IMPROVEMENT OF THE STORABILITY AND MAINTENANCE OF POSTHARVEST QUALITY OF CASSAVA USING SURFACE COATING

Abstract

Cassava (Manihot esculenta) is an important dietary source of carbohydrates for communities in tropical regions. However, the crop is highly susceptible to postharvest physiological deterioration (PPD) which affects its nutritional quality and leads to the unpalatability and unmarketability of the roots in a span of 2-3 days after harvest. Edible surface coatings have been found to be effective in preserving the quality of various food products. However, there are variations in effectiveness among the different coating solutions, hence the need for optimization of the concentrations. This study was undertaken with the objective of determining the most effective mode of coating application between the dipping and spraying method and investigating the effect of surface coatings on the postharvest shelf life and quality of a selected cassava variety (KME 1). The cassava (variety KME 1) was harvested from the JKUAT farm at physiological maturity and immediately transported to the postharvest laboratory in plastic crates where they were cleaned, sorted and then divided into homogenous batches for various treatments. There was significant difference (P≤0.05) between the two modes of application based on the cassava property being assessed. The colour, cyanide content, phenolic content and ethylene content were not affected by the different modes of application. The dipping method was adopted for subsequent coating as it was simpler to perform hence easily adaptable by the small scale farmers. The treatments used to determine the effect of coating on physical, physiological and chemical properties of cassava included 1%, 1.5% and 2% guar gum, 1.5%, 2% and 2.5% xanthan gum and 1%, 1.5% and 2.5% xanthan/guar gum w/v. There was an initial increase in the flesh firmness which later declined in all the treatments, though this was profound in the control samples. The final flesh firmness of the treated roots ranged from 8.4N±0.28 for the control roots to 42.6N±0.47 for the 1% xanthan/guar gum coated root. There was progressive loss in weight of the roots ranging from 17.5%±0.20 in the 2% xanthan/guar gum coated root to 31.4%±0.13 in the control roots. The total cyanide and total phenolic content also decreased with the best combination being 1% and 1.5% xanthan/guar gum coated root respectively. The ethylene and respiration rates were retarded by the coating process accompanied with the delayed onset of PPD. The browning of the flesh which accompanied PPD development led to a decrease in the L* values ranging from 73.1±1.54 in the control roots to 88.5±0.66 for the 2% xanthan coated roots which was the best. Based on the sensory evaluation results, the 1.5% xanthan/guar gum coated roots was most preferred as it was more acceptable by the panelists as compared to the other treated roots with an overall acceptability value of 6.73. The coating process significantly (P≤0.05) delayed the changes in the quality parameters measured. The results revealed that the use of 1.5 xanthan/guar gum combination as an edible coating can extend the cassava shelf life by up to 20 days when stored at ambient temperature as it maintained the quality of the root with regards to the properties measured in this study. The use of edible surface coatings can therefore be considered as a novel technology in a bid to increase the cassava root shelf life while preserving its quality. This technology can be easily taken by the producers and traders as a preservation technique which will in the long run be of economic benefit to all key players in the cassava value chain.