- Email: [email protected]
Food biotechnology: Frontiers of food functionality
BTA5OVW2.QXD
11/12/1999 3:22 PM
Page 483
483
Food biotechnology Frontiers of food functionality Editorial overview Willem M de Vos
0958-1669/99/$ — see front matter © 1999 Elsevier Science Ltd. All rights reserved.
ing high-pressure processing and high-intensity electric field pulse treatments are in fact reemerging technologies that are based on concepts developed earlier, as reviewed by Knorr (pp 485–491). In addition to maintaining functionality, these treatments share the advantage of instant distribution throughout the food samples, the preservation of foods, and the prospect of combination with temperature and time, allowing for targeted and sophisticated processes.
The production of foods by the processing of raw materials from plant or animal origin dates from more than two million years ago and reached a major milestone with the control of fire. This history of food production also features the first form of biotechnology that can be traced back to Biblical times with the production of fermented foods such as wine, bread or cheese. Both the heating of foods and the application of fermentation result in significant improvements in the safety and quality of foods. These properties, together with improving food production to satisfy the growing and ageing global population, continue to be major areas in food biotechnology and are subject of recent reviews associated with a series of symposia that cover food safety [1] as well as the application of lactic acid bacteria used in a vast variety of industrial food fermentations [2].
The vast majority of industrial food fermentations are initiated by starter cultures of selected strains that contribute to the functionality of the products. As indicated above, lactic acid bacteria are an important group of starters. They are used for the worldwide production of foods that add to the quality of life, such as cheese, butter or yoghurt from milk, sausages from meat, or — in conjunction with other microbes — wine or soy sauce from vegetables. In addition, several lactic acid bacteria, notably Lactobacillus spp., are presently marketed as probiotic cultures with a function in the gastro-intestinal tract that contributes to the health of the consumer. Furthermore, some lactic acid bacteria are exploited as producers of flavoring enzymes, peptides with antimicrobial activity, or metabolites that contribute to the flavor, conservation or texture of foods.
The application of fire and fermentation, however, also results in major changes in the functional properties of foods that may or may not be desired. Hence, food functionality is an area of immense importance that receives increasing attention, notably with the development of functional foods, that is, foods that affect beneficially one or more target functions in the body beyond adequate nutritional effects [3]. The markets for these functional foods are growing rapidly and it is expected that these future foods will bridge the gap between the food and pharmaceutical industry. Further progress in food functionality requires development of temperature-independent processing technologies that preserve and modify foods while maintaining functionality, molecular studies that relate structure and function of macromolecules in foods, and the selection or design of microbial fermentations that produce functional molecules. This series of reviews will discuss recent results and future developments in several of these areas while also addressing the impact of genomics on the food industry by including the recent progress on engineering of food microbes.
A variety of sophisticated expression systems have been developed for lactic acid bacteria allowing them to be used as food-grade cell factories for the production of functional molecules in bioreactors, food products, or the gastro-intestinal tract upon consumption [4]. Although some lactic acid bacteria tolerate oxygen, they have a simple fermentative metabolism that results in the production of the various isomers of lactic acid as main fermentation products. Hence, they may be excellent hosts for metabolic engineering, the more so because their genomes are relatively small and contain only a few duplicated genes. As a consequence, several successful examples of metabolic engineering have been reported that relate mainly to primary metabolism, as reviewed by Hugenholtz and Kleerebezem (pp 492–497). Functional biomolecules that now may be produced with significant yields and in a stereospecific way include the well-known compound ethanol, the flavor compound diacetyl — responsible for the buttermilk aroma — and the amino acid alanine, which is a taste enhancer and sweetener. The potential of producing vitamins is under investigation and may lead to novel functional foods, also known as neutraceuticals.
