REVIEW: TECHNICAL OPPORTUNITIES AND CHALLENGES TO UPGRADING FOOD BIO-PROCESSING IN DEVELOPING COUNTRIES
Rosa S. Rolle
Agricultural Industries Officer
Key words: Bioprocessing Technologies; Fermentation; Enzymes; Developing Countries
Summary
Bioprocessing technologies (food fermentations and the use of enzymes) offer tremendous opportunity for stimulating agro-industrial development in developing countries. These technologies are scaleable, economical, generally environmentally friendly, and are applicable in preserving and enhancing the nutritional quality and safety of foods. Optimisation of bioreactor processes and improvement of the quality of biological inoculants applied in bioprocessing, pose major challenges to the development of bioprocessing technologies in developing countries.
Introduction
Food processing in many developing countries is characterised by a large number of small-scale operations, which often process indigenous raw materials on a seasonal basis. In a number of instances, high post-harvest losses are sustained owing to limited knowledge of appropriate processing technologies and the inadequacy of processing facilities to accommodate crop production. Existing methodologies for the processing and preservation of foods in these countries must therefore be upgraded in order to meet food requirements, address food security challenges and minimise post-harvest losses.
The application of bioprocessing technologies is one area which may be targeted for stimulating development in developing country agro-industry in light of relatively low costs, minimal energy and infrastructural requirements and scaleability of the technologies involved. These technologies offer tremendous opportunity for innovation in food processing and preservation, and for improving the safety and nutritional quality of foods. Upgrading these technologies would also offer developing countries the opportunity to build on and develop their indigenous methodologies of food preservation. The scale up and improvement of bioprocesses applicable to food preservation however poses a number of challenges.
Bioprocessing Technologies
Fermentation and the use of enzymes, perhaps the oldest known bioprocessing technologies, and have been utilised in the preservation of foods for centuries. When applied in food processing, these technologies are characterised by three major steps: acquisition and pre-treatment of raw materials, an incubation step to allow the bioprocess to take place, followed by product recovery and post-processing. The quality of raw material used in food bioprocessing is largely dependent on breeding, farming and post-harvest handling practices. Unit operations such as peeling, dehulling, crushing, grating and pressing, may be applied in the pre-treatment of raw materials prior to incorporation of a biological inoculant which may either be microbial or enzymatic. The inoculated food medium is subsequently incubated in a bioreactor in order to allow the bioprocess to proceed. Post-bioprocessing operations such as sieving, sun-drying, and high temperature cooking are conducted in order to enhance storability of the finished product.
The level of technology applied in bioprocessing is generally reflective of both environmental and socio-economic conditions. Bioreactors applicable in food bioprocessing vary in sophistication from being a hole in the ground, to a fermentation vat or a shallow tray in household and village level processing, to sophisticated computerised systems with controls for industrial processing. Any or all of the three steps of a particular bioprocess may be targeted for upgrading or modification of bioprocesses. Improvement of biological inoculants and optimisation of bioreactor processes however pose major challenges to upgrading food bioprocessing technologies in developing countries.
Fermentation Technology
Fermentation is widely utilised as a means of food preservation in developing countries, particularly in areas where refrigeration, canning and freezing facilities are either inaccessible or unavailable. Fermentation enhances nutritional quality, through the biosynthesis of vitamins, essential amino acids and proteins; through improving protein digestibility; enhancing micronutrient bioavailability and degrading antinutritional factors. It improves the safety of foods by reducing toxic compounds, and producing antimicrobial factors such as bacteriocins, hydrogen peroxide, acetoin, diacetyl and organic acids (Daeschel 1989) which facilitate inhibition or elimination of food-borne pathogens. In addition to its nutritive and preservative effects, fermentation enriches the diet through the production of a diversity of flavours, textures and aromas. It improves the keeping quality and shelf-life of foods, while reducing cooking times and hence energy consumption required for the preparation of foods.
In a majority of indigenous food fermentation processing techniques, fermentation is allowed to proceed spontaneously under non-aseptic conditions using either submerged fermentation (SMF) or solid substrate fermentation (SSF) techniques. Technically, SMF involves soaking of pre-treated raw food material, submerged in water contained in a bioreactor which is generally a fermenting vat. SSF on the other hand, involves microbial overgrowth of the pre-treated raw food material in the absence of free water. Filamentous fungi, bacteria and yeast are the predominant microflora in SSF processes. Bacteria and yeast generally adhere to the food surface, while fungi penetrate the food for nutrient uptake.
