The Monthly Digest – Food Waste – February & March 2018

Food Waste and by-products

R & D abstracts – February & March 2018

Deep eutectic solvents pretreatment of agro-industrial food waste (research)

Waste biomass from agro-food industries are a reliable and readily exploitable resource. From the circular economy point of view, direct residues from these industries exploited for production of fuel/chemicals is a winning issue, because it reduces the environmental/cost impact and improves the eco-sustainability of productions. The present paper reports recent results of deep eutectic solvent (DES) pretreatment on a selected group of the agro-industrial food wastes (AFWs) produced in Europe. In particular, apple residues, potato peels, coffee silverskin, and brewer’s spent grains were pretreated with two DESs, (choline chloride–glycerol and choline chloride–ethylene glycol) for fermentable sugar production. Pretreated biomass was enzymatic digested by commercial enzymes to produce fermentable sugars. Operating conditions of the DES pretreatment were changed in wide intervals. The solid to solvent ratio ranged between 1:8 and 1:32, and the temperature between 60 and 150 °C. The DES reaction time was set at 3 h. Optimal operating conditions were: 3 h pretreatment with choline chloride–glycerol at 1:16 biomass to solvent ratio and 115 °C. Moreover, to assess the expected European amount of fermentable sugars from the investigated AFWs, a market analysis was carried out. The overall sugar production was about 217 kt yr−1, whose main fraction was from the hydrolysis of BSGs pretreated with choline chloride–glycerol DES at the optimal conditions. The reported results boost deep investigation on lignocellulosic biomass using DES. This investigated new class of solvents is easy to prepare, biodegradable and cheaper than ionic liquid. Moreover, they reported good results in terms of sugars’ release at mild operating conditions (time, temperature and pressure).

Procentese A et al (2018) Biotechnology for Biofuels 11:37

Engineering yeast for utilization of alternative feedstocks (research)

Realizing the economic benefits of alternative substrates for commodity chemical bioproduction typically requires significant metabolic engineering of common model organisms, such as Saccharomyces cerevisiae. A growing toolkit is enabling engineering of non-conventional yeast that have robust native metabolism for xylose, acetate, aromatics, and waste lipids. Scheffersomyces stipitis was engineered to produce itaconic acid from xylose. Yarrowia lipolytica produced lipids from dilute acetate at over 100 g/L. Cutaneotrichosporon oleaginosus was engineered to produce omega-3 fatty acids and recently was shown to accumulate nearly 70% lipids when grown on aromatics as a carbon source. Further improvement to toolkits for genetic engineering of non-conventional yeast will enable future development of alternative substrate conversion to biochemicals.

Yaguchi A et al (2018) Current Opinion in Biotechnology 53:122-129

Conversion of lignocellulosic agave residues into liquid biofuels using an AFEX™-based biorefinery (research)

Agave-based alcoholic beverage companies generate thousands of tons of solid residues per year in Mexico. These agave residues might be used for biofuel production due to their abundance and favorable sustainability characteristics. In this work, agave leaf and bagasse residues from species Agave tequilana and Agave salmiana were subjected to pretreatment using the ammonia fiber expansion (AFEX) process. The pretreatment conditions were optimized using a response surface design methodology. We also identified commercial enzyme mixtures that maximize sugar yields for AFEX-pretreated agave bagasse and leaf matter, at ~ 6% glucan (w/w) loading enzymatic hydrolysis. Finally, the pretreated agave hydrolysates (at a total solids loading of ~ 20%) were used for ethanol fermentation using the glucose- and xylose-consuming strain Saccharomyces cerevisiae 424A (LNH-ST), to determine ethanol yields at industrially relevant conditions. Low-severity AFEX pretreatment conditions are required (100–120 °C) to enable efficient enzymatic deconstruction of the agave cell wall. These studies showed that AFEX-pretreated A. tequilana bagasse, A. tequilana leaf fiber, and A. salmiana bagasse gave ~ 85% sugar conversion during enzyme hydrolysis and over 90% metabolic yields of ethanol during fermentation without any washing step or nutrient supplementation. On the other hand, although lignocellulosic A. salmiana leaf gave high sugar conversions, the hydrolysate could not be fermented at high solids loadings, apparently due to the presence of natural inhibitory compounds. These results show that AFEX-pretreated agave residues can be effectively hydrolyzed at high solids loading using an optimized commercial enzyme cocktail (at 25 mg protein/g glucan) producing > 85% sugar conversions and over 40 g/L bioethanol titers. These results show that AFEX technology has considerable potential to convert lignocellulosic agave residues to bio-based fuels and chemicals in a biorefinery.

Flores-Gomez CA et al (2018) Biotechnology for Biofuels 11 :7

Biovalorization of brewers’ spent grain for the production of laccase and polyphenols (research)

Brewers’ spent grain (BSG) is the main solid by-product of the brewing process and is typically disposed of as cattle feed. In this study, BSG was evaluated as a substrate for the production of polyphenols and the lignin-degrading enzyme laccase using fungal solid-state fermentation by Trametes versicolor. Laccases are finding increasing applications in the food industry and polyphenols have benefits for human health. After 14 days of fermentation with T. versicolor, there was a 3.4-fold increase in the extraction of total polyphenols compared with untreated BSG. Using BSG as the sole source of carbon and nitrogen, maximum laccase activity was achieved after seven days of treatment with an activity of 560 U/L. Based on these results, BSG is suggested to be a good lignocellulose waste material to produce value-added products such as the enzyme laccase and polyphenols.

Tisma M et al (2018) Journal of the Institute of Brewing (in press)

Valorisation of food and beverage waste via saccharification for sugars recovery (research)

Valorisation of mixed food and beverage (F&B) waste was studied for the recovery of sugars via saccharification. Glucoamylase and sucrase were employed to hydrolyse the starch and sucrose present in the mixed F&B waste because of the high cost-effectiveness for such recovery. The Michaelis-Menten kinetics model suggests that preservatives and additives in beverages did not inhibit glucoamylase and sucrase during saccharification. High levels of glucose (228.1 g L−1) and fructose (55.7 g L−1) were efficiently produced within 12 h at a solid-to-liquid ratio of 37.5% (w/v) in 2.5 L bioreactors. An overall conversion yield of 0.17 g sugars per g of mixed F&B waste was obtained in mass balance analysis. Lastly, possible industrial applications of the sugar-rich hydrolysate and by-products are discussed. This study is believed to cast insights into F&B waste recycling via biotechnology to produce high-value added products to promote the establishment of a circular bio-economy.

Kwan TH et al (2018) Bioresource Technology 255:67-75

Electric energy production from food waste: Microbial fuel cells versus anaerobic digestion (research)

A food waste resourceful process was developed by integrating the ultra-fast hydrolysis and microbial fuel cells (MFCs) for energy and resource recovery. Food waste was first ultra-fast hydrolyzed by fungal mash rich in hydrolytic enzymes in-situ produced from food waste. After which, the separated solids were readily converted to biofertilizer, while the liquid was fed to MFCs for direct electricity generation with a conversion efficiency of 0.245 kWh/kg food waste. It was estimated that about 192.5 million kWh of electricity could be produced from the food waste annually generated in Singapore, together with 74,390 tonnes of dry biofertilizer. Compared to anaerobic digestion, the proposed approach was more environmentally friendly and economically viable in terms of both electricity conversion and process cost. It is expected that this study may lead to the paradigm shift in food waste management towards ultra-fast concurrent recovery of resource and electricity with zero-solid discharge.

Xin XD et al (2018) Bioresource Technology 255:281-287