Although thermal processing continues to be an important technology for preserving foods, new technologies are being developed that are based on other physical parameters, such as pressure and electric fields. The result-
A specific example of metabolic engineering relates to the biosynthesis of extracellular polysaccharides, which is an important industrial property of several lactic acid bacteria. Notably, yoghurt bacteria produce significant amounts of
Addresses Wageningen Center for Food Sciences, Microbial Ingredients Section at NIZO Food Research, and Laboratory of Microbiology at Wageningen University, PO Box 557, 6700 AN Wageningen, The Netherlands; e-mail: [email protected] Current Opinion in Biotechnology 1999, 10:483–484
BTA5OVW2.QXD
11/12/1999 3:22 PM
484
Page 484
Food biotechnology
these exopolysaccharides, which affects the texture and mouthfeel of the product. In the review by van Kranenburg et al. (pp 498–504) the structures of the various food-grade exopolysaccharides are correlated to the conserved genetic clusters that are found in the production hosts. Based on these comparisons and functional studies that revealed the underlying biosynthetic pathways, predictions are made for the engineering of polysaccharides with new or modified functional properties. This review rightfully points out that exopolysaccharide engineering is still in its infancy with only a few examples emerging now in lactic acid bacteria and emphasizes the importance of this approach for future applications and studies aimed to relate structure to function. The concept that ingested live lactic acid bacteria contribute to the health of the consumer dates from the beginning of this century. Insight into the functionality of these so called probiotic lactic acid bacteria is increasing, as discussed by Vaughan, Mollet and de Vos (pp 505–510). Experimental evidence is accumulating for mechanisms that relate to host–microbe interactions, colonization factors, and stimulation of the immune system. In addition, molecular tools are being developed to monitor the presence of probiotic lactic acid bacteria, their functionality by assessing the gene expression in situ, and their effect on the microbial community of the gastro-intestinal tract. Finally, novel strains are being designed that have increased functionality, such as lactic acid bacteria that express foreign epitopes and have potential as live vaccines. These may be among the first examples to bridge the gap between the food and pharmaceutical industry.
Functional genomics of food microbes, including starters, pathogens, and food-spoilage organisms, will have a great impact on increasing food functionality by metabolic engineering, improving cell factories, and design of novel preservation methods, as discussed by Kuipers (pp 511–516). Several genomes of food microbes have already been sequenced, others genomes are under way, and several high-throughput technologies that have been developed for other systems can be applied. In addition, the safety of foods can be increased and claims related to the ingestion of specific microbes can be substantiated. It is noted that transcript-imaging of wild-type industrial strains and genetically modified strains may allow for the use of genomics in risk assessment studies. It may be expected that this may lead to a future streamlining of approval procedures allowing the use of genetically modified microorganisms in food. In conclusion, these reviews highlight the novel developments relating to functional food biotechnology that in the near future may benefit significantly from further developments in the genomics of microbes and man.
References 1.
Farber J (Ed): Int J Food Micorobiol 1999, 49:September issue.
2.
Konings WN, Kuipers OP (Eds): Ant van Leeuwenh 1999, 76:September issue.
3.
Diplock AT, Agett PJ, Ashwell M, Bornet F, Fern EB, Roberfroid MB: Scientific concepts of functional foods in Europe: consensus document. Brit J Nutr 1999, 81:510-515.
4.
De Vos WM: Gene expression systems for lactic acid bacteria. Curr Opin Microbiol 1999, 2:289-295.
11/12/1999 3:22 PM
Page 483
483
Food biotechnology Frontiers of food functionality Editorial overview Willem M de Vos
0958-1669/99/$ — see front matter © 1999 Elsevier Science Ltd. All rights reserved.
ing high-pressure processing and high-intensity electric field pulse treatments are in fact reemerging technologies that are based on concepts developed earlier, as reviewed by Knorr (pp 485–491). In addition to maintaining functionality, these treatments share the advantage of instant distribution throughout the food samples, the preservation of foods, and the prospect of combination with temperature and time, allowing for targeted and sophisticated processes.
The production of foods by the processing of raw materials from plant or animal origin dates from more than two million years ago and reached a major milestone with the control of fire. This history of food production also features the first form of biotechnology that can be traced back to Biblical times with the production of fermented foods such as wine, bread or cheese. Both the heating of foods and the application of fermentation result in significant improvements in the safety and quality of foods. These properties, together with improving food production to satisfy the growing and ageing global population, continue to be major areas in food biotechnology and are subject of recent reviews associated with a series of symposia that cover food safety [1] as well as the application of lactic acid bacteria used in a vast variety of industrial food fermentations [2].
The vast majority of industrial food fermentations are initiated by starter cultures of selected strains that contribute to the functionality of the products. As indicated above, lactic acid bacteria are an important group of starters. They are used for the worldwide production of foods that add to the quality of life, such as cheese, butter or yoghurt from milk, sausages from meat, or — in conjunction with other microbes — wine or soy sauce from vegetables. In addition, several lactic acid bacteria, notably Lactobacillus spp., are presently marketed as probiotic cultures with a function in the gastro-intestinal tract that contributes to the health of the consumer. Furthermore, some lactic acid bacteria are exploited as producers of flavoring enzymes, peptides with antimicrobial activity, or metabolites that contribute to the flavor, conservation or texture of foods.
The application of fire and fermentation, however, also results in major changes in the functional properties of foods that may or may not be desired. Hence, food functionality is an area of immense importance that receives increasing attention, notably with the development of functional foods, that is, foods that affect beneficially one or more target functions in the body beyond adequate nutritional effects [3]. The markets for these functional foods are growing rapidly and it is expected that these future foods will bridge the gap between the food and pharmaceutical industry. Further progress in food functionality requires development of temperature-independent processing technologies that preserve and modify foods while maintaining functionality, molecular studies that relate structure and function of macromolecules in foods, and the selection or design of microbial fermentations that produce functional molecules. This series of reviews will discuss recent results and future developments in several of these areas while also addressing the impact of genomics on the food industry by including the recent progress on engineering of food microbes.
