To maintain the freshness of agricultural products, researchers have done many researches to develop coating materials. Among them, chitosan has a natural an-
-timicrobial activity and has shown positive effects on various horticultural crops. Chitosan has known to form a thin layer on the epidermis of crops and to suppress the decay of agricultural products through antibacterial action when it sprayed on the crops. However, chitosan has the side effects of delayed maturation of crops when it treated at high concentration or repeatedly during the growing season of crops. The researchers have been conducting various researches on the development of post-harvest treatment methods. In Korea, chitosan-related technology was first introduced in the early and mid 90s, but the initially developed materials were introduced as a soil improvement agent rather than an antimicrobial coating agent because of confusion between chitosan and chitin and the active ingredient content of chitosan was not constant either. Moreover, the effects of chitosan treatment were not consistent because there were many products that expected indirect effects. Horticultural crops are more susceptible to various diseases due to lower disease-resistance at harvest time as they mature, so growers had to suppress the diseases by spraying with various chemical pesticides. However, it is often found that the pesticide residues are exist for a long period of time, and consumers are very sensitive to the residual toxicity of pesticides on horticultural products. Therefore, one purpose of this study is to investigate the effects of chitosan, a natural antimicrobial substance, on the horticultural crops and to find out the possibility of using it as a substitute for chemical pesticides. On the other hand, calcium is also effective in improving the storage stability of the horticultural crops before harvesting, but it is known that not only is it difficult to transport into the tissues, but also the spraying effect is not uniform. In some horticultural products, exposure to high carbon dioxide condition after harvest promotes calcium migration and bonding with the cell wall, which improves storage stability. So, we tried to look for possibilities for increasing the healthiness of the crop skin through chitosan/calcium mixture spray treatment that are expected to restricts gas permeation and increase carbon dioxide level and calcium content by forming a film on the surface of the horticultural crops. In the study of various fruits, chitosan/calcium treatment increased the fruit weight in examined two peach cultivars, especially it changed the fruit length/diameter index and they developed into round oblate shape. Calcium treatment contributed to enhancing or maintaining storage stability by increasing flesh firmness, but at concentrations above 600mg?L-1, the positive effect of chitosan were offset and fruit maturation was delayed. The treatment of chitosan/calcium mixture delayed fruit softening but the duration of effect was shorter when the storage temperature was high. The internal quality of the fruit affected more profoundly by the concentration of calcium added to chitosan, and the higher the concentration of calcium, the delayed fruit maturation was observed. In addition, treatment with chitosan/calcium mixture increased the tensile force of the skin by binding the exocarp and endocarp with aril of litchi fruit and increased the shelf-life through the improvement of pericarp healthiness. Moreover, chitosan/calcium treatment in blueberries and peach increased fresh weight statistically at harvest time, while aronia tended to increase in fresh weight, but there was no statistically significance. The negative effects of mixed solution of chitosan and calcium on the internal and external fruit quality did not found during harvest and storage period of two berries. The results of research on various vegetables are as follows. The preharvest spray treatment of chitosan on pepper was accompanied by a significant increase in yield was observed at harvest time, which was the result of an increase in the total number of flowers rather than an increase in individual fruit weight. The yields were greatly increased with treatment of chitosan/calcium mixture and stevia alone treatment, while the stevia mixed treatments showed a tendency to increase the initial yield. In case of bacterial spotting due to heavy rain during the pepper experiment, the disease incidence of stevia alone treatment was the highest with 53.1%, followed by untreated 49.1%, and chitosan/calcium/stevia mixture was 34.1%, while the chitosan/calcium treated group had the lowest incidence rate of 17.0%. In cucumber, treatment with chitosan/calcium mixture before harvest showed reduced weight loss during storage than untreated one. In addition, the chitosan/calcium treatment retained the external quality than untreated one after 24 days of storage. In broccoli, the fresh weight increased due to preharvest chitosan/calcium treatment and maintained high floret firmness during harvest time. Floret firmness retention effect was superior to the 15℃ condition at 4℃ storage condition. Consequently, chitosan improves the quality of fruits and vegetables by increasing the growth rates of fruits and vegetables, though it varies depending on the crops. It also expected to contribute to the enhancement of food safety by inhibiting the occurrence of diseases. In crops with a long harvest time like pepper, chitosan/calcium treatment effectively inhibited the drop of fruits and improved crop yields. In addition, this treatment helps to maintain the fruit retention by calcium transportation, and retarding aging of fruit by inhibiting ethylene production. However, the effect of calcium was not exhibited at high temperature, and the effect of chitosan / calcium treatment is thought to be strongly affected by temperature. Accordingly, further studies on storage stability and temperature management will be required for full-scale application of chitosan/calcium preparations. Considering the above results, chitosan has potential as a substitute for pesticides and may contribute to improve the yield of horticultural crops. Therefore, it is necessary to examine the effect of chitosan on broader horticultural crops in order to enhance the food safety and to improve the shelf-life.