Microbial transformation of propenylbenzenes for natural flavour production

Propenylbenzenes are common aromatic compounds that are often used as starting compounds for the production of various flavours. Recently, microbial transformation has emerged as an important approach for producing natural flavours in high quantities. Because the biotransformation processes are environmentally friendly and the products are considered 'natural', flavour production using this method is attracting more and more attention. This paper reviews recent advances in the application of microbial metabolism to propenylbenzenes and in subsequent flavour production. Vanillin, a valuable aromatic compound, is used as a model to show recent progress in high-value natural flavour production. Future research should focus on metabolic-mechanism characterisation and on optimisation of biotransformation to improve the yields of target products for scale-up and industrial use.     

生物技术方法生产香草醛研究进展

香草醛是重要的香味物质之一,广泛应用于食品、饮料和医药工业中。本文综述了生物技术方法生产香草醛常用的前体物质、所用微生物降解相应前体物质的代谢途径、对代谢途径中的酶进行的分子水平和基因水平的研究以及在转化工艺等方面的研究进展。     

Production of essential oils and flavours in plant cell and tissue cultures. A review

The production of essential oils and flavours by plant cell and tissue cultures is reviewed, including the biotransformation of added precursors. Methods which have been employed to increase secondary metabolism are discussed.     

Biotechnological production of 2-phenylethanol

2-Phenylethanol (2-PE) is an important flavour and fragrance compound with a rose-like odour. Most of the world's annual production of several thousand tons is synthesised by chemical means but, due to increasing demand for natural flavours, alternative production methods are being sought. Harnessing the Ehrlich pathway of yeasts by bioconversion of L-phenylalanine to 2-PE could be an option, but in situ product removal is necessary due to product inhibition. This review describes the microbial production of 2-PE, and also summarizes the chemical syntheses and the market situation.     

Flavour formation by amino acid catabolism

Microbial catabolism of amino acids produces flavour compounds of importance for foods such as cheese, wine and fermented sausages. Lactic acid bacteria are equipped with enzyme systems for using the amino acids in their metabolism and are useful for flavour formation of foods. Branched-chain amino acids (Leu, Ile, Val) are converted into compounds contributing to malty, fruity and sweaty flavours; catabolism of aromatic amino acids (Phe, Tyr, Trp) produce floral, chemical and faecal flavours; aspartic acid (Asp) is catabolised into buttery flavours and sulphuric amino acids (Met, Cys) are transferred into compounds contributing to boiled cabbage, meaty and garlic flavours.     

Destabilisation of microbial rennet

Summary Microbial alternatives to calf rennet (Chymosin;EC 3.4.23.4) have gained inceasing popularity in the production of cheese. However, in some processes their extended proteolytic activity can result in the development of unacceptable flavours. This report demonstrates the use of an acid pre-treatment to destabilise rennet obtained from Mucor meihei, hence reducing its activity half life.     

Fed-batch production of 2-heptanone by Fusarium poae

Summary Natural 2-heptanone is a key component of various dairy flavours. The production of this compound from octanoic acid by Fusarium poae is described in this paper. The yield of the fermentation can be considerably increased by stripping the product from the outlet gas by adsorption on an Amberlite XAD-4 column.Offprint requests to: P. H. van der Schaft     

Exploiting flavour preferences of common marmosets to increase palatability of a dry pellet diet

Although commercially available complete diets exist for common marmosets, the animals’ consumption of these diets (available in dry pellet form) is typically very low. Increasing consumption of the pellet diet could have positive consequences for the welfare of the marmosets as the pellets are designed specifically to meet their full nutritional requirements, and therefore an increase in intake should help to ensure that they take in an appropriate balance of nutrients. We carried out a series of studies targeted towards improving the palatability, and hence increasing the intake, of a complete dry pellet diet for marmosets. In Study 1 we attempted to determine which of a wide range of flavours appeared to be preferred by the marmosets. In Study 2 we tested the marmosets’ preferences for a smaller number of highly preferred flavours (as determined in Study 1) when actually added to the dry pellet diet in a series of paired preference tests. Finally, in Study 3 we tested whether adding the most highly preferred flavours (as determined in Study 2) to the dry pellet diet would in fact increase consumption of these pellets in comparison with unflavoured pellets. Despite finding strong and consistent preferences for particular flavours amongst the marmosets, we found that adding these to the pellets did not significantly increase consumption. Reasons for this are discussed, along with other potential modifications which might prove more successful in increasing consumption of pellet diets for marmosets.     

Plant production systems for bioactive small molecules

Bioactive small molecules are important dietary components of food, as well as being widely used in diverse industrial sectors, from flavours, fragrances and sweeteners through to natural pesticides and pharmaceuticals. Plants already manufacture many of these bioactives, but often in yields that are not commercially competitive. There are a variety of new pathway engineering, cell culture and molecular breeding strategies in use and in development to improve yield and the robust supply of bioactives in planta. In the future, biorefining applications are likely to play a significant role in providing chemical intermediates for bioactive production from biomass feedstocks.     