A variety of sophisticated expression systems have been developed for lactic acid bacteria allowing them to be used as food-grade cell factories for the production of functional molecules in bioreactors, food products, or the gastro-intestinal tract upon consumption [4]. Although some lactic acid bacteria tolerate oxygen, they have a simple fermentative metabolism that results in the production of the various isomers of lactic acid as main fermentation products. Hence, they may be excellent hosts for metabolic engineering, the more so because their genomes are relatively small and contain only a few duplicated genes. As a consequence, several successful examples of metabolic engineering have been reported that relate mainly to primary metabolism, as reviewed by Hugenholtz and Kleerebezem (pp 492–497). Functional biomolecules that now may be produced with significant yields and in a stereospecific way include the well-known compound ethanol, the flavor compound diacetyl — responsible for the buttermilk aroma — and the amino acid alanine, which is a taste enhancer and sweetener. The potential of producing vitamins is under investigation and may lead to novel functional foods, also known as neutraceuticals.
Although thermal processing continues to be an important technology for preserving foods, new technologies are being developed that are based on other physical parameters, such as pressure and electric fields. The result-
A specific example of metabolic engineering relates to the biosynthesis of extracellular polysaccharides, which is an important industrial property of several lactic acid bacteria. Notably, yoghurt bacteria produce significant amounts of
Addresses Wageningen Center for Food Sciences, Microbial Ingredients Section at NIZO Food Research, and Laboratory of Microbiology at Wageningen University, PO Box 557, 6700 AN Wageningen, The Netherlands; e-mail: [email protected] Current Opinion in Biotechnology 1999, 10:483–484
BTA5OVW2.QXD
11/12/1999 3:22 PM
484
Page 484
Food biotechnology
these exopolysaccharides, which affects the texture and mouthfeel of the product. In the review by van Kranenburg et al. (pp 498–504) the structures of the various food-grade exopolysaccharides are correlated to the conserved genetic clusters that are found in the production hosts. Based on these comparisons and functional studies that revealed the underlying biosynthetic pathways, predictions are made for the engineering of polysaccharides with new or modified functional properties. This review rightfully points out that exopolysaccharide engineering is still in its infancy with only a few examples emerging now in lactic acid bacteria and emphasizes the importance of this approach for future applications and studies aimed to relate structure to function. The concept that ingested live lactic acid bacteria contribute to the health of the consumer dates from the beginning of this century. Insight into the functionality of these so called probiotic lactic acid bacteria is increasing, as discussed by Vaughan, Mollet and de Vos (pp 505–510). Experimental evidence is accumulating for mechanisms that relate to host–microbe interactions, colonization factors, and stimulation of the immune system. In addition, molecular tools are being developed to monitor the presence of probiotic lactic acid bacteria, their functionality by assessing the gene expression in situ, and their effect on the microbial community of the gastro-intestinal tract. Finally, novel strains are being designed that have increased functionality, such as lactic acid bacteria that express foreign epitopes and have potential as live vaccines. These may be among the first examples to bridge the gap between the food and pharmaceutical industry.
Functional genomics of food microbes, including starters, pathogens, and food-spoilage organisms, will have a great impact on increasing food functionality by metabolic engineering, improving cell factories, and design of novel preservation methods, as discussed by Kuipers (pp 511–516). Several genomes of food microbes have already been sequenced, others genomes are under way, and several high-throughput technologies that have been developed for other systems can be applied. In addition, the safety of foods can be increased and claims related to the ingestion of specific microbes can be substantiated. It is noted that transcript-imaging of wild-type industrial strains and genetically modified strains may allow for the use of genomics in risk assessment studies. It may be expected that this may lead to a future streamlining of approval procedures allowing the use of genetically modified microorganisms in food. In conclusion, these reviews highlight the novel developments relating to functional food biotechnology that in the near future may benefit significantly from further developments in the genomics of microbes and man.
References 1.
Farber J (Ed): Int J Food Micorobiol 1999, 49:September issue.
2.
Konings WN, Kuipers OP (Eds): Ant van Leeuwenh 1999, 76:September issue.
3.
Diplock AT, Agett PJ, Ashwell M, Bornet F, Fern EB, Roberfroid MB: Scientific concepts of functional foods in Europe: consensus document. Brit J Nutr 1999, 81:510-515.
4.
De Vos WM: Gene expression systems for lactic acid bacteria. Curr Opin Microbiol 1999, 2:289-295.