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From waste to wealth: Production of bio-based chemicals from pineapple processing wastes

Name: Shivali Banerjee

Department: CTARA (IITB-Monash Research Academy)

Program:Ph D. (4th year)

Name of supervisor: Prof. Amit Arora (IITB); Prof. Antonio Patti (Monash University) & Dr. R Vijayaraghavan (Monash University)

Pineapple is one of the most popular tropical fruits consumed worldwide, and its global production was estimated to be 28.3 million metric tons in 2018-2019. The fruit is widely processed as canned juice/slices and generates a large quantum of waste (45-60% of the whole weight of fruit) in the form of crown, core, peels and pomace. The disposal of this organic waste requires a large capital investment; transportation costs being the major contributor. Landfilling is one of the most adopted methods for disposing of fruit waste; however, this method has a significant drawback of greenhouse gas emission. Developing countries such as India rarely have engineered landfills, and most of the waste is discarded over dumping grounds or is simply burnt off, which causes severe environmental pollution. 

Pineapple waste is a rich source of a proteolytic enzyme, bromelain, which shows promising applications in the food and therapeutic sectors. The peel, crown, and pomace are rich in carbohydrates which can be used to produce platform chemicals. Polyphenols are another class of compounds, present in pineapple peels, which show potential applications in food, cosmetic and therapeutic sectors. Most of the researchers have evaluated the valorisation of pineapple waste by extracting individual components with the major focus upon extraction of cellulose from pineapple leaves and bromelain from pineapple stem. 

My research aims at the valorisation of pineapple processing waste with an integrated biorefinery approach to achieve zero solid wastes. In my research, the peel waste is utilised as an unexplored source of hemicellulose (31.8 ± 1.9%) as a value-added product. The extracted hemicellulose is enzymatically hydrolysed to produce xylooligosaccharides (25.7 ± 0.4 g/100 g of xylan). Direct hydrolysis of pineapple peels with dilute nitric acid selectively produces xylose-rich liquor (~91% xylose yield) which could be converted to potential chemicals such as xylitol. In another valorisation step, bromelain is extracted from fresh pineapple waste, and the residual fibrous matter is found to be rich in total dietary fibre (69-75% of the fibrous residue) of which is mainly insoluble dietary fibre (98-99% of the total fibre). The extracted bromelain (specifically from pineapple core waste) is also tested for its efficacy to digest food proteins such as wheat gluten. In contrast to the conventional method of hydrolysis of wheat gluten with acids or microbial enzymes, pineapple core juice-assisted hydrolysis provides the advantages of cost-effectiveness and eco-friendliness. The dietary fibre concentrate is analysed for its functional properties to propose its application in food products. The higher insoluble dietary fibre content of the pomace makes it a suitable substrate which can be blend with soluble dietary fibres such as apple pomace (rich in pectin) to meet the requirements for both soluble and insoluble fibres. Since the pineapple pomace waste emerged out to be an excellent source of insoluble fibres with lower lignin content, its hemicellulose and cellulose content was fractionated and valorised into suitable high-value products such as xylooligosaccharides (XOS) and glucose. The glucose can further be converted into potential biofuels and biochemicals in the biorefinery portfolio. The products (bromelain, insoluble dietary fibre, XOS, xylitol and glucose) have an existing market demand in the food and therapeutic sector; therefore, the biorefinery approach might help in complete utilisation of pineapple waste. A techno-economic model is further developed to assess the economic feasibility of a biorefinery based on pineapple processing waste. The overall analysis shows that the waste, which is currently being disposed of in landfills or burnt away in some places, could be utilised as an excellent feedstock for the integrated recovery of value-added compounds such as bromelain and xylitol. Other feedstocks such as corn cob, mango processing waste, citrus processing waste, pomegranate processing waste and wastes from processing of different seasonal fruits could be integrated with pineapple processing waste to operate a large-scale facility to make the venture profitable in India.

Figure: Schematic of a biorefinery based on pineapple processing and on-farm waste (adapted from Banerjee et al. 2018)