High fructose syrup production from mixed food and beverage waste hydrolysate at laboratory and pilot scales
Graphical abstract
Introduction
The food waste problem has become one of the biggest environmental challenges in recent years. About 1.3 billion metric tons (MT) of food waste is generated around the globe per year, which accounts for roughly one-third of food produced for human consumption (FAO, 2011). Although food waste is produced throughout the supply chain, a large proportion is wasted at the consumption stage in the developed regions mainly because of consumer behaviour such as insufficient purchase planning and stringent quality standards (FAO, 2011). The average per capita food waste by household in Taipei, Hong Kong and Seoul is 0.07–0.13 MT year−1 (Environment Bureau, 2014), which is 10 times higher than that in South and Southeast Asia. This not only represents a waste of resources, but also intensifies the food crisis. The global population is projected to reach more than 9 billion by 2050, boosting the demands on agriculture for access to adequate food. It is estimated that global food production has to be doubled by turning another 20% of land on the Earth to farming in order to fulfil the food demand (Ramankutty and Rhemtulla, 2012). As food waste currently claims a significant proportion of agricultural output (i.e. 30% for cereals, 40–50% for root crops, fruits and vegetables, and 20% for oil seeds, meat and dairy), food waste recycling for nutrient recovery is inevitably needed in order to increase the efficiency of the whole food chain (FAO, 2017).
Sugar has been a historically important commodity in the human diet since the 18th century. Currently, high fructose syrup (HFS) is one of the most popular sweeteners in the food and beverage industry due to a number of advantages (White, 2014). First, it is relatively stable in low pH beverages and requires less labour to handle it. Then, it has a high tendency to develop colour which is useful in manufacturing baked products. Furthermore, the sugars have already pre-dissolved and are resistant to crystallisation and microbial growth as one of the traditional preservation methods. Most importantly, fructose is the sweetest dietary sugar which is nearly 1.2 times as sweet as sucrose (Hanover and White, 1993). Nowadays, HFS is primarily made from corn such that more than 7600 MT have been produced annually in the US since 2001 (USDA, 2017). Different grades of HFS including 42%, 55% and 90% of fructose content are commercially available for various applications (Long, 1986). Meanwhile, our recent study also turned 100% HFS into 5-hydroxymethylfurfural (HMF) by catalytic dehydration (Yu et al., 2018). Exploration of other possible agricultural feedstock for HFS production is reported in the literature such as cassava, sweet potato, wheat and rice (Johnson et al., 2009, Johnson et al., 2010). However, the intensive farming system to grow corn or other agricultural crops for HFS production often draws public criticism for being unsustainable, as it leads to serious environmental problems including massive deforestation, water scarcities, soil depletion and high levels of greenhouse gas emissions (FAO, 2017, Ramankutty and Rhemtulla, 2012). Also, these studies mainly focused on the sugar recovery by saccharification and fructose conversion by isomerisation whereas the downstream processing and calculation of the overall conversion yield were seldom addressed, which prevented further industrial development. Therefore, this study proposes utilisation of the waste stream generated in the industrial sectors for sustainable HFS production and demonstrates the entire conversion process accompanied with mass balance calculation.
