Abstract
Agricultural food waste is rich in cellulosic and non-cellulosic fermentable substance. In this study, we investigated the bioconversion of pineapple waste cell wall sugars into bioethanol by simultaneous saccharification and fermentation using Saccharomyces cerevisiae ATCC 4126. Soluble and insoluble cell wall sugars were investigated during the fermentation process. Moreover, the fermentation medium was investigated for protein, moisture, ash, lignin and glycerol determinations with a particular focus on the increase in single cell protein due to yeast growth, allowing a total valorization of the resulting fermentation medium, with no further waste production, with respect to environmental sustainability. Soluble and insoluble sugars in the starting material were 32.12% and 26.33% respectively. The main insoluble sugars resulting from the cell wall hydrolysis detected at the beginning of the fermentation, were glucose, xylose and uronic acid. Glucose and mannose were the most prevalent sugars in the soluble sugars fraction. The ethanol theoretical yield, calculated according to dry matter lost, reached up to 85% (3.9% EtOH). The final fermentation substrate was mainly represented by pentose sugars. The protein content increased from 4.45% up to 20.1% during the process.
Highlights
The amount of cell wall sugars detected in pineapple waste after enzymatic hydrolysis makes this substrate an interesting resource for bioethanol production
The enzymatic release of xylose and arabinose, sugars not fermented by wild Saccharomyces spp., suggest the use of mixed cultures and/or recombinant yeasts, or to the development of robust strains that could ferment hexoses and pentoses simultaneously, with high ethanol production
This would lead to the improvement of the final ethanol concentration and productivity, since, after fermentation, an amount of pentoses was left unutilized in the medium
Summary
Waste disposal is one of the major problems facing most food processing plants [1,2]. According to Campos et al [3], there is an increasing interest in the valorization of the wastes generated by the food industry, including waste generated as a consequence of the new developments in process engineering and the resulting byproducts [4]. Waste utilization in the fruit and vegetable processing industry is an important challenge that governments must address in order to promote sustainability [3,5]. These substrates have a high potential, due to their micro and macro composition [6,7], as a low-cost high-potency second-generation feed-stock that can undergo biodegradation [8]
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