"Uncontrolled" fermentation processes generally require lengthy incubation periods of two to three days. Sources of microorganisms include the raw material, the fermentation medium, the container in which the fermentation is conducted, and in some cases, samples of product saved from a previous batch of fermented product. The wide and varied microbial flora to which raw materials are exposed, results in tremendous variation in the overall quality of fermented food products.
Upgrading fermentation processes to enhance bioprocess efficiency while improving the safety and quality attributes of fermented food products would have a positive impact on nutrition and food security in developing countries, while reducing post-harvest losses.
Upgrading Food Fermentation Technologies
The development of starter cultures and improvement of process controls for food fermentations are perhaps the two areas which pose the greatest challenges to improving fermentation technology in developing countries.
Starter Cultures Substantial research into the identification and characterisation of micro-organisms associated with indigenous fermentations, is currently on-going in a number of developing countries, with the objective of starter culture development. In a number of cases however, where appropriate single and mixed culture starters which speed up the biochemical processes associated with fermentations have been identified, flavour and texture attributes of resultant products have been unacceptable to consumers. This implicates the requirement for research into correlating both flavour and texture development in natural fermentations with the activities of the predominant micro-organisms or groups of micro-organisms associated with fermentation processes. Other factors such as inhibition of the growth of spoilage micro-organisms, improvement of micronutrient bioavailability and vitamin content, and creation of uniform products at reasonable cost must also be incorporated into starter culture development. Genetic improvement of starter micro-organisms for enhancement of these desirable characteristics should also be considered where technological and financial conditions permit.
Starter culture development should be appropriate to the needs of the targeted beneficiary group. Thus where starter cultures are targeted for industrial processing, biochemically-defined and genetically improved cultures are appropriate. However for household and village-level processing, starter cultures might consist of crude mixtures of micro-organisms originating from batches of fermented foods, prepared under standardised conditions. Starter cultures such as ragi and koji which consist of crude mixtures of micro-organisms are widely utilised in countries such as China, India, Indonesia, Malaysia, Nepal, The Phillipines and Taiwan, and their production serves as a source of income in areas where they are utilised. Technologies utilised in their production and storage, may very well be applicable in the development of other biological starter materials for use in developing countries.
Bioreactor Control Bioreactors essentially optimise the growth of micro-organisms, and facilitate recovery of their products. In household and village level SMF processes the bioreactor is generally a fermenting vat, while on an industrial scale, bioreactors are closed fermentors equipped with temperature, pH, aeration and agitation controls.
Bioreactor technology for SSF processes is much less developed. Household and village level SSF technology involves heaping or spreading the pre-treated food material thinly in trays or over leaves, while industrial scale SSF is conducted in tray or rotating drum fermenters. High heat buildup and poor aeration and moisture transfer during SSF processes, are major limiting factors to upgrading this technology for use on an industrial scale (Gowthaman et al 1993; Ghildyal et al 1993; Cooke, 1994).
There is however a need for further development of SSF technologies in light of the comparative economic and environmental advantages of applying SSF technology in small-scale processing. SSF processes generally have low capital investment, energy and water requirements, generate minimal amounts of liquid waste and function economically in small scale operation.
Enzymes
Enzymes catalyse a number of specific reactions which produce changes in food constituents, leading to enhancement of texture, safety, appearance, nutritional value and flavours in foods. Enzymes also serve a diagnostic role as biosensors for toxicity and quality assessment in food processing. Through their antioxidant and biocatalytic activities, enzymes are applicable as non-thermal food preservatives.
Enzyme catalysed processes are scaleable with requirements for a simple manufacturing base, low capital investment and low energy consumption, and may be utilised in upgrading a number of food processing applications. Current and potential applications for the use of enzymes in developing countries were recently reviewed by Rolle (1997).
Developing Country Enzyme Applications
Five major roles may be targeted for the use of enzymes within the context of upgrading food processing operations in developing countries (Table 1 ). Enzymes increase productivity and efficiency in a number of agro-industrial processes without requirements for large scale expensive mechanical equipment. Fruit juice processing, edible oil extraction and the downstream processing of starches are three areas in which the application of enzymes improves yields and quality, lowers costs and facilitates mechanical processing.
Enzymes improve food safety by catalysing the degradation of indigenous toxic factors. They enhance nutritional quality by catalysing transformations which lead to improved digestibility, and enhancement of both nutrient bioavailability and nutrient density in staple foods.
Enzymes which exhibit antimicrobial properties are applicable in the non-thermal preservation of foods, while those which utilise oxygen as co-substrates, have an antioxidant effect in food systems thus preserving flavour and colour. The so-called "killer enzymes", i.e. enzymes which degrade other enzymes, also have a non-thermal preservative effect in foods, through the inhibition/inactivation of other undesirable enzymatic reactions.
