Post-harvest preservation for sustainable utilization of indigenous mushrooms and downstream processing of spoiled mushrooms to produce biodegradable plastic.

Abstract

Indigenous mushrooms have been enjoyed by local people since ancient times. These mushrooms grow naturally in the wild during the rainy season and during this time people scout for them and sell them on the informal market. Since the shelf life of the mushrooms is short, these informal marketers usually resort to drying the indigenous mushrooms to prolong their shelf life. However, there are other diverse methods which can be used to enhance their sustainable utilization. On the other hand sometimes cultivated mushrooms meant for sale in their fresh state get spoiled before being completely sold out. Therefore, this research aimed to preserve indigenous mushrooms for their sustainable utilization as well as to process spoiled mushrooms to make biodegradable plastic. Firstly, a questionnaire was used to conduct a survey to access market availability of indigenous mushrooms and the rate of spoilage of cultivated mushrooms. Responses were obtained from 26 branches of 3 types of modern markets. Results of the survey showed that none of these modern markets had indigenous mushrooms available, neither in their fresh or preserved state. The only types of mushrooms which were available were oyster mushrooms and button mushrooms, in their fresh state. It was also noted that about 35.37% of these cultivated mushrooms would spoil on the shelves with time. For sustainable utilization of both cultivated and indigenous mushrooms preservation techniques were explored. Preservation methods which were used on Amanita zambiana, Cantharellus spp and Cantharellus miomboensis included oven drying, pickling, steeping and freezing. Assessments of changes in the proximate nutritional composition, microbial load and sensory quality of the preserved mushrooms were done over a period of nine months. Results of the nutritional analysis showed that protein values of the mushrooms significantly decreased with time after preservation. It was also noted that the nutritional contents of the mushroom samples changed after the preservation procedures. The initial protein content of the preserved mushroom samples ranged from 12.17±0.05% to 14.27 ± 0.06% whereas after the last month of preservation they had significantly decreased to a range of 5.39±0.03% to 9.55±0.02%. Pickled samples had a significantly increased content of lipids from an initial range between 9.34±0.02% and 12.42±0.02% to a final range of 14.91±0.02% to 19.27±0.02%. The ash content of the samples decreased from an initial range of 9.22±0.01% to 12.74±0.03%, to a final rage of 3.02±0.01% to 6.87±0.04±%. The crude fibre content of pickled and steeped samples also decreased from an initial range of 4.23±0.03% to 6.76±0.02% to a final range of 2.87±0.01 to 5.07±0.02. Results showed that the initial range of the microbial counts of the fresh samples was 4.95±0.12 log cfu/ml to 4.98±0.05 log cfu/ml respectively whereas the preserved samples had microbial loads which ranged from 4.42±0.03 log cfu/ml to 4.95±0.11 log cfu/ml. Hedonic scales were used to access the aroma, colour, texture overall acceptability of the preserved indigenous mushrooms and in general pickled mushrooms had higher sensorial scores ranging from 7.9 to 8.5.Spoiled Pleurotus ostreatus mushroom was used to produce a bioplastic and it was noted that it`s weight decreased by an average of 5.5±0.23% and 2.2±0.02% under soil and laboratory degradation respectively, showing that the plastic was biologically degradable. The overall conclusion from the study was that preservation methods can be used to enhance utilization of indigenous mushrooms and spoiled mushrooms can be processed to make biodegradable plastic. Out of this study it was also concluded that even after the rainy season ends, indigenous mushrooms can still be found in the market in the form of whole steeped mushrooms, pickled mushrooms, frozen mushrooms or dried mushrooms. On the other hand spoiled mushrooms can be added to the other sources of biodegradable plastic which are already available. More research on preservation of other various types of underutilized mushroom types is recommended and other hand research on starch extraction methods which result in high yields of starch is also advisable.