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Role of chemicals in postharvest management of litchi

Sahay, S., Mishra, P. K., Shirvastava, P., Singh, R. K., Singh, M. P., Rashmi, K., Kumar, V.
Acta horticulturae 2018 no.1211 pp. 93-100
Colletotrichum, European Union, Litchi chinensis, Penicillium, anthocyanins, catechol oxidase, cell membranes, chitosan, chlorine dioxide, coatings, color, discoloration, disinfectants, electrolytes, enzyme activity, ethylene, exports, fumigation, fungi, harvesting, hydrochloric acid, industry, longans, market value, microbial activity, pericarp, polyamines, polyphenols, postharvest diseases, postharvest losses, postharvest technology, residual effects, shelf life, sulfur, sulfur dioxide, weight loss, India
Litchi (Litchi chinensis Sonn.) is an important subtropical fruit of high commercial value. However, after harvesting of fruits rapid pericarp browning and degradation during storage reduce the market value. Generally, 20-30% postharvest loss of litchi is assumed and it may increase up to 50% also before utilization, especially due to infection of the several microorganisms. Several research works have been done in India and abroad to understand the effect of different chemicals on postharvest life of litchi. In this aspect, researchers from different parts of the world reported that just a few chemicals such as chlorine dioxide (ClO(2)), sulphur dioxide (SO(2)), hydrogen chloride (HCl), chitosan and polyamines (PUT, SPM and SPD) have a potential role to improve the shelf life of litchi by minimising the microbial activities during storage. Especially ClO(2) is one of the disinfectants which is more effective in inhibiting postharvest diseases, i.e., Colletotrichum spp., by damaging the growth of cell membrane of the fungi resulting in improved quality litchi fruits. Hence, it is widely used by various export industries throughout the world. SO(2) fumigation is also extensively used to manage some fungi such as Penicillium spp. and Colletotrichum spp. However, while working with SO(2), it was observed that the treated litchi fruits have some residual effect and therefore the European Union (EU) allows the maximum limit of sulphur residue concentration as low as 10 mg L-1 in the edible portion of fruits. HCl dip treatment is also found beneficial to recover attractive red colour of litchi. Reports of different researchers indicated that the application of polyamines (PUT, SPM and SPD) and chitosan coating on stored litchi fruits delayed changes in substance of anthocyanin, flavonoid and total phenolics contents, ethylene synthesis, browning, polyphenolase activity, peroxide level, electrolyte cell leakage, reduced weight loss, enhanced storability of litchi fruit but chitosan partially inhibited polyphenol oxidase (PPO) activity of longan fruit to prevent the peel from discoloration. Finally, the use of above chemicals proficiently enhanced storage life of litchi fruits by reducing postharvest disease incidences.