In fact, food and beverage (F&B) waste is an ideal feedstock for HFS production but the possibility of such conversion has never been explored. F&B waste is generated due to lack of coordination between different actors in the food supply chain and high expectation of quality by customers (FAO, 2017). As reported by Quested et al. (2013), 60% of the beverage waste in the United Kingdom is avoidable. Over 75% of the F&B waste disposed of from oatmeal manufacturing plant is actually edible (Hyman, 2009). Our recent studies analysed the composition of a number of F&B wastes including potato chips, oatmeal, bakery products, juices, energy drinks, and soft drinks (Haque et al., 2017, Kwan et al., 2018). It was found that most of them either contain large amounts of starch (30–60%, w/w) or high levels of free sugars (∼100 g L−1 fructose, glucose and sucrose) (Haque et al., 2017, Leung et al., 2012, Kwan et al., 2018). Valorisation of F&B waste by saccharification not only provides an environmentally-benign waste treatment method, but also produces sugar-rich hydrolysates that can be converted into HFS by isomerisation and downstream purification processes. As reported in our recent studies, the F&B hydrolysate contained high levels of glucose (260.7 ± 9.4 g L−1) and fructose (54.7 ± 1.9 g L−1), and about 0.17 g of sugars were recovered from a gram of F&B waste by saccharification, clarification and filtration (Kwan et al., 2018, Yu et al., 2018). Although the HFS derived from F&B waste might not be socially acceptable for human consumption, it is an ideal feedstock for the production of HMF and bio-based plastics via different polymerisation pathways (Kaur et al., 2018, Yu et al., 2018). Kaur et al. (2018) recently proposed the conversion of F&B waste into bio-based plastics, such as polyethylene furanoate, polyethylene terephthalate, and poly(lactic acid), which casts insights into the transformation of the plastics industry into a circular economy. However, there are a few drawbacks that have to be investigated and overcome. First, the preservatives, additives and colourants originated from the F&B waste should be removed from the hydrolysate. Then, a composition analysis is needed to check if the HFS derived from F&B waste conforms to existing industrial standard. Lastly, generation of by-products and sugar recovery should be evaluated by mass balance analysis since the F&B waste contains around 10% of crude protein and 20% of crude lipids which will end up in the by-product streams and a portion of sugars could be lost during downstream processing.
In this context, the aim of this study was to produce HFS using mixed F&B waste hydrolysate by isomerisation and a cascade of downstream processing technologies including adsorption, ion exchange chromatography and ligand exchange chromatography. Mixed F&B waste hydrolysate was prepared and obtained from our recent studies (Yu et al., 2018). A laboratory-scale study was first conducted to evaluate the technical feasibility, followed by a pilot scale investigation to explore the feasibility of upscaling. The HFS derived from mixed F&B waste was analysed according to industrial standards to check the appropriateness for application in the F&B industry. Lastly, mass balance analysis was conducted to summarise the entire conversion process from mixed F&B waste to HFS with calculation of the conversion yield and identification of by-product streams.
Section snippets
Preparation of mixed food and beverage waste hydrolysate
Saccharification of mixed F&B waste was carried out in a 10 L paddle mixer at 50 °C and 50 rpm for 24 h. The solid-to-liquid ratio was set to be 70% (w/v). The hydrolysis broth was harvested and centrifuged at 10,000 rpm for 15 min to separate the remaining solids and crude lipids, followed by clarification and filtration for removal of suspended solids. The hydrolysate was frozen at −20 °C until used in downstream processing. The handling of F&B wastes and results of saccharification were reported in
Composition of mixed food and beverage waste hydrolysate
Saccharification was proposed as a mean to recycle F&B waste by sugar recovery in our recent study (Kwan et al., 2018). Composition analyses were conducted on the hydrolysate and the results are summarised in Table 1. The hydrolysate is rich in glucose (260.3 ± 7.8 g L−1) and fructose (54.1 ± 1.6 g L−1) without other monosaccharides. It makes the hydrolysate a favourable feedstock for manufacturing HFS because it does not require additional steps to separate other monosaccharides and less energy is
Conclusions
Conversion of F&B waste into HFS was successfully demonstrated. The hydrolysate contained high levels of glucose and fructose, and a number of impurities including preservatives, caffeine, colourants, ions and soluble proteins. Pilot-scale downstream processing recovered over 89% of sugars and removed the impurities efficiently. The HFS was also confirmed to meet the industrial standard. The results from this study demonstrate that mixed F&B waste is an ideal feedstock for HFS production from
Consent for publication
All authors have approved the manuscript to be published.
Competing interests
The authors declare no conflict of interest.
Funding
This work was supported by the Industrial Technology Funding from the Innovation and Technology Commission (ITP/087/15TP) in Hong Kong.
Disclaimer
The views expressed in this manuscript are those of the authors and do not necessarily reflect the position or policy of PepsiCo Inc.
Acknowledgments
We would also like to thank PepsiCo Inc. and Novozymes® for providing industrial sponsorship. Furthermore, we acknowledge Starbucks Hong Kong for the expired bakery waste used in this study as an in-kind donation. Special thank is dedicated to Dr. Ir. Hendrik Waegeman and Ir. Emile Redant at Bio Base Europe Pilot Plant in Belgium for providing professional consultancy and sharing their industrial experience.
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