Expression of soluble Saccharomyces cerevisiae alcohol dehydrogenase in Escherichia coli applicable to oxido-reduction bioconversions

Six-carbon aldehydes and alcohols belong to flavours and fragrances with wide application in the food, feed, cosmetic, chemical and pharmaceutical sectors. In the present study, we prepared the expression system for production of recombinant yeast alcohol dehydrogenase 1 (YADH1) from Saccharomyces cerevisiae which is suitable also for catalysis of the interconversion of C-6 aldehydes and alcohols. We have demonstrated that an effective three-step strategy can overcome the insolubility problems during YADH1 production in Escherichia coli. We used trxB and gor deficient expression strain, decreased concentration of isopropyl β-D-1-thiogalactopyranoside and lowered temperature to 20°C during induction. Finally, kinetic parameters of recombinant YADH1 were determined and we concluded it is a promising enzyme also for the interconversion of C-6 alcohols/aldehydes in green note volatile production.     

Plant cell and tissue culture: alternatives for metabolite production

Plant cell culture systems represent a potential renewable source of valuable medicinals, flavours, essences and colourants that cannot be produced by microbial cells or chemical syntheses. However, only a few cultures produce these compounds in commercially useful amounts. The low productivities are associated with our poor understanding of the biochemistry of these systems. Recent advances in molecular biology, enzymology, physiology and fermentation technology of plant cell cultures suggest that these systems will become a viable source of important natural products. This review examines the sate of the art of production of medicinal plant secondary metabolites by plant cell cultures.     

Effects of industrially produced flavours with pro- and antioxidative properties on the formation of the heterocyclic amine PhIP in a model system

PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) is a heterocyclic aromatic amine belonging to a class of mutagens found in food. This project studied the effects of commercially available flavours of spices on the formation of PhIP, one of the most common heterocyclic aromatic amines in heated meat and fish products. The model reactions were carried out in diethylene glycol. Highest amounts of PhIP were obtained at 200 degrees C, a heating time of 60 min and an equivalent molar ratio of phenylalanine and creatinine. With this model system, the influence of Monascus red and flavours extracted from thyme, marjoram and rosemary on the formation of PhIP was tested. The flavours were added to the model system in different amounts. The oxidative properties were determined with the rancimat method. It was shown that all tested products, independent of their pro- or antioxidative properties, increased PhIP in the model system.     

Response surface methodology in media optimization for production of β-carotene from <Emphasis Type="Italic">Daucus carota</Emphasis>

Plants are a valuable source of a vast array of chemical compounds including fragrances, flavours, food additives, colours, natural sweeteners, industrial feedstocks, anti-microbials and pharmaceuticals. The present study reports on application of Response Surface Methodology (RSM) in media optimization for suspension culture for the production of β-carotene. Growth kinetics of carrot cells in suspension culture has been carried out to understand the relationship between growth and β-carotene formation. The maximum production of β-carotene obtained using the optimized medium was 13.614 μg/g dry weight cell mass. The μ (specific growth rate) and t _d (doubling time) were found to be higher for 20 g DW/l inoculum size.     

Acquisition of flavour preferences in pigs through interactions with conspecifics that had previously consumed flavoured protein solutions

It is known that pigs can acquire flavour preferences by brief social interactions with conspecifics that previously consumed a flavoured solid feed. However, there is no information about whether a flavoured solution could support flavour preferences through social transmission. Ninety-six pigs (49 days old) were housed in 12 pens (8 pigs/pen). Four animals per pen were randomly selected to act as observers and four as demonstrators. Demonstrator animals were temporarily moved to an empty pen where a protein solution was offered (porcine digestive peptides (PDPs), 4% weight/volume) with the addition of 0.075% aniseed (six pens) or garlic (six pens) powdered artificial flavours for 30 min. Afterwards, demonstrators were returned to interact with observer animals for 30 min. A choice test (30 min) between aniseed and garlic PDP was performed for each observer group after the interaction. Observers showed a higher intake of solutions previously consumed by their demonstrator conspecifics (648 v. 468 ml; SEM 61.36, P < 0.05). As with flavoured solid feeds, protein solutions containing artificial flavours can create preferences in pigs for those flavours through social transmission from conspecifics.     

Lactic acid bacteria: starters for flavour

Abstract Changing milk into other organoleptically acceptable products by fermentation requires particular attributes of the bacteria. These include rapid acid production from lactose and development of suitable quantities of the volatile compounds, diacetyl and acetaldehyde. These compounds must not be over-produced nor should they be accompanied by off-flavours. More knowledge has accumulated concerning starter cultures for milk fermentation than for any of the other cultured foods. We are approaching the time when we can tailor-make mixed cultures of known species of bacteria to provide specific flavours because we are becoming more aware of their metabolic activity within a given foodstuff. To provide and keep a good starter for a particular fermented product it is essential to know what is expected of it in terms of flavour and aroma. This knowledge is not always available and many products are poor because of this. Knowledge of the biochemical pathways leading to flavour production can help in making the right choice of starter.     

