The virtuous reuse – upcycling (1,2) - of waste from agro-industrial chains can allow 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 removed from recycling (in feed or inputagriculture), energy valorisation or disposal, to trace the Lansink scale(or 'waste hierarchy', symbol of the circular economy).
These materials – available in abundance, at negligible cost – they can in fact be used as raw materials or substrates to extract or synthesize prebiotics, through bio-processes that use enzymes. The residues thus lend themselves to conversion into various bioactive compounds.
2) Agricultural and industrial waste
Lateral streams of the agri-food chains generate enormous quantities of waste which can be classified into two macro-categories:
- agricultural, field or process waste. Such as straw, stems, stems, leaves, husks, husks, peels, fruit pulp or stubble, molasses, brewer's grains, coffee grounds, bagasse (from sugar cane and sweet sorghum milling), etc.
- agro-industrial co-products, such as potato peelings, citrus fruits, tomatoes, soybean cakes and other oilseeds, etc.
3) Bioactive compounds
The enzymatic hydrolysis of agro-industrial residues and by-products allows to obtain bioactive compounds of nutritional value, functional ingredients, also with prebiotic action. (4) Using the most appropriate enzymes – or enzymatic systems – in relation to the different matrices.
Most of agro-industrial waste is composed of lignocellulosic materials (cellulose, hemicellulose and lignin), from which to extract oligosaccharides (xylo 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 bonded to a terminal glucose molecule. The use of industrial by-products rich in sucrose, such as molasses, can represent an economic and profitable alternative to produce prebiotics.
These by-products often they do not even require a preliminary treatment, immersion in hot water being sufficient to obtain the substrate necessary for enzymatic catalysis.
Ganaia et al. (2017) demonstrated that the FTase of Aspergillus flavus allows FOS to be synthesized from sixteen different agricultural wastes including wheat bran, corn straw, sugar cane bagasse, cassava husks, apple pomace, orange peels, beets and bananas. (6)
3.2) Galacto-oligosaccharides, GalOS
GalOS, galacto-oligosaccharides, are oligomers of galactose (e.g. lactosucrose, lactulose). Lactose is one of the substrates needed to produce these prebiotics, acting as an acceptor and/or donor of galactosyl moieties. The synthesis of lactosucrose and lactulose also requires sucrose or fructose, which instead act as acceptors of galactosyl bonds.
Whey – co-product of the dairy industry – is an ideal candidate for these forms of upcycling thanks to the appreciable concentration of lactose (about 4,5-6,0%). Kaur et al., 2020) (7) In addition to the valuable protein, which is also useful to extract.
Violinist et al.(2020) achieved a high conversion rate (80%) of whey lactose into GalOS, thanks to a β-galactosidase of Streptococcus thermophilus. It was thus possible to synthesize about 1 kg of GalOS from 3 kg of powdered whey permeate. (8)
3.3) Xylo-oligosaccharides, XOS
XOS extension, xylo-oligosaccharides, can be extracted from biomass rich in hemicellulose, also widespread among agricultural and agro-industrial waste. The xylan (constituent of hemicellulose) recovered from biomass is converted into XOS with the help of endo-xylanase enzymes. (9)
Wheat Straw and corn cobs can be used to extract hemicellulose by autohydrolysis, the cheapest bio-process. (10) Although chemical processes, including those based on alkalis and acids, are the most popular. Other wastes used are rice and coconut husks as well as sugar cane bagasse residues (11).
3.4) Other prebiotics
Numerous other prebiotics compounds can be extracted or produced from various sources of waste from the agri-food chain. Some studies have focused on the conversion of leftovers to obtain manno-oligosaccharides, isomalto-oligosaccharides, pectin oligosaccharides. (3)
4) Benefits for the gastro-intestinal system
The resistance of prebiotics hydrolysis confirms their ability to reach the colon without being decomposed by the gastric juices of the stomach. The fermentability tests in turn allow to:
- verify the ability of substances to promote the growth of beneficial microorganisms,
- follow their conversion into bioactive metabolites, which play essential roles in human physiology and metabolism (12,13).
5) Provisional conclusions
The global market of prebiotics reached 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 .14%. (XNUMX)
The upcycling processes of agro-industrial waste into bioactive compounds via enzymatic bioprocesses still have areas for improvement that deserve further research and development.
Dario Dongo and Giulia Pietrollini
(1) Dario Dongo. Upcycling, the highway to 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, DA, 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 mental health? GIFT (Great Italian Food Trade). 14.2.23
(5) L. Bhatia, A. Sharma, RK Bachheti, AK 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) MA Ganaie, H. Soni, GA Naikoo, et al. (2017). Screening of low cost agricultural waste to maximize the fructosyltransferase production and its applicability in generation of fructooligosaccharides by solid state fermentation. International Biodeterioration & Biodegradation, 118 (2017), p. 19-26, doi:10.1016/j.ibiod.2017.01.006
(7) R. Kaur, D. Panwar, PS 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, HM Nguyen, S. Wenig, HA 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, AK Samanta, AP Kolte, S. Senani, M. Sridhar, KP 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, AK Samanta, AP Kolte, S. Senani, M. Sridhar, KP 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 intestine, 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