Postharvest behaviour and quality changes of green pods of cowpea (Vigna unguiculata ssp. unguiculata) in relation to storage temperature and plastic packaging

Although cowpea green pods have been traditionally used in folk diets in tropical and sub-tropical regions, very little is known about their behaviour and physicochemical changes after harvest. For this reason, we studied the effect of storage temperature (2, 5 and 10 degrees C) and plastic packaging (using perforated polyethylene, flexible vinyl and polyvinylchloride films) on the visual quality and some physicochemical characteristics of cowpea pods of two genotypes, stored for 7 days and kept in the packages for 2 days at 20 degrees C, in order to study the shelf life period. During cold storage the lower the temperature, the better was the appearance of the pods. However, after shelf life, pods became in most cases non-marketable due to chilling injury at 2 and 5 degrees C or weight loss (up to 25%), shriveling and decay at 10 degrees C. Only pods enclosed in flexible vinyl and stored at 10 degrees C could still be marketable after 2 days at 20 degrees C. Weight loss was higher in the perforated and flexible vinyl than in the polyvinylchloride film, which, due to its low permeability to water vapour was unsuitable, causing water condensation and decay to pods during shelf life. Cold storage did not significantly affect pods content in total soluble solids, except a reduction in the polyvinylchloride film after shelf life. It had also no effect on chlorophyll content, which increased during shelf life, except in the PVC film. Firmness of pods either did not change or increased during storage, irrespective of the postharvest handling. Cowpea pods are highly perishable and susceptible to chilling; therefore, they may be stored successfully for 7 or more days at low temperatures provided they are enclosed in plastic packages of proper permeability and will not be exposed at ambient temperatures during the shelf life period.