BACKGROUND OF THE THESIS
INTRODUCTION
- Literature review and fundamental theory (chapter 2)
- Experimental Methods (Chapter 3)
- Results and discussion (Chapter 4)
- Economic evaluation of the process (Chapter 5)
- Summary, Conclusions, Recommendations and contributions of this work (Chapter 6)
Recently, attention has been paid to research on the extraction of bioactive compounds from BSG. The views are to determine the optimal operating parameters and the economic feasibility of the process.
THEORY AND LITERATURE REVIEW
Structure of brewers spent grain
Studies show that most phenolic acids (mainly ferulic acid and p-coumaric acid) are found in the peel and aleurone layer (Nordkvist et al., 1984). Total phenolic acids are reported to be concentrated in the lignocellulosic wall at about 0.6-0.9% in concentration while lower in the endosperm section at less than 0.1%.
Chemical characterization
The multi-layered lignocellulosic wall has three parts, namely the seed coat, the aleurone and the pericarp layer (Kunze & Kunze, 2010). This is the reason for the high content of sugars such as xylose, arabinoxylans and glucose found in the grain (Mussatto et al., 2006).
Generation of Brewer’s Spent Grain
Malting process
Brewing process
The effect of brewing and malting on the phenolic compounds present in BSG
BSG as a cattle feed: Animal nutrition
BSG in human diet
Bioethanol production
BSG as a carrier in Brewing
Polysaccharides production
BSG as a natural source of antioxidants
An antioxidant is defined as a substance which, when present in small amounts in a particular living cell, significantly delays or prevents oxidation of that cell (Halliwell, 1995). In the food industry, an antioxidant is a substance that has the technical function of slowing down the oxidation of nutrients, such as lipids, sugars and proteins, the oxidation of which leads to an inevitable deterioration of the organoleptic properties of a food.
Natural antioxidants vs synthetic antioxidants
Halliwell, (2008) reported that antioxidants have properties such as scavenging free radicals (mainly O2* and chelation of metal ions that inhibit cellular damage).
Major classes of natural antioxidants
This antioxidant is in the form of pigments responsible for the red, orange and yellow color in foods. Polyphenolic compounds have gained interest especially in the cosmetic industry for the production of body oils and lotions (Kris-Etherton et al., 2002; Dillard & German, 2000).
Uses of polyphenols
- Polyphenols as food preservatives
- Polyphenols as dietary supplements
- Polyphenols as cosmetics additives
These compounds are available on the market in a pure form or in defined solutions so that they can be added very easily in the desired amount. This is very attractive especially in the cosmetic industry as most of the body creams and oils on the market do not contain natural products.
Classification of polyphenolic compounds
Polyphenols have been reported to be potential dietary supplements such as α-tocopherol, β-carotene and rutin (Figuereo et al., 2016). Research has shown that green tea extracts, avocado oil and grape seed extract are valuable ingredients in most cosmetic products (Whitney P & Silvina, 2016; Pyo et al., 2016).
Flavonoids
- Flavonols
Singh et al., (2014) reported that flavonols have known antioxidant activity at low concentrations and may act in several ways to inhibit oxidation.
Phenolic acids
Other polyphenols
Extraction of valuable compounds is the first activity performed in the conceptual development phase of the commercial process. There are several methods that can be used for extraction as described in this section, including soxhlet extraction and maceration.
Preservation of BSG
Pre-treatment methods
However, it has been shown (Silva et al., 2012) that screening ground BSG is difficult due to the uneven distribution of polyphenols in the grain. In BSG, the phenolic components are usually concentrated in the cell walls of the aleurone layer and the shell.
Solid-liquid extraction
- Soxhlet extraction
- Maceration extraction
Due to the diverse nature of the polyphenols to be extracted, there is no one standard method that is ideal for all extractions (Che Sulaiman et al., 2017). This extraction technique was used by Meneses et al. 2013a) when they evaluated the effectiveness of different solvent compositions (methanol, ethanol, acetone, hexane, ethyl acetate, water, methanol/water mixtures, ethanol/water mixtures and acetone/water mixtures) of BSG.
Assisted extraction methods
- Microwave assisted method
- Ultrasound assisted method
Microwave-assisted extraction (MAE) is an advanced technique (Moreira et al., 2013) which uses the solvent with the help of microwave energy. Several authors have also made a comparison between microwave-assisted extraction methods and conventional methods for various medicinal plants such as Salvia miltiorrhiza bunge (Pan et al., 2002), Dendrobium candidum (Cui et al., 2014).
