneficial for the future. Hot water treatments are used on seeds for disease management. It is also used on mangoes and other stone fruits during postharvest. Therefore, the objective of the project is to determine whether hot water treatment can reduce decay incidence in tomatoes. 3
Materials 24 ripe tomatoes Soft rot inoculum Erwinia spp. Nail Thermometer Hot water bath (52 C ) Ambient water tub (25 C ) Materials used in the experiment included 24 ripe tomatoes brought from grocery store, inoculum from tomato that had soft rot symptoms, nail for wounding the tomatoes, thermometer to measure water temperatures, hot water bath, and a tub filled with ambient water. 4
Four Treatments HOT WATER 6 wounded tomatoes, no inoculum 6 wounded tomatoes, with inoculum AMBIENT WATER 6 wounded tomatoes, no inoculum 6 wounded tomatoes, with inoculum There are four treatments: 1. Non inoculated tomatoes in hot water 2. Inoculated tomatoes in hot water 3. Non inoculated tomatoes in ambient water 4. Inoculated tomatoes in ambient water 5
Procedure Inoculation w/ soft rot Hot water: 52 C for 5 mins Ambient water: 25 C for 5 mins Hot water Stored at 20 C for 13 days Tomatoes were sterilized with 85% ethanol for 1 min and dried Tomatoes were wounded with sterilized nail No Inoculation Hot water: 52 C for 5 mins Ambient water: 25 C for 5 mins Ambient water 24 tomatoes were fully dipped into 85% ethanol for 1 minute and dried under fan for 30 minutes. All tomatoes were wounded with sterilized nail. The nail was re sterilized after each stab with alcohol and flame. The wound site was circled with marker. 12 tomatoes were inoculated with a drop soft rot bacteria at wound site and the other 12 tomatoes were not inoculated. For non inoculated tomatoes, 6 tomatoes were placed in hot water treatment at 52 C for 5 minutes and other 6 tomatoes were placed in ambient water treatment at 25 C for 5 minutes. They were taken out and placed in separate plastic bins lined with wet paper towels. For inoculated tomatoes, 6 were placed in hot water treatment at 52 C for 5 minutes and other 6 tomatoes were placed in ambient water treatment at 25 C for 5 minutes. They were taken out and placed in separate plastic bins lined with wet paper towels. The bins were stored in 20 C for 13 days. Soft rot symptoms were observed every 2 days. 6
*The temperature for hot water was based from Dr. Francisco Ernesto Loayza Davila dissertation on Application of Heat Stress and Their Effect on the Antioxidant Composition of Fresh Tomatoes. 6
Results Hot Water No Inoculum 2 out of 6 showed decay at wound site Inoculum 4 out of 6 showed decay at wound site, but progress at slow rate TIME The results shown here are from the first reading to the last reading of each treatment. The tomatoes were observed at wound site for decay and tissue break down. For non inoculated tomatoes in hot water, 2 out of 6 tomatoes showed decay at wound site. There were tissue break down observed in one of the tomatoes. There were yellow liquid exuding from the wound sites. For inoculated tomatoes in hot water, 4 out of 6 tomatoes showed decay at wound site, but the progression of decay was slow. Wound site increase in size, but there was no complete tissue break down. 7
Results Ambient Water No Inoculum 1 out of 6 showed decay at wound site Inoculum 3 out of 6 showed decay at wound site, but one progressed at faster rate TIME For non inoculated tomatoes in ambient water, 1 out of 6 tomatoes showed decay at wound site with complete tissue break down and liquid exuding from wound site. For inoculated tomatoes in ambient water, 3 out of 6 tomatoes showed decay at wound site. One progressed decay at a fast rate (circled) when compared to hot water treatment, and the tomato showed tissue break down. 8
Conclusion Decay incidences were recorded for all treatments Hot water treatment did not prevent decay, but showed a slower progression of rot Some tomatoes in non inoculated treatments showed decay symptoms. Possibly due to pathogen already internalized in tomato Decay incidences were observed for all treatments. Hot water treatment did not prevent decay, but it showed a slower progression of rot at wound site. Tomatoes in the noninoculated treatments showed decay symptoms as well, but this may be due to pathogen already internalized in the tomato prior to the experiment. 9
Literature Bartz, J. 2018. Class notes: Controlling postharvest diseases. HOS 5085C Gustavsson, J., C. Cederberg, U. Sonesson, R. van Otterdijk, A. Meybeck. 2011. Global Food Losses and Food Waste: Extent Causes and Prevention. Rome, Food and Agriculture Organization (FAO) of the United Nations. Loaya Davila, F.E. 2014. Application of heat stress and their effect on the antioxidant composition of fresh tomatoes. Dissertation. University of Florida. Zhou, B., Y. Lou, E. Turner, Q. Wang, K.R. Schneider. 2013. Evaluation of current industry practices for maintaining tomato dump tank water quality during packinghouse operations. 10