Wine,geology mapping and the value of place in McLaren Vale

In the wine‐producing region of McLaren Vale, South Australia, the development of a detailed geology map has worked to increase understandings about the physical diversity of vineyard land. I argue that the production and deployment of social/scientific knowledge through the map is instrumental in strategic imaginings of the viticultural space of McLaren Vale. Ethnographic examination of ‘District Tastings’ of single‐vineyard Shiraz wines shows how the geology map provides a framework for understanding and promoting relationships between vineyard geology and wine flavours. This process feeds into debates over possible delineation of official winemaking ‘subregions’, which may provide a mechanism for the generation of economic value based on discourses of quality and distinctiveness. The map's depiction of geological diversity is embraced by wine producers, who seek to add value to their product through appeals to a purported uniqueness, scarcity or specialness based on geological terroir.     

Biotechnological approaches to the understanding and improvement of mature cheese flavour

There have been important milestones in biotechnological practice that have led to the determination and production of superior cheese flavours. Within the past year, the use of gas chromatographic techniques and sensory methodologies has been optimised by several groups in efforts to evaluate the organoleptic properties of a number of mature cheeses. The hydrolysis of milk caseins, small peptides, free amino acids and fatty acids, and the generation of sulfur-containing compounds are uniformly assumed to result in the formation of specific cheese aromas. Giant strides have been taken in molecular technology to aid the dissection and exploitation of the metabolic pathways that lead to the formation of these flavour constituents. Specific advances in molecular technology have included metabolic engineering of lactic acid bacteria for enhanced flavour development.     

Exposures to conditioned flavours with different hedonic values induce contrasted behavioural and brain responses in pigs

This study investigated the behavioural and brain responses towards conditioned flavours with different hedonic values in juvenile pigs. Twelve 30-kg pigs were given four three-day conditioning sessions: they received three different flavoured meals paired with intraduodenal (i.d.) infusions of 15% glucose (F(Glu)), lithium chloride (F(LiCl)), or saline (control treatment, F(NaCl)). One and five weeks later, the animals were subjected to three two-choice feeding tests without reinforcement to check the acquisition of a conditioned flavour preference or aversion. In between, the anaesthetised pigs were subjected to three (18)FDG PET brain imaging coupled with an olfactogustatory stimulation with the conditioned flavours. During conditioning, the pigs spent more time lying inactive, and investigated their environment less after the F(LiCl) than the F(NaCl) or F(Glu) meals. During the two-choice tests performed one and five weeks later, the F(NaCl) and F(Glu) foods were significantly preferred over the F(LICl) food even in the absence of i.d. infusions. Surprisingly, the F(NaCl) food was also preferred over the F(Glu) food during the first test only, suggesting that, while LiCl i.d. infusions led to a strong flavour aversion, glucose infusions failed to induce flavour preference. As for brain imaging results, exposure to aversive or less preferred flavours triggered global deactivation of the prefrontal cortex, specific activation of the posterior cingulate cortex, as well as asymmetric brain responses in the basal nuclei and the temporal gyrus. In conclusion, postingestive visceral stimuli can modulate the flavour/food hedonism and further feeding choices. Exposure to flavours with different hedonic values induced metabolism differences in neural circuits known to be involved in humans in the characterization of food palatability, feeding motivation, reward expectation, and more generally in the regulation of food intake.     

Characterization of lipoxygenase isoforms in olive callus cultures

Lipoxygenase activity is critical for the development of flavours and aromas in olive oils. We have partly purified isoforms of molecular mass 95 kDa that have activity against linoleic or alpha-linolenic acids by a simple procedure from olive callus cultures.     

Solanesol: added value from Solanaceous waste

Isoprenoids, also known as terpenoids, are the largest and oldest class of natural products known. They are comprised of more than 40,000 different molecules all biosynthetically related via a common five carbon building block (isopentenyl). Many isoprenoids are of commercial interest and are used as fragrances in cosmetics and flavours, colorants and nutritional supplements in foods and feeds as well as being phytomedicines. Their industrial relevance also means they are compounds of high value with global markets in the range of $1 billion per annum. Solanesol is a 45-carbon, unsaturated, all-trans-nonaprenol isoprenoid of high value. Recently this molecule has received particular attention because of its utility, both in its own right and as a precursor in the production of numerous compounds used in the treatment of disease states. Instability in supply and spiralling costs have also lead to the search for sources. In this article existing sources and the potential strategies and tools available to create sustainable biosources are reviewed.