High pressure extraction methods
- Supercritical fluid extraction (SFE)
- Subcritical water extraction (SubCWE)
In another work, Spinelli et al., (2016) optimized the extraction conditions to extract polyphenolic compounds and flavonoids from BSG. Deng et al., 2016) have reported several other factors affecting the extraction of polyphenols, such as solvent selection, solid-solvent ration, shaking speed, temperature, and time.
Types of solvent used
For example, Meneses et al., (2013b) investigated the effect of five different solvents (ethanol, methanol, acetone, ethyl acetate and hexane) and their mixtures in water (ethanol: water mixture, acetone: water mixture and methanol: . water mixtures) for the extraction of polyphenols from BSG. Addai et al., (2013) investigated the influence of solvents on the extraction of polyphenolic compound from papaya cultivar.
Effect of solvent to feed ratio
Dent et al., (2013) pointed out that a mixture of solvents such as ethanol, acetone, methanol and ethyl acetate is more effective in extracting covalent molecules. This research showed that the type of solvent to be chosen depends on the nature of the polyphenols to be extracted as well as the non-toxicity of the solvent for industries that produce polyphenols for human consumption (Abu Bakar et al., 2009; Meneses et al., 2013a).
Effect of temperature
Effect of particle size
To develop a cost-effective process for commercial applications, a deep understanding of the mass transfer properties such as diffusion and hydrodynamic data and solubility is required (Ricardo et al., 2016). In the washing stage, known as the rapid extraction stage, the extraction rate is rapid and gradually increases as the polyphenols, which are already on the surface of the solid matrix, are released into the solvent (Crossley & Aguilera, 2001; Rakotondramasy-Rabesiaka). et al., 2009).
Modelling of extraction kinetics
According to Fernandez-Pérez et al. (2008) the selling price of BSG extracts was found to be $8.17/entity. Iron-reducing ability of plasma (FRAP) as a measure of ""antioxidant power"": the FRAP assay.
Modelling of Batch and Semi-continuous processes
EXPERIMENTAL METHODS, OPTIMISATION AND KINETIC STUDIES
Brewer’s spent grain (BSG)
Chemicals
Pre-treatment of BSG
Solvent selection
- Soxhlet extraction
- Maceration extraction
Methods of analysis for solvent selection
- Determination of global yield
- Determination of total phenolic content
- Measurement of antioxidant activity
- DPPH radical scavenging activity assay
- Ferric reducing antioxidant power (FRAP) assay
- HPLC-DAD analysis for individual components
After weighing, a fresh solvent was added to the dried extract and the sample was taken for analysis of total phenolic content and antioxidant activity. In this paper, two methods, DPPH and FRAP assays, were used to determine the antioxidant activity of BSG extracts.
Statistical analysis
Response surface design
Design of Experiments
Analysis of variance (ANOVA)
Verification of the model parameters
Experiments with 6 identical cups with the same solid to feed ratio were performed at the same time with the same operating conditions. The assumption made was that all beakers operate under the same conditions and measurement volumes.
Kinetic models
A comparison was made between the base scenario simulation and four other alternative schemes to select the best process. The selection of the best process was based on the profitability indicators, payback period, return on investment (ROI) and net present value (NPV).
Modelling of the base case scheme
- Registration of components
- Estimation of Prices
The selling price of the BSG residue after the extraction process was obtained from Fernandez-Pérez et al., (2008). The selling price of the main product BSG extract was calculated based on the Sigma Aldrich.
Initialization of unit procedures and scheduling
Process simulation and economic evaluation
To calculate FCI in Equation 3.9, direct costs were added to indirect costs of the developed process.
Sensitivity analysis
By adjusting the scale-up or scale-down factor in Figure 3-7, SuperPro Designer® simulated the new process by solving new mass and energy balances and performing the new economic analysis.
EXPERIMENTAL RESULTS AND ANALYSIS
Global yield
The global percentage yield was calculated using the mass of the extract and the original BSG mass sample. According to the research done in this work, there is no literature on the worldwide yield for the extraction of polyphenols from BSG using soxhlet extraction.
Total Phenolic Content (TPC)
Meneses et al., (2013b) also reported that the higher total phenol content was obtained when using 70% (v/v) acetone compared to using water and ethanol. Roby et al., (2013) evaluated the influence of solvent extraction on the extraction of polyphenolic compounds from extracts of three aromatic plants (thyme, sage and marjoram).
Antioxidant activity
- Reducing power using FRAP assay
- Radical scavenging activity towards DPPH free-radical
Payne et al., (2013) reported that the FRAP assay is the only assay that directly measures antioxidants (or reductants) in a sample compared to other assays that measure free radical inhibition. Extraction yield optimization was performed using RSM, according to (Montgomery et al., 2016).