Micro-organisms associated with food fermentations, secrete a number of enzymes which catalyse the hydrolysis of carbohydrates, lipids, proteins, anti-nutritional and toxic factors. Thus enzymes are applicable in accelerating fermentation processes. In soy sauce production for example, a koji which constitutes a relatively crude source of enzymes is used for starch and protein hydrolysis. However the use of microbial enzyme preparations has been shown to accelerate the rate of soy sauce fermentations and improve flavour and yields of the product (Nielsen, 1997).
The application of enzymes offers developing countries considerable flexibility, and opportunity for innovation in diversifying their utility of agricultural products. The production of sweeteners from starches, and brewing with the use of indigenous grains such as sorghum and millet rather than with imported malt and barley, are both examples of product diversification through the application of enzymes.
Table 1 Potential Areas For the Application of Enzymes in Developing Countries
ROLE
|
EXAMPLE |
| Upgrading mechanical processing |
|
| Improvement of food safety and nutritional quality |
|
| Non-thermal preservation
Acceleration of fermentation processes
Diversified use of agricultural products |
|
Although the use of enzymes in household and village level processing in developing countries is widespread, the overall quality of enzymes used is relatively crude in the form of leaves, pounded grains, plant exudates and chopped fruits. While these sources of enzymes are appropriate in use within the context of household and village level processing, the upgradation of agro-industrial processes will necessitate the use of higher quality enzymes and the standardisation of these enzyme activities.
Upgrading Enzyme-Catalysed Processes
Enzyme catalysed processes may be upgraded through improvement of the quality of enzymes utilised in processing. Where feasible, upgrading the purity of enzymes of plant and animal origin through the use of biochemical techniques, and standardising these enzymatic activities is one technical option which might be considered. An alternative option would be the use of microbial enzymes of specificities similar to those derived from plant and animal sources. The use of microbial enzymes in food processing is advantageous in that microbial enzymes exhibit a broad spectrum of characteristics (pH optima, temperature etc.) and are consistently obtainable in relatively large quantities.
SSF and SMF techniques are both applicable in the production of microbial enzymes, however the low cost, low-technology requirements of the SSF process, makes it a more appropriate technology for the production of enzymes in a majority of developing countries. The production of enzymes can be feasibly integrated with food processing operations, since a number of food processing wastes, serve as substrates for the production of enzymes (Jha et al. 1995, Babu & Satyanarayan 1995; Ofuya & Nwajuba 1990).
The instability of purified enzymes poses yet another constraint to the use of enzymes in agro-processing, although a number of food-grade enzymes can generally be stabilised using substrates, specific ligands, glycerol, sugars and polyhydric alcohols. The applicatioin of enzymes in food processing is generally relatively easy, however the production of high quality enzymes requires a relatively high level of technically skilled personnel.
Conclusions
Bioprocessing technologies offer great potential for economically upgrading the agro-processing sector in developing countries. Bioprocessing industry requirements would also stimulate the development of other income-generating activities such as the production of enzymes and starter cultures. Successful development of bio-processing based food industry is however largely dependent on skilled and trained personnel in relevant fields.
References
Babu, K.R. Satyanarayana, T. 1995 Alpha amylase production by thermophilic Bacillus coagulans in solid substrate fermentation. Process Biochemistry 30, 305-309.
Cooke, P.E. 1994 Fermented foods as biotechnological resources. Food Research International 27, 309-316.
Daeschel, M.M. 1989 Antimicrobial substances from lactic acid bacteria for use as food preservatives. Food Technology 43, 164-167.
Ghildyal, N.P., Ramakrishna, M., Lonsane, B.K. and Karath, N.G. 1992 Gaseous concentration gradients in tray type solid state fermentors-Effect on yields and productivities. Bioprocess Engineering 8, 67-72.
Jha, K., Khare, S.K. & Gandhi, A.P. 1995 Solid state fermentation of soy hull for the production of cellulase. Bioresource Technology 54, 321-322.
Nielsen, P.M. 1997 Improving soy sauce production and quality using enzymes. World of Ingredients. 6, 36-38.
Ofuya, C.O. & Nwajuba, C.J. 1990 Fermentation of cassava peels for the production of cellulolytic enzymes. Journal of Applied Bacteriology 68, 171-177.
Rolle, R.S. 1998 Review: Enzyme Applications For Agro-Processing in Developing Countries: An Inventory of Current and Potential Applications. World Journal of Microbiology and Biotechnology. 14:In press.
Legends to Figures
Figure # Legend
1 Essential steps of a food bioprocessing operation