The virtuous reuse – upcycling (1,2) – of waste from agro-industrial supply chains can enable the production of prebiotics, bioactive compounds and functional ingredients with high added value.
A recent scientific review (Gonçalves et al., 2023) indicates the state of the art and perspectives on the conversion of materials by enzymatic bioprocesses. (3)
1) Upcycling of agro-industrial waste into prebiotics, premise
Agro-industrial waste can be diverted from recycling (into feed or agricultural inputs ), energy valorization or disposal, to move up Lansink’s ladder (or ‘waste hierarchy’, an emblem of the circular economy).
These materials-available in abundance, at negligible cost-can in fact be used as raw materials or substrates to extract or synthesize prebiotics, through bio-processes using enzymes. The residues thus lend themselves to conversion into various bioactive compounds.
2) Agricultural and industrial waste
Side streams in agrifood supply chains generate huge amounts of waste that can be classified into two macro-categories:
- Agricultural, field or process waste. Such as straw, stems, stalks, leaves, husks, fruit pulp or stubble, molasses, brewers’ treads, coffee grounds, bagasse (from grinding sugarcane and sweet sorghum), etc.
- Agro-industrial co-products, such as potato peels, citrus fruits, tomatoes, soybean cakes and other oilseeds, etc.
3) Bioactive compounds
Enzymatic hydrolysis of agroindustrial residues and co-products allows obtaining bioactive compounds of nutritional value functional ingredients, including those with prebiotic action. (4) Making use of the most appropriate enzymes-or enzyme systems-relating to different matrices.
The bulk of agro-industrial waste consists of lignocellulosic materials (cellulose, hemicellulose and lignin) from which to extract oligosaccharides (xylus and cello-oligomers). Some processes also allow the extraction of mannan and galacto-oligomers, (5) as well as various prebiotic polymers.
3.1) Fructo-oligosaccharides, FOS
FOS, fructooligosaccharides, are polymers of fructose residues linked to a terminal glucose molecule. The use of sucrose-rich industrial by-products, such as molasses, can be a cheap and profitable alternative to produce prebiotics.
These byproducts often do not even require pretreatment, immersion in hot water being sufficient to obtain the substrate needed for enzymatic catalysis.
Ganaie et al. (2017) demonstrated how the FTase of Aspergillus flavus allows synthesizing FOS from sixteen different agricultural wastes including wheat bran, corn straw, sugarcane bagasse, cassava husks, apple pomace, orange peel, beet, and banana. (6)
3.2) Galacto-oligosaccharides, GalOS
GalOS, galacto-oligosaccharides, are oligomers of galactose (e.g., lactosucrose, lactulose). Lactose is one of the substrates required to produce these prebiotics, acting as an acceptor and/or donor of galactosyl portions. Synthesis of lactosaccharose and lactulose also requires sucrose or fructose, which instead act as galactosyl bond acceptors.
Whey-a co-product of the dairy industry-is an ideal candidate for these forms of upcycling because of its appreciable lactose concentration (about 4.5-6.0 percent. Kaur et al., 2020) (7) In addition to valuable proteins, which it is also useful to extract.
Geiger et al. (2020) achieved a high conversion rate (80%) of lactose from serum to GalOS by β-galactosidase from Streptococcus thermophilus. It thus proved possible to synthesize about 1 kg of GalOS from 3 kg of whey permeate powder. (8)
3.3) Xylo-oligosaccharides, XOS
XOS, xylo-oligosaccharides, can be extracted from biomass rich in hemicellulose, also common among agricultural and agro-industrial wastes. Xylan (a constituent of hemicellulose) recovered from biomass is converted to XOS with the help of endo-xylanase enzymes. (9)
Wheat and cob straw can be used to extract hemicellulose by autohydrolysis, the most economical bio-process. (10) Although chemical processes, including those based on alkalis and acids, are most in vogue. Other wastes used include rice and coconut husks, as well as sugarcane bagasse residues (11).
3.4) Other prebiotics
Numerous other prebiotic compounds can be extracted or produced from various sources of waste from agri-food supply chains. Some studies have focused on the conversion of leftovers to manno-oligossaccharides, isomalto-oligosaccharides, and pectin oligosaccharides. (3)
4) Benefits for the gastro-intestinal system
The resistance of prebiotics to hydrolysis confirms their ability to reach the colon without being decomposed by the stomach’s gastric juices. Fermentability assays in turn allow:
- Testing the ability of substances to promote the growth of beneficial microorganisms, and
- follow their conversion into bioactive metabolites, which play essential roles in human physiology and metabolism (12,13).