Preliminary tests
Based on the above results, it can be concluded that water is the best solvent for this research work. Therefore, we can conclude that milling has a significant effect on the extraction of polyphenols from BSG.
Response Surface Method (RSM)
Seeding after milling was attempted but the results obtained were not significant enough (p > 0.05) as shown in Appendix A.
Actual Responses
Selection of Model
Analysis of variance (ANOVA) for the 2FI model
Although there are small chances (< 5% for all responses) that Model F values may occur due to noise, all responses have Model F values less than 2, indicating that the model is significant. This may be due to the variables chosen (time, temperature, solvent/feed ratio and shaking speed) having no effect on the responses.
Normal probability plot
The more polyhenolic compounds extracted, the greater the antioxidant activity of the BSG extracts. The response surface has a small standard error of design of 0.393 which further indicates that the overall mean is a more accurate reflection and predictor of the response as a function of solvent to feed ratio and time than the model.
Verification of predicted data
In the extraction of polyphenols, we observed a dominance of the washing rate compared to the diffusion rate for all temperature ranges. The extraction rate was found to be 15 min regardless of the temperature increase, and the washing rate was calculated to be more dominant than the diffusion rate.
MODELLING, SIMULATION AND ECONOMIC ANALYSIS
Process description
After completion of extraction, the samples are then filtered and the extract water is taken for analysis. To determine the production yield and the time of extraction, experiments were conducted on a laboratory scale as illustrated with the process flow diagram in Figure 5.1.
Scaling up
The filtered aqueous extract was dried in a spray dryer and the powdered extract was weighed to obtain the mass per batch and the total yield of the process. Based on laboratory experiments, the extraction of bioactive compounds from BSG is in batch mode instead of continuous with a default annual operating time of 7920 h.
User-defined components
Estimated prices for simulation
Unit operations construction
- Tray dryer
- Storage drum
- Extraction vessel
- Vibrating screen
- Evaporator
The extraction process took place when the materials were transferred from the storage drum. It was found that 95% of the water was removed using a rotary evaporator after 4 hours.
Scheduling time
The process time (PT) based on the mass flow rate was estimated to be 600 kg/h for all units. After completing the process specifications, simulating the process model by selecting the "Tasks: Solve M & E Balances" and "Tasks: Perform Economic Analysis" option on the main menu, the complete results were viewed and analyzed for the material balances and the economy of the base case simulation.
Material balances
SuperPro Designer® modeled a global extraction yield of 27% (1.51 kg extract out of 5.6 kg BSG fed). This global yield is higher than that obtained in laboratory experiments for the extraction of BSG with water as solvent.
Debottlenecking strategy to improve production and profitability
Alternative Scheme 1
Four debottlenecking schemes as shown in Table 5.10 were developed based on the baseline simulation to improve annual production by increasing the number of batches. Furthermore, the addition of a grinder, which increased the product yield from 3 wt% to 5 wt%, did not significantly influence the number of batches.
Alternative scheme 2
Increasing the number of groups appears to be ineffective as the return on investment remains negative. This implies that, in this work, increasing the number of groups had an insignificant impact on the profitability of the process.
Alternative scheme 3
The main limitation for all the developed schemes is the low income of the final product. Efforts were then made to increase the value of the end product, while reducing operating costs.
Alternative scheme 4
Although the annual throughput has been increased, the economic analysis of all the three proposed schemes shows that the ROI values (Table 5.10) are still well below the desired 30. The calculations of this scheme show that the capital investment can be recovered in 1.76 years since the operating costs exceed the total revenue.
Prices for equipment in selected scheme 4
Unit cost analysis for selected scheme 4
The factoring method within the SuperPro Designer® software was used in the estimation of physical costs and economic parameters are the standard numbers in the software, as shown in Figure 5-10. An increase in equipment capacity has a direct relationship with the increase in operating costs as more raw materials are required.
Profitability analysis
This was because SuperPro Designer® did not take into account the year the plant was built. Time and time bottlenecks in the process had less impact on the economy, so all strategies to eliminate the bottlenecks were unsuccessful until value added to the product was introduced.
SUMMARY, CONCLUSION, RECOMMENDATIONS AND CONTRIBUTIONS
A batch process was chosen as the operating mode for process modeling and simulation. The development of the process included a conceptual phase where experiments were carried out in the laboratory and modeling and simulation carried out using SuperPro Designer® software.
A novel application of microwave-assisted extraction of polyphenols from brewery spent grain with HPLC-DAD-MS analysis. Valuation of brewery spent grain using a fully recyclable integrated process for the extraction of proteins and arabinoxylans.