5) Interim Conclusions
The global prebiotics market touched 33.44 billion yuan (US$4.87 bln) in 2021 and is expected to reach 87.69 billion yuan (US$12.77 bln) in 2030, with a CAGR of 11.3 percent. (14)
Processes for upcycling agroindustrial waste into bioactive compounds via enzymatic bioprocesses still have areas for improvement that deserve further research and development.
Dario Dongo and Giulia Pietrollini
Notes
(1) Dario Dongo. Upcycling, the high road of research and innovation. GIFT (Great Italian Food Trade). 1.1.23
(2) Dario Dongo, Giulia Pietrollini. Upcycling economy, upcycled food. The revolution against waste. GIFT (Great Italian Food Trade). 31.1.23
(3) Gonçalves, D.A., González, A., Roupar,et al. (2023). How prebiotics have been produced from agro-industrial waste: An overview of the enzymatic technologies applied and the models used to validate their health claims. Trends in Food Science & Technology. doi:10.1016/j.tifs.2023.03.016
(4) Giulia Pietrollini. Probiotics, prebiotics and psychobiotics, a revolution for the health of the psyche? GIFT (Great Italian Food Trade). 14.2.23
(5) L. Bhatia, A. Sharma, R.K. Bachheti, A.K. Chandel. (2019). Lignocellulose derived functional oligosaccharides: Production, properties, and health benefits. Preparative Biochemistry & Biotechnology, 49:8, 744-758, DOI: 10.1080/10826068.2019.1608446
(6) M.A. Ganaie, H. Soni, G.A. Naikoo, et al. (2017). Screening of low cost agricultural wastes to maximize the fructosyltransferase production and its applicability in generation of fructooligosaccharides by solid state fermentation. International Biodeterioration & Biodegradation, 118 (2017), pp. 19-26, doi:10.1016/j.ibiod.2017.01.006
(7) R. Kaur, D. Panwar, P.S. Panesar (2020). Biotechnological approach for valorization of whey for value-added products. Food industry wastes, Academic Press, pp. 275-302, doi:10.1016/b978-0-12-817121-9.00013-9
(8) Geiger, H.M. Nguyen, S. Wenig, H.A. Nguyen, C. Lorenz, R. Kittl, et al. (2016). From by-product to valuable components: Efficient enzymatic conversion of lactose in whey using β-galactosidase from Streptococcus thermophilus. Biochemical Engineering Journal, 116-2016, pp. 45-53. doi:10.1016/j.bej.2016.04.003
(9) N. Jayapal, A.K. Samanta, A.P. Kolte, S. Senani, M. Sridhar, K.P. Suresh, et al. (2013). Value addition to sugarcane bagasse: Xylan extraction and its process optimization for xylooligosaccharides production. Industrial Crops and Products, 42-1-2013, pp. 14-24. doi: 10.1016/j.indcrop.2012.05.019
(10) Liu X, Liu Y, Jiang Z, Liu H, Yang S, Yan Q. (2018). Biochemical characterization of a novel xylanase from Paenibacillus barengoltzii and its application in xylooligosaccharides production from corncobs. Food Chem. 2018 Oct 30;264:310-318. doi: 10.1016/j.foodchem.2018.05.023
(11) N. Jayapal, A.K. Samanta, A.P. Kolte, S. Senani, M. Sridhar, K.P. Suresh, et al. (2013). Value addition to sugarcane bagasse: Xylan extraction and its process optimization for xylooligosaccharides production. Industrial Crops and Products, 42-1-2013, pp. 14-24. doi: 10.1016/j.indcrop.2012.05.019
(12) Paola Palestini, Dario Dongo. Microbiome and gut, the second brain. GIFT (Great Italian Food Trade). 14.2.19
(13) Dario Dongo, Andrea Adelmo Della Penna. Gut microbiota, diet and health. GIFT (Great Italian Food Trade). 19.6.20
(14) Food and Beverage – Prebiotics Market (2022). https://www.reportsanddata.com/report-detail/prebiotics-market Reports and data
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
Graduated in industrial biotechnology and passionate about sustainable development.
